Jan 26 CP4 movie; 94fr, 3Mb. 
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Weather information and summaries are compiled from the NCAR RAP (Research Applications Program) WISP94 operational weather summaries. These summaries may have been edited, on occasion, and supplemental information added. Since all of this information is considered preliminary, neither RAP nor ATD will be held responsible for its contents.
Jan 26 (Wed) Mar 6 (Sun)
Jan 27 (Thu) Mar 11 (Fri)
Jan 29 (Sat) Mar 12 (Sat)
Jan 30 (Sun) Mar 20 (Sun)
Feb 7 (Mon) Mar 21 (Mon)
Feb 8 (Tue) Mar 22 (Tue)
Feb 10 (Thu) Mar 23 (Wed)
Feb 12 (Sat) Mar 24 (Thu)
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Feb 25 (Fri)
Feb 28 (Mon)
A vigorous upper system moved across southern CO from 00z to 12z Wed and surface cyclogenesis occurred near CO-KS-OK border. Upslope flow began late in the day on Tues and increased continually throughout the night. Upper level dynamics moved in late Tues night and a relative lack of moisture was the only drawback for a huge dumping of 1-2 feet in the Front Range. Highest snow accumulations occurred where the moisture was in place while the dynamics were the best in extreme Ne CO, Nw KS and Sw NE. Storm produced some thundersnow, especially in southern part of the state as the dynamics were the best. Snow first showed up on NexRad around 9:00 PM local down near Colorado Springs and moved northward toward DEN by midnight. It started with a lot of virga because of the lack of moisture in low-levels. By around midnight we started to see snow falling here in Boulder as it continued northward. We had some brief heavy snow around 1:00 am local but generally overnight received only light snow; daybreak revealed only around 2 inches. Daybreak did bring more snowfall as a snowband set up oriented E-W from near DEN eastward to KS border. That snowband appeared to be most strongly affected by the upper level dynamics as it shifted slowly northward and eastward. Embedded in this flow were a few small-scale bands oriented N-S and moving directly westward. Throughout the day after 10:00 am local an echo-free region appeared north-south from I-25 eastward to Byers and slowly moved northward thru the day. That was the western edge of the main echoes and only light snow fell
Jan 26 CP4 movie; 94fr, 3Mb.
Summary discussion for Thursday, 27-Jan-94 (G. Thompson, RAP)
Vigorous upper low that moved thru Wed continued a north-east track and by 12z Thur was in eastern NE. Plenty of moisture was left behind this system as sfc to 550mb was nearly saturated most of the day. There were mostly n-nw winds behind the system and a few snow-showers persisted overnight and all day on Thurs. My morning discussion said that snow showers should diminish during the day as models indicated a slow drying trend and plenty of upper-level subsidence. The drying was even slower than I anticipated and a snow band situated right over the city of DEN persisted for the ENTIRE day. Looking at the mesonet in the morning, it appeared that a weak Longmont anti-cyclone was setting up. As the day progressed it was obvious that this was the case and the snowband continued throughout the full day and into the early night hours. Mobile CLASS launched a few soundings from the road, first near Lafayette, then another near west DEN, then another out east near Watkins. Each sounding showed 30kt north-easterlies from 700 up to 500 with more northerly component lower than that. After discussing the conditions at the 11 breifing, Roy Rasmussen suggested the precip was caused by 2-4 km convergence or similar mechanism. It seems the Longmont anti-cyclone is the best explanation for the snow bands. Skew-t's indicated the cloud between 1.5 and 4 km, however, farther ne of Longmont, cloud tops were much lower and barely any precip was falling until reaching the CYS ridge where more light, occasional snow was falling. A brief study of the Denver snowband was conducted using Mobile Class and the NCAR CP4 radar.
Jan 27 CP4 movie; 30fr, .8Mb
Summary discussion for Saturday, 29-Jan-94 (G Thompson)
Had some light snow in the region early Saturday morning which
appeared to be due to mostly upper level features. The DARRRE station
was down overnight and we had no model runs or satellite pics.
