Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 23 2024 00:52:31 FOUS30 KWBC 230052 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 852 PM EDT Thu Aug 22 2024 Day 1 Valid 01Z Fri Aug 23 2024 - 12Z Fri Aug 23 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHERN ARIZONA AND SOUTHERN UTAH... A Slight risk remains over portions of northern AZ into southern UT. Convection across this region continues to pose an isolated to scattered flash flood risk this evening. Do expect the convection=20 to begin to lose intensity by 06z, however in the meantime locally heavy rainfall rates will remain. A Marginal risk also extends across portions of eastern CO into southwest NE and northwest KS. An increasing axis of moisture transport will continue to allow for upscale growth of this convection through the evening hours. Cell mergers through the evening will result in a localized flash flood threat. Thereafter convection should begin to forward propagate off to the southeast resulting in a lowered flood threat. However with strong moisture transport/convergence on the southern extent of this convective complex, we could see some backbuilding over western KS which=20 may drive some flash flood risk overnight. Chenard Day 2 Valid 12Z Sat Aug 24 2024 - 12Z Sun Aug 25 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE FOUR CORNERS REGION/INTERMOUNTAIN WEST AND NORTHEASTERN FLORIDA... 21Z Update... Added a small Marginal Risk area to the Jacksonville, FL area with the surface front still lingering in place. This is partially contingent on rainfall this afternoon, but the potential for very localized FFG exceedance exists. Otherwise, no change to the previous forecast over the Four Corners region with an expected slight decrease in moisture. 12Z HREF still favoring southeastern AZ where the highest neighborhood probs for >1"/hr rates exist tomorrow afternoon (~30-40%). Fracasso 09Z issuance... The anomalous moisture feed that allowed for the active periods prior will vacate to the northeast with a skinnier axis of elevated PWATs generally focused from the AZ/NM state line up through the Inter Mountain West of UT/CO. This positions the the Four Corners area up through the Wasatch as the the main targets for heavy convection during the afternoon and evening Friday before the setup dwindles the back end of the period. A secondary focus across the terrain in Southeast AZ over into the NM Bootheel will also be an area that could see some scattered heavy rain signals with some support from global deterministic and ensemble members. Current QPF signal is modest with areal averages closer to 0.25-0.5" with a maxima focused near the Four Corners over Southwestern CO (>1"). The secondary max is across the Wasatch through the terrain in Western CO where isolated totals >1" are plausible, but more sporadic in coverage compared to the Four Corners region. Overall, the setup is more benign in the grand scheme, especially considering the previous active periods. Kleebauer Day 3 Valid 12Z Sat Aug 24 2024 - 12Z Sun Aug 25 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST/FOUR CORNERS AND SOUTH FLORIDA... ....Southwest and Four Corners... Lingering moisture and relative instability coupled with progressive shortwaves cutting through the Interior Mountain West will set up another round of isolated convection during the afternoon and early evening hours Saturday before a gradual dissipation with the loss of diurnal heating. Pockets of heavy rainfall are forecast across a similar corridor from D2, so some of the antecedent conditions could be favorable for greater impacts pending what occurs the period prior. Overall ensemble QPF footprint still indicates a max of 1-2", at best, within the strongest cores. This is still enough for flash flooding within complex terrain and especially around any burn scars. The previous MRGL risk was relatively unchanged. ....Interior Northwest... Removed the Marginal Risk area from northwestern MT and northern ID due to a decrease in QPF from the guidance and general lack of ingredients supporting heavy rainfall. ....South Florida.. Incoming moisture flux with roots from the Caribbean will make headway into South Florida with area PWAT anomalies shifting closer to +1 to +2 deviations above normal. Quasi-stationary front to the north will maintain its presence with a sharp delineation point of where the moisture pooling will reside. Considering a favorable axis moisture, instability, and the general sea breeze pattern across the area, a MRGL risk of excessive rainfall was maintained across the Southern FL Peninsula. Highest threat area currently is across Southwest FL near Naples, but will be monitoring the entire area over to the urban corridor on the opposite coast as the most impactful areas for flash flood concerns. Fracasso/Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4MsQlJSbT83hwgUuiwAl6kAtnVzbth8sthnRCxBS2Kqp= tAW_fONmarNIVVrah6goFC7bUi8DorbxHeM-lOoXHE_Wr0M$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4MsQlJSbT83hwgUuiwAl6kAtnVzbth8sthnRCxBS2Kqp= tAW_fONmarNIVVrah6goFC7bUi8DorbxHeM-lOoXYvfXVWU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4MsQlJSbT83hwgUuiwAl6kAtnVzbth8sthnRCxBS2Kqp= tAW_fONmarNIVVrah6goFC7bUi8DorbxHeM-lOoXOoJf_G0$=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) .