161 FOUS30 KWBC 080046 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 846 PM EDT Sat Jun 7 2025 Day 1 Valid 01Z Sun Jun 08 2025 - 12Z Sun Jun 08 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE OHIO RIVER VALLEY AND MID-SOUTH INTO THE SOUTHEAST... 01Z Update... ...Midwest and Central Appalachians... Thunderstorms will continue develop in advance of an eastward moving wave currently along the MO/IL border. This activity should mainly form along the warm front currently extending from StL through southern IN and organize a bit in the warm air advection regime. PW increases behind the front to around 1.75", above the 90th percentile for early June, along with tall, skinny CAPE profiles per model soundings that will make for efficient, low- topped convection and scattered flash flood events. Of particular concern will be the potential for flash flooding overnight from central IN along the mid-upper OH Valley through WV. Southwest low- level inflow increases over the terrain in the very moist environment with the right entrance region of an upper level jet streak providing divergence aloft. Locally significant flash flooding will be possible given the terrain and relatively wet antecedent conditions of the Slight Risk area. ...Mid-South through Southeast... Forward propagating MCS pushes east over SC this evening with fast motion. The leading cells that developed ahead of the line when it was over GA are not occurring as much over SC, so the associated flash flood threat is low overnight. The next line of activity has developed across south-central AR and is moving close to its orientation axis, causing repeating cells. This will continue until enough cold pool can develop to begin a propagation southeast into LA and over north-central MS/AL which continues rest of the overnight. Despite dry antecedent conditions and high FFG, the Slight Risk is maintained for potential for 2-4" rainfall with high hourly rates and potential scattered instances of flash flooding. ...Southern Plains... Third consecutive night of supercells from the south-central High Plains developing and shifting southeast. Expanded a Marginal Risk from North Texas to these cells based on current motion and CAM guidance like recent runs of the RRFS which maintain this activity through tonight. This swath is mainly between the heaviest rain from last night, but there is an isolated flash flood threat as this activity propagates southeast. ...Northeast... Low pressure has shifted well east of New England bringing rainfall with it. Some heavy rain remains along the front over Long Island, though the rates are not excessive. The EROs in the Northeast have been removed. Lamers/Jackson Day 2 Valid 12Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE CENTRAL APPALACHIANS AND MID ATLANTIC... AS WELL AS THE SOUTHERN PLAINS... ...Central Appalachians into the Mid-Atlantic... The heavy rain and associated flash flood threat is likely to be ongoing across portions of the region at the beginning of the outlook period (12 UTC Sunday). Model guidance today has generally begun to focus the QPF signal across the region such that there is much better consistency between the global ensembles and hi-res ensembles (both RRFS experimental ensemble and HREF operational). Therefore, confidence was sufficiently high to go with a relatively big departure from the existing more focused Marginal Risk area, and go with a broad Slight Risk. The biggest change was to areas of eastern Virginia and central Maryland, which previously had ERO probabilities of less than 5 percent, but hi-res guidance is now consistently showing some localized maxima in excess of 3 inches into the coastal plain. Greatest concern within the Slight Risk area is in the Allegheny Mountains, Potomac Highlands and Laurel Highlands of northeast West Virginia, the Maryland Panhandle, far southwest Pennsylvania, as well as the Shenandoah Valley and Blue Ridge Mountain region of far northwest Virginia. These areas have been very wet lately, with 30-day rainfall double to triple the normal amount, and a significant portion of the same area received between 1 and 4 inches of rain in the past day or so. Rainfall may be enhanced in these areas by a subtle southeasterly low-level jet that should increase between 06 UTC and 18 UTC Sunday due to a developing low level cyclone ahead of an eastward propagating mid-upper level wave. If the low becomes situated near the OH-WV border by the beginning of the outlook period, which has been a trend over the past couple model cycles (along with a deeper low overall), the LLJ would be likely to be enhanced. This may create orographic enhancement to the rainfall and could help some convective features and bands persist for a greater duration where the orographic enhancement is most pronounced. Any convection is likely to be low-topped, with model forecast soundings showing a high melting level (above 12,000 feet) and a low equilibrium level (between -10C and -20C), with PWs above the 90th percentile for early June. This would be likely to lead to dominance of efficient, warm rain processes with little to no ice present in the cloud. This could support rapidly developing flash flooding where convective features can persist. Meanwhile, further east into the coastal plain and I-95 urban corridor from Richmond to Baltimore, models have also converged on an increased heavy rainfall threat. In these areas, greater instability will be present -- enough to support organized clusters of thunderstorms that could produce very heavy rain rates at times. The heavy rain should be less persistent as compared to the mountainous areas, but that would be offset by higher instantaneous rain rates. Therefore, these areas were also included in the Slight Risk and could see some flash flooding impacts. ...Southern Plains to the Southeast... Fewer changes were made to the existing Day 2 outlook from the Southern Plains into the Gulf Coast region. A Slight Risk remains centered on North Texas and southern Oklahoma, and many models now show a rainfall maxima in excess of 3 inches somewhere in the area. Although a forward propagating MCS may develop with time, there is enough signal in the model guidance for a corridor of enhanced QPF that some training of intense convection seems possible. This would be most likely either via (1) individual cells and clusters developing near the front ahead of the advancing convective line and subsequent cell mergers, or (2) slowing or stalling of the convective line on the southwest periphery of the developing cold pool. If either of these scenarios develops, flash flooding would be possible via heavy rainfall sustained for a couple hours at any one location. Although the Gulf Coast is not in a Slight Risk at this time, it will need to be monitored, as some (but not all) recent hi-res model runs show significant localized rainfall extremes in excess of 6 inches. An examination of individual model runs indicates this would be most likely where convective outflows interact with the coastal convergence zone. Lamers Day 3 Valid 12Z Mon Jun 09 2025 - 12Z Tue Jun 10 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS A LARGE PORTION OF THE SOUTHERN AND EASTERN UNITED STATES... Very few changes were made to the existing Marginal Risk, which encompassed a broad area in the southern and eastern United States along and ahead of a slowly advancing cold front. The air mass ahead of the front will be characterized by above normal PWs and widespread moderate to strong instability. Therefore, a day with abundant areas of active convection containing relatively high rain rates is expected. Confidence is not very high at this time in the detail, particularly where concentrated areas of heavy rainfall and/or localized extreme events may occur. However, based on today's model guidance, this seems most likely in the following locations, where a Slight Risk upgrade may eventually be needed: 1. Eastern Great Lakes and Central Appalachians. Instability is projected to be more limited in these areas, but recent rainfall may lead to wet conditions in advance, and there is better model consensus on areas of over 1 inch QPF. 2. The Gulf Coast. A combination of strong instability and high PWs would support organized convection and high rain rates, but there is less model agreement on placement. 3. West Texas into Northeast New Mexico. PWs will be increasing and quite anomalous (over the 90th percentile) along with fairly strong instability. These areas will be removed from stronger mid- upper level flow, likely leading to overall slower storm motions. Lamers 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