Kavouras radar display again came through as we could at least get a
broad overview of what was going on. It showed a 300mb jet streak
oriented N-S from Idaho into Utah. Later, looking at the model
analyses, there was a vort max moving thru WY and western NE. These
dynamics produced two periods of snow showers that moved south from
CYS to DEN. The other big factor for Sat wx was an arctic front
hanging out to our east in central NE and western SD. I truly mean
"hanging out" -- some people argued that the NGM and ETA brought in
this front in during the day on Sat while MM5 said no-way! Associated
with this arctic front was an inverted trof which usually spells
murder on westward moving arctic air until the trof is squashed. This
was the case with this one. Pressure falls all day in Se CO and N NM
still couldn't wipe out the inverted trof. All of this meant that the
arctic air just stayed put and moved nowhere for the entire day Sat,
meaning any prediction of upslope clouds assoc with arctic air pushing
west were not realized. So the MM5 was extremely impressive with its
handling of the cold air and the NGM and ETA were terrible.
Back to the mesoscale and the 2 snowbands:
The first one was generally weaker and produced only light-to-moderate snow across a general region from CYS-DEN-AKO. This one moved southward rather quickly from CYS near 13z to DEN around 16z and weakened. Behind this the winds increased sharply and turned from the N-NW in northern portions of the mesonet. From Loveland southward though the winds were lighter and in some cases variable with under 5kts reported. Skew-t's showed that the atmosphere was still extremely moist from sfc to 550mb (all of which was left behind by the storm on Wed-Thurs); therefore any flow moving up a terrain feature produced SW-, as was the case upwind of the CYS ridge and Palmer divide. After this first snowband/surge passed thru the region, it appeared as though a Longmont anticyclone developed, with FCL, Nunn, Briggsdale, CYS, FTM and AKO reporting N-NW winds and sometimes gusty while the DEN metro area reported variable winds of 5kts with LGM reporting a weak southerly wind. The MM5 model did a very good job with this surge and the associated snow (although model-predicted accumulations were too low). Upon further inspection it appeared that a surge was responsible for the early snow as well as associated upper level PVA.
The second band also appeared first in the northern portions of the mesonet and moved southward thru the day. CHILL radar came up around 19z and weak echoes were in the vicinity of Gill and GXY at that time. This feature moved S-SW and intensified and by the time it reached here at 21z had nearly 30dBz max along a narrow band oriented NW to SE from Erie to Stapleton. The portion of the band near Boulder stayed stationary for the most part as the southern band moved more westward as it was probably warped by the Longmont AC. Then it stayed pushed-up against the foothills with little change and Boulder received the most snow. It finally dissipated after 2-3z as the upper-level features were less supportive. It is unclear whether this band was due to another surge although MM5 did predict one that would pass thru our area around 0-3z. Finally during the night Sat, the inverted trof to the east began to break down and the cold air slowly came in by morning, but with no real upslope cloud or snowbands associated with it. By then winds swung back to mostly northerly and the Longmont AC appeared to weaken substantially.
Jan 29 CP4 movie; 40fr, 1.2Mb
Summary discussion for Sunday, 30-Jan-94 (John Brown, NOAA)
The day was dominated by weak dynamics, a steep lapse rate in the
lower half of the troposphere, and ample moisture. Though moisture
was plentiful, cloudd cover was mostly scattered in the morning, such
that there was plenty of sun. It was no surprise, then, when weak
convection began forming by mid-morning. This continued all day,
modulated primarily by a Longmont anti-cyclone circulation, such that
most convection early in day was concentrated along the foothills,
near as we could tell. Later in the day, a NW-SE band was noted on
the Denver WSR88D display, with the band running from near Fort
Collins SEwd. This was around 22Z or so.
Most areas in the Boulder vicinity got 0.2" or so of snow. Visually, there were signs of SLW (Super-cooled Liquid Water) only in the more active towers -- glaciation appeared to occur rapidly, and the air (at least in the Boulder vicinity) was filled with ice crystals during the afternoon. No snowfall greater than S- was noted. No wave clouds.
It appeared that the arctic front that was apparrent on Sat 29th never really made it in. Apparent early in the day was a frontal trof from western SD, south to western KS. This trof gradually filled during the day. The front was marked by temperature contrast, and especially theta contrast. A shallow, colder airmass lay east of the front.
