Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 19 2023 08:36:39 FOUS30 KWBC 190836 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 436 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 also added for the first 3 to 6 hours of the day 1 time period when the training is expected to continue. 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. The moderate risk was drawn for the consistent hrrr axes.=20 Additional 3 to 5" precip totals possible in the persistent area of training after 1200 UTC Wed, 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 Valid 12Z Thu Jul 20 2023 - 12Z Fri Jul 21 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE CENTRAL/SOUTHERN HIGH PLAINS, THE SOUTHERN TO CENTRAL APPALACHIANS AND ACROSS THE EASTERN L.P. OF MICHIGAN... ....Lee of the Central Rockies into the Central to Southern High Plains... Additional shortwave energy expected to rotate east southeastward on the northeast side of the Southwest upper high, pushing east southeast from the lee of the Central Rockies into the Central to Southern Plains. These height falls will be moving along and to the north of a surface front dropping southward from Central Plains into the Southern Plains during Thursday. Post frontal upslope flow and enhanced upper divergence will help initiate convection in the vicinity of southeast WY/western NE/northeast CO Thursday afternoon. This activity will likely enhance into organized convection pushing southeastward southeast CO/western to central KS/far northeast NM and the TX/OK Panhandle region Thursday night into the early hours of Friday in a region of above average PW values and CAPE values 1500 -3000 j/kg. Stream flows are still mostly above average across these areas, although much of the area has been dry over the past week. There may be some overlap to locally heavy rains amounts day 1 over portions of southeast CO into western KS with the potentially more organized day 2 amounts. No significant changes to the previous outlook with only a slight southward expansion of the slight risk into far northeast NM and far northwest TX. Widespread 1-2"+ amounts possible with localized values of 3-5"+. There remains some spread in the axis of heaviest amounts. An upgrade to moderate remains possible as we get more hi res input in subsequent cycles. ....Southern to Central Appalachians into the Northern Mid-Atlantic... A narrow slight risk area was maintained day 2 from far eastern TN, Southwest VA through WV into northwest to north central PA.=20 The strong northern stream height falls moving into the Upper MS Valley late day 1 will continue to press eastward through the Great Lakes, OH Valley and Southern to Central Appalachians day 2. Increasingly difluent upper flow, defined frontal convergence and southwest upslope into the Appalachians will support increasing convective coverage ahead of this front. The slight risk through the Southern to Central Appalachians was to cover where potentially heavy rains coincide with the relatively low FFG values stretching across the Southern to Central Appalachians. ....Eastern L.P. of Michigan... A slight risk was also added for the eastern portions of the L.P. of Michigan where ffg values are relatively low and an organized convective squall line along and ahead of the above mentioned cold front will likely push across Thursday afternoon with hourly rainfall amounts of 1"+ possible. Oravec Day 3 Valid 12Z Fri Jul 21 2023 - 12Z Sat Jul 22 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE TENNESSEE VALLEY AND NORTHEAST NEW MEXICO... ....Lower Mississippi Valley into the Tennessee Valley... An axis of above average PW values will stretch west to east from the Southern Plains into the Lower MS Valley/TN Valley and Southeast in the vicinity of the west to east oriented front forecast to be moving slowly south and southeast day 3. Similar to days 1 and 2, shortwave energy moving west to east along the southern edge of the westerlies and this frontal zone will enhance lift in the above average PW axis and support potential for widespread scattered convection along the boundary. A slight risk was maintained over the TN Valley and expanded westward into western TN/far southeast MO to cover areas that are expected to see some heavy rains days 1 and 2. ....Southern High Plains... Low level easterly upslope flow will strengthen day 3 as the cold front continues to sink southward through the Southern High Plains. Added a small slight risk area for model consensus region of potentially heavy rains over northeast New Mexico. This potential precip area coincides with relatively low ffg values where precip over the past week has been 2 to 3 times average in places. ....Eastern New York State into New England... The strong northern stream height fall moving through the eastern Lakes into the Appalachians day 2 will continue to press eastward through New England day 3. Additional moderate to locally heavy precip totals possible day 3 from eastern New York State into central to northern New England. No significant changes made to the previous marginal risk area. Heavy rains over the past week have raised stream flows to high across these areas, with isolated runoff issues possible from additional .50 to 1" amounts. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_az5-u-MO11TANIxJuObN-z5sKoytBFUIooq9DnXXYSA= oMfqgI9jE9e5qEJ3qzWadj5RfAy73SxVBpnWeEZuDnrkzjk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_az5-u-MO11TANIxJuObN-z5sKoytBFUIooq9DnXXYSA= oMfqgI9jE9e5qEJ3qzWadj5RfAy73SxVBpnWeEZucDuBB10$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_az5-u-MO11TANIxJuObN-z5sKoytBFUIooq9DnXXYSA= oMfqgI9jE9e5qEJ3qzWadj5RfAy73SxVBpnWeEZuy_ochFo$=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) .