Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 09 2023 06:27:40 AWUS01 KWNH 090627 FFGMPD CAZ000-091630- Mesoscale Precipitation Discussion 0031 NWS Weather Prediction Center College Park MD 126 AM EST Mon Jan 09 2023 Areas affected...much of northern to south-central CA Concerning...Heavy rainfall...Flash flooding likely Valid 090624Z - 091630Z Summary...An approaching strong atmospheric river will begin to impact a large portion of CA over the next few hours. Hourly rainfall totals are likely to steadily increase through Tuesday morning, reaching 1 inch shortly after 12Z in the Santa Lucia Range. Elsewhere, peak hourly totals of 0.5 to 1 inch can be expected. Areas of flooding and debris flows will become likely, especially in burn scars and other areas of sensitive terrain. Discussion...Long loops of total precipitable water showed an elongated fetch of higher moisture stretching back to 150E (tropical western Pacific) containing contiguous values over 1 inch and small pockets of 1.5+ inches approaching 130 W. Infrared satellite, surface observations and RAP model analysis data helped place a strengthening surface low near 38.5N 129.1W at 05Z with an occluded/cold front arcing south and southwest into the east-central Pacific. A warm front extended southeast from the triple point and warm advection showers have already moved into central CA with hourly rain totals of 0.3 to 0.4 inches in the Santa Cruz Mountains ending 05Z. GOES West Derived Motion Vectors showed the presence of a 150 kt speed max near 32N 139W near 250 mb, an indication of a fairly strong Pacific storm system taking shape offshore of CA. As the occluded/cold front nears the central CA coast between 09-12Z, a large plume of IVT with peak values over 800 kg/m/s is expected to reach San Francisco Bay and areas just northward. Quick hitting hourly rainfall totals into the Coastal Ranges north of San Francisco Bay are expected to increase to over 0.5 inches, perhaps above 0.8 inches. As the front progresses farther inland beyond 12Z, the cold front is likely to slow its southward translation down the coast with peak IVT values of 800-1000 kg/m/s setting up roughly perpendicular to the Santa Lucia Range. The favorable orthogonal orientation of the 850 mb flow to the axis of terrain, forecast to reach as high as 50-60 kt, will support orographic enhancement of rainfall rates with 00Z HREF probabilities of 1+ in/hr as high as 60 percent in Monterey County by 15Z. Downstream, through the Sacramento and San Joaquin Valleys, locally heavy rain will be possible with over an inch in a few places by 16Z. Snow levels will steadily rise across the Sierra Nevada, with forecasts by the 00Z models showing 8000+ ft snow levels by 18Z. Upslope enhancement through 40 to 60+ kt of 850-700 mb flow will allow for hourly rainfall totals over 0.5" in some locations. Much of CA has been anomalously wet over the past few weeks and ending Sunday morning, the 2-week rainfall anomalies for much of north-central to south-central CA were 300 to over 600 percent above average, coinciding with well above average soil moisture. 0-40 cm soil moisture from Sunday night at midnight were over the 98th percentile in many locations of central CA. The addition of 2 to 4 inches of rain through 16Z (locally higher) and high rain rates will likely lead to areas of flooding, especially in burn scars and other areas of sensitive terrain. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8xkXpUhdm4Omeng19JdPjgiSlz6728PWiyoV9ecxK4RM70s-Zes8AW3ixLZ9c45LFCJT= TTG-lG1o9hxvtdv8aFXR6g8$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41192228 40762143 39792055 38972027 38361994=20 37561944 37001895 36541865 35821843 35541847=20 35571867 35921894 36071912 36251937 36231960=20 36031986 35721999 35181978 34921955 34981896=20 34881867 34701845 34441832 34211835 34021847=20 33861887 33931922 34191980 34392086 35812199=20 37692336 39982474 40622443 40802352 40982303=20 =20=20=20=20=20=20=20=20=20=20=20=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) .