Jan 30 CP4 movie; 28fr, .8Mb
Summary discussion for Monday, 07-Feb-94 (J.Reisner)
Since, the high pushed south faster to our east; during the morning southerly flow started developing over the plains. In response to this flow, a weak and shallow Denver Cyclone developed. This cyclone appeared to propagate towards the northeast during the day. The cyclone may have been responsible for keeping the cold air and low clouds in the Denver area during the day. Note that stations in WY mixed-out during the day with CYS warming from 19 F to 33 F in two hours.
The cause of this warming brings up another important point. During the day the westerlies have increased in intensity. Presumably some of this warming in WY is the result of turbulent mixing associated with the increasing westerly flow. Though temperatures changed little over northeast CO, low-level moisture decreased (based on class soundings). Likewise, pressure falls during the afternoon have been rather substational with greater than 5 mb falls over northeast CO.
Another note is the wave approaching the west coast and the pressure rises noted over northern WY. The pressure rises to our north appear to signal the beginning of a surge which will be affecting us tommorow. The wave to the west has substational moisture associated with it (based on satellite images), and also rather cold temps aloft (based on severe weather over LAX). The wave to the west is leading to the development of a low pressure system to our east. This low-pressure system may be responsible for some shallow upslope snow tomorrow.
Feb 07 CP4 movie; 72fr, 2.2Mb
Summary discussion for Tuesday, 08-Feb-94 (J.Reisner)
Around 0600 UTC winds at DEN/Stapelton switched briefly to the southwest. At this time the temperature jumped to 43 F, but just as quick the winds switched back to the northwest with a resulting rapid decrease in surface temperature. Similiar behavior was noted at CYS and BOU. The exact cause for this oscillation is unclear and did not appear to be associated with any surge (pressure at Denver continued to fall during this time).
By 1200 UTC a surge from the north went by DEN (hit CYS about 2.5 h earlier). At CYS the temperature dropped from 37 F to 12 F within an hour while at DEN the temperature dropped from 33 F to 17 F within an hour. Pressure increases of > 5 mb over 4 h did occur with the passage of the surge over several stations in northeast CO.
Once the surge went through the area it got hung-up on the Palmer Divide. Overrunning led to the development of light snow (< 5DbZ) over areas north of the Palmer Divide. Very little accumulation was noted with the snow; however, Ben stated that 1/4" did accumulate at Hudson. By 1800 UTC most of the light snow had dissipated, but by this time convective snow showers forming over the Continental Divide began to advect over areas north of FCL. During the afternoon the convective bands continued to increase in intensity, with a mesonet station in WY (VDW) reporting S+ at 2030 UTC.
Note that the models missed this storm from the beginning with the MRF forecasting a cut-off low to form. Instead, we got split flow with the main dynamics going farther south. Additionally, the models did not handle the cold air very well with the models, as usual, failing to bring the cold air into the area.
Feb 08a CP4 movie; 72fr, 2.2Mb
Feb 08b CP4 movie; 72fr, 2.3Mb
Summary discussion for Tuesday, 09-Feb-94 (J.Reisner)
Yesterday, after a surge moved through northeast CO during the early morning hours (about 1200 UTC), the cold air mass over northeast CO slowly began to deepen and by 0000 UTC was finally able to reach the first gate at Platteville. Note that none of the numerical models, including MM5, correctly forecasted the time in which this surge would make it into northeast CO. Unfortunately, all the models brought this surge down later in the day.
Though some light snow occurred behind the initial surge, the main weather activity present yesterday was associated with convective snow bands which began to form over southeast WY by 1800 UTC 8 Feb. At first it appeared that the bands were being randomly forced; however, by mid-afternoon the development of a rather coherent band to the north of FCL was a signal to me that either an upper-level feature, a low-level surge, or CSI was responsible for forcing the band. Since the atmosphere was relatively unstable (-1.6 LI at Grand Junction), I ruled out CSI. Next, I looked for evidence of a surge and noticed that although an increase in pressure was occuring near the bands, no increase in windspeed was evident in their wake. Hence, I ruled out the possibility of a surge forcing the bands. Thus, I began to concentrate on trying to find the an upper-level wave. Based on a rather exhaustive analysis, Ed Szoke and myself concluded that a weak upper-level wave coming down in the west-northwest flow was responsible for forcing the bands.
