Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 03 2022 08:22:30 FOUS30 KWBC 030822 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 321 AM EST Sat Dec 03 2022 Day 1 Valid 12Z Sat Dec 03 2022 - 12Z Sun Dec 04 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL CALIFORNIA COAST, THE WEST-FACING SLOPES OF THE SIERRA NEVADA RANGE IN CENTRAL CALIFORNIA, AND SOUTHEASTERN ARIZONA... ....California... An upper level cutoff low centered off the coast of OR will drift southeastward towards the northern CA coast today. This forcing will team up with a subtropical disturbance and associated Pacific moisture to drive it into central CA today. The front moving into the Point Conception area will continue drifting northward through the morning, with some intensification in the rainfall rates as the upper levels increasingly contribute to the heavier rainfall rates. That said, instability is very low in this area, so the mountains will be the primary driver of heavy rain. This area of rain will stall between Monterey Bay and Point Conception today, which should allow for several (2-4) inches of rain to fall into the coastal mountains. The only real change from inherited was to nudge the southern end of the Marginal a bit north towards Point Conception, since there is a well defined back edge to the rain moving north and is not expected to move back south once that back edge moves through. Hourly rainfall rates have been one quarter inch or less so far, which is well below anything that would cause flooding. Further inland, the unidirectional southwest flow will run up nearly perpendicular to the Sierras of eastern California today. These much higher mountains will then wring out even more precipitation than the coastal mountains. While the highest peaks can expect snow, the high snow levels should allow much of the precipitation to fall as rain. The inherited Marginal Risk area remains unchanged. Expect 3 to locally 5 inches of rain near or over the mountains that will runoff quickly, causing isolated flash flooding in the foothills.=20=20 ....Southeastern Arizona... The inherited Marginal Risk area was trimmed a bit to align with the forecast axis of heaviest precipitation, in coordination with the EPZ/El Paso, TX, TWC/Tucson, AZ, and ABQ/Albuquerque, NM forecast offices. The heaviest rainfall, which could exceed 2 inches in 24 hours in isolated spots, extends from the Mexican border northeast through metro Tucson and then northeast to the=20 New Mexico border. The Marginal Risk was removed from New Mexico as the guidance becomes better aligned further north and west. This separate plume of moisture from the one impacting the California Coast will have some upper level support in the form of a right entrance region of an upper level jet along with highly anomalous moisture featuring PWATs of 1.25 inches, which is over 5 standard deviations above normal for this time of year. Thus, the moisture has very tropical origins. With that said, the lack of instability will be the primary factor reducing rainfall rates over this area. Meanwhile soil moisture in this area is around average for this time of year. Wegman Day 2 Valid 12Z Sat Dec 03 2022 - 12Z Sun Dec 04 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6CUsVlf3v4exq5T5Dc9lRVORGvCBsBQW5kafsb8fQoFS= rjOY5HjF1vOLIohhFJpWXA2FMhfcBjBsyZJAke74sNE6hM8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6CUsVlf3v4exq5T5Dc9lRVORGvCBsBQW5kafsb8fQoFS= rjOY5HjF1vOLIohhFJpWXA2FMhfcBjBsyZJAke74P0aGouY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6CUsVlf3v4exq5T5Dc9lRVORGvCBsBQW5kafsb8fQoFS= rjOY5HjF1vOLIohhFJpWXA2FMhfcBjBsyZJAke74aooZh04$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .