Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 19 2023 08:27:18 FOUS30 KWBC 190827 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 426 AM EDT Sat Aug 19 2023 Day 1 Valid 12Z Sat Aug 19 2023 - 12Z Sun Aug 20 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF SOUTHERN CALIFORNIA...=20 =20 Portions of the West...=20=20 An upper level low stuck near the central CA coast, the approach of Hilary from the south, a deep southerly flow across the Great Basin keeps precipitable water anomalies up to 4 sigmas above the mean to mid to late August from the Desert Southwest northward into Montana. For areas from Las Vegas southward, the 1.75-2.25"+ precipitable water values will be approaching all-time records, so there will be moisture to spare. While there is concern that cloudiness from Hilary, already moving into southeast AZ, will present some problems in building up instability across portions of the Southwest and Great Basin, the appearance of a low-level jet out of the Gulf of CA right at the end of the period early Sunday morning right near the apex of the monsoonal surge is of significant concern and could lead to convection during the late night of Saturday into early Sunday morning at an atypical time.=20 Some of the guidance shows local amounts of 5"+. The most likely spot would in and near the eastern slopes of the Peninsular Ranges within Southern CA and where the Moderate Risk area saw some expansion into the neighboring deserts due to input from the 00z HREF and the local forecast offices.=20 =20=20 =20=20 Florida...=20=20 An easterly wave is expected to move through the Keys and southern FL by Sunday morning, though it looks less amplified in the guidance when compared to previous days. Inflow at 850 hPa is expected to increase to 15-20 kts, which should increase the effective bulk shear enough to lead to greater convective organization than seen on Friday. Probably due to the progression of the feature, amounts weren't overly high in the guidance.=20 However, should any convective training or mergers occur, 3" an hour totals and local amounts of 5" cannot be ruled out, which would be most problematic in urban areas. Since the guidance QPF was generally modest, left the risk level as Marginal. As the wave appears less amplified, shaved some of the northern portion of the Marginal Risk area away. South Carolina/Georgia coasts... The guidance signal has become a bit weaker with the heavy rain signal since this time yesterday, likely due to the low-level inflow into the region becoming more divergent and weaker, so removed the Marginal Risk from the outlook.=20 =20 Roth=20=20 Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8OI_kOCfv0zfKyJF2i8vfBTJGE8Cy2ZB-aNrxCyIJgQ_= VKEmT37JTKiHbK7zj5wVzjLGNR3xTMAD43Lr6dDqALeVhCM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8OI_kOCfv0zfKyJF2i8vfBTJGE8Cy2ZB-aNrxCyIJgQ_= VKEmT37JTKiHbK7zj5wVzjLGNR3xTMAD43Lr6dDqxM9TYmw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8OI_kOCfv0zfKyJF2i8vfBTJGE8Cy2ZB-aNrxCyIJgQ_= VKEmT37JTKiHbK7zj5wVzjLGNR3xTMAD43Lr6dDqQ3JnNJs$=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) .