Whatever was responsible for forcing the bands, it should be noted that they did produce some pretty heavy snows, especially in WY, with one station in Chuck's WY mesonet data receiving over 0.5" liquid during the day. During the evening, as the bands progressed further south into northeast CO, snowfall amounts decreased with FCL reporting about 2" snow depth with DEN only a trace. Note that with the passage of the bands at DEN the skies cleared and the winds came out of the south. Though the 20 km 1200 UTC MM5 run gave some hint that these bands would be present during the day, the bands produced by the model were not as coherent as those observed.
Wave Clouds:
Due to the presence of low-level upslope clouds and convective snow bands very little attention yesterday was placed on noting if wave clouds were present.
During the early morning hours (1400 UTC ) of today some high-level wave clouds were evident to the southwest of BOU and to the north of LAR (John Marwitz). During the late morning and early afternoon wave activity continued to increase to the north of BOU, but decreased somewhat from BOU to the south. Note that on the 2100 UTC satellite image, relatively small wavelength mountain waves were occuring in WY.
Summary discussion for Thursday, 10-Feb-94 (J.Reisner)
None reported over northeast CO.
Wave Clouds:
Yesterday was a good day for wave clouds over WY. J. Marwitz flew the WY King Air yesterday and reported wave clouds in the -10 C to -20 C range. The MM5 (6km domain) did predict that the main area for wave clouds should occur over Wy.
Another interesting item of note is the high winds over Wy. Several highway department mesonet stations reported winds in excess of 60 m.p.h. An unofficial gust of over 100 m.p.h. was recorded to the southeast of LAR around 0300 UTC 10 Feb.
Today was another good day for waves clouds with cloud base temperatures around -15 C and bases about 10000 ft above the ground. By early afternoon the area was fairly socked-in with wave clouds in all directions from BOU. Several of the wave clouds appeared to be convective in nature with virga being reported to fall from them. In fact, during the day WSR88-D radar showed echos ranging anywhere from 0 DbZ to 10 Dbz. Note that once again, MM5 predicted cloud ice to present in the region and, surprisingly enough, an extensive area of snow below the area of ice.
Two other items of interest: 1) the 2200 UTC Platteville profiler showed very strong wind shear (trapped waves) below 500 mb; 2) a Denver cyclone at 2200 UTC was present in the mesonet.
Summary discussion for Saturday, 12-Feb-94 (J.Reisner)
Yesterday, an upper-level trough with cold mid-level temperatures approached from the west. Associated with the trough was a rather strong Pacific cold front. Early in the morning (1500 UTC 11 Feb) the front was in southern WY. Winds ahead/behind the front were out of the south-southwest/north-northeast with clouds and light snow noted behind the front.
During the late morning and early afternoon the front moved slowly towards the south reaching CYS around 2000 UTC. At the same time, with the approach of the trough and daytime heating, convective snowbands began to develop in the mountains of CO and along and immediately behind the front. An hour after frontal passage CYS reported moderate to heavy snow.
After passing through CYS the front began to pick up speed and moved rather quickly through northeast CO. Winds began to increase with several mesonet stations reporting > 40 m.p.h. Platteville profiler showed > 35 m.p.h. at the third gate. The convective snowbands continued to develop further south and by 2200 UTC Denver was reporting heavy snow.
As was predicted by the models, the snow was quickly over with the heavist snow being over at DEN by 0300 UTC 12 Feb, and the light snow ending by 0800 12 Feb. Snowfall totals for the storm were as follows: CYS 6", DEN 4", Longmount 1-1.5", BOU 3", Golden 6-8". As inferred from the snowfall totals, local topography probably played a part in enhancing snowfall accumulations, with upslope with respect to the CYS ridge and the Palmer Divide playing a role. After the 700 mb wave moved through northeast CO, the snow ended, the skies cleared, and temps dropped. By this morning, sky conditions were clear over the area with light winds.
Feb 11,12 CP4 movie; 97fr, 3.0Mb
Summary discussion for Monday, 21-Feb-94 (J.Davis)
We observed what will probably turn out to be the best upslope cloud of the whole project today. The King-Air flew two missions, the first was between CYS and SNY (I don't know where the second one was). Some large drops were observed during the first mission, in a turbulent layer near the cloud top. The Electra was unable to fly because of the broken compass.
Snow began along the Front Range between 2 and 3 PM, with bands coming off the mountains. The bands eventually extended nearly to Nebraska, which prompted discussions as to whether CSI was acting. Places that were mostly in the band got about 3 inches of snow. The upslope cloud remained in place over much of the area all day and last night. Liquid water showed variations characteristic of scavenging by snow, but PLT did rise to 0.4 g/kg at one point. Lots of icing reports as a result. The King-Air instruments were coated by several inches of ice on the first flight.
Feb 21/22 CP4 movie; 82fr, 3.0Mb
Feb 22/23 CP4 movie
Summary discussion for Friday, 25-Feb-94 (C.Davis)
There was not nearly as much upslope cloud this morning as I expected, but some low clouds were evident over northeastern CO. The arctic front made a dramatic passage last evening, turning winds in Boulder from gusts to 60 knots from the west to gusts over 30 knots from the northeast and very impressive temperature falls. About 6 inches of snow fell at Cheyenne, but about 1/2 inch here. Soundings show the classic upslope-cloud temperature and moisture profiles, except that the cloud is missing. Things are very near saturation in the stable layer, so it wouldn't take much ascent to produce a cloud, and apparently there is a small amount of ascent to the northeast.
Some snowshowers are present along the Front Range, but they are dissipating. It may clear out here, but I'm not sure. The cloud out to the northeast (near AKO, SNY) should hang in for a few hours anyway. Wave clouds are abundant to the northwest with some great trapped waves visible on the satellite pix
Feb 24 CP4 movie; 75fr, 2.4Mb
Feb 25 CP4 movie; 80fr, 2.7Mb
Summary discussion for Monday, 28-Feb-94 (J.Brown)
[Note: forecaster's comments are related verbatim; no attempt has been made to expand any idiosyncratic abbreviations.]
This was a VERY interesting day. Not a good day for the forecaster, but partly for that reason, a very interesting day.
In summary, the day started out with 2 matters of interest, but also in light of the dissappointing lack of predicted snow overnight, these matters were not immediately grasped. But, by 1500z, it was apparrent that there was an area of upslope St over western KS with ZL underneath that presented some interesting SLW psblties. After doing some work over the K-band radar N2UW was sent down to SW KS where large drops of SLW were noted in absence of shear. They did a missed apch at GCK as well to get a sndg.
Meanwhile, Greg Stossmeister pointed out snow at CPR in early mrng, and it was noted that this was asstd wi the west edg of upper moisture. This west edg was also the E edg of a dry band on the 6.7 micron water-vapor imagery, which in turn was asstd with a stg Nly jet. This jet was that typical bhnd trofs, being a wedge of low PV air with the point of the wedge pointing to the left of the jet into the high PV to the left of the jet, and in this case having its Ewdmost penetration at about 250 mb. It should be noted that this upper configuration is very typical.
There was one difference that should be noted, however, that the PV max was nrly colocated with the western edg of the moisture, and not with the dry band, as is more typical.
In any case, after the St flt to KS, attn became focused on this band of enhancement on the IR. This in fact did diminish durg the mrng, but did also have some definite identity in the vis imagery, which sgstd mushy conv in a broad band. This began to affect Wx in SE WY by late mrng. By 18Z htg induced conv was aprnt locally, concentrated nr the fthls, as stg sgstn of LGM anti had become aprnt on mesonet. As this band of enhancement apchd, it seemed to reintensify as it interacted with preexisting conv asstd wi the LGM anti, wi the most intns cell dvlpmt being in Larimer County and Nrn Boulder County, nr fthls. This intensification occurred primarily after 1930Z, and about 2200Z reached something like peak intensity, as the IR enhancement passed ovhd. The mass then moved SE and wknd, seemingly caught up to be in phase with the IR ehancement and upper PV max.
