Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Mar 21 2023 17:46:27 AWUS01 KWNH 211746 FFGMPD CAZ000-220600- Mesoscale Precipitation Discussion 0115 NWS Weather Prediction Center College Park MD 145 PM EDT Tue Mar 21 2023 Areas affected...Near Coastal Portions of Central and Southern California Concerning...Heavy rainfall...Flash flooding possible Valid 211800Z - 220600Z Summary...Localized/isolated instances of flash flooding are possible through the overnight hours across near coastal portions of Southern and Central California with localized rainfall rates possibly exceeding 0.5"/hr at times (with additional rainfall totals locally as high as 1.5-3.0 inches). Discussion...The first round of heavy precipitation is gradually coming to an end across Southern California this morning, as a distinct dry slot begins to envelop the area (per GOES-West water vapor and CIRA composite advected layered precipitable water imgery). Total precipitable water (TPW) in association with the primary band of moisture transport (and the core of the primary atmospheric river) ranges from 0.9-1.1 inches (near the max moving average per NKX sounding climatology), whereas the air mass to the north and west of San Diego (behind and accompanying the dry slot) ranges from 0.5-0.8 inches (between the 75th and 90th percentiles, per VBG and NKX sounding climatology). Low-level flow (and associated moisture transport) is also expected to decline as the atmospheric river sinks southward, from as high as 45-55 kts currently to a variable range of 20-40 kts this evening and overnight. While the more direct impacts of the atmospheric river are gradually coming to an end (with 12-hr localized rainfall maxima via MRMS generally between 1-2 inches), our attention will be turning to a second round of precipitation driven by a strong vorticity maxima that is rounding the parent mid-level low/circulation (located just offshore of the San Francisco/Santa Cruz region). This feature may further deepen the associated surface low pressure off the Central California coast in the near term (where mesovorticies have become more apparent via KMUX radar imagery over the past several hours) with steepening low-level lapse rates spreading across both the Central and Southern CA coasts. This will increase the potential for moderate to heavy showers from late afternoon into the overnight (with localized hourly rates possibly exceeding 0.5"/hr and additional totals of 1.5-3.0 inches, particularly along the west to southwest looking slopes of steeper terrain). Isolated instances of flash flooding are considered possible, particularly near burn scars or other sensitive terrain (including low-lying and poor drainage sections of populated metropolitan areas). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6nggx-fXK4GtjG36gD1_t1O2kqJXpy9X0oSAIz2gO_j4YWPj1eG6nyN6jRAFat_1U1MR= 0E5oX2HoX5LkfJ9DLcB9wwM$ for graphic product... ATTN...WFO...HNX...LOX...MTR...SGX...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 37652202 37652139 37222124 36862080 36012012=20 35721998 35161952 34751923 34751872 34451805=20 34111696 33851669 33581646 33121630 32571631=20 32461726 33091756 33511812 33851883 34231961=20 34322046 34862086 35292124 35952190 36732215=20 37402255=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) .