Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
041 FOUS30 KWBC 211558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Sat Sep 21 2024 Day 1 Valid 16Z Sat Sep 21 2024 - 12Z Sun Sep 22 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN HIGH PLAINS... ...New Mexico into Texas/Oklahoma Panhandles... The large-scale flow across the southern Great Basin will continue to draw moisture northward at the low levels while becoming increasingly diffluent aloft in response to the approach of an upper low moving across the Four Corners this morning. Precipitable water values are forecast to exceed 1.5 inches across parts of West Texas by late afternoon while the right entrance region of an upper level jet rounds the base of an upper trough and tracks over the region. This combination should help support multi-cell storms capable of producing isolated rainfall rates of an inch or more and storm total rainfall amounts in excess of 2 inches over portions of northeastern New Mexico into the Texas Panhandle during the afternoon or evening hours with an associated risk of flash flooding. 12Z CAMs have honed in on northeastern NM into the OK/TX Panhandles while decreasing any heavier rainfall threat north of the KS border, and have thus trimmed the northern part of the MRGL and SLGT risk areas a bit. ...Northern AZ into southern UT... Added a small Marginal Risk as the upper low moves across this region, with a continued threat of isolated convective cells capable of producing ~0.50"/hr rates for a time. Main threat would be over more sensitive areas near steep terrain (e.g., around Zion NP). ...Mid-Atlantic... Non-zero threat of isolated/urban flash flood threat for the DC/Baltimore metro area this afternoon with developing convection. Antecedent conditions have been fairly dry, and the guidance still shows a bit of spread, so opted to keep out the region with the 16Z update. Fracasso/Bann Day 2 Valid 12Z Sun Sep 22 2024 - 12Z Mon Sep 23 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE MID MISSISSIPPI VALLEY TO THE SOUTHERN HIGH PLAINS... The focus for areas of heavy rainfall will continue to be along a plume of deeper moisture...precipitable water values generally at or above 1,75 inches...from the western portion of Texas northeastward to where it begins to encounter a cold front moving in from the northern United States. An upper level shortwave trough over the central and southern Rockies on Sunday morning will eject eastward during the day...aiding the formation of storms over parts of western Texas capable of heavy downpours around the time of maximum heating. Farther to the east...model guidance tends to generate at least some convection capable of producing isolated 2 to 3 inch rainfall amounts over portions of Missouri as moisture flux convergence occurs ahead of a cold front pushing southward. Mesoscale guidance...available through the first 12 hours of the Day 2 period for the overnight EROs...does show low-end potential for 2 inch per hour rates embedded within a broader area where probabilities of 1 inch per hour rates are on the order of 10 to 25 pct. There was already a Slight Risk introduced here and only needed a bit of realignment to fit the latest guidance. Bann Day 3 Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF THE MISSISSIPPI VALLEY EASTWARD INTO THE OHIO VALLEY... As the large scale upper trough continues to move eastward on Monday...the plume of available moisture gets elongated and the moisture flux along the front becomes less well defined. There will be some broader upper support along the front which will have taken on a more east-west orientation...so there is at least some potential for problems from run off with 1 to 2 inches or rainfall over portions of Illinois into Indiana. But with convection expected to become increasingly elevated and with flash flood guidance tending to be 2.5 inches per hour or greater...will maintain a Marginal Risk area for now and evaluate the need for an upgrade if rates/amounts pick up in later model cycles. 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