Quantitative Precipitation Forecast
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248 FOUS30 KWBC 101614 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1214 PM EDT Mon Jun 10 2024 Day 1 Valid 16Z Mon Jun 10 2024 - 12Z Tue Jun 11 2024 ...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL ACROSS THE PORTIONS OF THE NORTHERN PLAINS, SOUTHERN HIGH PLAINS AND TEXAS, SOUTHERN FLORIDA, AND PARTS OF EASTERN GEORGIA-SOUTH CAROLINA... ...Southern High Plains... ...16Z Update... Minimal changes were made to the Day 1 update, mainly to expand the Marginal Risk area into North TX (including the DFW Metro) to account for trends with some of the 12Z CAMs (WRF-ARWs especially). The 12Z RAOB out of FWD indicated a PW of 1.93", which is close to the 99th percentile per the SPC Sounding Climatology. Surface frontal boundary nearby along with some subtle left-exit region upper forcing via a 70-90kt upper level jet streak will enhance the potential for some slow-moving, somewhat more organized convection (multicell clusters), a few of which could lead to excessive short term rainfall rates with ML CAPEs of 1000-2000 J/kg. Hurley Previous discussion.. A forming closed low straddling NM/TX border will slowly settle east/southeast through the period and across the entire region there should be fairly high moisture remaining in place (PWs 1.25-1.75") that will support scattered thunderstorms. Showers and thunderstorms across the Southern Rockies and adjacent High Plains may result in isolated to widely scattered areas of flash flooding during this period. Recent rains will likely have increased soil sensitivity for new locations within this region thus maintaining a Marginal Risk area. ...Eastern Georgia into the South Carolina Lowcountry... ...16Z Update... Included a Marginal Risk over this region with the 16Z update. This based on some of the more recent high-res CAM trends at 12Z, including the HREF exceedance probabilities. The concern here will be an isolated flash flood risk with west to east training of convection, along and south of the surface frontal boundary (and strong deep-layer instability gradient) as a shortwave impulse traverses the base of the longwave trough. PWs between 1.6-1.8" along with ML CAPEs of 1000-2000 J/Kg will lead to localized 1.5-2.0"/hr rainfall rates underneath the strongest cores, and potentially 3+ inches within 3 hours. Hurley ...Northern Plains... The flash flooding threat remains lower-end Marginal across the Northern Plains. Some training storms are possible, which could cause isolated instances of flash flooding in flood-sensitive areas where local 1-hr FFG is as low as 1 inch. Areal averages will be up to 1.5 inches with very local 2 inches possible. This area could be considered for Marginal Risk removal with future updates. ...South Florida... With the frontal boundary stalled across the Southeast moisture will continue to advect northward across South Florida which will increase convective coverage, particularly along the sea breeze fronts on both sides of the Peninsula. Any potential for flash flooding will be limited given the ongoing moderate to locally severe drought. However, with the influx of moisture (PW values of 2-2.5 inches) and continued slow storm movement, possibly over urban areas, will result in isolated instances of flash flooding, and a bit further north up the Peninsula into portions of central Florida on Monday afternoon. A Marginal Risk for excessive rainfall remains in effect for South Florida. Campbell Day 2 Valid 12Z Tue Jun 11 2024 - 12Z Wed Jun 12 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN FLORIDA... ...Southern Florida... Deep tropical moisture will continue to stream northward and pool over the state near the stalled frontal boundary which will continue to fuel the more widespread unsettled/stormy weather across the Keys and southern Florida. PWs are forecast to be well above 2.5" and could approach daily max values by Wednesday. The environment has the potential for slow moving storms capable of several inches of rain along with intense rain rates. The Keys and southwest portions of the peninsula will have the great risk for excessive rainfall and associated flash flooding, but the threat extends to the southeast coast and into portions of central Florida as well. Widespread 1 to 3 inch totals with locally higher amounts as high as 5 inches are possible on Tuesday. The guidance is in general agreement that the higher totals will be along the west coast from Ft. Meyers south. However, even the slightly lower forecast totals into the east coast could still cause local flooding concerns, particularly in urban areas. ...Southern Plains... The shortwave will progress during this period shifting the convection as well. This extra source of lift combined with the very moist airmass pooled over the region will trigger scattered to numerous thunderstorms during the afternoon and evening hours. Areal average of 1 to 2 inches will be common with isolated maxes nearing 3 inches will be possible. At this time the Marginal Risk seems adequate for the level of risk but it is possible that an upgrade to a targeted Slight Risk may be needed with future updates with more certainty and CAMs guidance pinpointing where the heaviest rainfall will be. Campbell Day 3 Valid 12Z Wed Jun 12 2024 - 12Z Thu Jun 13 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN FLORIDA... ...Southern Florida... The stalled front is expected to be draped across northern Florida while tropical air continues to amass over the region. PW values of 2/2+ inches will be on the order of 2.5-3 standard deviations above the average for this period. Convection will be very efficient in dumping several inches of rain across the nearly saturated rural and urban areas of South Florida and the Keys. A Slight Risk for Southern Florida and the Keys and a Marginal Risk for Central Florida were maintained from the previous day 4. The nature of this multi-day event with storm total rainfall amounts potentially rising into the double digits, there may be the need for an upgrade in future updates. ...Texas... Persistent convection associated with the shortwave moving across the Souther Plains will persist during this persist across east- central portions of the state. While amounts are on the lower end the recent rains will have increased soil saturation thus lowering the amount of rain needed to become problematic. A small Marginal Risk was maintained for the eastern Hill Country and points east for an elevated risk for excessive rainfall. 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