Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
194 FOUS30 KWBC 281957 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 357 PM EDT Fri Jun 28 2024 Day 1 Valid 16Z Fri Jun 28 2024 - 12Z Sat Jun 29 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL PLAINS TO THE MIDWEST TODAY AND TONIGHT... ...16Z Update... No changes were needed to the previously issued Slight Risk. Recent hi-res guidance continues to show enhanced QPF at some locations within the Slight, with rounds of evening to nocturnal convection the most concerning for flash flooding. The Marginal Risk was expanded eastward into Michigan/northern Ohio compared to the previous issuance, as the 12Z hi-res models and thus the HREF have storms well ahead of the cold front extending that far east before 12Z, with the possibility of rain rates exceeding FFG. Also trimmed the Marginal on the northern side as rain moves out of portions of the Upper Midwest and any additional convection along the surface low track looks isolated. Back into the central Rockies/High Plains, severe weather is likely the primary threat, but supercells and multicell convection could produce an isolated flooding threat if high rainfall rates arise. Elsewhere, a Marginal Risk remains in place in southeastern Arizona/far southwest New Mexico. Coverage of monsoonal convection does not look to be as high as earlier this week, but the best chance for instability to form and take advantage of the 90-95th percentile PW values that remain in place is in that area. Some convection cannot be ruled out farther north in Arizona though. Scattered thunderstorms across Florida and the Gulf Coast could cause a localized urban flash flood threat, but the threat appears sub-Marginal especially because hi-res models often overdo rain amounts/rates there. Tate ...Previous Discussion... The latest guidance continues to show a slight southward/slower shift compared with earlier runs...and tended to follow suit...as yet another shortwave makes its way eastward across the Plains. This next setup has more potential due to the addition of a cold front that will be progressing southeast out of the Upper Midwest. With ample moisture in place ahead of the shortwave, a boundary to help focus convection an low level mean flow roughly aligned with the boundary...the potential for training cells/repeat convection with some intense downpours sets up a risk of flooding especially if there is overlap with the heavy rainfall footprint from the past 10 days to 2 weeks from northwest Missouri into portions of Iowa as well as from overnight convection leading up to the start of the Day 1 ERO. A Marginal Risk area extends northward into the western portion of the Great Lakes region ahead of the northern stream system scoots along the international border this afternoon and evening. Bann Day 2 Valid 12Z Sat Jun 29 2024 - 12Z Sun Jun 30 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE LOWER GREAT LAKES AND UPSTATE NEW YORK AS WELL AS NORTHEAST NEW MEXICO... ...2000Z Update... The main change to the Day 2 ERO was to add a Slight Risk into northeastern New Mexico. A stalling/meandering front in that area will combine with PWs increasing to above the 90th or 95th percentile. Hi-res models are focusing on that area for convection with high rain rates, and thus the 12Z HREF has probabilities of 30-40 percent chance of exceeding FFG, with higher probabilities to 70 percent of exceeding 10-year ARI. This all warrants a Slight Risk that was coordinated with the Albuquerque WFO. The reasoning below remains valid for the Marginal to Slight Risks in the northeastern quadrant of the U.S., with some expansion of the southern Slight Risk northward into far southwestern New York and eastward into more of Pennsylvania, per recent model trends (especially the hi-res). Continued to hold off on any embedded Slight Risk in the south-central Plains/Mississippi Valley due to considerable model spread in the highest QPF. Tate ...Previous Discussion... Coverage of showers and thunderstorms should be increasing over portions of the Ohio Valley prior to the start of the Day 2 outlook period at 29/12Z. Precipitable water values look to be approaching 2 inches over parts of the Ohio Valley will be in place by the time height falls from a sharpening mid-level trough approaching from Canada arrives. The broad-scale ascent afforded by the approaching shortwave...the deep moisture and wet bulb zero values at or above 10 kft suggest some intense downpours are possible. With at least some risk of cell training and perhaps some interaction with terrain...felt an upgrade to Slight Risk was needed...although the antecedent conditions may mitigate the flooding potential somewhat. A second Slight Risk was introduced across portions of upstate New York which was more hydrologic sensitivity than the Ohio Valley given recent rains. Concern for excessive rainfall extends southward and westward from these Slight Risk areas along/near a cold front making its way into the Tennessee Valley/Central Plains and southern Rockies. Precipitable water values in the 2 to 2.25 inch range should be pooling along the front from the eastern seaboard as far west as Arkansas and Oklahoma by 30/00Z. Model guidance shows a lot of spread in this region and a Marginal Risk was maintained due to the potential for any cells that form to be efficient rain makers. Bann Day 3 Valid 12Z Sun Jun 30 2024 - 12Z Mon Jul 01 2024 ...THERE IS A MARGINAL RISK OVER PORTIONS OF THE EASTERN SEABOARD, SOUTHWEST U.S., CENTRAL PLAINS, AND NORTHERN HIGH PLAINS... ...2000Z Update... A Marginal Risk area was added to central Kansas. This area is arising as a concern especially in the hi-res models that go out that far. Storms are likely to be ongoing Sunday morning, propagating east from Saturday`s southern High Plains convection. This will be on the cusp of the instability gradient, a typically favored location for storms with high rain rates. It is possible the risk area will shift around in placement in future model cycles if models vary. No significant changes in forecast reasoning for the other Marginal Risk areas. The Four Corners Marginal was expanded north a bit to be consistent with recent model guidance. Tate ...Previous Discussion... ...Eastern U.S... Showers and thunderstorms capable of producing heavy to possibly excessive rainfall will persist along and ahead of a progressive front associated with a northern stream trough. Current guidance continues to focus the heaviest rainfall amounts and rates over portions of the Mid-Atlantic seaboard at the time of maximum instability extending into portions of the coastal Carolinas. Overall the upper dynamics should keep cells moving but with precipitable water values approaching 2 inches along/near the front...flooding is possible in areas of poor drainage and urban areas. ...Southwest U.S... Moisture begins to get drawn northward from Mexico on the western side of a sprawling mid-level high over the Southern Plains. Isolated to widely scattered late afternoon and evening convection has the potential to produce locally heavy rainfall as the sub- cloud layer moistens up in response to precipitable water values over 1.5 inches crossing the border into southern Arizona by early evening. ...Plains of western North Dakota and eastern Montana... A mid- level trough will be moving out of the Northwestern US and emerging from the northern Rockies by afternoon helping to focus late day convection. Any convection that forms during the day should encounter deeper moisture over North Dakota by the evening...leading to a threat of excessive rainfall. Model guidance does show increasing moisture transport into the region by a strengthening low level jet during the evening with at least some concern for convection to persist into the night given the model shear profile. 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