Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
255 FOUS30 KWBC 041954 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 354 PM EDT Sat May 4 2024 Day 1 Valid 12Z Sat May 04 2024 - 12Z Sun May 05 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL TODAY AND TONIGHT ACROSS PORTIONS OF THE SOUTHERN PLAINS... ..Southern Plains and Gulf Coast... 16Z update... Very small adjustments were made to the Marginal`s northern bounds and the southern bounds of the Slight Risk to adjust for a very small southward trend with the QPF footprint. Consensus still favors the highest amounts to focus near the Texas Hill country and surrounding locations to the immediate east and north. Hi-res guidance is showing several hours where the hourly rainfall rates will be 2-2.5 inches/hr with a couple instances where it surges to 3-4 inches/hr. Campbell The focus of attention becomes the Southern Plains as a mid- and upper level trough emerges from the southern Rockies later today and encounters an atmosphere becoming increasingly moist and unstable over much of Texas given persistent flow off the Gulf of Mexico. The general consensus of guidance opinion is that storms will be forming along the dry line in West Texas and then develop upscale and towards the east in central Texas. As the storms develop, there will be cell mergers and other interactions, as well as possible training that could lead to local rainfall totals to 5 inches. In addition...soils in this area have been saturated due to rainfall from thunderstorms as recent as yesterday. Thus, the Slight Risk area was expanded south to include much of central Texas. The surrounding Marginal was expanded further south to account for likely guidance changes prior to the event. Most of the flash flood producing rainfall is expected overnight tonight/early Sunday morning with a gradual northward and eastward expansion across the Plains. Also made an expansion of the Slight Risk southward towards southeast Texas in deference to signals from the 00Z HRRR of a complex that bows out and spreads yet more rain into the area that does not need any more late tonight/early Sunday morning. Bann ...Eastern Ohio and Tennessee Valleys, Appalachians and Mid- Atlantic... Convection is firing up across portions of the Carolinas/Mid- Atlantic region as confluent deep moisture streams interact with the shortwave energy lifting out of the Southeast. Scattered areas of heavy rainfall (1.5 to 2 inches/hr) and localized flash flooding will be possible. There may be isolated max accumulations nearing 3 inches where storm motion is slow. Further north across the eastern portions of the Tennessee and Ohio Valleys there will be ample instability and mid-level forcing to support stronger cells to move southward, especially into flashy prone areas. A Marginal Risk area was hoisted for this period, spanning from central Georgia north to eastern Ohio and southern Pennsylvania. Campbell ...Sacramento Valley of California... Maintained the Marginal Risk area with few changes as a deep and cold low moves into the Pacific Northwest and spread rain into the lower elevations of northern California. Latest guidance continues to advertise 1 to 3 inches of rain possible in the foothills of the Sacramento Valley and west aspect of the mountains at lower elevations. This continues to be a low-end Marginal...but excessive rainfall is possible in the event the rainfall rates are enhanced by any thunderstorms. Bann Day 2 Valid 12Z Sun May 05 2024 - 12Z Mon May 06 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST TEXAS... 21Z update... Given the uptick in QPF trends over the water-logged locations of southeast Texas, a Moderate Risk was raised for this period. Areas of flooding are ongoing and additional rainfall will only serve to aggravate or worsen conditions. Hi-res guidance is depicting severals hours of rainfall rates pulsing from 1 to 3+ inch/hour as the cells cross the state. Over half of these solutions show the heavy rains tracking across areas south and east of of the Houston metro, so there may be the need for an expansion of the Moderate Risk with future updates. Campbell They system over the Plains today will continue to move eastward on Sunday. Storms will likely be ongoing in portions of eastern/southeastern Texas at the start of the period Sunday and will continue pushing eastward with training of cells appearing likely along an east- west- oriented boundary on the south end of a more progressive line of storms. There is inherent and typical uncertainty with where that line will set up, especially with recent large southward shifts in the guidance and a fairly large spread within any suite of guidance. Thus, to cover the large changes in the guidance, as well as very recent and ongoing heavy rain across southeast Texas, maintained the large Slight Risk area. For the Ozarks region, significant uncertainty also exists, as the area will be on the northern side of the strong shortwave trough driving all of the convective activity. The big concern is whether or not the active convection farther south will disrupt the feed of moisture and instability. For the moment...will not make too many changes to the guidance that led to an expansion of the Slight into parts of Missouri and Arkansas earlier. Bann Day 3 Valid 12Z Mon May 06 2024 - 12Z Tue May 07 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL AND NORTHERN PLAINS ON MONDAY AND MONDAY NIGHT... 21Z update... There is a growing consensus for much of eastern Montana and surrounding areas to get a soaking rain for this period. Much of this region has nearly saturated soils which has reduced the 3-hr FFG to as low as 1 inch. Portions of the Bear Paw Mountains in north-central Montana still have liquid equivalent of 1 to 2.5 inches in the snowpack. Rain over this snowpack will likely speed up snowmelt while increasing the amount of water available for runoff. Areas of local flash flooding will be possible. For the Central Plains, the latest guidance and WPC forecast shifted the QPF to the east/northeast about 100-150 miles. This resulted in trimming the back edge of the Marginal to central South Dakota to northeast Oklahoma and expanding the eastern boundary into southern Minnesota and eastern Iowa. The Slight Risk was shifted eastward and now encompasses eastern Kansas/Nebraska, southeast South Dakota, western Iowa and western Missouri. Campbell Heavy rainfall that results in flash flooding is possible from convection that is expected to develop over the Plains on Sunday as an upper trough ejects northeastward across the northern/central Plains on Monday. Precipitable water values of 1.2 to 1.6 inches will be drawn northward on 850 mb flow of 30 to 45 kts and modest height falls ahead of the trough aloft and a surface dry line. Rainfall rates over 1.5 inches per hour appear reasonable given the amount of instability to aid updraft strength. The broadly diffluent aloft that forms could result in repeated rounds of heavy rainfall in some cases but broader/larger scale organization may keep individual cell motion progressive enough to mitigate at least some of the excessive rainfall potential. Bann 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