606 FOUS30 KWBC 210749 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 AM EDT Sun Jun 21 2026 Day 1 Valid 12Z Sun Jun 21 2026 - 12Z Mon Jun 22 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FOR PARTS OF THE CENTRAL PLAINS, MIDDLE MISSISSIPPI VALLEY, AND OHIO VALLEY... ...Northern Missouri through central Illinois and Indiana... By the start of the day 1 forecast period a potent shortwave and related surface low/MCV are expected to eject eastward out of the central Plains into the Midwest, driving the flash flood threat today from Kansas to Indiana. The regional radar representation early this morning over the central Plains is complex, with several clusters of thunderstorms and a trailing stationary axis of heavy rainfall across northwest Kansas. The expectation for the start of this day 1 outlook (12Z Sat) is for these thunderstorms to organize into a larger MCS spanning from northern MO to south-central KS. However, compared to normal forecasts within 12 hours, there remains some uncertainty with respect to the location of the heaviest rainfall. However, scattered instances of flash flooding are still expected within the MDT risk and locally significant flash flooding impacts cannot be ruled out. 00Z CAMs and radar were utilized to define the western edge of the SLGT and MDT risk areas and to highlight training potential over south- central and southeast KS at the start of the forecast period. Another axis of heavy rainfall is possible this morning and through the day into the Midwest near the lifting warm front and surface low/MCV. PWs and IVT above the 90th climatological percentile (per the 00z GEFS) overlapping with soils likely still recovering from recent heavy rain in the Midwest will lead to a swath of at least scattered flash flooding. Antecedent ground conditions are likely to exacerbate flash flooding where 2"/hr rainfall rates occur, especially across parts of central IL and central IN, where NASA SPoRT-LIS 40 cm soil moisture is above the 80th percentile and rivers remain swollen from previous rainfall over the last week. 00z HREF and REFS neighborhood probabilities for at least 3" per 6-hrs are between 30-50% across northern MO to central IL and southern IN, which would exceed local FFG. While the overall system will remain fairly progressive, flow oriented parallel to the trailing front/outflow boundary could prompt thunderstorm redevelopment late this afternoon and evening extending from central MO to southern IN and northern KY. This potential for repeating storms allowed for the MDT to shift a bit south with this update and adds additional potential for locally severe flash flooding. ...Southeast Kansas to Southwest Missouri... The southwestern flank of the ongoing MCS this morning is expected to extend from south-central KS to southwest MO as 850 mb flow is expected to become quite convergent. This may also become a focus for reforming activity later tonight associated with additional shortwave activity moving eastward across the Plains. However, there is some uncertainty surrounding if this boundary can sink further south during the day and keep storms somewhat progressive or situated over OK and AR instead. Regardless, this all combines for guidance to currently depict current QPF amounts of 3-4" and an average localized max of 6". Parts of southwest MO have saturated antecedent ground conditions due to a recent wet weather pattern, with NASA SPoRT-LIS depicting pockets above the 80th percentile in the 0-40cm soil moisture layer. Lastly, 00Z REFS and HREF probabilities are agreeable with 20-60% values for exceeding 3" per 6-hrs between the two potential rounds, though may be underdone across south-central and southeast KS for this morning's activity based on radar and HRRR/RRFS trends. ...Upper/Middle Texas Gulf Coast to Southwest Louisiana... A very moist atmosphere remains in place along with an upper low over South Texas to help foster additional heavy rainfall chances, primarily this morning, across the middle TX coast to southwest LA. A remnant outflow boundary located in the northwest Gulf this morning is expected to lift northward as return flow increases and spark convection early this morning. PWs over 2.4" will allow for any thunderstorms to contain 2-3"/hr rates and may linger in a localized manner over similar locations and cause isolated to scattered flash flooding. This area remains overly saturated from prior torrential rains the last few days, which increases the concern somewhat for additional flash flooding impacts today and thus the addition of a SLGT risk in the excessive rainfall outlook. ...South Dakota... Previously outlooked SLGT risk was removed with this update as the slow-moving upper low produces scattered meandering thunderstorms, but coverage is not expected to be enough for more than isolated flash flooding in an area with fairly dry antecedent ground conditions. Still, isolated flash flooding is possible and supports the MRGL risk designation. ...Southern Mississippi, Alabama, and the Florida