Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 03 2024 23:27:06 FOUS30 KWBC 032326 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 626 PM EST Sun Nov 3 2024 Day 1 Valid 01Z Mon Nov 04 2024 - 12Z Mon Nov 04 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND THE OZARKS... ....Southern Plains and the Ozarks... The axis of heaviest rainfall expected across Oklahoma and=20 Arkansas and southern Missouri tonight into early Monday morning.=20 A longwave trough over the Southwest is shifting eastward.=20 Embedded shortwave disturbances as well as a developing 90 kt jet=20 streak will move over the region through tonight. A well-=20 established low level jet (LLJ) will continue to advect plentiful=20 Gulf moisture northward into the area. The result will be training bands of storms in OK/AR and into MO. Soils across OK, AR, into=20 southern Missouri have been saturating due to recent heavy rainfall. This is likely to cause widely scattered to scattered instances of flash flooding. Given the plentiful moisture, training storms, saturating soils, and some flood prone areas, the heavy rain could cause localized flash flooding. The Ozarks remain in the highest risk area. The=20 topography will help to focus the heavy rainfall into the=20 valleys...which could result in rapid river, stream and creek=20 rises. This also locally increases the flash flooding threat as=20 compared to the same amount of rain falling over relatively flat=20 terrain. Flash flooding remains likely as amounts could locally=20 exceed 5 inches. Changes to the inherited risk areas were minor. ....Upper Midwest... In the upper Midwest, the eastward shift in the guidance and a=20 more west to east movement of the expected convection should limit=20 how much instability and moisture reach the upper Mississippi=20 Valley. It's likely any remaining convection will be in a much=20 weakened state by the time the rain reaches this area. Since=20 similarly dry conditions and drought have impacted the upper Great=20 Lakes in recent weeks, the largely stratiform nature of the rain=20 should mean all of the rain will be beneficial with no flooding=20 concerns noted. Changes to the inherited risk area were minor. Roth/Wegman Day 2 Valid 12Z Mon Nov 04 2024 - 12Z Tue Nov 05 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST TEXAS THROUGH PORTIONS OF WESTERN LOWER MICHIGAN... 20Z Update: Changes were few and far between for the D2 ERO with the primary deviation being a slight shift eastward with the risk areas given the latest trends within the forecast precip. A secondary area of development over the course the evening into tomorrow morning will generate another outflow dominant convective pattern with a general expansion of the precip further to the north and east leading to areas downstream in the Ozarks becoming the benefactor of the heaviest precip. There's a strong consensus for heavy rain totals exceeding 3" across the above area with a the 12z HREF neighborhood probabilities exceeding 70% for the >3" threshold extending from Southeast OK up through Northwest and North-Central AR into Southeastern MO. EAS probabilities follow suit with an axis of 50+% of >2" probs located over the same area with a 20-30% for >3" encompassing a good portion of the Ozarks. The antecedent conditions leading in are relatively dry in the grand scheme with the NASA SPoRT indicators leveling off the soil moisture percentiles below 40% for much of the area anticipating heavy rain. The more complex terrain does offer a slightly better risk than typical compared to areas in the plains, so the prospects are within the higher end of the SLGT risk margin, but just outside the MDT risk upgrade for the time being. Pending the evolution of the activity tonight, an upgrade may be necessary, targeting locations likely centered over Northwest AR into Southern MO. Will continue to monitor the situation closely as it evolves. ...Previous Forecast.. Few changes were made or needed to the Slight Risk area across the middle of the country. A deep longwave trough will continue move eastward but begin to weaken and lift northward back into the jet stream on Monday. As it does so, associated jet streaks will intensify downstream of the trough, which will support its deamplification. The LLJ that has been supplying Gulf moisture will also elongate towards the north reaching as far north as lower Michigan by Monday. This will cause the resultant moisture to focus in a SSW to NNE corridor from Texas to Michigan. Unidirectional SSW flow will support training thunderstorms. The strongest storms are expected from Texas through Missouri, which will have access to the greatest Gulf instability and moisture. The storms will gradually weaken the further north you go, but are expected to maintain their integrity into Wisconsin and Michigan. The topography of the Ozarks will further locally enhance rainfall totals due to some upslope support. Due to overlap with the rainfall footprint Monday with that expected today, there is some potential for a Moderate Risk upgrade from western Arkansas into southern Missouri. However, this will be highly dependent on how much rain falls in that area today/Sunday. Total rainfall amounts will be somewhat lower on Monday as compared to Sunday, hence the importance of rain falling over the same areas as Sunday to enhance the flooding threat to Moderate Risk levels. Thus, the potential for an upgrade will continue to be evaluated. Wegman Day 3 Valid 12Z Tue Nov 05 2024 - 12Z Wed Nov 06 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MISSISSIPPI AND OHIO VALLEYS... 20Z Update: Very minor adjustments were made to the MRGL risk located across the Mississippi and Ohio Valleys as the overall pattern and subsequent rainfall forecast maintained continuity from run-to-run. Areal average QPF runs between 1-2" for the period with the heaviest rainfall likely relegated over the Mid Mississippi Valley Tuesday morning and afternoon before petering out as the disturbance shifts eastward. Main threats will be relegated to mainly urban and small stream flooding with more isolated flash flood concerns in terms of an areal extent. ...Previous Forecast.. By Tuesday, a progressive cold front pushing across the Mississippi Valley and associated upper level trough and shortwave will separate...with the upper shortwave ejecting northeastward into the Great Lakes, leaving the front behind. The combination of steady forward movement of the storms through the day followed by the rapid diminishing of any and all upper level support by Tuesday night will rapidly diminish the flooding threat as storm coverage and intensity also diminish. With some supply of Gulf moisture continuing on Tuesday, the storms that form through the day will still have enough punch to cause locally heavy rainfall. However, the eastward progression of the front should allow this rain to fall largely over areas that remain dry today/Sunday and Monday. Antecedent dry conditions will preclude much of the flooding threat by Tuesday, so only isolated flash flooding in urban and flood prone areas is anticipated. The Marginal Risk is largely unchanged from previous forecasts. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_5Zoof50v4Zi-zW6yZ96iaR1VCVa8jUi5CcW5X7e2hQo= 3IXlunDMjQ9N5UGuwkSyt0AzalrVp-TtyelR_5jip9bbkvU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_5Zoof50v4Zi-zW6yZ96iaR1VCVa8jUi5CcW5X7e2hQo= 3IXlunDMjQ9N5UGuwkSyt0AzalrVp-TtyelR_5jiJtlmiFA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_5Zoof50v4Zi-zW6yZ96iaR1VCVa8jUi5CcW5X7e2hQo= 3IXlunDMjQ9N5UGuwkSyt0AzalrVp-TtyelR_5ji2uHtX28$=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) .