As this was going on, interesting things were occurring at the surface. Early, there was a wshft at CYS fm NNW-N to NNE. (I think this was about noon LST.) Soon after, the Nrn mesonet stns had a similar shft. However, there was no chg in temps asstd wi this, wi plains wet bulb temps rmng 2-3 C. Another interesting thing is that nr fthls by 2000Z, there began to be evidence of cooling at FOR and LVE (as I recall), wi wnds turning more into NNW. This cooling spread Swd, not by adv, but in situ, I think, as pcpn dvlpd Swd. By 2100Z or so (roughly), there was clrly a sml region nr the fthls having slgtly cooler temps (3-4 deg C as opposed to 6-8 farther E) and NNW winds, whereas winds farther east were NNE (see beginning of para). This cold area slowly spread Ewd as radar echo activity spread E as well (well, really SE). The leading edg of this became a density currentbased on the abrupt nature of the wshfts that occurred subsequently as this spread SEwd into the DEN area, and farther E.
Another interesting aspect of this dvlpmt was a pressure surge. Durg the mrng, there was some press rise at CPR, and isallobaric field was vry wk, wi the only thing of note the pressure surge in Wrn KS SE CO that mvd SEwd into OK and Tx panhandle. There was a very wk tendency for pressure rises over WY and UT. I think there was probably a wk pressure rise asstd wi the IR enhancement, probably cooling by conv. Whether a merger with this preexisting wk pressure rise, or a new dvlpmt, the cooling nr the fthls became asstd wi a marked pressure surge that had a magnitude substantially greater than could possibly have existed in WY durg the mrng.
After about 23z the intensity and coverage of radar echo began to go downhill. Bhnd the SEwd mvg enhancement, accommpanied by the pressure surge, reflectivity diminished rpdly. However, about 30 min after the back edge of the band passed, there resumed snow adjacent to the fthls fm Larimer county Swd. The K-band radar revealed an interesting aspect to this. Generating cells seen on RHIs were embedded in the Wly flo above about 3 km AGL. As pcpn fm these fell, it was sheared SWwd in the NE - N flo blo 2 km or so AGL. This was seen remarkably clrly on the K-band display. The 88D PPI showed that these Ewd mvg cells croaked after they moved more than 20 km or so E of Ern edg of Fthls. This ptrn continued, but slowly diminished, for several more h. Finally, about 0330Z, the intensity and coverage of echo began decr rpdly, and by 0400 we called it a day. Clds clrd rpdly over Boulder between 0500 and 0600Z.
The Platteville profiler indcts that the Nlies reached their dpst point at 23Z, about 550 mb, after increasing in depth all day. After this time the wlies worked their way down to about 600 mb by 0300 Z.
Feb 28 CP4 movie; 117fr, 4.2Mb
Interesting day, but not quite as anticipated. The upslope oozed in
more slowly than anticipated, and was shallower and warmer. In some
respects, eta was best on this, but at the same time eta had too much
SE flow on plains, that is it had fcst the high too strongly into the
Gt Plains, much as the other models. Its just that the eta kept the
areas immediate to the high terrain too warm.
As a result, upslope clouds did not advance into CO as anticipated.
Above 600 mb, however, the fcst worked out fairly well. Shallow
upslope did get into Western NE, and it is there that the most
favorable conditions for SLW were judged to be. Soundings, however,
did not show this layer to be more than a few hundred m deep, and at a
temp close to 0C. Some of the 12 z sndgs showed temps up to +8 or so
nr 800 mb ovr ne CO.
Over WY, underneath the middle level cloud band, there was virga. It
appears likely that this moistened and cooled the layer between the
mid-level cloud bases and the top of upslope to reduce the stability
interface between the two and bring the relatively dry air intervening
too close to saturation. Soundings suggested this and also that there
was waa (warm air advection?) sufficient to cause upward motion that
brought the layer above the aforementioned shallow upslope to
saturation. In any case, ATD mobile near BFF had a 18z sounding that
showed saturation through a deep layer, extending to -8 or so. The
airplane evidently worked this stuff and got at -12C up to 0.5 m/s up
and a bag sample. Al Cooper said that this was not uniform ascent;
the cloud had evidence of some convective-like elts on top, and this
was in those. [ed: hope this is clear enough!].
Radars were turned on, but didn't see anything except the mid-level
clouds and precipitation (max about 25 dbz). This was mainly in WY.
