Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Oct 10 2023 15:54:16 FOUS30 KWBC 101554 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1153 AM EDT Tue Oct 10 2023 Day 1 Valid 16Z Tue Oct 10 2023 - 12Z Wed Oct 11 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH TEXAS... ....16Z Excessive Rainfall Outlook Discussion... Few changes needed. 12Z HREF neighborhood probabilities show low-end probabilities for 2 inch per hour rate...and less than 5 percent (but non-zero) risk of rainfall exceeding 3 hour QPF late this evening or earl Wednesday morning over far southern Texas as remnant energy and moisture associated with Lidia and Max traverse the area and potentially interact with a developing wave over the western Gulf of Mexico. The previously issued ERO captured both probabilities within the Slight Risk area. 12Z soundings showed a plume of precipitable water values in excess of 2 inches from MMMZ to MMMY that was nosing into far southern Texas where values were barely sub-two inches. With southerly flow ahead of a developing wave resulting in additional moisture transport into the Texas...precipitable water values of 2.00 to 2.25 inches appears likely by later today. This deep moisture, along with favorable forcing, will raise the threat for locally heavy rain across the region. Expect the greater instability to remain near the immediate coast or just offshore, limiting rainfall rates inland.=20 These lighter rates may result in beneficial rains for most areas, however cannot rule out the threat for isolated flooding especially for urbanized areas and where soils are already relatively moist from last week's rain. Bann Day 2 Valid 12Z Wed Oct 11 2023 - 12Z Thu Oct 12 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE GULF COAST... ....Gulf Coast/Southeast... A wave developing over the northwestern Gulf of Mexico on Tuesday is forecast to track east across the northern Gulf on Wednesday before reaching the Southeast coast by early Thursday. Increasing southwesterly flow will feed deep moisture into a boundary lifting north ahead of the wave, with PWs increasing to over 2.25 inches (2 to 3 standard deviations above normal) along the central to eastern Gulf Coast. There remains some uncertainty regarding the evolution of this system, with some models such as the NAM, depicting a more amplified system with deeper moisture and heavier rains spreading farther north and west. A more suppressed solution, similar to the GFS and ECMWF, was more preferred, with the deeper moisture and greater instability likely to remain centered near the coast or offshore. A Slight Risk was maintained over portions of the Florida Panhandle where the preferred guidance shows the greatest threat for heavy amounts, with some potential for several inches near the immediate coast. For areas farther to the north, ample moisture with favorable forcing but limited instability are likely to support an extended period of moderate rain and a lesser excessive rainfall threat. ....Mid Missouri and mid Mississippi Valleys... An upper trough is forecast to dig southwest across the northwestern U.S., with a closed low developing over the central Rockies and High Plains by early Thursday. A strong low level jet developing over the Plains is forecast to feed increasing moisture into a slow-moving boundary extending east ahead of deepening cyclone over the central High Plains. Elevated convection is forecast to develop by late in the day, with the threat for heavy rainfall increasing as PWs climb to around 1.25 inches (1 to 2 standard deviations above normal). Redeveloping and west-to-east training storms may further raise the potential for localized heavy amounts.=20=20 Pereira Day 3 Valid 12Z Thu Oct 12 2023 - 12Z Fri Oct 13 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE MID MISSOURI VALLEY... ....Northern Plains/Mid Missouri Valley/Upper Midwest... A deep cyclone developing over the central Rockies and High Plains early Thursday is forecast to drift east across the Plains and into the mid and upper Mississippi Valley by early Friday. Strong southerly winds ahead of the system will continue to transport moisture into a region of strong ascent afforded in part by favorable upper jet forcing. For most areas the combination of ample moisture and strong forcing, but little instability, will produce an extended period of moderate rains, resulting in locally heavy accumulations but limited impacts. A Slight Risk was maintained along the mid Missouri Valley where greater instability and deeper moisture along the axis of strongest inflow may help to increase rainfall rates and the threat for short-term heavy accumulations and rapid runoff. Training storms may also raise the threat for heavy amounts and excessive runoff across this region. ....Southeast... The preferred guidance shows the low pressure emanating from the Gulf on Days 1 and 2 moving quickly off of the Southeast coast Thursday morning. However, rich moisture and mid level energy embedded within deep southwesterly flow in its wake may continue to produce periods of heavy rainfall across portions of north Florida and southeast Georgia.=20 Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9txQ7X1PL-m4wv8kegqStnkstoqcAIYnuqmmDqG7NDUP= rLdcDJGB3_Nfuc305SWHPDUFPhA1bIojzzjJeU3lxPlUU08$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9txQ7X1PL-m4wv8kegqStnkstoqcAIYnuqmmDqG7NDUP= rLdcDJGB3_Nfuc305SWHPDUFPhA1bIojzzjJeU3lr4F_V18$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9txQ7X1PL-m4wv8kegqStnkstoqcAIYnuqmmDqG7NDUP= rLdcDJGB3_Nfuc305SWHPDUFPhA1bIojzzjJeU3lAYWTVqI$=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. 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