Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 24 2024 19:48:54 FOUS30 KWBC 241948 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 348 PM EDT Wed Apr 24 2024 Day 1 Valid 16Z Wed Apr 24 2024 - 12Z Thu Apr 25 2024 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS IN AND NEAR EASTERN OKLAHOMA AND WESTERN ARKANSAS... 16 UTC update... Signals for heavy rainfall this afternoon are pretty weak from the latest 12z guidance, and HREF exceedance probabilities are very low to nothing across the eastern OK/western AR. Still though, the ingredients are there and models have not been depicting the ongoing convection into OK this morning well, so opted to keep the marginal given potential for any developing storms to tap the anomalous moisture/instability. No major changes to the marginal risk area put in place overnight. See previous discussion below for additional details. Santorelli Previous discussion issued at 0700 UTC... ....OK/AR... OK/AR will remain an area of diffluent 1000-500 hPa thickness just east of a migrating mid- level ridge axis translating east from the Four Corners region. At the surface, a front will lift north Wednesday night into early Thursday in advance of the approaching upper level trough from the Southwest. Mid-level capping should be minimal based on the forecasted 700 hPa temperatures, under 9C. Precipitable water values 1-2 sigmas above average for late April -- 1.5-1.75" -- are forecast by the model consensus to be in place near and just north of the surface front with elevated CAPE of 1000 to 2000 J/kg (higher to the south) may allow for stronger cells capable of high rainfall rates. Effective bulk shear/low- level inflow should increase to 35-40 kts. Non- traditional cell training within a WNW steering flow near and poleward of the front could allow for hourly totals to 2" and local 4" amounts. While the 00Z HREF isn't sold on 3"+ amounts in the area, precipitable water values in the area have trended upwards each day, and now the 00z Canadian Regional, though at a smaller scale, supports the wetter ECMWF solution. Went ahead and introduced a Marginal Risk in this update. Roth Day 2 Valid 12Z Thu Apr 25 2024 - 12Z Fri Apr 26 2024 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF THE SOUTHERN AND CENTRAL PLAINS... A mid-level trough over the southwestern U.S. is forecast to=20 eject out across the central and southern High Plains by Friday=20 morning, spurring development of a surface cyclone across the High=20 Plains. Winds at 850 mb will be south to south-southwest across the Great Plains but with increased magnitude -- up to 50-60 kt --=20 and moisture transport will allow precipitable water values to=20 exceed 1.5" across portions of the Plains and Midwest. A broad area of instability east of a forming central High Plains surface low=20 and attendant cold front/dryline, with values of 1000 to 3000 J/kg=20 from northern TX/southern OK into KS and NE. Initially, some convection may be ongoing at the start of the period over OK/AR along a warm front lifting northward, but additional storm development is anticipated to occur during=20 Thursday afternoon ahead of the cold front/dryline in KS/OK with=20 thunderstorm development expanding through the evening and early=20 overnight across TX and northern locations including NE and IA.=20 Strong to severe thunderstorms are likely, ramping up the=20 precipitation potential, despite decently fast cell motions. Deep=20 layer south- southwest flow supports training of cells with rains=20 up to 2.5" in an hour and local amounts up to 6". Models continue to show good agreement for the slight risk across portions of=20 KS/OK/AR/MO which portions of could overlap with some heavy rainfall potential tonight into Thursday morning. The surrounding marginal risk was extended slightly from the overnight issuance southward along the cold front into central TX, eastward along the warm front into the Tennessee Valley, and westward more into Nebraska/South Dakota to the north and west of the surface low. Santorelli/Roth Day 3 Valid 12Z Fri Apr 26 2024 - 12Z Sat Apr 27 2024 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS NEAR AND NORTH OF THE ARKLATEX AND NEAR THE ILLINOIS/IOWA BORDER... As a surface cyclone pulls northeast across the Plains and Midwest, moisture and instability will lift northward through the Midwest. Inflow at 850 hPa will be near or above 50 kts with precipitable=20 water values as much as 2 standard deviations above normal and=20 more than sufficient instability to help organize convection.=20 Within a broad marginal risk from the northern Plains to Upper=20 Midwest and southward along the cold front into the lower-mid MS=20 Valley and eastern Plains, continued two slight risk areas - one=20 near the IA/IL border and another across northeast TX, southeast=20 OK, and northwest MO. Both of these slight risks remain due to=20 heavy rainfall expected Wednesday into Thursday, and some recent=20 rainfall during the past week. Cell training is possible, with some strong to severe storms as per the latest SPC Outlooks. Hourly=20 rainfall totals to 2" with local amounts to 4" are possible. Santorelli/Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7MpB_g3Ftr030PB9M8m7fIkxLbHzYS4xRw3olIsAi78k= NMoeIq1bac6sj_ow4vcms1AsQpC3-A85hVAkj3voYtmyDOc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7MpB_g3Ftr030PB9M8m7fIkxLbHzYS4xRw3olIsAi78k= NMoeIq1bac6sj_ow4vcms1AsQpC3-A85hVAkj3voORUFIHE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7MpB_g3Ftr030PB9M8m7fIkxLbHzYS4xRw3olIsAi78k= NMoeIq1bac6sj_ow4vcms1AsQpC3-A85hVAkj3vo4FByXe4$=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) .