Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 13 2025 05:45:44 AWUS01 KWNH 130544 FFGMPD CAZ000-131740- Mesoscale Precipitation Discussion 0033 NWS Weather Prediction Center College Park MD 1244 AM EST Thu Feb 13 2025 Areas affected...portions of northern, central and southern CA Concerning...Heavy rainfall...Flash flooding possible Valid 130543Z - 131740Z SUMMARY...Areas of heavy rain will overspread a sizable portion of northern to south-central CA through 18Z Thursday ahead of an approaching occluded cyclone. Some locations may see hourly rainfall in excess of 0.5 inches for several hours with the greatest potential for high rates along the Santa Lucia Range. 12 hour rainfall totals of 3 to 5+ inches are likely within areas of favored terrain and heavy rain may produce areas of flooding/flash flooding within urban areas and/or sensitive burn scars. DISCUSSION...Loops of GOES West water vapor imagery through 05Z showed a strengthening closed mid to upper-level low centered near 42N 134W. A strong, zonally oriented 250 mb jet axis was located across 36N 140W, south of the closed low, with winds in excess of 150 kt located as far east as 134W per GOES West DMW vectors. The location of the upper level jet max west of the upper trough axis indicated the longwave trough was digging southward, but the parent closed low appeared to be generally moving toward the east. A ribbon of moisture streamed from west to east across the eastern Pacific Ocean along a cold front connected into an occluded cyclone over the eastern Pacific. TPW and LPW imagery showed that the plume of moisture extended thousands of miles back to the west, originating in the tropical west-central Pacific. However, anomalous moisture was already located just off of the CA coast with 00Z soundings from OAK and VBG showing PWAT values between the 90th percentile and climatological max for mid-February. Warm advection rainfall was already occurring in advance of the warm front analyzed southeastward toward the south-central CA coast, roughly 60 miles west of the coast of Monterey County. As the closed low continues to advance off toward the east over the next 6-12 hours, the attendant cold front is forecast to steadily advance east and southeast, reaching the northern coast of CA around 12Z. IVT values will steadily increase across the central CA coast through 12Z peaking between 800-900 kg/m/s in the vicinity of San Francisco. IVT values will remain above 600 kg/m/s for a good portion of the central to south-central CA coast for several hours with 850 mb winds peaking between 50-60 kt. The orientation of the 850 mb flow is expected to be perpendicular to the coast from North Bay to Point Conception. Hourly rainfall in excess of 0.5 inches will become likely in and around the higher terrain of San Francisco Bay by 09Z, perhaps lasting for 3-5 hours. Farther south, hourly rainfall may reach 1 in/hr along the Santa Lucia Range given the favorable orthogonal orientation of the low level flow to the axis of the mountain chain. Downstream into the Sierra Nevada, snow levels are expected to be near 7000 ft which will result in rainfall impacts to potentially extend up to a relatively high elevation. Hourly rainfall in excess of 0.5 inches may exceed 6 hours in duration for portions of the central Sierra Nevada and Santa Lucia Range. Sub-hourly rainfall rates over 0.25 inches in 15 minutes will be possible within area of orographic ascent and boosted by weak instability, though CAPE values are forecast to remain focused below ~4 km AGL and stay below 250 J/kg by a majority of the most recent guidance prior to 18Z. 12 hour rainfall totals through 17/18Z are expected to peak in the 3 to 5 inch range for the Coastal Ranges into the upslope regions of the central Sierra Nevada, through higher totals may occur within the Santa Lucia Range given a favorable low level wind orientation. While flooding/flash flooding will be possible, it is expected to remain on the low end of the scale and may be focused across urban areas or perhaps lingering sensitivity on any area burn scars. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5Xmh9Oowt5YmUjifd4UFwIY0mxZaT2flnAljU8G1GJgFwfOn4sGM2mM1sT_wTJ33SY2v= mCQsmDq9al77Us9izFuTJMQ$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MTR...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 40782243 40652194 40112164 39712119 39512070=20 39232058 38912037 38572025 38051987 37581950=20 37421919 37171914 37021903 36751880 36571874=20 36271862 35941838 35501850 35381881 36001952=20 36032012 35642002 35171970 34622061 35212158=20 35932251 37862346 39302456 39972518 40592460=20 40532360 40662277=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .