Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 30 2024 15:57:45 FOUS30 KWBC 301557 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1157 AM EDT Tue Jul 30 2024 Day 1 Valid 16Z Tue Jul 30 2024 - 12Z Wed Jul 31 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE MID MISSISSIPPI VALLEY, LOWER OHIO VALLEY, UPPER TENNESSEE VALLEY INTO THE SOUTHERN APPALACHIANS... 16z Update: Generally only minor changes were needed to the inherited risk areas with this update. An ongoing MCS over IA looks increasingly likely to survive and continue to grow upscale as it dives southeast across portions of IA,IL,KY today into this evening. The 12z 3km NAM and ARW2 are missing this feature, and thus are not preferred solutions. The 12z ARW and recent HRRR runs appear to be handling this feature better. While this complex=20 should generally be forward propagating and thus progressive in=20 nature...there is some concern for downstream discrete cell=20 development within an axis of enhanced instability. If this occurs this afternoon then a locally increased flash flood risk will exist where these cells merge into the forward propagating MCS. This=20 appears most probable over portions of southern IL/IN into KY.=20 Then by tonight expect another organized convective complex to=20 develop in the vicinity of IA. More uncertainty on the exact=20 location of this complex...but central IA seems most probable at=20 the moment...and in the organizing phase of this complex cell=20 mergers and some flash flood risk is possible overnight into early=20 Wednesday. Elsewhere did expand the Marginal risk into portions of VT and NH that were hit with heavy rainfall and flooding last night. Not expecting an organized flood threat...however guidance indicates=20 at least some isolated convective development this afternoon as=20 moisture and instability returns north. Shortwave ridging will=20 probably limit the duration and coverage of activity...but=20 localized heavy rainfall will still be possible. Chenard ....Previous Discussion... ....Mid Mississippi Valley, Lower Ohio Valley, Upper Tennessee Valley and Southern Appalachians... Another day of active convection likely in the broad west northwesterly mid to upper level flow from the Mid to Upper Mississippi Valley, into the Ohio Valley, Tennessee Valley and Central to Southern Appalachians. Shortwaves in this flow will be pushing through an area of above average PW values, 1 to 1.5+ standard deviations above the mean. While there is a lot of model qpf detail spread, there is consensus for a northwest to southeast oriented axis of potentially heavy rains across these areas. The two previous slight risk areas were consolidated into a more elongated slight risk area that corresponds well with the latest HREF mean and the higher HREF neighborhood probabilities for 1 and 2"+ amounts and the axis of HREF EAS probabilities for 1"+ amounts. There has been some overlap in the slight risk area of precip over the past 48 hours and potential for additional heavy rains in this axis. ....Central Appalachians, Mid-Atlantic into NY State... Much above average PW values, 1 to 2.5+ standard deviations above the mean also expected to push northeast from the Central Appalachians, across the Mid-Atlantic and into NY State. There is a lot of qpf spread in the latest model suite, but consensus for potential for widespread moderate to locally heavy totals. HREF neighborhood probabilities are high for 1"+ amounts, but drop off significantly for 2"+ amounts. The HREF EAS for 2"+ amounts is showing probabilities of less than 5%, illustrating poor overlap in HREF heavy rain areas. A marginal risk is depicted across these areas, with the previous issuance slight risk along the northeast PA/Southern Tier of NY removed. ...Northern Rockies... Only some small changes made to the marginal risk area across portions of the Northern Rockies from northern Idaho into southwest Montana. Latest guidance continues to show potential for an organized area of moderate to locally heavy precip ahead of a fast moving vort pushing east from the Pac NW into the Northern Rockies in the 1200 UTC Tue to 0000 UTC Wed period. The marginal risk corresponds to where the HREF neighborhood probabilities show spotty high values in the 1200 UTC Tue to 0000 UTC Wed period. The overall quick movement of the vort should keep precip amounts from being very heavy, but anomalous PW values 2 to 2.5 standard deviations above the mean will support some short term rainfall rates of 1 to 1.5" per hour, supporting potential for isolated runoff issues in areas of steep terrain and over burn scars. ....Southwest... No changes expected to the large scale flow with the upper ridge remaining centered over the Southern Plains. This will again support shortwaves rotating northward on the western side of this ridge into the Southwest, supporting scattered convection, localized heavy rains and isolated runoff issues. ....Southwest Florida... No significant changes to the marginal risk area over