Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 06 2025 15:57:54 FOUS30 KWBC 061556 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Fri Jun 6 2025 Day 1 Valid 16Z Fri Jun 06 2025 - 12Z Sat Jun 07 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS, THE LOWER OHIO, LOWER TENNESSEE AND MIDDLE=20 MISSISSIPPI VALLEYS AND NEW ENGLAND... 16Z Update...=20 Prior discussion remains valid outside of a few changes based on morning guidance. Overall, a stationary boundary stretching over 2000 miles from the Northeast to the Southwest will provide a focus for numerous convective complexes of varying size and magnitude. Widely scattered instances of flash flooding can be expected with the potential for locally considerable impacts. A SLGT risk was added for the LUB CWA in western TX along with the expanded MRGL along the dry line to the TX Big Bend. Similar setup to yesterday is expected to compound the potential for isolated to scattered flash flooding, particularly if developing HP supercells this afternoon impact urban regions with 2-5" totals.=20 Additionally, the SLGT risk across New England was expanded a bit=20 based on current radar and satellite trends showing a shortwave=20 passing over the Interior Northeast that will help spark=20 thunderstorm activity along an east- west oriented stationary front extending through southern New England into central PA. 12Z HREF=20 and most 12Z CAMs are particularly impressive with the high-end=20 potential over NH given slow-moving convection initiating off the=20 higher elevations. 12Z HREF probabilities for greater than 5" are=20 as high as 25% across parts of NH. For the Ohio and Tennessee valleys, the SLGT risk was expanded eastward into eastern KY based on latest radar trends as a potent MCV over southern MO riding along the stationary front draped over the Ohio Valley. See MPD 308 for more information. 12Z HREF was not overly impressive in magnitude across this region for 2"+ amounts, but coverage is expected to widespread enough to lead to scattered instances of flash flooding. Snell Previous Discussion... ....South-Central Plains..... There is a strong model signal for another round of organized convection late Friday afternoon into Friday night/early hours of Saturday across the south-central plains as additional shortwave energy is forecast to drop east southeastward from the Central Rockies into the Central to Southern Plains Friday into Friday night/early Saturday. The low level flow is expected to again strengthen into the west to east oriented frontal zone across the Southern Plains, supporting potential for another round of organized convection in the vicinity of this front. PW values along this front will remain above average...2+ standard deviations above the mean, supporting heavy precip potential. There is fairly good model consensus for an axis of heavy rains along this front from far southeast CO/far southwest KS, across much of OK into the OK/KS/MO/AR border region. The slight risk was drawn to fit the axis of the highest HREF neighborhood probabilities for 2"+ amounts and the HREF EAS axis of highest probabilities for 1"+ amounts. The next round of organized convection will likely track along the same areas that are currently receiving heavy rainfall late Thursday evening into early Friday for northern OK, compounding the potential flash flooding concerns and leading to the potential for more widespread and considerable impacts overnight. ....Mid Mississippi Valley, Lower Ohio Valley, Lower Tennessee Valley... The lead area of shortwave energy initiating current early morning convection across the Southern Plains will be pushing toward the Mid Mississippi Valley, Lower Ohio and Lower Tennessee Valleys Friday afternoon/evening. Similar to areas upstream along the west to east oriented frontal zone that extends into the Mid MS, Lower OH,Lower TN Valley, PW values will be above average, 2+ standard deviations above the mean. Convection likely to enhance Friday afternoon/evening ahead of these height falls in the much above average PW axis, supporting heavy rain potential and localized flooding issues. A slight risk area was added from the previous issuance, aligned with where the axis of the highest HREF neighborhood probabilities for 2"+ amounts and the HREF EAS axis of highest probabilities for 1"+ amounts are forecast. ....Southern Great Basin into the Central to Southern Rockies... Not a lot of changes expected to the large scale flow across the southern Great Basin into the Central Rockies. PW values forecast to remain above average with additional shortwave energy moving across