Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 16 2023 08:06:04 FOUS30 KWBC 160805 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 405 AM EDT Thu Mar 16 2023 Day 1 Valid 12Z Thu Mar 16 2023 - 12Z Fri Mar 17 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY... Models remain in good agreement in showing height falls on the southern end of the amplifying trof across the mid section of the nation pushing from the Southern Plains into the Lower Mississippi Valley day 1. The overall pattern remains favorable for increasing convection as strengthening southerly to south southwesterly flow ahead of these height fall raise PW values to 2+ standard deviations above the mean along and ahead of the associated eastward moving cold front. Strong frontal convergence and favorable upper difluence in this high PW axis will support potential for widespread heavy precip totals day 1 from east Texas/far eastern OK, eastward across much of Arkansas, northern Louisiana, far southeast Missouri and far western Tennessee and far western Mississippi. Simulated radars from the 0000 utc hi res guidance suggests heavy rain may come in two waves. An initial area of convection forming late morning into early afternoon across these regions, followed by a potentially organized convective squall line ahead of the southeastward moving frontal boundary late afternoon into Thursday night. The initial area of convection may be slower moving and have potential for a period of training in a southwest to northeasterly direction. The second round likely will be more progressive, but HREF probabilities for .50 and 1"/hour totals are greater with the second round associated with the cold frontal passage. The northern portion of the slight risk area over southeast OK into south central AR has seen more heavy precip recently than areas farther to the southeast, with stream flows greater here. No changes made to the previous slight risk area, with this area encompassing where the HREF neighborhood probabilities are highest for 2"+ totals day 1. Only some slight changes to the previous marginal risk area, with a small adjustment to the northeast into southeast Missouri to cover the model spread of heavy qpf amounts. Oravec =20 Day 2 Valid 12Z Fri Mar 17 2023 - 12Z Sat Mar 18 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER MISSISSIPPI VALLEY TOWARD THE SOUTHERN APPALACHIANS... The surface cold front moving through the Lower Mississippi Valley early Friday morning is expected to remain very progressive during Friday as it pushes through the remainder of the Lower Mississippi Valley and into the northern Gulf of Mexico by early Saturday.=20 While PW values will remain above average along and ahead of this front, 1.5 to 2 standard deviations above the mean, the expected progression of the front and associated convection should preclude any widespread runoff issues day 2. No significant changes made to the marginal risk area from the previous outlook for this period, with the marginal risk area drawn to fit the model consensus for moderate to locally heavy precip totals. Much of the marginal risk area has stream flows at or below average levels. This and the expected progression should keep any runoff issues to isolated in nature. Oravec Day 3 Valid 12Z Sat Mar 18 2023 - 12Z Sun Mar 19 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6waeQ66imS2SfbcuwXUlbg1ufY4eNJQmTs3y0atYatWf= EhpesBz2SJTnV737_F7kkA2sQoWWnsHXRhgnnLSzy2V464w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6waeQ66imS2SfbcuwXUlbg1ufY4eNJQmTs3y0atYatWf= EhpesBz2SJTnV737_F7kkA2sQoWWnsHXRhgnnLSz2JazwiQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6waeQ66imS2SfbcuwXUlbg1ufY4eNJQmTs3y0atYatWf= EhpesBz2SJTnV737_F7kkA2sQoWWnsHXRhgnnLSzs_oSnAQ$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .