FOUS30 KWBC 251558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Thu Jun 25 2026 Day 1 Valid 16Z Thu Jun 25 2026 - 12Z Fri Jun 26 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FOR A PORTION OF SOUTH-CENTRAL GREAT PLAINS... ...Plains to Mid-Mississippi Valley... Shortwave trough drifts east across KS today in a more zonal flow pattern than prior days as the high over west Texas is suppressed. This flow runs parallel to a slow-moving front bisecting KS into MO. Surface cyclogenesis over eastern CO will shift east with the shortwave trough and along the quasi- stationary front. 12Z CAMs generally agree with a farther south solution both for the ongoing convection over south-central KS and the afternoon/evening activity with the shortwave. The 12Z FV3LAM does not have the morning convection and is thus too far north. The 12Z NAMnest is also farther north, but with the evening convection, so this will have to be monitored through the rest of the day. For now, the Moderate Risk is expanded west and south a bit given radar and CAM trends. The thermodynamic posture for this evening will be seen as reputable for heavy convective cores as regional theta_E's remain elevated across the Central and Southern Plains to Mid-Mississippi Valley with the core of greatest SBCAPE positioned along and south of US54 in southeastern KS to southwest MO. It is this area where HREF probabilities for rates >1"/hr are most noteworthy with modest probabilities (20-35%) for upwards to 2"/hr in the stronger cell cores. The strengthening nocturnal LLJ and intensifying isentropic ascent across the area downstream of the surface low will create a period of widespread heavy rainfall over that area of southern KS into southwestern MO. Flow running parallel to the boundary only adds for the potential of back- building until the surface low and attendant shortwave can finally eject eastward into the Mid- Mississippi Valley which can be noted in the hourly composite radar forecasts via various CAMs. Elevated antecedent soil moisture and lingering hydrologic concerns across southeast KS into southern MO only add to the heightened risk of flash flooding as the area will likely struggle to maintain any additional rainfall, especially significant totals over 2". The SLGT risk expands east through the areas above with an elevated SLGT through the St. Louis metro as heavy rain shifts east ahead of the shortwave trough across eastern MO and southern IL overnight. ...Southeast U.S... Gulf moisture converging along a remnant stationary front should trigger diurnal activity over AR/southern MS/AL and GA as best depicted in the 12Z RRFS. A disturbance along this boundary should be a mechanism for targeted low- level convergence in a zone of favorable boundary layer moisture and instability. Signals for locally heavy rainfall of 2+ inches are noted in the deterministic CAMs with the HREF blended mean QPF between 12z Thursday to 00z Friday showing pockets of 1.5-2" located from the MS coastal areas through the I-10 corridor towards Tallahassee, back up into southern GA, as far east as Savannah/Brunswick in this latest cycle. This is coincident with the 500mb vorticity trajectory of our mid- level impulse generated from the previous period of thunderstorms which provides a better target point for heavy rainfall compared to just your standard pulse convection regime we see in the summer. Modest HREF neighborhood probs of 20-40% exist for localized totals >3" across the aforementioned areas, enough to account for potential isolated flash flood concerns, mainly within more urbanized/developed areas across the Southeast. As a result, maintained the previous MRGL risk with an expansion over New Orleans. ...Interior West... Multiple shortwaves and elevated moisture presence across the Interior Mountain West will lead to another afternoon and early evening of scattered convection with localized flash flood concerns today. The threat remains low-end for the time being given the current QPF outputs, however this could still provide some isolated flash flood prospects in those terrain focused zones across UT/CO, as well as any heavy rain encounters in the favored slot canyon areas littered over western CO into UT. The previous MRGL risk was generally maintained. ...Northeast... A potent shortwave trough located over the Northern Great Lakes into the neighboring Ontario Province will allow for a focused area of ascent downstream of the mean trough as the Northeastern U.S. nestles squarely into the left exit region of a modest 110kt jet ejecting eastward across the Great Lakes. Sufficient deep layer moisture and added shear with the incoming disturbance will aid in maintenance of an area of quick-moving convection across NY state through central and northern New England later this afternoon. High probabilities for >1" and low probs for 2" indicates a general pattern of 1-2" with perhaps a few pockets exceeding 2" in the setup over the Hudson Valley into VT/NH, enough to warrant at least a low to modest threat of localized flash flood concerns, especially given some of the more saturated soils located over the region as noted via the latest NASA SPoRT 0-10cm soil moisture percentiles >90%. The previous MRGL risk was generally maintained with only some expansion south and east where FFG is lower. Jackson/Kleebauer Day 2 Valid 12Z Fri Jun 26 2026 - 12Z Sat Jun 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE MID-MISSISSIPPI AND OHIO VALLEYS... ...Mid-Mississippi and Ohio Valley's... Shortwave ejecting out Missouri Friday morning will continue to progress through the Ohio