Panhandle... Additional scattered thunderstorms are likely for the central Gulf Coast states and Florida Panhandle, an area that has experienced rounds of extreme rainfall over the last several days. A MRGL risk remains in effect today, which highlights the potential for isolated flash flooding. Thunderstorms are expected to remain widely scattered as a front lifts well north towards the southern Appalachians today. Thus, limited focus for storms to remain over one area for enough duration to produce more than 3-4" of rain and expectation that a MRGL will suffice even though FFG remains drastically lower than normal for this part of the country. As always, urban areas will be most susceptible to flash flooding impacts should storms set up directly overhead and linger given the moist southwesterly flow in place. Snell Day 2 Valid 12Z Mon Jun 22 2026 - 12Z Tue Jun 23 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT FROM THE SOUTHERN PLAINS TO THE NORTHEAST... ...Northeast and Mid-Atlantic... The day 2 forecast period will feature a progressive trough axis pushing from the Great Lakes to the Northeast with a trailing frontal boundary reach southwest to the Southern Plains and above average PWs along the axis to help create excessive rainfall concerns. Areas of the Northeast and I-95 corridor as south as Washington D.C. are subject to thunderstorm prospects with the best chance for flash flooding likely to occur in the urban footprint from D.C. to NYC with an expansion inland to central PA. Current probs off the latest ensembles and National Blend indicate a large zone of 30-50% probs for >2" across the aforementioned area above with deterministic outputs closer to 2-3.5" into parts of Southern New England. The 00z HREF (only covers through 00Z 6/23) and 00Z REFS indicate 30-60% neighborhood probabilities for at least 2" per 6-hrs from D.C. to NYC and would be enough for some urban flash flooding concerns. There has been additional uncertainty farther north and east with how far to extend the SLGT risk, but given typical mesoscale uncertainties and limited instability, in coordination with local forecast offices the SLGT risk was confined a bit. Look for additional refinements once the full suite of CAMs is available, especially with increasing PWs near the 90th climatological percentile and a nearby warm front in the area for potential focused axis for thunderstorms. ...Southern Plains to Central Appalachians... Across the Southern U.S., heavy precipitation will preclude another round of convection forming along a quasi-stationary front draped from the Southern High Plains to the Southeastern CONUS. Probs for >1" are highest in-of the areas of Eastern OK into the Lower Mississippi and southwestern Tennessee Valleys. Elevated theta_E's and PWAT anomalies +2 dev. or greater indicate a formidable environment capable of continued heavy rain potential that will likely produce rainfall of 2-4", at least in some of the thunderstorm activity that develops. The focal point along the front will likely be where the heaviest rain will occur, or at least be a low-level convergence mechanism that can enhance regional convection. There's high enough confidence in the location of convection for the D2 period to overlap with areas that will have seen several inches the periods prior which led to a level 2/4 SLGT risk positioned over portions of the Southern Plains through parts of the Southern Plains, Lower Mississippi Valley and neighboring Tennessee Valley. The risk extends through the Smokey Mountains up into parts of the Central Appalachians in eastern KY up into WV as the convergence regime follows the frontal positioning over these areas. Greatest chances for multiple rounds of slow-moving thunderstorms capable of 2"+ hourly rainfall rates currently appears to be over southeast OK into central AR and will be monitored closely once CAMs are within range of the forecast time period. Latest "longer range" REFS and HREF probabilities for at least 3" are scattered throughout the region. Snell Day 3 Valid 12Z Tue Jun 23 2026 - 12Z Wed Jun 24 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN EFFECT FROM PARTS OF THE CENTRAL PLAINS TO THE SOUTHEAST... ...Central Plains to Southeast... Day 3 is a transition period into a more typical summertime regime for the CONUS with a longwave trough over the Northern U.S. and a dome of mid and upper ridging orienting itself across the southwestern CONUS. Positioning of the trough/ridge pattern will cause a persistent northwesterly flow within the mid and upper levels across the Central and Southern High Plains over into the Lower Mississippi Valley as progressive shortwave pulses eject out of the Rockies and ride the prevailing northwesterlies in place between the ridge and trough. This highlights potential for MCS development and flash flooding scenarios from the Front Range and points southeast as the steering flow orients between the base of the trough and the northeastern flank of the ridge. This is historically projecting