IOP 5, 18 Jan 2001

IOP 5: 18 January 2001

Time Period of IOP

1300 UTC 18 Jan  2001- 0228 UTC  19 Jan  2001

Overview of IOP

On (Wednesday) 17 January a system was forecast to move through the study area  early in the day on (Thursday) 18 January with a weaker warm-frontal rainband  and a stronger cold-frontal rainband later in the day. A decision was made to try to fly  the Convair-580 in both rainbands with back-to-back flights (with a layover in Hoquiam), with an initial door closed time of 7 am local time,. By 9 pm local time on Wednesday, the forecast models strengthened the warm frontal part and weakened the cold frontal part, further motivating the back-to-back flight strategy. By 5 am local time on Thursday, the radar showed that the warm-frontal band had come in ~6 h earlier than forecasted, precluding an aircraft study of that band. Interestingly, this rainband was beneath a region of lower (darker) clouds on the Washington coast seen on the infrared satellite imagery, and the large precipitatio-free area behind this band was beneath the region of higher (brighter) clouds ~2 degrees longitude offshore. The flight was delayed indefinitely as the Coordinator and Radar Scientist attempted to determine if and when a cold-frontal band would enter the study area. This rainband finally appeared on the S-Pol radar, and the Convair-580 intercepted it. It was quite shallow (tops around ~14,000 ft.), indicating perhaps a surface occluded frontal band. The rainband was strong and linear north of the flight track (along the 240-degree radial from the radar), but weakened and meandered south of the flight track, and had a cellular nature along its length. The Convair-580 completed its vertical stack. After the Convair-580 had left the area, the rainband consolidated into a more filled-in and linear feature (though still quite cellular), and then it broke up again with landfall.

Convair-580 Summary

UW Flight Number:


Period of Flight:

    2016-2330 UTC,  18 January 2001

Main Accomplishments of Flight:

    Profile of clouds and precipitation in advancing but weakening diffuse cold front.

Instrument Problems:

    SPEC HVPS. No recording of 35 GHz radar data.

Flight Scientist:

    Nick Bond

Approximate UTC Timeline (Local time = UTC – 8 hours) Activity for UW Flight 1851:

2016 Engines on.
2026 Take off from Paine Field.  Ferry to operating area.  Instruments working.
~2051 Beginning descent for low-level run.
2057 Past coastline.
2059 Start of low-level run at 3,000 ft.
2121 Back in precipitation.
2129 Out of precipitation.
2131 Back in precipitation.
2140 End of low-level leg.
2146 Beginning 7,000 ft run at ~–1 deg C.  HVPS malfunctioning.
2157 End of 7,000 ft run.
2201 Begin 10,000 ft run at ~–4 to –5 deg C.
2213 Temporary break in precipitation.
2222 End of 10,000 ft run.
2226 Start of 13,000 ft run.  Near cloud top in and out (mostly out) of cloud.  Temperature ~–9 to –10 deg C.
2232 Hit patch of crystals.  Wind 200 deg at 30 33 m s–1.
2242 End of 13,000 ft run.  Heading back to Paine Field.
2325 Touch down at Paine Field
2330 Engines off.

S-Pol Radar Summary

         1300 UTC Thur 18 Jan:
             Radar switched from dual-pol to long-range mode.
             Scan cycle switched from NWS-Surveillance to Long Range
            (with RHIs after 1335 UTC).

         2045 UTC Thur 18 Jan:
             Radar switched from long-range to dual-pol mode.
             Scan cycle switched from Long Range to Research.

          0220 UTC Fr 19 Jan:
             Scan cycle switched from Research to NWS-Surveillance
            (with RHIs up to 1540 UTC Fr 19 Jan).

Summary of Navy Sonde Launches from Westport

          Launch times:
               1525 UTC Thur 18 Jan
               1803 UTC Thur 18 Jan
               1902 UTC Thur 18 Jan
               2129 UTC Thur 18 Jan
               0228 UTC Fr 19 Jan

       Notes: Test launch of Loran sonde with PNNL system at 2141 UTC Wed 17 Jan produced temperature and   RH but no winds.

Summary of NWS Sonde Launches from Quillayute (UIL) and Salem (SLE)

Launches are generally started ~1 h before a standard 3-hourly synoptic time, so some sondes are reported as occurring 1 h before the standard synoptic hour.

UIL Launch Times:

   1200 UTC Sat 18 Jan (standard)
   1800 UTC Sat 18 Jan (special)
   2000 UTC Sat 18 Jan (special)
   0000 UTC Fr 19 Jan (standard)

Note: 0200 UTC UIL sonde was launched because a request for cancellation did not reach the sonde launcher in time.