An interesting feature today was that the McCook profiler showed 20-25
kt of E wnd at lowest 2-3 gates for upwards of 6-8 h. None of the
other profilers showed this, but MCK sfc winds were likewise E to ENE
gusting 20 kts or so. No other surface station reported winds this
consistently strong either. The movement of the pressure rise center,
the one that has been tracked since yesterday morning, to the south of
them was accompanied by a decrease after 16z or so, but still this
wind was deemed remarkable.
This proved to be a more challenging forecast day than I was
anticipating. The blow-by-blow stuff is in 940311.not.
Overall I think things evolved as anticipated. However,
the precipitation forecast I made was lousy.
In thinking about the day's forecasting, some points come to mind.
Overall, then, we can say that the dynamic part of the forecast
guidance was good, in contrast to last weekend, when models were in
marked disagreememt, and were generally poor. How did MM5 affect my
forecast? I think I bought it more because it fit my preconceived
notions than because I a priori trusted it.
This managed to be a fairly good day for WISP, in spite of a poor snow
forecast for Boulder. N308D flew down in the Arkansas Valley and got
some bag samples that they took back to FNL. In the process of coming
back this way, they noted overcast low St below them, and after
dropping the bag, flew closer to home, doing some coordinated flights
with N2UW.
From a forecast standpoint, this day went pretty well. Model
forecasts from yesterday said that the upslope would weaken after 12Z
N of Palmer Rdg were correct, and as pressure fell to N, areas N of
Palmer Rdg became divergent at the sfc by mid morning. Clouds rapidly
thinned thereafter, and became broken by noon, and scattered by 21Z.
There were only convective showers of consequence ovr mts to
complicate matters today. As usual, the ARTCC scale 1500 m pressure
analysis and the 3-h change field were the most useful products for
the short-term forecast.
Regional Conditions around:
WYO King Air is now up over GXY and reporting decent icing conditions so
getting exactly what we'd hoped with shallow liquid upslope cloud. Expect
this to continue til 18z on upslope side of Palmer Divide but decreasing from
the north before then. Update from King air is now some clearing up near GXY
as they head a bit further south.
Blue skies this morning except a few cirrus wave clouds at very high
altitudes which are diminishing and re-appearing as I write this. Expect
mild sunny conditions with some breezes but overall just a great day to
be outdoors. Wave clouds today are minimal and fleeting with some hanging
together off the Laramie Range. The better wave clouds should be off the
Wind River, Bighorn and over Yellowstone regions. Don't expect much of any
better wave clouds than already exist for all day Monday.
Suggested to Illinois guys to do their last clear air flight today
and looks like that was a good idea. Now only the -35 wave cloud
eludes them and expect some of that tomorrow.
Looks like above says it all. Nothing to say except "wish I could be
outdoors". No wave clouds, only a few cirrus here locally.
Moisture slug in G. Basin area assoc with ejecting S/W from Pacific NW
trof is the concern of late. Some mediocre wave clouds in Utah at 14z
and some now forming in CO and southern WY. Suspected Tues would be
pretty decent wave cloud day in southern WY with more limited moisture
in CO so less likely to have many sustained wave clouds. Pretty much
just a mediocre wave cloud day in WY with almost nothing in CO. LND
sounding was nearly moist adiabatic because of the dynamics assoc with
above S/W, GJT had only a thin layer of high moisture at 600mb and DEN
was bone dry. Unfortunately, Craig sounding time-series showed a
drying trend so CO wave clouds were minimal at best.
Main, deep moisture continued early AM trend of dividing WY in half
along the SW-NE diagonal as upper flow followed that line. This
continued but enough out-lying moisture in all of UT and entered
west-northwest CO creating the source for wave clouds around RKS, CYS,
LAR, 4DG. Wind flow strengthening aloft from southwest thru day today
and some winds kicked up here in Front Range around sunset as lee trof
developed.
Only problem we've seen is relative steep lapse rates and current obs
of cumuliform clouds instead of more lenticular in nature. Satlt
supports this idea as clouds appear to be more cumuliform than I
anticipated.
Electra did fly these clouds but problem as stated above was that most
of the clouds were not lenticular but more cumuliform. Nonetheless, the
Cloud Isotope Project people seem quite happy as they exhausted their last
flight. YEAH, no more -35 wave cloud forecasts!!!
Overall not nearly as much good wave clouds as I anticipated in WY.
WINDY!
Sfc low near GRI with tight pressure gradient from GCC down to ABQ and
upper level jet riding overhead with 100kt winds. Now in NVA from the
S/W moving across ne WY and w SD to help kick the winds stronger.
Looking at time-series of mesonet showed winds really kicked up around
9z FCL, 11z Boulder. Not much moisture with westerly flow and Electra
is down for the day because they're taking out Ron Smith's
instruments.
No wave clouds today except way up in northern WY, just a Fuehn cloud
over the divide for the entire day, not surprisingly. Winds
continuing all daylight hours before decreasing after sunset with a
gradual wind shift to east-southeast flow as the low in NE continues
eastward.
No moisture returning to state when the easterly winds did begin to
show up around 4z Thurs. We'll see what happens in the wee hours on
Thurs. I forecast a weak upslope cloud much like Sunday Mar 20 with
some seeder-feeder stuff going on from upper level moisture, dynamics
and jet-streak.
Main cause of busted forecast was initial ejected S/W came through
during nighttime hours was stronger than forecast, created more NVA
behind it, dried things out more than expected and main S/W in the
cut-off low very slow to progress eastward. Calif cut-off progged
to move much quicker than it did, and caused yet another busted fcst.
Really think models aren't yet ready for this type of test. Even MM5
busted by OVER forecasting the RH at mid and upper levels.
END OF PROJECT!!!!!!!!!!!!!
CP4 operated in support of RAP for NEXRAD algorithm development.
Summary Discussion for Sunday, 06-Mar-94 (John Brown)
Mar 06 CP4 movie; 91fr, 3.6Mb Summary Discussion for Friday, 11-Mar-94 (John Brown)
What I was counting on is that precipitation would begin over and very
near foothills, cooling things down, thereby creating an adverse
pressure gradient, turning the NE upslope locally to flow parallel to
foothills. This scenario had the flow then veering with height, with
overrunning of this cooler air at, say, 700 mb, creating upward motion
over plains adjacent to foothills. I think the flaw in this reasoning
as far as the forecast for Boulder is concerned, is that not enough
precipitation fell far enough E to cool the air down near the
foothills, and so create a sufficiently strong overrunning flow with
ascent far enough east to permit particles to land in Boulder. Having
said this, the PTL profiler did show veering from NNE at 500 m to
lighter ENE at 3 km, so this argument is not fully valid. It is also
possible that the air coming in from NE was so dry that only by the
time foothills were reached was it moist enough to allow much
precipitation to fall through it. Of course, also, the higher terrain
can get more precipitation in a uniform precipitation event that has
no cloud below 2500 m or so just because particles that happen to fall
on the foothills will have experienced less evaporation than those
that fall on plains. Mar 11 CP4 movie; 75fr, 2.9Mb Summary Discussion for Saturday, 12-Mar-94 (John Brown)
Mar 12 CP4 movie; 82fr, 2.6Mb Summary Discussion for Sunday, 20-Mar-94 (Greg Thompson)
That's it for today, time to go home! Mar 20 CP4 movie; 61fr, 2.0Mb Summary Discussion for Monday, 21-Mar-94 (Greg Thompson)
Mar 21 CP4 movie; 24fr, .9Mb Summary Discussion for Tuesday, 22-Mar-94 (Greg Thompson)
Summary Discussion for Wednesday, 23-Mar-94 (Greg Thompson)
Summary Discussion for Friday, 25-Mar-94 (Greg Thompson)
Ops director notes said profilers not showing any upslope flow all day
Fri but models were indicating a weak surge in WY late in the day.
King Air went to hunt it down but didn't find much. Time-series of mesonet
did show surge coming down CYS ridge around 22z with only wind
shift and RW- (reported by Ben at Briggsdale). Mar 24/25 CP4 movie; 82fr, 3.4Mb Mar 25 CP4 movie; 106fr, 4.1Mb Summary Discussion for Saturday, 26-Mar-94
About this Page
This document was set up in February, 1994 by
Bob Rilling and
Cathy Stack.