Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 16 2023 08:17:46 FOUS30 KWBC 160817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 416 AM EDT Tue May 16 2023 Day 1 Valid 12Z Tue May 16 2023 - 12Z Wed May 17 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE OHIO VALLEY TO THE CENTRAL AND SOUTHERN APPALACHIANS... ....Ohio and Tennessee Valleys and the Central and Southern Appalachians... A frontal boundary draped from the Missouri Bootheel and east is providing a focus for showers and thunderstorm development. These storms tracking east into the southern Appalachians may result in locally higher rainfall totals as the mountains act as additional forcing, though their impact is not expected to be major. The storms may weaken and dissipate some in the immediate lee of the mountains of southern Virginia, but are likely to reintensify as they move across the Virginia Tidewater. Much of the Ohio/ Tennessee Valleys and the Appalachians have 3-hr FFG in the 2-2.5 inch range with embedded locations as low as 1 inch. There will be plenty of moisture, forcing and instability available over this region to yield heavy rainfall. There was a general southward trend with the QPF and as such, the Marginal and Slight Risk areas were adjusted southward across southern Indiana, Ohio and West Virginia to reflect this. ....Mogollon Rim of Arizona... Abnormally high amounts of atmospheric moisture remain over the region, holding steady around 0.75+ inch which is +3.5 sigma for central Arizona this time of the year. Although the forcing will be on the weaker side it should be adequate to trigger convective activity that could produce heavy rain and isolated flash flooding, especially on any old burn scars, slot canyons, and dry washes. The Marginal Risk area was maintained for this period and was expanded a little further southeast across western New Mexico. ....Intermountain West... Showers and thunderstorms are expected across the region as a strong shortwave trough skims well northeast of the area. Antecedent moisture and orographically enhanced forcing for ascent may lead to locally heavy downpours and isolated flash flooding. Some of the latest guidance depicts the heaviest amounts to be areas to the west and north-northwest of Great Falls, Montana which is a small shift from the previous runs. Campbell Day 2 Valid 12Z Wed May 17 2023 - 12Z Thu May 18 2023 ....THERE IS A MARGINAL RISK OF FLASH FLOODING FOR PORTIONS OF THE COASTAL SOUTHEAST AND ALONG THE MOGOLLON RIM OF ARIZONA... ....Mogollon Rim of Arizona... Much of the same environment and weather pattern will remain in place during this period. A weak, but still notable upper level trough will track southeast across northwestern Mexico on Wednesday. PW values to nudge even higher, approaching 1 inch (+4 sigma), as southerly flow off the Pacific and up the Gulf of California advect into the region. As the trough moves east, the signal for potential heavy rain shift as well. The Marginal Risk already in effect remains in good order as it highlights the areas with an elevated threat for flash flooding and excessive rainfall. ....Coastal Southeast... The slow-moving front will settle across the Gulf states and portions of the Southeast by Wednesday, with will continue to provide a focus convection. Deep moisture drawn northward over this stalled boundary will keep the threat for thunderstorms high, though the flash flooding threat will be low, as FFGs are very high over this region despite somewhat wetter than normal soils. The main flash flooding threat will be in the urban areas of the Marginal Risk, including New Orleans, Gulfport, Mobile, Pensacola, Tallahassee, Valdosta, and Savannah. A small westward expansion was made in South Carolina. Campbell 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!7akQQm68LXo-e1f0Sa34eEi7QBY76OP-N_hg-Vxd4Dgh= yeaiX3Wi03PgsrgwfzUsN-xbIGVpPHumBts3zI8nQJTAAR0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7akQQm68LXo-e1f0Sa34eEi7QBY76OP-N_hg-Vxd4Dgh= yeaiX3Wi03PgsrgwfzUsN-xbIGVpPHumBts3zI8n-vl1fyQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7akQQm68LXo-e1f0Sa34eEi7QBY76OP-N_hg-Vxd4Dgh= yeaiX3Wi03PgsrgwfzUsN-xbIGVpPHumBts3zI8nRkF9nAM$=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) .