240 FOUS30 KWBC 140018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 818 PM EDT Mon Apr 13 2026 Day 1 Valid 01Z Tue Apr 14 2026 - 12Z Tue Apr 14 2026 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER MIDWEST... ...01Z Update... General thinking in terms of convective development and propagation continues this evening, as the activity is now beginning to exhibit more upscale growth from northwest IA- southern MN into central-nothern WI. While, more sfc-based convection expands across northwest IA, with CAPEs between 3000-4000 J/Kg per the latest RAP/SPC mesoanalysis. Convection becomes more elevated with the forced ascent along and north of the warm front, with a deep elevated mixed layer (EML) and MUCAPEs still healthy between 1500-2500 J/Kg. Over time, the activity will continue to grow upscale into an MCS, with some likely southward propagation later tonight as the south-southwesterly LLJ strengthens to 45-55 kt early this evening before veering southwesterly. By midnight CDT, the latest RAP shows weakening Corfidi Vectors (less than 10 kts), indicative of the strengthening upstream propagation as the robust LLJ aligns with the mean 850-300 mb flow while also reaching/ exceeding the magnitude of the mean deep-layer flow. This will favor a higher probability of training convection overnight withing the Slight Risk area, which was expanded southward into much of southeast WI, while also upstream to include the activity expanding across southeast MN and far western WI. Other adjustments to the Slight and Marginal Risk areas were based on the latest trends in the CAM guidance, including recent HRRR runs and 18Z HREF QPF exceedance probabilities. Hourly rainfall rates underneath the strongest cells (esp HP supercells) will reach 1.75-2.25" within an hour. For further information, please refer to the latest Mesoscale Precipitation Discussions or MPDs 100 and 101, both valid until 0330Z. Hurley Day 2 Valid 12Z Tue Apr 14 2026 - 12Z Wed Apr 15 2026 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS THE CENTRAL L.P. OF MICHIGAN... 21z update... ...Great Lakes Region... With the introduction of a Slight Risk across portions of WI, MI for the current Day 1 period, the affects of today's rainfall activity will likely result in changes and adjustments to this forecast. The synoptic environment did not change much with another leading shortwave/vorticity center lifting out over the mean ridge in the Great Lakes region. This will drive stronger confluence of the LLJ across Iowa to break out another round of strong/severe thunderstorms Tuesday evening. Overall deep layer steering flow and fairly orthogonal ascent over boundary reinforced by day 1 thunderstorm activity should help to focus a similar west to east (WNW to ENE) oriented axis of training thunderstorms. Upper-level dual jet couplet will further enhance up-scale growth to a broader complex to maintain through the overnight period, likely tracking through areas along or just south of the Day 1 activity. Still, most of the area remains at near or above record spring rainfall and soils are fairly saturated, so with cells capable of 1.5-2"/hr rates and localized totals of 2-3+" suggest the placement of a Slight Risk of Excessive Rainfall across portions of eastern WI and central MI (along and north of I-94). ...Pecos River Valley through Southern Plains into Ozark Plateau... Little change in expected evolution, storm mode across this area with the new 12z suite of guidance. Isolated cells along the dry line will be initially slow moving eventually locally expanding into smaller clusters after sunset. High moisture, slow cell motions may result in locally heavy rainfall 3-4", but will be isolated to widely scattered in nature. As such overall coverage suggests the Marginal Risk in place will suffice. The Marginal Risk area is connected to the area of concern over the Great Lakes and while there was some consideration of splitting the Marginal areas north of the Ozark Plateau to the Iowa border, but the threat remains non-zero and confidence is not that high on precise areas to remove; just note the coverage will decrease northward along the dry-line with best probability near the Lower Pecos and south- central OK based on current guidance suite. Gallina Day 3 Valid 12Z Wed Apr 15 2026 - 12Z Thu Apr 16 2026 ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM TEXAS TO THE UPPER MIDWEST/GREAT LAKES REGION... 21z update... The surface to mid-level environment remains very similar to the prior 3 days, with a stark dry line extending from the Pecos River Valley across the Southern Plains into the Upper Mississippi Valley. The longer wave mid-level trough is starting to finally ejecting northeast into the central Plains though weakening as it progresses northward. The deep layer moisture axis and instability shift slightly eastward. As such clusters of thunderstorm activity with ample 1.5" Total PWats should result in rates up to 2"/hr and localized totals over 3" resulting in widely scattered clusters along/ahead of the main front, maintaining the need for the axis of Marginal Risk from northeast TX across the Ozark Plateau. Across the Great Lakes, overall moisture and instability will be reducing compared to prior days with warm front (mid-level confluence axis) continuing to drift further south across the Great Lakes. This moves further from the hydrologically sensitive/saturated areas of the northern Great Lakes region, but multiple days of stronger activity (current D1 and D2 periods) are likely to result in areas that will have saturated ground conditions by Day 3. Currently, the best overlap and probabilities for the most active convection on day 3 to be across NE IL across N IND into S MI and a Slight Risk may be required; however, without soil conditions becoming saturated yet, will hold off on delineating a categorical Slight Risk at this time. Gallina 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