Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 19 2023 08:26:37 FOUS30 KWBC 190826 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 426 AM EDT Wed Jul 19 2023 Day 1 Valid 12Z Wed Jul 19 2023 - 12Z Thu Jul 20 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF WESTERN KENTUCKY INTO NORTH CENTRAL TENNESSEE... ....Tennessee Valley... Heavy rains likely to continue into the post 1200 UTC Wednesday time period across the Tennessee Valley region. While the latest hi res models continue to show a range of locations for potential training, they continue to advertise training potential early Wednesday morning in a northwest to southeasterly direction that may continue into the post 1200 UTC Wednesday period from western Kentucky, south into north central Tennessee. Portions of this region have already seen heavy rains from the two initial batches of rain to progress southeastward during Tuesday from the Lower MO Valley into the TN Valley, lower ffg values and raising stream flows. The axis of the slight risk area was shifted westward from the previous issuance this period to better match where the post 1200 UTC organized activity may be. A small moderate risk area was added for the first 3 to 6 hours of the day 1 time period. The last several runs of the hrrr have been very consistent with the heavy rain axis and has been verifying fairly well with the observed radar. Depending upon how long the training continues after 1200 UTC will determine how much addition rains are possible. Models may have a bias of being too slow to push the convection downstream, possibly not lingering as long over the risk areas as indicated. At the moment, given the training potential, several more inches of rain are possible after 1200 UTC, exacerbating any ongoing flooding issues from pre 1200 UTC rains. ....Lower Missouri Valley toward the Lower Ohio Valley... In the wake of the early day 1 heavy rains over the Tennessee Valley, additional convection is possible along and to the north of the frontal boundary stretching east to west from the Mid Mississippi Valley/Lower Missouri Valley into the Central to Southern Plains. PW values expected to remain above average in the vicinity of this front...1.75-2"+. Additional shortwave energy riding west to east along the southern edge of westerlies across the Central Plains into the Lower MO Valley will support enhanced uvvs in this high PW axis and additional heavy rainfall threat along this front late Wednesday night into the early hours of Thursday. At the moment, model consensus for overlap of previous heavy rains Tuesday and additional late Wednesday night/early Thursday morning rains are across central to southeastern MO. A slight risk was extended farther northwestward to cover this overlap potential.=20 Farther west along the east to west oriented front, locally heavy rains are possible across much of Kansas into southeast Colorado given the above mentioned favorable upper difluence, high PW axis along this front. These areas, however, have been relatively drier than areas farther to the east along the front through the Lower MO Valley into the TN Valley. At the moment, the threat level was kept at marginal across these areas. ....Upper Mississippi Valley... No changes made to the marginal risk from the previous extending northeastward through the Upper MS Valley into the Upper Lakes region. Models remain consistent in showing a narrow axis of above average PW values and instability along and ahead of the associated cold front ahead of strong height falls pushing eastward from the Northern Plains into the Upper MS Valley. Model consensus continues to be for fairly progressive convection across this area. With precip mostly below average over the past few weeks across the Upper MS Valley and lower than average stream flows, believe the threat for excessive rainfall will remain marginal. ....Northern Sierra, Great Basin into portions of the Southwest... Only some slight changes made to the previous marginal risk areas the Great Basin and Southwest. PW values expected to remain above average, 1 to 2+ standard deviations above the mean, from the northern Sierra, eastward across portions of the Great Basin into the Central Rockies. Scattered diurnal convection likely in this above average PW axis, supporting isolated runoff issues. A small marginal risk area also maintained over southeast AZ into southwest NM where isolated slow moving cells again possible Wednesday afternoon. Locally heavy rains also possible Wednesday ahead of a surface front pushing east along the Mid-Atlantic coast. Kept the small slight risk area across far southeast Virginia in the urbanized Hampton Roads region. Farther to the north, the marginal risk was extended north into far southeast PA and northern NJ to cover heavy rainfall potential over areas that have relatively low ffg values.=20 Oravec Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_osZ6AyNQui8l9LvLgbVOhqg4KkGOOANynM2ZW0nDo1V= 8q-CFXyymor0XaXqHN8m5sNJ5-iBbGQxRfThzDYhxP6d7nQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_osZ6AyNQui8l9LvLgbVOhqg4KkGOOANynM2ZW0nDo1V= 8q-CFXyymor0XaXqHN8m5sNJ5-iBbGQxRfThzDYhNTgKOBc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_osZ6AyNQui8l9LvLgbVOhqg4KkGOOANynM2ZW0nDo1V= 8q-CFXyymor0XaXqHN8m5sNJ5-iBbGQxRfThzDYhmkMy1fw$=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) .