778 FOUS30 KWBC 071952 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Tue Apr 7 2026 Day 1 Valid 16Z Tue Apr 07 2026 - 12Z Wed Apr 08 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE ATLANTIC SIDE OF THE FLORIDA PENINSULA... 16Z Update: Weak shortwave trough across the eastern Gulf will migrate through the Peninsula over the course of the afternoon and early evening with a surface low progged just off the eastern FL coast. Combination of deep layer moisture established across the southern half of the Peninsula on the order of +1 to +2 deviations above climo along with the aided ascent provided by the shortwave and surface low alignment will create an environment favorable for locally heavy rainfall along the eastern FL coast. There will likely be a dual QPF maxima positioned near the Space Coast (Daytona Beach to Cape Canaveral), as well as a second positioned from West Palm Beach down to the Miami metro as noted via the latest CAMs output and associated hi-res ensemble. The area across the Space Coast will see the benefit of some RER jet dynamics and prevailing east-northeast flow coupled between the sprawling high across the northeastern CONUS and the surface reflection off the southeastern FL coast. Current radar indicates some modest frictional convergence in proximity to the Cape Canaveral area which has been well-forecast over the last series of HRRR/RRFS runs. 12z HREF neighborhood probabilities for >3" are running between 60-80% between the area from Daytona Beach down to just north of Melbourne, but only limited probs for >2" on the EAS fields which signals more localized maxima compared to a larger heavy rain footprint and broader flash flood potential. That said, this area is still recovering from being impacted yesterday, so the threat for flash flooding is a little higher than normal within any stronger cells. The SLGT risk remains in place over this area down through the east-central portion of the coast to account for this threat. Further south across southeastern FL, a frontal boundary is analyzed from Fort Myers through West Palm Beach with a weak shortwave progression over the western Gulf making headway into the Peninsula. The combination of the surface reflection and added ascent and shear pattern from the mid-level disturbance will likely induce an area of convective development over the Everglades later this afternoon, migrating eastward into the southeastern metro corridor providing instances of scattered heavy rain areas that could enhance flash flood prospects within the urban zones. Rates from cells just off the coast this morning were able to reach between 3-5"/hr already with the environment in place which lends credence to those pockets of potentially heavy rainfall that could spur up flash flooding in a short period of time. HREF neighborhood probs for >3" are between 60-90% over the corridor from West Palm down to Miami with the maximum likely over eastern Broward to northern Miami-Dade. This makes sense given the positioning of the boundary bisecting these areas which could be a focal point for convection to develop and align before pivoting off the FL coast. The SLGT risk from previous forecast was unchanged given the above. Kleebauer Day 2 Valid 12Z Wed Apr 08 2026 - 12Z Thu Apr 09 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE EASTERN FLORIDA PENINSULA... 20Z Update: A persistent pattern of northeasterly flow into the eastern FL Peninsula along with a quasi-stationary front bisecting portions of the state will lead to another round of scattered convective activity capable of localized flash flooding. The best chance for this to occur will be across the urban settings along the I-95 corridor stretching from Daytona Beach down to the Miami metro with the latest HREF blended mean QPF generally heaviest near the Treasure Coast. This is coincident with the alignment of the stationary front where convergence would be maximized in the vicinity of the front allowing storms to anchor and provide a more prolonged heavy rain scenario when storms develop. Other prospects for heavy rain will likely be along the immediate coast due to frictional convergence spurred by the prevailing northeasterly surface flow coupled with a moderate effective shear layer between 30-40kts out of the southwest. This setup is relatively favorable for anchored storms along the immediately coastal plain, especially when accompanied by at least modest instability, which is forecast via a 500-1500 J/kg MUCAPE during Wednesday afternoon. Areal neighborhood probabilities for >3" remains very similar to today's output (50-80%) up and down a majority of the eastern FL Peninsula with a targeted area situated across the Treasure Coast and immediate Miami metro corridor. Some of the deterministic CAMs outputs are fairly robust with 5-8" of rainfall in some areas that see the prolonged convective anchoring that occurs within proximity to the aforementioned front which at least signals a ceiling outcome (10th percentile maxima) for the setup. PWATs will remain above normal around 1-2 standard deviations above normal over the southern half of FL which would be sufficient for those heavier cores to materialize when convection occurs. Considering some overlap over the past few days, especially the current D1 of a SLGT risk, and in coordination with the Miami and Melbourne WFO's, another SLGT risk was introduced for the new D2 update to account for the threat. Kleebauer Day 3 Valid 12Z Thu Apr 09 2026 - 12Z Fri Apr 10 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE CENTRAL PLAINS AND MIDWEST... 20Z Update: The general synoptic pattern across the Central CONUS remains consistent on a run-to-run basis as locally heavy rainfall from Kansas to points east-northeast through Northern IL will allow for a threat of isolated flash flooding on Thursday night into Friday morning. A weak shortwave ejecting out of the Central Rockies will intersect a slow-moving cold front propagating out of the Upper Midwest and Northern Plains creating a focused axis of ascent along and just ahead of the front as it migrates through the Plains and Central Midwest. Areal QPF average of 1-3" is forecast within vicinity of the front with much of the rain occurring in a window between 00-12z Friday, a lot of the setup stemming from the introduction of a modest nocturnal LLJ enticing convergence along the front. The magnitude of rainfall and antecedent soil moisture anomalies pin this into the traditional MRGL risk threshold, in agreement with the latest CSU First Guess Fields. Kleebauer ..Previous Discussion.. There is a growing consensus among the models for heavy to excessive rainfall threat shaping up on Thursday given strengthening return flow from the Gulf region encounters the leading edge of colder air coming out of Canada and the northern US. Precipitable water values between 0.8 and 1.0 inches and CAPE values in excess of 1500 J per kg will encounter the front...resulting in storms that could result in heavy to potentially excessive rainfall Thursday into Thursday night/early Friday. 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