Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 31 2024 21:35:41 AWUS01 KWNH 312135 FFGMPD CAZ000-010502- Mesoscale Precipitation Discussion 0042...Corrected NWS Weather Prediction Center College Park MD 435 PM EST Wed Jan 31 2024 Corrected for Typo in third paragraph Areas affected...Northern and Central California Concerning...Heavy rainfall...Flash flooding possible Valid 312122Z - 010502Z Summary...A shallow convective line with 0.50-1"/hr rainfall rates is traversing through northern California along a cold front associated with strong low pressure offshore. This southward translating line may lead to instances of flash flooding going into tonight, focused along the northern and central California coastline.=20=20 Discussion...The KBHX (Eureka,CA) radar this afternoon continues to track a shallow convective line gradually marching inland along a cold front associated with a strong 968 mb cyclone in the Eastern Pacific. As highlighted in MPD 041, this activity is embedded within a plume of widespread stratiform rainfall as a long fetch (3000+ miles) of Pacific moisture streams northward ahead of the cold front, with precipitable water values 200-350% of normal noted across northern California and the Pacific Northwest per blended TPW. For much of today, rainfall rates have hovered in the ..25-.50"/hr range, generally focused in favorable upslope areas of the California Coastal Range. However, the passage of the frontal band over the last hour ushered in observed rainfall rates of ..60-.90"/hr in the vicinity of KHBX, along with several reports of flooding along Highway 254. This narrow cold frontal convection is expected to expand and translate to the south along the coast as strong frontogenetic forcing focuses the activity in the presence of 600-700 kg/m/s IVT ahead of the front, and low (but non-negligible) 100-200 J/kg of MUCAPE. The very favorable upper-jet dynamics highlighted in MPD 041 will also persist into tonight, including strong left-exit forcing and widely diffluent 350-250 mb flow. This scenario is reflected by the 12z HREF suite, which maintains rainfall rates of .5-1"/hr along the front going into tonight. The progressive nature of the cold front will likely limit a more robust flash flooding threat. However, 1 HR FFGs are low (.75-1"/hr), and increasing stratiform rainfall ahead of the convection will precondition soils for flash flooding aside from vulnerable urban population centers. Thus, several instances of flash flooding remain possible going into tonight. Asherman ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-jdTINFYJkyjCDvmBjhpxDpsWZOAZLT91veFWsp_xiP_CV38tB10qeVIXaXPZjjje0SD= kFfCcFMowwWXWNvQHrb098A$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MTR...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41772400 40892325 38832227 36032064 35492148=20 37952328 39872429 41172457=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) .