509 FOUS30 KWBC 032002 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 402 PM EDT Fri Apr 3 2026 Day 1 Valid 16Z Fri Apr 03 2026 - 12Z Sat Apr 04 2026 ...THERE IS SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS INTO THE OZARKS, MISSOURI VALLEY, AND UPPER MISSISSIPPI VALLEY... ...16Z update... The forecast remains on track, only small edits were needed to account for QPF trends. Convection is already underway near the triple point in the Midwest and should ignite this afternoon ahead of and along the cold front over the Plains. The best potential for flash flooding remains across North Texas and central and eastern Oklahoma where the low level jet and frontal dynamics will be favorable for training/repeating storms and with the potential for high rainfall rates exceeding 2 inches per hour. A Slight Risk remains in effect for this activity and encompasses areas that are expected to receive 3-5 inch rainfall totals, with locally higher amounts possible. A Slight Risk also remains in effect from eastern Iowa into far northwestern Illinois and far southwestern Wisconsin where strong storms in the vicinity of the triple point low will produce heavy rainfall on top of relatively moist soils. There is potential for 3-5 inch rainfall totals in this area, and scattered instances of flash flooding could be a possibility. Dolan ...Previous Discussion... At the mid-levels, a stout wave over the Intermountain West (centered over Wyoming) will migrate eastward throughout the day, spreading increasingly strong mid-level flow and height falls from the High Plains eastward toward the Mid/Upper Mississippi Valley. At the surface, strong 850mb flow and poleward flux of moisture/instability will become established along and ahead of a low initially across the Kansas/Nebraska border region at the beginning of the forecast period and persist through 12Z Sat. Late in the forecast period, a cold front will migrate southward across the southern Plains. Areas of scattered thunderstorms are expected along and ahead the front and low especially during the afternoon and evening, with several areas of flash flooding expected. The primary area for flash flood potential will exist along the OK/TX Red River vicinity southward toward central Texas and the Big Country. Scattered thunderstorms are expected to develop during the afternoon and evening across the region, with CAMs suggestive of training/repeating behavior and local areas of 2-5 inch totals. The glancing influence of the aforementioned mid-level wave across the region lends some doubt on degree and location of daytime/afternoon convective coverage, which should modulate the flash flood risk substantially. Even if convection materializes as depicted by CAMs, antecedent dryness of ground conditions are a mitigating factor for a more widespread or significant flash flood risk. Persistent training will likely be needed for ground conditions to lose receptiveness to rainfall on a widespread basis. Both pre-frontal convection and convection moving in along a surface cold front late represent two distinct regimes for heavy rain and flash flood potential - with that risk eventually spreading toward I-35 in Texas and the DFW Metroplex area through early Saturday. Farther north, convection along the front will likely sweep through portions of Missouri and Oklahoma, with a greater risk/potential for multiple mergers and/or convective clusters with southward extent. Areas just southeast of Kansas City received copious amounts of rain Thursday and will probably not have fully recovered before the incoming thunderstorm threat through early Saturday, necessitating maintenance of Slight Risk probabilities there. Lastly, models (primarily CAMs) depict potential for repeating/training convection across portions of northeastern Iowa and vicinity through much of the day (from 16-18Z through well into the evening) along/near a surface warm front and well ahead of an eastward-moving cold front that should reach the area late in the forecast period. NASA Sport soil moistures suggests slightly more moist ground conditions in these areas, and the advance of the mid-level wave and confluence on the northern end of strong 850mb flow all point to prolonged deep convective potential. 