Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 23 2025 08:39:01 FOUS30 KWBC 230838 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 438 AM EDT Sat Aug 23 2025 Day 1 Valid 12Z Sat Aug 23 2025 - 12Z Sun Aug 24 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST AND FOR PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES... ....Southeast into the Appalachians... Convection that occurred on Friday has increased the amount of soil saturation and consequently the sensitivity for flooding from additional rainfall. With similar environmental conditions today... 1500 to 2500 J per kg of CAPE, lingering mid- and upper- level vorticity aloft with a weak circulation center hugging the Georgia/South Carolina coastline and elevated precipitable water=20 values...there will an elevated threat for scattered areas of flash flooding across the region particularly for Georgia and the=20 coastline. Areal averages of 1 to 2 inches will be common with=20 very isolated maxes upwards of 4 to 6 inches remain possible near=20 the coast. ....West... Little change in the large-scale pattern resulted in the Excessive Rainfall Outlook being very similar to the one on Friday. Scattered to numerous showers and thunderstorms across southern and eastern=20 California and across the interior west with the eastern extent=20 likely back over the Central Rockies. Heaviest QPF footprint is=20 currently situated over the Sangre de Cristos and San Juan mountains southward into northern New Mexico given embedded=20 shortwave energy and orographics providing areas of focused ascent. The more prone slot canyon, burn scar remnants, and dry washes=20 will once again be the target of interest for flash flood=20 prospects with model guidance continuing to show localized maximum rainfall rates on the order of 1 to 1.5 inches during the time of maximum heating that persists into the evening. Bann Day 2 Valid 12Z Sun Aug 24 2025 - 12Z Mon Aug 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SOUTHWEST AND FOR PORTIONS OF THE CENTRAL ROCKIES TO THE CENTRAL PLAINS... ....West... Maintained the Slight Risk area in parts of Utah and northern=20 Arizona where models still depict convection occurring over/near=20 vulnerable slot canyons, burn scars and normally dry washes during=20 from later today into the evening...much like the placement and=20 timing of storms that occurred on Friday. The driving forces will=20 continue to be weak shortwave energy embedded within the=20 anticyclonic flow across the Intermountain region. Father east...the risk of excessive rainfall starts to spread out away from the central Rockies Front Range and out over the adjacent plains. Deep layer shear is going to be enhanced as the flow aloft is forecast to be northwesterly at this point while low level flow from the southeast draws air with higher dewpoints/precipitable water values upslope. Spaghetti plots along with the RRFS continue to show potential for 2 to 3 inch rainfall amounts extending as=20 far east as western Kansas by the end of the period. Given the=20 precipitable water values forecast...the most active convection=20 could drop 1 to 2 inch rainfall amounts in an hour. The previously issued Slight was largely unchanged. ....Appalachians to Mid-Atlantic and Pennsylvania/New York... A deepening area of low pressure north of the border will force a=20 cold front to sweep eastward from the Great Lakes into the eastern=20 third of the country on Sunday. The airmass ahead of the front=20 across the central and southern Appalachian chain is forecast to=20 have 500 to 1000 J per kg of MLCAPE and precipitable water values=20 generally in the 1.5 to 1.75 inch range at the start of the day=20 which drops during the day. The area over portions of Pennsylvania=20 and New York continue to have a longer window of opportunity for=20 locally heavy rainfall. As a result...maintained the northern end=20 of the Marginal risk area near a region of lower flash flood=20 guidance due to the potential for heavier rainfall rates and=20 amounts overlapping. ....Coastal North Carolina...=20 A weak surface feature hugging the coastline will focus and=20 support locally heavy rainfall near the coast of North Carolina on=20 Sunday and Sunday night. Present indications are that the activity=20 should remain off-shore. However...even a subtle slowing of its=20 forward speed or shift in track could bring moderate to heavy=20 rainfall to the immediate coastline of North Carolina late Sunday. ....Southern Georgia and northern Florida... On-shore flow of moist air interacting with the southern end of the front associated with the low pressure/amplifying upper trough to the north should combine for convection capable of producing heavy rainfall Monday and Monday evening across portions of southern=20 Georgia into the northern Florida peninsula.=20 Bann Day 3 Valid 12Z Mon Aug 25 2025 - 12Z Tue Aug 26 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL ROCKIES FRONT RANGE TO THE SOUTHERN PLAINS ON MONDAY... Broad, cyclonic flow aloft will be in place across the Plains on Monday while low level flow should continue to be drawn northward at low levels of the Southern Plains...with a boundary extending front northern Texas into northeast New Mexico and southern Colorado helping to focus late day storms. The airmass south of the front is expected to have precipitable water values approaching 2 inches across the region and values potentially in the 2 to 2.25 inch range near the Red River. Stability does not appear impressive at this point...but the atmosphere should support locally heavy rainfall should convection develop anywhere between Oklahoma/northern Texas westward into the plains of eastern Colorado and northeast New Mexico. The Slight Risk area was embedded within a broader Marginal Risk area extending across much of the central and southern portion of the Great Basin and eastward to the central and southern Rockies=20 Front Range. Once again...weak shortwave energy embedded within a=20 broad upper leads to yet another round of late day showers and=20 thunderstorms. Slot canyons...normally dry washes and burn scars remain most at risk for flooding. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-8HFJSn0uBLIiR5M5CxALEDBQjQnmpXKwg-KxZxPD1Ex= YWmGZfMkq12UicRp0ACd81ADlbrfyM8BucCRcIxXj2J1jJM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-8HFJSn0uBLIiR5M5CxALEDBQjQnmpXKwg-KxZxPD1Ex= YWmGZfMkq12UicRp0ACd81ADlbrfyM8BucCRcIxXJElCoHE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-8HFJSn0uBLIiR5M5CxALEDBQjQnmpXKwg-KxZxPD1Ex= YWmGZfMkq12UicRp0ACd81ADlbrfyM8BucCRcIxXGcCQaJQ$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .