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Project Status: 4 January 2008 2030UTC

IOP #4 Going Wild

Weather Status: IOP#4 is meeting and exceeding all expectations with heavy rain, high winds, strong upslope, high IPW, etc. Rainfall was very intense in the ARB with rainfall rates of 0.6 inches/hr occurring at BLU before 4 Jan 19UTC (11L) power failure. The high winds have brought havoc to some observing sites as either power or telecommunications are down. A very strong barrier jet has set up in the Central Valley and Sierra foothills and is probably the culprit for these failures. Over a million Central Valley residents are without power at this hour. Freezing levels that started at about 4500-5000ft yesterday have climbed to 6000-7000 ft today so the event has been mostly rain. Winds aloft at jet level in the Pacific are 235kts with an unprecedented jet streak, falling into the rear of this massive trough. The associated surface low off the coast is 960MB (surface pressures like a category 1-2 hurricane, except more massive in horizontal scale).Winds at 700mb in the ARB area are predicted to reach 90kts between 4 Jan 21 (13L) and 5 Jan 00UTC (16L). The frontal passage is predicted to occur about 5 Jan 00-01UTC (16-17L) with rapid cooling expected and the freezing level lowering below BLU after that time. This means the rain transitions to snow. Winds behind the front will decrease a bit and blow more out of the WSW to W. Peak precipitation is probably occurring at this hour with decreasing precip rates after the front. Both the NAM and local models are bringing in over 2 inches in the 4 Jan 21 (13L)-5 Jan 00GMT(16L) period. Precip rates will likely decrease to 0.3-0.5/3hr through 5 Jan 12UTC (4L). A slight lull is hinted at by the models but another minor short wave re-intensifies the snow Saturday night (6 Jan 00-03UTC [5/16-19]). This wave will sustain snow through Sunday. By 7 Jan 00UTC (6/16L) the winds shift more to the NW and precip will decrease to 0.1inch/3hrs. By Monday precipitation will be very light to non existent so a pretty solid break is expected during that time. The next system is due late Tuesday (9 Jan 00UTC [8/16L]) with warm advection re-establishing itself over the area and likely producing another rain event. QPF shows this to be a 1-2 inch event ending Wednesday. After that it looks like ridging will hold sway over the area Thursday through the weekend (10-13Jan).

Summary: Extreme rain and wind event through 5 Jan 03UTC[4/19L); changing over to snow after that time ending 7 Jan 03UTC(6/19). Next system Tuesday (9 Jan 00UTC [8/16L]) to Wednesday late (10 Jan 03UTC[9/19L]), likely a moderate rain event.

Observational Summary: Winds are playing havoc with many of the HMT systems. At 4 Jan 21UTC (13L) the HYDROX radar dish was declared uncontrollable owing to the winds. All scanning was rendered impossible. Crews were locking the azimuth and elevation and were preparing to abandon the site. An abandonment was planned anyway for 5 Jan 00UTC (4/16L) with the onset of snow to ensure the crew would not be trapped at the site in the heavy snow extending into late Sunday.The HYDROX did collect valuable data for the onset of the moisture plume and during the most intense precipitation.Power was out at BLU making key surface measurements impossible. At other sites power or communications eliminated data from the Chico, Cazadero, Colfax and Slough House profilers. Surface stations at BLU and Lee Vining were out. Special soundings will continue at OAK and RNO though 08UTC as noted yesterday. A power failure at SHS has rendered the soundings there inoperative. If power is restored soundings will continue through 5 Jan /12UTC. A decision about continuing operations at SHS will depend on the prediction of power restoration. The current shift will remain on duty until information on power is obtained.

Decision summary: HYDROX radar operations terminated as soon as possible. OAK and RNO special soundings continue until 5 Jan 08 UTC (00 L). SHS soundings will continue if power is likely to be restored; if not, site will be vacated. Shift 4 would be last on duty.

Product Summary: Observational products from named sites above are unavailable. High resolution models are available after a missed cycle at 4 Jan 06UTC (3/22L).

McGinley, GSD

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