3-5 inch totals cannot be ruled out in this regime. A Slight Risk has been added to the outlook in these areas as a result. Though less widespread, additional convection should traverse wet ground conditions across portions of Ohio, Pennsylvania, and southern New York State, supporting continued Marginal probabilities in that area. Cook Day 2 Valid 12Z Sat Apr 04 2026 - 12Z Sun Apr 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE ARKLATEX AND THE LOWER MISSISSIPPI VALLEY... Much of convective evolution during the D2/Sat forecast period will depend on convective details from lingering convection across Arkansas and Texas left over from D1/Fri. East-northeastward progression of a mid-level wave toward the Great Lakes will aid in southeastward movement of a cold front from the Plains through the Ozarks/Mid-Mississippi Valley during the forecast period. This front will gradually become more parallel to weakening flow aloft from Texas to Mississippi, supporting additional opportunities for training convection as storms organize along remnant outflows and backbuild, with the potential for areal average rainfall in the 1-2" range leading to isolated instances of flash flooding. A more focused threat has been identified supporting the introduction of two Slight Risk areas within the broader Marginal Risk. The first is across portions of the ArkLaTex southwest through northeast Texas. The latest hi-res guidance supports the maintenance of ongoing convection within the Slight Risk for the day 1 period across Oklahoma continuing southeastward along the front into Saturday morning. A wave of low pressure along the front in northeast Texas will also help to maintain/enhance the development of this convection as well as briefly slow the progression of the front northeast through the ArkLaTex, allowing for heavier rainfall totals as storms persist over the region for a longer amount of time before the front begins to sweep southward faster later into the afternoon. The latest 12Z CAMs show the potential for locally heavy totals of 3-4" with rain rates of 2-2.5" per hour. The second region is across portions of the Lower Mississippi Valley later in the day where moist southerly flow from the Gulf will bring a pool of ~70 degree dewpoints northward. These high dewpoints along with daytime heating will lead to a region of 1000-2000 J/KG CAPE supporting the development of heavy- rainfall producing thunderstorms ahead of the front. The combination of this initial development in addition to a second round of storms expected along the front with similarly high rain rates of ~2" per hour will also lead to the potential of locally heavier totals in the 3-4" range. While dry antecedent conditions/high FFGs may limit the overall threat, the potential for these higher rain rates/totals within the highlighted Slight Risks should be sufficient enough for at least a localized/urban scattered flash flood threat. Farther north, convection is likely to be progressive across much of the Lower Ohio Valley along with potential for inhibited destabilization due to more widespread convection across the Lower Mississippi Valley. Too much uncertainty exists to reduce the Marginal Risk area at this time. Notable exceptions to this general regime exist, however, from northern Ohio into southern New York State and Pennsylvania, where models suggest appreciable daytime heating and moderate instability developing. Storms may not be all that fast moving either in Pennsylvania as that region should reside on the southern extent of stronger mid-level flow into southeastern Canada. Convective coverage is a bit uncertain, but any greater-than-anticipated coverage of convection in this environment could locally raise flash flood concerns - especially with low FFGs noted across that area. Putnam/Cook Day 3 Valid 12Z Sun Apr 05 2026 - 12Z Mon Apr 06 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH TEXAS ON SUNDAY... ...20Z Update... The latest model guidance supports the prior forecast reasoning with the potential for isolated heavy rainfall-producing storms as moisture pools along the frontal boundary. There is some concern that the front will be progressive enough that moisture/CAPE will be swept out of south Texas before the start of the period limiting any threat, but at least for now guidance retains at least some potential. This is particularly true closer to the Gulf Coast portion of the risk area where a surface wave and slower progression of the front into the Gulf further east may keep the front along the south Texas coast long enough to lead to some storms. Putnam ...Previous Discussion... Maintained the Marginal Risk of Excessive rainfall area that was introduced by the WPC Medium Range desk as a west- to- east oriented front makes its way southward. Deeper moisture should be pooling along and south of the boundary with precipitable water values around 1.75 inches in place at the start of the outlook period. Given uncertainties detailed in the Day 2 period with respect to the timing and placement...combined with the 03/00Z NCEP global models now showing the front to be more progressive than in earlier runs which led to CAPE being swept out of South Texas faster...was not inclined to introduce a Slight Risk area at this point. At the same point...spaghetti plots from the non-CAM ensembles still show enough members with 1 inch QPF and a few contours of 2 inch QPF to support keeping the Marginal area with only minor nudges around the periphery. 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