Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 20 2023 15:36:44 FOUS30 KWBC 201536 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1136 AM EDT Mon Mar 20 2023 Day 1 Valid 16Z Mon Mar 20 2023 - 12Z Tue Mar 21 2023 ....16Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 2 Valid 12Z Tue Mar 21 2023 - 12Z Wed Mar 22 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS COASTAL AREAS OF SOUTHERN CALIFORNIA AND CENTRAL ARIZONA... ....Southern California... A strong closed low diving southeast across the Northeast Pacific and inland into central California and the Great Basin will direct another atmospheric river (AR) into California and Arizona through Tuesday and the overnight hours. Strong 850 to 700 mb moisture flux expected on the south side of this closed low, impacting areas from the central California coast range , southeast through the Transverse and Peninsular Ranges and into the southern Sierra during the day on Tuesday, progressively spreading inland into the Southwest Tuesday night into early Wednesday . The National Water Model has been showing several streams with high flows across the central California coast range, southeast into coastal southern California, including the Transverse and Peninsular Ranges, which coincides with anomalous soil moisture values as per NASA SPoRT maps. The latest guidance continue to depict a broad area of 1 to 3+ inches over the southern to central Valley/foothills of the Sierra with the heaviest precip here expected to fall as snow in the Sierra, with no significant contribution to runoff from snow melt expected. The snowpack in the Transverse Ranges is very limited to small areas of the highest elevations which will greatly limit or negate any snowmelt contributing to any flooding. The Marginal and Slight Risk areas remain in good order but required minimal adjustments to reflect the latest WPC QPF and trends. ....Central Arizona... Higher snow levels are expected for the terrain of central Arizona as the AR reaches the area, which will limited snowmelt along the higher elevations of the Mogollon Rim to contribute more to any flash flooding in the area. With PW anomalies creeping up to +_4 and +5 standard deviations, most of the guidance are signaling up to 3 inches of rainfall for the higher elevations, with lesser amounts forecast for locations to the south and west. The conditions for excessive rainfall and rapid runoff will be more favor for points north and east of the Phoenix metropolitan area. The inherited Slight and Marginal Risk areas remain reflective of the level of threat for flooding concerns. Therefore, no adjustments were made with this issuance. Campbell Day 3 Valid 12Z Wed Mar 22 2023 - 12Z Thu Mar 23 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7xQCwkO3_ZQpc19a2xPjw71wHVM9btbKgPy_Ewrn7JDU= sn_bvm7_45iOuFskKIoWNGFdj4dQLopi_iswyZGSeRGairI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7xQCwkO3_ZQpc19a2xPjw71wHVM9btbKgPy_Ewrn7JDU= sn_bvm7_45iOuFskKIoWNGFdj4dQLopi_iswyZGSpVVdldw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7xQCwkO3_ZQpc19a2xPjw71wHVM9btbKgPy_Ewrn7JDU= sn_bvm7_45iOuFskKIoWNGFdj4dQLopi_iswyZGS8EoJyYw$=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) .