Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
788 FOUS30 KWBC 312110 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 510 PM EDT Fri May 31 2024 Day 1 Valid 2057Z Fri May 31 2024 - 12Z Sat Jun 01 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE UPPER MIDWEST AND SOUTHEAST U.S. INTO THE LOWER/MID MISSISSIPPI VALLEY... ...20Z Update... Based on the latest observational and mesoanalysis trends, have updated the Day 1 ERO to (a) add a Slight Risk area across northeast NE- Southeast SD into northwest IA and much of southern MN, and (b) pare much of the Slight risk west of AR-LA. Despite the earlier heavy rainfall/antecedent wet soils, shortwave ridging is limiting the converage of any renewed convection, despite the airmass recovery (destabilization) this afternoon. Per the latest high-res CAMs (HRRRs and 18Z HREF), less-organized or spottier convection later this afternoon and evening may result in additional localized instances of flash flooding, though mainly south of where the heaviest rainfall had occurred over the past 24hrs. Hurley ...16Z update... Sinking air over parts of Oklahoma western/central Oklahoma/Texas has reduced convection and will limit redevelopment later today/overnight therefore trimmed back the western bounds of the Marginal and Slight Risk areas. A bowing MCS moved through eastern Texas this morning and has slowed progression while boosting development across the Gulf Coast and southern Louisiana. Heavier showers expected for southeast Louisiana, southern Mississippi and western Florida necessitated an eastward expansion of the Slight and Marginal Risk areas. Multiple boundaries within this very moist environment over much of Arkansas and Louisiana and surrounding locations could lead to very isolated heavy, possibly extreme rainfall amounts to materialize; however confidence on the intensity and location remains uncertain. Further north, a nice axis to 1 to 3+ inches will be possible from northwest Iowa to southeast Minnesota/western Wisconsin parallel to the advancing cold front. Campbell Multiple clusters of convection in rather close proximity to each other during the overnight hours preceding the start of the Day 1 period prevented any one storm from becoming dominant...but the multiple boundaries left behind has muddled the picture of what will be on-going as of 31/12Z. And how the models have struggled certainly has not helped. As a result...the Day 1 Excessive Rainfall Outlook depicts a broader and more diffuse picture than is normally preferred early on. As the day progresses...trends in the guidance suggests that the convection should be more progressive than what occurred on Thursday...but that does not preclude the possibility of additional rain falling on areas that received heavy rainfall in recent days (especially over portions of Louisiana and Mississippi) before mid-level energy begins to shift northeastward and spread any associated rainfall into parts of the Mid- Mississippi Valley by 12Z Saturday. The option for an upgrade to a Moderate remains but not done at this time with the uncertainty...but clearly even a brief period of intense rainfall in areas already waterlogged could exacerbate any on-going flooding. Maintained the Marginal Risk over the Colorado High Plains and adjacent areas introduced on Thursday given the potential for isolated convection capable of producing brief downpours. Bann Day 2 Valid 12Z Sat Jun 01 2024 - 12Z Sun Jun 02 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHEAST US INTO THE LOWER MISSISSIPPI VALLEY... 21Z update... Minor reduction of the Marginal Risk near the Sand Hills where FFG is notably higher than surrounding locations and along the northern bounds across southern Michigan. Otherwise the area highlighted by the Marginal Risk remains in good order. There was a notable increase of QPF along part of the central Gulf Coast and into western Florida where the latest guidance is suggesting heavy rain to materialize a bit further east than previous cycles. The Slight Risk area as a whole was translated a bit east/south and expanded coverage from southeast Louisiana to western Florida. In turn the Marginal was adjusted east as well across Florida and toward the Georgia state line. There are hints that the Pensacola vicinity could have downpours yielding upwards of 3 inches locally. Campbell The shortwave that started lifting northeastward into the Mid- Mississippi Valley will continue to focus and support convection capable of producing heavy rainfall mainly across parts of Mississippi. Guidance continues to show the potential for isolated 3 to 5 inch amounts within the Slight Risk area. Concern in the western portion of the Slight Risk area where flash flood guidance has been lowered by recent bouts of rainfall while areas on the eastern side of the Slight Risk area should be in a better position to receive higher rainfall rates given a persistent axis of precipitable water values at or above 1.75 inches across Alabama. This is roughly coincident with the low-end probabilities for 3 inches of rainfall in an hour as shown by the HREF probabilities. Farther west...the still expect convection over the western High Plains from southwest Nebraska southward into western Oklahoma/Texas panhandle and extending nearly as far south as the Rio Grande. Spaghetti plots showed moisture beginning to return as low level winds backed during the afternoon. Bann Day 3 Valid 12Z Sun Jun 02 2024 - 12Z Mon Jun 03 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL PLAINS AND UPPER MISSISSIPPI VALLEY... 21Z update... Although there is spread amongst the guidance on where areas of moderate/heavy rain will be there is a growing signal from far northeast Kansas north/northeastward to central/northern Minnesota and western Wisconsin. Parts of this region has had recent rains to raise soil saturation which has lowered the threshold needed for flooding concerns to arise. Areal averages of 1 to 3 inches are forecast with local maximums of 4+ inches possible. A Slight Risk area was raised for this period covering northeast Kansas/northwest Missouri to central Minnesota/western Wisconsin. Campbell Surface low pressure forming over eastern Montana/eastern Wyoming and the western Dakotas Saturday evening will increase moisture transport east of the Rockies as a fast moving/low amplitude trough emerges out over the northern and central plains on Sunday. The surface low and an attached cold front will help focus and support convection capable of producing locally heavy rainfall. Moisture flux anomalies increase to more than 3 standardized anomalies above climatology ahead of the approaching cold front...which allows precipitable water values to approach 1.5 inches in the northern Plains. Farther south...isolated thunderstorms are also expected later in the day and in the evening in confluent flow along the dry line which also has the potential for locally intense rainfall and isolated flooding. 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