a case of thunderstorm maturation and upscale growth over the area between CO/KS down through OK/TX with potentially the Red River Basin as a focus for thunderstorm activity. Eventually, this ends up migrating into the ArkLaTex and/or Lower Mississippi area which is showing up in the QPF footprint on ensembles. There has been little variance in the recent global ensemble suite with the deterministic output also showing very similar outcomes, at varying magnitudes with the synoptic evolution generally stable with run-to-run continuity. Should CAMs come into better focus for aforementioned MCS activity over the region, a SLGT risk could be introduced in future updates. Snell Day 4 and Day 5 Valid 12Z Wed Jun 24 2026 - 12Z Fri Jun 26 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND SOUTHEASTERN U.S ON BOTH WEDNESDAY AND THURSDAY... Both the D4 and D5 time frames remain in a more typical summertime regime for the CONUS with a longwave trough over the Northern U.S. and a dome of mid and upper ridging orienting itself across the southwestern CONUS. Positioning of the trough/ridge pattern will allow for persistent northwesterly flow within the mid and upper levels across the Central and Southern High Plains over into the Lower Mississippi Valley as progressive shortwave pulses eject out of the Rockies and ride the prevailing northwesterlies in place between the ridge and trough. Global deterministic and their ensembles continue to depict a setup conducive for scattered to widespread convective activity with general organization likely to occur over the course of each evening as thunderstorms grow upstream and migrate southeast within the prevailing northwesterlies between 700-300mb. Moisture and instability will remain elevated across much of the aforementioned areas with the latest NAEFS output signaling a northwest to southeast alignment of PWAT anomalies between +1 to +2 standard deviations from the WY Front Range down to the ArkLaTex. This is historically projecting a case of thunderstorm maturation and upscale growth over the area outlined within the anomaly field with a correlation of a defined theta_E ridge focused within that same zone. This would allow for convective initiation upstream over the Front Range with organized convective evolutions to drawn southeastward along the theta_E gradient and oriented with the mean flow aloft. This would likely entail convection motioning into KS/OK and pivoting eastward towards the ArkLaTex as progs indicate the positioning of a quasi- stationary front situated across the Lower Mississippi Valley which would turn to a focal point for convection. ML outputs are a bit further south with the potential as the EC-AIFS Ensemble even promotes the threat for heavy convection towards the Red River Basin, so there is some opportunity for southern adjustments in the mean QPF as we move closer, so long as that signal remains stable in the means. Overall, there has been little variance in the recent global ensemble suite with the deterministic output also showing very similar outcomes, at varying magnitudes with the synoptic evolution generally stable with run- to-run continuity. The entire setup continues through Day 5, as well, with repetition in the mid and upper pattern as multiple vorticity maxima slide out of the Central Rockies and migrate east- southeast through the mean flow between the trough and ridge setup. There is now some indication the ridging breaks down as a the heights across the west get squashed in favor of a much stronger upper trough migrating out of the northeastern Pacific into the Pacific Northwest and Northern Rockies. The signal is showing up within the 500mb Height Anomalies on both the ECENS and GEFS, a solid consensus in the pattern breaking down somewhat as we move into the end of the week. This will likely signal an end to the persistent northwesterlies after the D5 window, however strong shortwave ejections will still be plausible, as noted via the D5 window where there's growing favor for heavy precip to occur across much of the Central Plains during the period Thursday and Thursday night. Greatest probabilities within the >1" PQPF are situated over southwestern NE down through KS into OK with a general 25-50% already showing up across the region. For a convective pattern at 5-day leads, this is a relatively formidable signal in the threat for heavy rainfall, so both the D4 and D5 time frames are likely going to see some short term forecast upgrades as we gain further consensus in the deterministic, especially as we step into the range of the CAMs. PQPF for >2" over 72hrs (D3-5) is between 30-60% across the ArkLaTex into the Lower Mississippi area of southern AR. This is the most likely location for an upgrade in the risk, especially as the recent NBM continues to pin this area as the focal point for overlapping convection in the D3-5 window. MRGL risks remain the forecast for both the D4 and D5 periods for the time being. Kleebauer 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 $$