Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Mar 14 2023 08:38:22 FOUS30 KWBC 140838 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 437 AM EDT Tue Mar 14 2023 Day 1 Valid 12Z Tue Mar 14 2023 - 12Z Wed Mar 15 2023 ....THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA... ....California and the Great Basin... An ongoing atmospheric river event is forecast to continue through today into Wednesday, producing widespread heavy precipitation across California, with considerable to locally catastrophic flooding impacts expected for portions of the coast, Central Valley, and the Sierra Nevada foothills. A cold front that pushed east across eastern Washington and northeastern Oregon yesterday remains draped across southwestern Oregon and northwestern California this morning. This boundary will likely remain a focus for moderate to heavy precipitation as an approaching shortwave directs moisture into the boundary. This shortwave is forecast to amplify through the morning, supporting a strengthening surface low that is expected to move northeast along the boundary and bring additional periods of moderate to heavy rains across far northern California later today. These additional rains on top of already saturated conditions and high snow levels, prompted the continuation of a Moderate Risk along portions of the Northern California coast to the northern Sierra foothills today. A more isolated threat is expected farther east as moisture spreads along the boundary into northern Nevada, where locally heavy rains along with melting snow may produce flooding. Meanwhile, farther to the south as the previously noted shortwave continues to amplify and approach the coast, strong southwesterly flow ahead of the wave will direct a long-fetch of deep tropical moisture into Central and Southern California. A powerful low level jet will take aim at the region, driving this anomalous plume of moisture across the region. Guidance continues to show PW anomalies climbing in excess of 4 standard deviations above normal across much of Central and Southern California by the afternoon. This moisture, along with strong upper forcing supported by a coupled upper jet, is expected to support the development of heavy precipitation across Central California this morning before shifting south into Southern California by the afternoon. While some of the 00Z guidance did back away some, it still appears that the coastal ranges and the southern Sierra foothills will take the brunt of the heavy rain today. Overnight HREF guidance indicates that accumulations of 3-6 inches, with locally heavier amounts are likely for these areas. The HREF even shows some high neighborhood probabilities for amounts of 8 inches or more centered along the Santa Lucia Mountains and southern Sierra foothills. Given the likelihood for heavy rain, along with the already saturated soils, a High Risk was maintained along the much of the Central California Coast, with a Moderate Risk extending farther to the south into Southern California, including the Los Angeles Metro. A High Risk was also maintained along the southern Sierra foothills where in addition to the heavy rain, melting snow is likely to contribute to flooding concerns.=20=20=20=20=20=20 Pereira Day 2 Valid 12Z Wed Mar 15 2023 - 12Z Thu Mar 16 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHERN CALIFORNIA AND THE SOUTHWEST... ....California and the Southwest... While drier conditions are expected across much of California, a heavy to excessive rainfall threat may continue through Wednesday morning across portions of Southern California. The mid-to-upper level shortwave and associated surface low impacting California on Tuesday are expected to move east into the Intermountain West by early Wednesday. Onshore flow and deeper moisture back along the trailing cold front may continue to impact portions of Southern California, with additional heavy rains possible, especially in the upslope regions of the Peninsular Ranges. As the shortwave moves east, its associated frontal boundary and accompanying axis of deeper moisture are expected to move across the Great Basin and Arizona. This moisture interacting with favorable upper jet forcing may produce isolated runoff concerns, especially in the upslope areas of Arizona into portions of southern Nevada and southwestern Utah. Pereira =20 Day 3 Valid 12Z Wed Mar 15 2023 - 12Z Thu Mar 16 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF EAST TEXAS AND THE LOWER MISSISSIPPI VALLEY... ....Eastern Texas to the lower Mississippi Valley... The mid to upper level trough moving east across the western U.S. Tuesday and Wednesday is expected to amplify over the northern Plains on Thursday, with a deep closed system developing over the Upper Midwest Thursday night into Friday. Strong southerly flow will begin to tap moisture moisture from the Gulf of Mexico, drawing it north ahead of the system's trailing cold front as it advances east from the southern Plains into the lower Mississippi Valley. Both the GFS and ECMWF show PWs climbing to around 1.5 inches along a southwesterly 40-50 kt low level jet centered across eastern Texas into Louisiana. This moisture is expected to interact with favorable mid-to-upper level forcing to support convection, with heavy rain rates developing across the region on Thursday. As the front begins to reorient west-to-east, training storms along the front may bolster the threat for heavy to excessive amounts across portions of the region. The overnight guidance showed a fair amount of spread regarding the location of heavy amounts and therefore forecast confidence is limited.=20 However, the overall consensus generally supported a southerly shift which is reflected in this outlook. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-XVnM2pWoHBGQYAJmh33BTtoH8Mz_7NFshnPASiL3Dv4= a0rhcfrxTkUpp6Jp55p7pmsc4HfkubsWKjQRRa4klX5bMfo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-XVnM2pWoHBGQYAJmh33BTtoH8Mz_7NFshnPASiL3Dv4= a0rhcfrxTkUpp6Jp55p7pmsc4HfkubsWKjQRRa4kskjvuwo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-XVnM2pWoHBGQYAJmh33BTtoH8Mz_7NFshnPASiL3Dv4= a0rhcfrxTkUpp6Jp55p7pmsc4HfkubsWKjQRRa4kbbIW_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) .