Valley the rest of the D2 time frame. Quasi-stationary front will remain positioned along and just north of the Ohio River leading to an emphasis on convection within proximity of the boundary. The 00z HREF does not go beyond the 00z Saturday hour, however, the 12hr period between 12z Fri - 00z Sat is very much indicating some significant rainfall in-of that area of the Mississippi/Ohio River confluence and surrounds. HREF neighborhood probabilities for at least 3" in that 12hr period are solidly between 30-60%, a signal that usually correlates to heavy rainfall with rates sufficient for flash flood prospects. Thermodynamically and kinematically, this setup is one that favors locally significant rains with most guidance in agreement on areas of 2+ inches during the back end of D1 heading through D2. The threat will continue to extend east through southern IN and OH with the eastward advancement likely to extend as far as western PA down through the Central Appalachian front in PA/MD/WV. Current indications are for the heaviest rain to likely focus west of I-79 in WV, so the SLGT risk remains situated closer to the OH/WV/KY border and points west with a MRGL further east. A high-end SLGT is forecast over the confluence area of the Mississippi/Ohio rivers and surrounds, which includes: southern IL/IN, eastern MO, and western KY where consensus for 2-4" has grown over the course of the last 24hrs. ...Montana... A potent shortwave trough will migrate through the interior Northwest U.S. leading to a regionally amplified setup capable of producing locally heavy rainfall across central and eastern MT. Steering flow will be pretty fast overall, so any convective activity will likely be moving relatively quickly with the flow to the east-northeast after genesis. That said, environment for mature mesocyclones and stronger convective cores will be capable for periods of heavy rainfall during any of these thunderstorms as they migrate through the High Plains of MT. Rates between 1-1.5"/hr will be plausible at peak intensity leading to pockets of 1-2" of rain falling in a short window as storms traverse over the area. The previous MRGL risk was maintained to account for the threat. ...Northern ME... Shortwave trough moving through Quebec will pivot across northern ME as we move into Friday afternoon. Sufficient buoyancy and mid- level forcing brought upon by the disturbance and boundary layer priming in the afternoon will lead to a round of thunderstorms capable of producing locally enhanced rainfall that could impact more sensitive areas of northwest ME. As of now, the prospects for locally 1-2" of rainfall have increased the past succession of runs from NWP with some deterministic outputs pointing to a quick inch or more over the northern Appalachian area of western ME advancing into interior Aroostook county in northern ME. The previous MRGL risk was maintained for the threat as guidance still favors the potential. Kleebauer Day 3 Valid 12Z Sat Jun 27 2026 - 12Z Sun Jun 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE OHIO VALLEY... ...Ohio Valley... Longwave pattern begins to pivot toward a more amplified western trough with a ridge rapidly materializing across the Southeastern U.S. as we step through the weekend. A broad upper trough will be positioned over the Pacific Northwest through the interior with a succession of strong mid-level shortwaves ripping through the lead side of the mean trough. There's growing support for a mid-level shortwave to eject out of the Central Plains on Saturday morning and migrate east-southeast through the Mid-Mississippi Valley, eventually making headway into the central and southern Ohio Valley by Saturday afternoon as it moves around the northern periphery of the ridge building to the south. Heavy rainfall from the previous period will act as a primer for any additional rainfall leading to a heightened threat for flash flooding in those terrain locations in eastern KY up into WV. CSU First Guess Fields have the region firmly in the MRGL risk just given the signal, however the antecedent ground conditions will favor a tick up in the forecast risk with a SLGT risk in place across the aforementioned area. Hardest hit locations with convection Saturday afternoon and evening will likely see 1-2", locally higher during the threat which would be sufficient for at least scattered flash flood prospects for the D3. The previous forecast was generally maintained with the SLGT risk extended a bit further north up the I-79 corridor towards Morgantown, WV. ...Northern Plains... Robust upper trough will be positioned over the Pacific Northwest and the interior with falling heights and an ejection of several stronger shortwaves pivoting around the primary upper circulation. A period of strong to severe thunderstorms are forecast in-of the High Plains of MT and ND as a robust shortwave makes an appearance by late-Saturday afternoon through the evening. Ample shear and moisture anomalies creeping above the 90th percentile up over the Northern Plains will be sufficient in locally enhanced rainfall rates, especially in any supercell cores and multi-cell mergers that transpire once the LLJ kicks in after 00z. A broad MRGL risk is in effect for the threat up across the area with a potential for a targeted upgrade in future updates once the CAM signals come into their temporal windows. Kleebauer Day 4 and Day 5 Valid 12Z Sun Jun 28 2026 - 12Z Tue Jun 30 2026 ...The probability of rainfall exceeding flash flood guidance values is less than 5 percent... Oravec 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 $$