Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Apr 14 2023 08:22:07 FOUS30 KWBC 140822 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 421 AM EDT Fri Apr 14 2023 Day 1 Valid 12Z Fri Apr 14 2023 - 12Z Sat Apr 15 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH FLORIDA & THE MID-ATLANTIC/CENTRAL APPALACHIANS... ....South Florida... Heavy rains yesterday caused some of the major roads in the Fort Lauderdale to Miami corridor to become flooded. Additional showers and thunderstorms are expected to fire up near the coast during the afternoon and evening hours, which will aggravate the already sensitive area. A Marginal Risk area was raised for the coastal/urban areas of southeast Florida. ....Mid-Atlantic and Central Appalachians... A deep mid/upper level low is expected to lift northward and weaken/open into Friday night. Moist easterly flow ahead of the advancing warm front will bring a surge of higher moisture through the region, characterized by PWs of up to 1.5 inches. With available instability (~1000 J/kg CAPE), locally intense rainfall will be possible across the Piedmont region. A secondary round of convection is possible during the afternoon/early evening associated with the main upper level shortwave moving overhead. The combination of steeper lapse rates and peak heating could bring another round of heavier showers and thunderstorms. Some of the hi-res guidance is depicting hourly rainfall of 1 to 1.5+ inches/hr across the Carolinas, as well as, eastern Kentucky, western Virginia and southern West Virginia. The 3-hr FFG are as low as 1.5 inches in the areas of higher elevation and around 2-2.5 inches elsewhere. The inherited Marginal Risk area was reshaped to trim out parts of South Carolina where the latest trends have lowered and then expanded east-west into western Kentucky, Tennessee and southern West Virginia where intense rainfall may quickly surpass local FFG and lead to isolated flooding concerns. Campbell Day 2 Valid 12Z Sat Apr 15 2023 - 12Z Sun Apr 16 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE LOWER AND MIDDLE MISSISSIPPI RIVER VALLEY... ....Western U.P. of Michigan, northern Wisconsin and the Arrowhead of Minnesota... Recent snowmelt across the region has lowered local 6-hr FFG to 0.25 inch. While the rain-snow line may play a role in northeastern Minnesota, rain will be the dominant precipitation type further east. 24-hour forecast rainfall totals are expected to generally range between 1/2 and 3/4 inch through early Sunday morning, but the potential with moisture advection of exceeding the 1/4 inch in 6 hour threshold for meeting FFGs is significant. There is unanimous model agreement that temperatures will remain above freezing in this area between now and the rainfall on Saturday, so there's no reason to expect snowmelt will not continue around the shores of Lake Superior. While the rain is never expected to be heavy, the low FFGs and the forecast rainfall alone are worthy of consideration of a Marginal Risk introduction for this area with future forecast updates. Wegman ....Lower to Mid-Mississippi River Valley... A subtropical jet with an embedded shortwave trough is expected to track through the central U.S. which will provide the large scale forcing for ascent early in period. PW values will be near 1.5 inches with possible surges of 1.75 inches along the Gulf Coast of Louisiana, Mississippi and Alabama. With deep moisture drawing northward the environment will be conducive for locally heavy rainfall to spread across the Lower and Middle Mississippi Valley. Later on, a stronger shortwave trough will approach as it departs the Rockies. Showers and thunderstorms will fire up along and ahead of this approaching cold front mainly after 00Z and have the potential to dump 1 to 3 inches over the Mississippi Valley. Some of the this region has had recent rains, and are 150 to 600 percent of normal. These sensitive soils could quickly become over saturated and lead to isolated/scattered areas of flooding. The Marginal Risk area that is already in effect covers much of this sensitive region. Given the latest QPF trends and WPC forecast, the western and northern bounds of the Marginal were expanded. 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!9ksre1I4SZREKn7Q4jQdMu4tFY-VdQoP869WAQiPrDFw= 1E_ccl4QTCnrc02TocC5afOHAK0m_7G_1yAPjNP2uYoil9E$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9ksre1I4SZREKn7Q4jQdMu4tFY-VdQoP869WAQiPrDFw= 1E_ccl4QTCnrc02TocC5afOHAK0m_7G_1yAPjNP2u-8qWFg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9ksre1I4SZREKn7Q4jQdMu4tFY-VdQoP869WAQiPrDFw= 1E_ccl4QTCnrc02TocC5afOHAK0m_7G_1yAPjNP2SaYON1c$=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) .