Southwest Florida. Above average PW values expected to persist across the southern portion of the FL Peninsula day 1, along and south of the east to west trof axis stretching from the Atlantic into South Florida. The marginal risk continues to fit in well with the high HREF neighborhood probabilities for 1, 2 and 3"+ totals. This heavy rain potential will support isolated runoff issues, especially in more urbanize regions. Oravec Day 2 Valid 12Z Wed Jul 31 2024 - 12Z Thu Aug 01 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY INTO THE MID WEST AND OVER PORTIONS OF NORTHERN NEW ENGLAND... ....Upper Mississippi Valley into the Midwest... The progressive northern stream flow will continue into day 2 with the next strong area of height falls expected to push eastward across the Northern Plains and into the Upper Mississippi Valley. There is potential for additional organized convection/heavy rainfall to push eastward with these height falls across eastern portions of the Northern Plains and into the Upper Mississippi Valley as low level southerly flow strengthens into the west to east oriented frontal boundary expected to stretch from the NE/SD border, east across northern IA into northern IL. 850-700 mb moisture flux anomalies into this front expected to rise to 2 to 3 standard deviations above the mean in the 0000 to 1200 UTC Thursday period. There are still a lot of model qpf spread with some typical latitude differences with the max qpf axis. The day 2 slight risk area was drawn to favor the more southern solutions of the NAM, NAMNEST and CMC. ....Eastern New York State into western New England... The strong height falls moving out of the Central Appalachians into the Northern Mid-Atlantic day 1, will progress across eastern NY State into New England day 2. There is a typical amount of qpf spread for the day 2 period, but general consensus for potential of moderate to locally heavy rainfall amounts in a region of much above average PW values ahead of these height falls. A small slight risk area was added along the VT/NH border where very heavy rainfall amounts have occurred early Tuesday morning and where several models show potential for additional heavy rains during day 2. Otherwise,a broad marginal risk area was maintained from the previous issuance to capture the heavy rainfall spread in the models across this area day 2. ....Southwest... Similar to the day 1 period, the mid to upper level ridge will remain centered over the Southern Plains. Scattered convection again likely over portions of the Southwest as shortwave energy again rotates northward on the western side of this ridge and into the Southwest. Localized heavy rains and isolated runoff issues again possible for southeast Arizona into southwest to central New Mexico. Oravec Day 3 Valid 12Z Thu Aug 01 2024 - 12Z Fri Aug 02 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE UPPER MISSISSIPPI VALLEY, ACROSS THE LOWER GREAT LAKES, OHIO VALLEY INTO THE CENTRAL APPALACHIANS AND ACROSS PORTIONS OF THE SOUTHWEST AND SOUTHERN CALIFORNIA... ....Upper Mississippi Valley, Lower Lakes, Ohio Valley... The strong height falls pushing through the Northern Plains into the Upper Mississippi Valley day 2 will sink more to the southeast into the Mid Mississippi Valley/Mid West region day 3. Additional heavy rains likely ahead of these height falls and the associated surface low in a region of above average PW values and anomalous 850-700 mb moisture flux. There are some large model qpf difference's with respect to the axis of the heaviest rains. The marginal risk was drawn to encompass this range form the northern solutions of the UKMET/GEM from southern WI into the southern L.P. of MI, to the southern solution of the NAM and EC from southern IL, southern IN, southern OH, into northern KY. Given the spread and low confidence at the moment with which qpf axes is the best, the risk level was kept at marginal. ....Southwest into southern California... The upper ridge over the Southern Plains is forecast to build to the west and northwest across the Rockies, Great Basin and Southwest during day 3. This will help to push the axis of above average PW values farther west into southern to central California and southern Nevada. This will support an expanding area of scattered diurnal convection into portions of central and southern CA/southern NV from days 1 and 2. The marginal risk area was also expanded westward from the previous issuance to include western AZ, southern NV into southern to south central CA. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7FiNaTwJE0t_ioQuRH07FHt33kYsfx1txsudyJu-UBua= P6SSRZDRKfCY5MjVbFrWf-HcOocm-0CPzJZBBQc7Jmx0RZU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7FiNaTwJE0t_ioQuRH07FHt33kYsfx1txsudyJu-UBua= P6SSRZDRKfCY5MjVbFrWf-HcOocm-0CPzJZBBQc7A26GEu4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7FiNaTwJE0t_ioQuRH07FHt33kYsfx1txsudyJu-UBua= P6SSRZDRKfCY5MjVbFrWf-HcOocm-0CPzJZBBQc75vRr2n8$=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) .