Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 13 2024 08:11:32 FOUS30 KWBC 130811 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 410 AM EDT Wed Mar 13 2024 Day 1 Valid 12Z Wed Mar 13 2024 - 12Z Thu Mar 14 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL PLAINS...LOWER MISSOURI VALLEY AND MID-MISSISSIPPI VALLEY... A stationary frontal boundary is expected to drape southwest to northeast from eastern portions of the Central Plains into the Lower Missouri Valley and Mid Mississippi Valley regions. The low level southerly flow is expected to re-strengthen into this front late Wednesday into Wednesday night/early Thursday, with 850-700mb mb moisture flux anomalies increasing to 1 to 2 standard deviations above the mean by early Thursday morning. This will support potential for an increasing area of organized overrunning convection along and to the north of this front, with potential for localized areas of training or more than one batch of convection moving over the same area. The marginal risk area fits well with where the HREF neighborhood probabilities are high for 1"+ totals day 1 from northeast Kansas/southeast Nebraska, across northern Missouri, southern Iowa and northwest Illinois.=20 While the HREF 1"+ probabilities are high over a large area, the EAS probabilities are showing a much smaller area of probabilities of over 40% along the Iowa/Missouri border area, suggesting poor hi res model overlap of 1"+ areas. 2"+ HREF neighborhood probabilities are showing a very small area of high probabilities over the Iowa/Missouri border area, and low EAS probabilities for 2"+ amounts. Hourly probabilities for 1"+ totals during the 0000 to 1200 UTC period are generally less than 20%. At the moment, the risk level is kept at marginal with hourly FFG values mostly 1.5" and greater. Changes to the previous outlook were to elongate it approximately 100-120 nm to the east and west and to narrow it on the north end by about 60 nm. Oravec Day 2 Valid 12Z Thu Mar 14 2024 - 12Z Fri Mar 15 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER ARKANSAS VALLEY INTO THE LOWER MISSISSIPPI VALLEY... The low level southerly flow is expected to once again strengthen significantly late Thursday into early Friday across the eastern portions of the Southern Plains into the Lower Arkansas and Lower Mississippi Valleys downstream of the strengthening closed low over the Southern Great Basin. 850-700 mb moisture flux anomalies and PW anomalies rise to 2 to 2.5+ standard deviations above the mean along and ahead of the associated cold front pushing southeast through the Southern Plains into the Lower Arkansas Valley. There is a strong model signal for heavy precipitation from northeast Texas, southeast Oklahoma, northern Louisiana, much of Arkansas, northwest Mississippi, far western Tennessee, far southeast Missouri, far southern Illinois and far western Kentucky in a region of favorable large scale conditions, strong frontal convergence, well defined upper difluence, late Thursday into the early hours of Friday. Similar to the past few model cycles,there continues to be north-south model spread with respect to where the max convective qpf axis will set up. The NAM continues to be the northern outlier, the EC and EC mean, the farthest south and the GFS, GEFS mean and UKMET in between. The slight risk continues to be drawn to encompass the current model spread, with only some minor changes from the previous outlook for this period. The slight risk is across areas that have had below average precip over the past few weeks and subsequently relative high FFG values. The heaviest precip totals over the past few weeks and the most saturated soils area well to the southeast of the slight risk area across portions of the South and Southeast.=20 Given this and the continued spread in the max qpf axis, the risk was kept at slight for the time being.=20 Oravec Day 3 Valid 12Z Fri Mar 15 2024 - 12Z Sat Mar 16 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST TEXAS, ACROSS THE LOWER MISSISSIPPI VALLEY AND INTO PORTIONS OF THE SOUTH... The surface frontal boundary pressing southeastward day 2 into the Southern Plains, Lower Arkansas Valley and Mid Mississippi Valley will begin to accelerate to the southeast day 3 through the Tennessee Valley and Lower Mississippi Valley, moving slower to the south into the Southern Plains. An axis of anomalous PW values, 1.5 to 2.5+ standard deviations above the mean will accompany this southeastward moving front day 3. This and the continued overall favorable large scale conditions ahead of this front will support another day of potentially widespread heavy precip along and ahead of the front. There is the typical amount of spread with respect to the max qpf axis, but overall model consensus for potentially heavy rains. The day 3 qpf axis does move back over areas of Mississippi, Alabama and Georgia that have had above average precip over the past week or two, resulting in higher stream flows and greater soil saturation. There were not a lot of changes made to the previous broad slight risk area, extending it slightly farther to the west across northeast Texas to cover the model spread. The northern portion of the marginal risk area over the Northeast was cutback to the Central Appalachians to better fit the latest model qpf. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-8hcey-elCVpkJr8F6rdGEEHWQF0uNOTzSV0Xzp0Q1KJ= G3ViHPcoAQ2rDGviA7R7bdSQfRu1W24M4fKcTTt9BwTz8WE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-8hcey-elCVpkJr8F6rdGEEHWQF0uNOTzSV0Xzp0Q1KJ= G3ViHPcoAQ2rDGviA7R7bdSQfRu1W24M4fKcTTt9p7y-Ye0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-8hcey-elCVpkJr8F6rdGEEHWQF0uNOTzSV0Xzp0Q1KJ= G3ViHPcoAQ2rDGviA7R7bdSQfRu1W24M4fKcTTt98RThAwE$=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) .