Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
557 FOUS30 KWBC 281545 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1145 AM EDT Sat Sep 28 2024 Day 1 Valid 16Z Sat Sep 28 2024 - 12Z Sun Sep 29 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE OHIO AND TENNESSEE VALLEYS AS WELL AS FOR CENTRAL AND SOUTHWEST FLORIDA... ..16Z Update Summary.. Only minor changes were necessary for each respective MRGL this period. Kleebauer ...Ohio/Tennessee Valleys... 16Z Update: The remnants from Helene continue to spin over the Ohio Valley with the surface reflection becoming increasingly diffuse as noted by the 12z observations. The upper support is still present, but the limited instability is noted within the latest 12z soundings out of KILN and KBNA with modest moisture but meager lapse rates and weak capping across the boundary layer. Persistent cloud cover will limit destabilization at the surface leading to less of a convective concern over the region and more towards lingering stratiform with embedded rates between 0.25-0.5"/hr at peak intensity. Antecedent conditions are the main driver for isolated flash flood concerns after yesterdays rainfall with FFG indices running closer to 0.5-1"/hr for potential opening the door to a low-end threat likely ~5% threshold necessary. The threat will subside in full after sunset as any destabilization potential quickly fades and rates fall to well-below any threat for flash flood concerns. This will likely be the last forecast with a MRGL over the Ohio Valley for D1 with a removal at the 01z update. Across the Central and Southern Appalachians, persistent flooding allows for an extremely low threshold for any flooding risks as additional rainfall is "Insult to injury" for the region. A maintenance of the MRGL was warranted to cover for any threat lingering over the region. Kleebauer ...Florida... 16Z Update: Current radar/sat composite indicates the best convective concerns remain confined over West-Central and Southwest FL within the prevailing southwest flow off the Gulf into the western shore. Modest SBCAPE within the 12z KTBW sounding maintain a positive posture for convective initiation and potential that will last through the afternoon. PWATs between 1.9-2" run near +1 deviations according to NAEFS, a signal that usually points towards a low-end threat, at best over the FL coasts with less of a chance further inland. This is primarily an urban flash flood risk from Tampa to Fort Meyers with a time frame between now and 23z as the period of interest before the threat dwindles. HREF probs for >3" run between 35-50% over the above area, just enough for the area, especially after dealing with rainfall from Helene. Kleebauer Day 2 Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024 ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC/APPALACHIANS AS WELL AS THE NORTHERN FLORIDA PENINSULA... ...Mid-Atlantic/Central Appalachians... During this period the remnant low of Helene will get picked up by the upper level jet and track eastward into the Mid-Atlantic and Central/Northern Appalachians. There will be an increase in available instability which may lead to localized enhanced rainfall rates for portions of the Shenandoah Valley and west to the Allegheny Front in Maryland, West Virginia, and Virginia; which may result in isolated to widely scattered instances of flash flooding. The level of threat continues to be handled well with the Marginal Risk that is currently in effect. There may be a need for a Slight Risk with future updates depending on model trends and observations. ...Florida... Convection will continue to fire up in proximity to a stalled frontal boundary draped across northern/central Florida. Storm motion may be fast-moving with some tracking over areas hard-hit by Helene, but because progressive nature of the convection a Marginal Risk remains appropriate for this period. Campbell Day 3 Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024 ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC/CENTRAL APPALACHIANS... The lingering upper low over the East and accompanying moisture from Helene will continue to produce some showers and thunderstorms over portions of the Appalachians and Mid-Atlantic into Monday. Heavy intensity and accumulations are not expected to be widespread or heavy, however the recent wet period keeps an elevated threat for excessive rainfall and isolated flooding concerns. A Marginal remains in effect from south-central Virginia to central Pennsylvania. Campbell Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt