Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Mar 14 2023 22:54:34 AWUS01 KWNH 142254 FFGMPD CAZ000-150615- Mesoscale Precipitation Discussion 0108 NWS Weather Prediction Center College Park MD 653 PM EDT Tue Mar 14 2023 Areas affected...Northern California Concerning...Heavy rainfall...Flash flooding possible Valid 142252Z - 150615Z SUMMARY...Additional heavy rainfall over the next several hours will continue to encourage substantial areal runoff, and at least a localized flash flood threat given saturated soil conditions and high streamflows. DISCUSSION...The latest GOES-W IR satellite imagery shows a well-defined and strong mid-level shortwave trough crossing northern California which is driving surface low pressure bodily across the state and in connection with a well-defined atmospheric river event. Already there has been as much as 3 to 6 inches of rain across portions of the Cascade Range of northern California with a focus on Shasta and Trinity counties. Satellite imagery shows a compact, but strong deformation zone crossing Humboldt and Trinity counties currently with cooling cloud tops and with aid from the left-exit region of the upper-level jet crossing the region. This is resulting in strengthening vertical ascent and heavy rainfall rates that are occasionally exceeding a 0.50"/hour. Meanwhile, just to the east across the far northern part of the Sacramento Valley near Redding, and into the Cascade Range, there is an axis of enhanced low to mid-level convergence associated with the low track and interaction with a separate front draped over top of it. This is driving an increase in locally concentrated, but heavy rainfall across Shasta County. Adjacent upslope areas of the northern Sierra Nevada are also seeing an increase in locally heavy shower activity with a few linear bands setting up given convergent, but moist upslope flow. In fact, the 18Z HREF and several runs of the HRRR have been insisting on some localized stripes of very heavy rain with rates occasionally approaching 1"/hour over the next few hours across these areas, and especially over parts of Shasta County to the north and northeast of Redding. Expect locally an additional 2 to 3 inches of rain before the aforementioned low begins to exit the region and takes the broader atmospheric river event off to the east and away from the region. These additional rains will continue to encourage substantial areal runoff problems given the saturated soil conditions and high streamflows. Localized flash flooding is possible where the heavier rainfall rates over the next few hours set up. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9usKp4yUSOZaFYa9Z0x_y4MuQka9t5J1Si3CdXsuAbss1ZWc0lC_PhKRgW6Z8aCQRI7S= _THkKYnhExrq6vnOH60Dbxw$ for graphic product... ATTN...WFO...EKA...MFR...REV...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41352282 41192206 40742141 39642064 39202064=20 39062101 39442158 39812195 40042247 40092331=20 40092376 40342414 40972397 41252344=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) .