Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 04 2023 19:31:22 AWUS01 KWNH 041931 FFGMPD CAZ000-050329- Mesoscale Precipitation Discussion 0017 NWS Weather Prediction Center College Park MD 230 PM EST Wed Jan 04 2023 Areas affected...Northern California...Central California Concerning...Heavy rainfall...Flash flooding possible Valid 041929Z - 050329Z Summary...A strong atmospheric river event is underway across much of northern and central California. Persistent heavy rainfall atop widespread compromised soils will yield an uptick in flash flooding chances going through the afternoon, particularly atop burn scar areas. Discussion...Regional radar mosaic depicts stratiform rainfall ongoing over portions of northern and central California, containing recently observed hourly rainfall rates upwards of ..10-.20 in/hr along portions of the Sacramento Valley. This inland rainfall denotes the remnant wave of precipitation within a strong atmospheric river plume flowing northeast as an explosive hurricane force low continues to deepen offshore and slowly migrate northeast. Meanwhile, GOES IR imagery and radar continue to track a band of shallow convection and stratiform rain associated within the approaching frontal band of the aforementioned storm. Going through the afternoon into tonight, the expectation is for offshore shallow convection and upslope enhanced rainfall to slowly migrate inland over northern and central California, on the heels of the activity this morning. The overall environment ahead of the front remains very favorable to promote enhanced rainfall rates with this incoming activity, including strong left-exit region jet forcing, layered diffluence, persistent low-level convergence, and a deep pre-frontal tropical moisture feed. Thus, rainfall rates exceeding .75-1 in/hr are not out of the question tonight, particularly within any developing shallow convection over north-central California. Soil conditions over northern/central California remain very susceptible to additional runoff, even more so given the leading round of rainfall earlier this morning. In fact, the AHPS precipitation analysis going into this morning showed widespread 125-300% greater than normal rainfall over the last 30 days atop northern/central California. Within this area of anomalous monthly rainfall are numerous burn scar areas, highlighted in the graphic above. Morning HREF probabilities of ARI exceedance corroborate the increase overall flash flooding potential going into the afternoon/evening hours. By 0Z tonight, the HREF suggests increasing probabilities (10-25%) of 10 year ARI exceedance along the Cascades toward the Transverse Range, with a scattered signal for 100 year ARI exceedance (5-15%) noted. Thus, flash flooding chances are expected to ramp up through today, with locally significant flash flooding possible atop areas of burn scar. Shallow landslides are also possible given the high degree of soil saturation present. Asherman ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4Wkh8y8siwpjukuq0k9669Xpnf0i9NnXtE-_FKlQ0hoiK1iXY8AxOC4MRbGIa11a7x3J= 7aTkGaTpqNaqPnzsORYtUS0$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41742389 41682310 41562261 41412216 40802174=20 40712132 40582106 40292104 40212098 40132071=20 39862075 39472061 39212023 38691987 37891968=20 37721958 37391943 37041934 37081973 37382043=20 37382046 37052066 36552041 35722029 35492079=20 35952153 37602285 38482354 39262414 40642468=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) .