the region in the west south west flow aloft. This should support another day of widespread scattered convection and localized heavy rain and isolated runoff issues. No significant changes made to the previous marginal risk area across this region. ....East-central New York into Central New England... A slight risk area was added for portions of east-central New York State into central New England from central to southern New Hampshire, across southeast Vermont, western Massachusetts into east central NY state. There is good agreement in the last hi res guidance for enhancing convection in the 1800 UTC Friday to 0000 UTC Saturday period in the axis of above average PW values along the slow moving frontal boundary draped across this area. The slight risk was drawn to fit where the axis of high HREF neighborhood probabilities are for 2 & 3"+ totals. This corresponds also to where the HREF hourly probabilities for 1"+ totals are high in the 1800 UTC Friday to 0000 UTC Saturday period. Oravec Day 2 Valid 12Z Sat Jun 07 2025 - 12Z Sun Jun 08 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE LOWER ARKANSAS VALLEY, LOWER MISSISSIPPI VALLEY INTO THE LOWER TENNESSEE VALLEY... ....Lower Arkansas, Lower Mississippi and Lower Tennessee Valleys.. The second round of height falls moving into the Central to Southern Plains day 1 will continue to push east southeast toward the Mid to Lower MS Valley, OH and TN Valleys during day 2. Upper difluence is forecast to be well defined Saturday into Saturday night/early Sunday in an axis of above average PW values that will remain along the west to east oriented frontal boundary across these areas. This should support potential for another round of organized convection along this front. There is some spread with the qpf axes, but consensus that heavy amounts are possible along this front. The slight risk area was extended approximately 50m to 100 miles farther to the southeast across northern MS and northern AL to cover the current model spread. ....East central NY State into Central to Northern New England... Another round of convection possible early day 2 along the frontal boundary pushing through the northeast as a sharpening northern stream trof pushes eastward across northern NY into New England. The HREF neighborhood probabilities for the 12 hour period from 1200 UTC Saturday to 0000 UTC Sunday, are high along this front for 1 and 2"+ amounts. The previous marginal risk area was extended farther west into east central NY state to cover these higher 12 hour probabilities. There may need to be an upgrade to the risk level in future issuances depending upon where the heavy rains occur during day 1. Oravec Day 3 Valid 12Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS NORTH TEXAS INTO SOUTHERN OKLAHOMA... ....North Texas/Southern Oklahoma... Additional shortwave energy likely to push east southeastward late Sunday afternoon/evening from the lee of the Central to Southern Rockies into the Southern Plains. This will again re-strengthen the low level flow into the west to east oriented front forecast to remain across the Southern Plains, supporting another round of organized convection along the front. There is fairly good agreement on the day 3 qpf axes in the models. resulting in good continuity with the slight risk area. The marginal risk area was extended farther to the northwest into southeast Colorado to cover the model qpf spread. ....Lower Mississippi Valley into the Southern-Central Appalachians and Mid-Atlantic... Broadly diffluent mid to upper level flow expected day 3 ahead of the height falls pushing out of the Mid to Lower MS Valley, TN and OH Valley region. With PW values expected to be above average...1.5 to 2+ standard deviations above the mean...widespread scattered convection possible from the Lower MS Valley, across the Southern to Central Appalachians and into the Mid-Atlantic. The previous marginal risk area that was across the South was extended north through the Southern to Central Appalachians and into the Mid- Atlantic across the lower FFG values. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8vVVhpE2WalifTwq_biKxs_HNxASFULPjk_ixf1-s9OT= _XaJh727rbDvfLFohQduTURWVPh6cgGZcLuU9X1wPc3q9lM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8vVVhpE2WalifTwq_biKxs_HNxASFULPjk_ixf1-s9OT= _XaJh727rbDvfLFohQduTURWVPh6cgGZcLuU9X1wcgCywKM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8vVVhpE2WalifTwq_biKxs_HNxASFULPjk_ixf1-s9OT= _XaJh727rbDvfLFohQduTURWVPh6cgGZcLuU9X1w8x3qDFs$=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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