963 FOUS30 KWBC 171909 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 309 PM EDT Fri Apr 17 2026 Day 1 Valid 16Z Fri Apr 17 2026 - 12Z Sat Apr 18 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM OKLAHOMA THROUGH PORTIONS OF THE MIDWEST... 16Z Update: Minimal changes were made from the previous forecast, with a broad high-end SLGT Risk area from OK through central MO. The SLGT Risk region was expanded ever-so-slightly southwest further into central OK to account for good agreement with ML models (ECAIFS and AIGFS) in handling the tail-end of the cold front, albeit not as impactful. An upper level trough in the northern Plains will pickup a cutoff low in the Southwest, enhancing upper-level divergence due to jet coupling in the Central Plains. A strong cold front will continue tracking southeastward as a result through the central and southern Plains, which will meet a moist Gulf airmass with a relatively robust southerly LLJ. Low-level convergence will be maximized upon this interaction, and with high PWAT anomalies (widespread +3 standard deviations across northeast OK, southeast KS, and MO), heavy rainfall is expected. Updated neighborhood probabilities remain over 90% to exceed 2" in much of MO and KS, and 60% to exceed 3" in southeast KS. Blanco-Alcala ..Previous Discussion.. A strong cold front tracking southeast across the Plains will run into a moist and unstable air mass driven by a robust low level jet streaming north off the western Gulf and into the Great Lakes. Meanwhile, a strengthening upper level jet will develop across Texas and Oklahoma Friday night that will further enhance lift across the Slight Risk region, particularly the southern part of it. The result will be a series of waves of strong thunderstorms that will feed on the influx of moisture and instability to allow for frequent redevelopment and training as the entire complex of storms pushes southeast. The strongest storms and most persistent rainfall will occur over areas hard-hit in recent days with prior heavy rainfall, so soils in areas from southern Oklahoma to western Missouri are already near saturation and well above normal for soil moisture content for this time of year. Urban areas from Kansas City to Tulsa will be especially vulnerable should persistent heavy rains set up over those metro areas. Meanwhile, a portion of the Ozarks could also introduce a topographic factor to any flooding potential. A higher-end Slight (25-40% chance of flash flooding) is in effect from northwestern Oklahoma through central Missouri. Meanwhile, further north into the Midwest, the storms are more likely to organize into a single line of storms more quickly. However, these areas have even more saturated soils due to more recent rains. When added the urban factor in cities such as St. Louis, Chicago, and Milwaukee, even a shortened period of heavy rainfall could still result in widely scattered instances of flash flooding. The Slight Risk in this area was expanded north up Lake Michigan to Green Bay, but elsewhere remains little changed. Wegman Day 2 Valid 12Z Sat Apr 18 2026 - 12Z Sun Apr 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GULF COAST AND LOWER MISSISSIPPI VALLEY... 20Z Update: The MRGL Risk area remains mostly unchanged from the previous forecast. The main exception being a removal of the northern portions of the area including parts of central MS, which has seen a decrease in neighborhood probs. New probs suggest a moderate possibility (40%) of over 1", with little to no chance of an excess of 2". The progressive nature of the cold front and the slightly decrease QPF and further justified the removal of the area. Blanco-Alcala ..Previous Discussion A strong cold front sweeping south down the Plains will provide the primary forcing for a line of strong thunderstorms to form as the front uplifts a warm and moisture-laden air mass from the Gulf. Due to close proximity to the Gulf, PWATs are likely to spike to between 1.5 and 1.75 inches Saturday evening. This will support thunderstorms capable of very heavy rainfall. The line will generally be progressive, moving south. Further, the Marginal Risk area is generally covering some of the highest FFG areas in the country. Thus, the flash flooding threat is largely focused on the urban factor in areas such as Houston, Beaumont, and Alexandria. Most of the convective activity is expected at or after sunset, so any flooding that occurs will be more dangerous. Wegman Day 3 Valid 12Z Sun Apr 19 2026 - 12Z Mon Apr 20 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR DEEP SOUTH TEXAS... Remnants of the previously mentioned cold front set to impact the Gulf Coast on Saturday will continue to feed in moisture to the deep south of Texas on Sunday. Upon reaching and entering the Gulf, the tail-end of the front will stall just offshore of the southern Gulf Coast. This will produce a low-level inverted trough just off the east coast of Texas, with the low-level wind regime shifting to a more easterly flow. PWATs will approach and exceed 2 inches off the coast, which with the aforementioned easterlies will result in moist onshore flow from the Gulf. This will result in showers and thunderstorms in the Deep South of Texas, and will have the possibility of bringing heavy rain. Currently, any higher end flash flooding impacts will be inhibited by a variety of factors. The low-level flow appears to be on the weaker side, with a suite of global ensembles suggesting 15kt onshore flow. Additionally, FFG guidance remains high, and with unfavorable upper-level forcing by way of subtle ridge, any flash flooding would need to come by way of training setup. At this point, any instance of this appears to remain quite isolated. Blanco-Alcala/Wegman 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