Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri May 05 2023 01:01:49 FOUS30 KWBC 050101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 900 PM EDT Thu May 04 2023 Day 1 Valid 01Z Fri May 05 2023 - 12Z Fri May 05 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR INTERIOR SECTIONS OF THE NORTHWEST AND PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO PARTS OF THE MID-SOUTH... ....Northern Intermountain West... Shrank the Marginal Risk to include portions of western ID and eastern OR/WA which is downstream of an upper vort lobe apparent in WV imagery as over northeast NV this evening which will continue to lift north tonight. Instability is limited to areas downstream of the vort lobe and maximize, along with PW, over the Columbia Basin. Deep layer southeasterly flow should keep activity moving with a general risk for repeating activity where it becomes oriented with the deep layer flow. ....Central/Southern Plains into the Mid-Mississippi Valley and Mid-South... Deep layer WSWly flow downstream of a trough over the Western U.S. to a ridge axis that shifts east across AR/MO tonight is an area of abundant Gulf moisture, instability, and shear. Three distinct areas of current activity; along the Red River, north-central Texas and along the Rio Grande south of Del Rio should continue progressing east rest of this evening as depicted by most CAMs and especially the WoFS. Heavy rain with three hourly rainfall of 2-4" is likely from each of these increasingly organized areas with the WoFS favoring the southernmost for the most development over the next few hours. Ample southerly flow bringing moisture/instability should allow maintenance of this activity as it progresses east overnight. FFG remains high over these sections of Texas, so the Marginal Risk was maintained here with only trimming of the western section. Farther north over OK/southern KS and east into MO/AR there is plenty of moisture and instability advection overnight to allow regeneration of activity which would be a repeat of areas affected earlier in central OK. Ongoing activity in western KS is not handled well by CAMs and despite western KS in a drought there is a repeating activity risk, so the Marginal was expanded west a ways over southern KS. Jackson Day 2 Valid 12Z Fri May 05 2023 - 12Z Sat May 06 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE MID-SOUTH AND TENNESSEE VALLEY AND THE CENTRAL/NORTHERN INTERMOUNTAIN WEST... ....Mid-south and Tennessee Valley into the Southern Appalachians and Parts of the Southeast... 21Z update... While the exact track of where the highest QPF will be remains a bit uncertain, the overall trend the past 3 cycles have been further south and with lighter amounts. WPC QPF for this issuance followed suite. In addition, the current area of convection tracking across the eastern Texas/Oklahoma/Kansas, southern Missouri and northwest Arkansas has been more east than the expected northeast path. This may support the southern trend that we're seeing with the day 2 period. Especially if it quickly dives south/southeast as hinted by the ECWMF/UKMET/HREF by having 1+ inches from eastern Arkansas to southwest Alabama. Given the consist lowering of QPF and southward shift, the Marginal Risk area was shrunk down and orientated more WNW to ESE and the Slight Risk area was removed. Campbell Organized elevated convection north of the surface warm front at the start of Day 2 (12Z Friday), again possibly an MCS, will track east-southeast along with WNW-ENE oriented vort lobe, while individual cell motions will be southeasterly per the 850-300 mb thickness orientation and layer Corfidi vectors. Once again, the models show latitudinal differences with respect to the stripe of heaviest rainfall; however, the ECMWF remains rather consistent over the past 3-4 runs. Given the pool of strong deep-layer elevated instability (MUCAPEs 2000-3000+ J/Kg) upstream and into the western portions of the outlook area, along with the favorable forcing ahead of the convectively-enhanced shortwave, WPC continued to side with a QPF closer to the operational ECMWF and NAM CONUS-Nest. There will be an enhanced potential for cell training Friday night with the uptick in low-level flow, which in this thermodynamic environment would foster hourly rainfall rates up of 1.5-2.5". Therefore we opted to continue the Slight Risk inherited from yesterday's Day 3 ERO. ....Central and Northern Intermountain West... 21z update... no changes made at this time. Campbell Upper level pattern changes very little across these areas Fri-Fri night, with broadly difluent upper level flow east of the H5-H3 trough axis (though the favorable upper level forcing does shift a bit northeastward into western-central MT). As was noted in the Day 1 ERD, the favorable forcing and weak deep-layer instability (relatively steep mid-level lapse rates) along a ribbon of above-average PW will favor isolated hourly rainfall rates of 0.50-1.00". These rates, along with the recent snowmelt and possibility of occurring over burn scar areas, could foster localized short-term runoff issues. As a result, the Marginal Risk that was inherited from yesterday's Day 3 ERO continues in today's Day 2 ERO. Hurley Day 3 Valid 12Z Sat May 06 2023 - 12Z Sun May 07 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_V8MAOoM0--TZ9q_Sa_meDvCKh0rCCyAlIJP9-_4UVZ7= _UIN5z5WGM-8CoKVKhoUrJ-CQJg7n4ZhoGrhGyK0eDHyzuY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_V8MAOoM0--TZ9q_Sa_meDvCKh0rCCyAlIJP9-_4UVZ7= _UIN5z5WGM-8CoKVKhoUrJ-CQJg7n4ZhoGrhGyK0JBe5cuw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_V8MAOoM0--TZ9q_Sa_meDvCKh0rCCyAlIJP9-_4UVZ7= _UIN5z5WGM-8CoKVKhoUrJ-CQJg7n4ZhoGrhGyK0gH87-50$=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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