Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 06 2024 00:58:40 FOUS30 KWBC 060058 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 858 PM EDT Thu Sep 5 2024 Day 1 Valid 01Z Fri Sep 06 2024 - 12Z Fri Sep 06 2024 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FOR A PORTION OF SOUTHEAST LOUISIANA... 01Z Update...=20 ....Central Gulf Coast... Surface low is centered about 100mi southeast of Matagorda Bay Texas and the stationary front extending east (but offshore into the Bay) should provide the focus for heavy rainfall overnight. Recent RAP runs depict a northward drift to this low late tonight which may allow instability, currently limited to along/off the Upper TX and LA coasts, to push somewhat inland, but likely remain south of I-10. Convergent low level flow over the front into the Central Gulf Coast should continue to allow localized enhanced rain over areas that have been quite saturated over the past day. Therefore, decided to maintain the Moderate Risk over the Baton Rouge to NOLA urban corridor and the Slight Risk from just south of Galveston=20 across southern LA/MS. Heavy rain will move toward/into the FL Panhandle overnight, though since the rain has been sequestered offshore for most of the past day, the Marginal Risk there should suffice for overnight. ....Georgia Coast and Jacksonville Metro... Convection will continue to develop overnight in the onshore flow=20 north of a stationary front near St. Augustine with sufficient=20 instability, high precipitable water values, high freezing levels=20 and weak steering level flow. Areas of the southern GA Coast are saturated from heavy rain over the past day, so the Slight Risk is maintained for overnight.=20 ....New Mexico... Introduced a Slight Risk to the highly flash flood prone Sacramento mountains that still have fresh burn scars from this season given the regional radar depiction of heavy cells approaching with a strong cold front pushing down eastern NM. Otherwise, the mainly diurnal convective storms should diminish around midnight with the Marginal Risk maintained elsewhere over NM.=20 Day 2 Valid 12Z Fri Sep 06 2024 - 12Z Sat Sep 07 2024 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL MAINLY ACROSS SOUTHEAST LOUISIANA... ....Gulf states and Southeast... Introduced a Moderate risk that was largely confined to southeast Louisiana where low pressure riding along a quasi- stationary front will continue to focus and support areas of heavy to potentially heavy rainfall on top of widespread moderate to heavy rainfall in the Day 1 period. A mid and upper level trough will be digging across the western Gulf Coast region which increases low- level frontogenesis along the central-eastern Gulf Coast to the Georgia Coast. Heaviest short-term rainfall rates should be confined to a corridor where precipitable water values of 2.2 to 2.5 inches, tall/skinny CAPE profile and greatest low-level FGEN along the quasi- stationary surface boundary align. While there continues to be some spread on exactly where the highest QPF will focus...two camps of thought are developing with the broader/coarser guidance being slower to move the heaviest rainfall off shore while the higher resolution guidance favored a faster solution that brings more drying in from the north with correspondingly lower QPF. Given the probabilistic nature of the Excessive Rainfall Outlook, opted to introduce the Moderate risk area to highlight the potential for additional heavy rainfall with some overlap into the lower QPF shown by the higher res guidance favored by the WPC QPF desk. Either way...there is a general consensus for 1 to 3 inch amounts in the rain area and several pieces of guidance that indicate isolated maxes of 4 to 8 inches, especially along the coastline. Bann Day 3 Valid 12Z Sat Sep 07 2024 - 12Z Sun Sep 08 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE EASTERN GULF COAST AND SOUTHEAST ALONG WITH PORTIONS OF THE NORTHEAST... 2030 UTC Update... Trimmed away some areal coverage of the Marginal Risk area in the Northeast U.S. given an overall lack of instability to help support rainfall rates (an idea supported by pretty meager model QPF). Otherwise, few changes needed. Bann Previous Excessive Rainfall Discussion... ....Gulf Coast and Southeast... Slow moving convection will continue to focus along the draped frontal system along the Gulf Coast and Southeast U.S. Abundant Gulf moisture will continue to feed into the region leading to higher rainfall rates. Multi-day rains will have increased soil saturation and lowered flash flood guidance by this period thus there will be a continued threat for excessive rainfall and local flooding concerns. A Marginal Risk is in effect across northern Florida and southern Georgia. ....Northeast... An upper trough/low will pivot across the region during this period sending showers and thunderstorms across the Northeast where multiple recent rains have increased soil sensitivity. A Marginal Risk area is in effect for eastern New York, northeast Pennsylvania, northern New Jersey and northwest Vermont. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!41hdENBUZdMFxfAlxJctL5EeatwPdiR19A-zBgzFHjV7= 9HgZ-JbtegMIDCgzlDCibQ7_X2gdCCDpHFVTCblplZxI6ho$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!41hdENBUZdMFxfAlxJctL5EeatwPdiR19A-zBgzFHjV7= 9HgZ-JbtegMIDCgzlDCibQ7_X2gdCCDpHFVTCblpyAqd07I$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!41hdENBUZdMFxfAlxJctL5EeatwPdiR19A-zBgzFHjV7= 9HgZ-JbtegMIDCgzlDCibQ7_X2gdCCDpHFVTCblpvwtFt24$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .