FOUS30 KWBC 271944 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 344 PM EDT Tue Oct 27 2026 Day 1 Valid 16Z Tue Oct 27 2026 - 12Z Wed Oct 28 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST FLORIDA... 16Z Update.. Virtually no change was made to the inherited Day 1 ERO with this update. Easterly onshore flow associated with a surface low pressure system based over the Bahamas is still expected to provide moisture for thunderstorms, but meagar instability and high FFGs will limit the possibility of widespread flash flooding. Isolated instances of flash flooding still remain possible, but this should be fairly confined to the east coast of Florida. As such, the MRGL risk was kept with very minimal adjustments. Blanco-Alcala ..Previous Discussion.. ...Southeast Florida... An area of low pressure will linger over the Bahamas while gradually moving northwards, resulting in persistent northeasterly flow across much of Florida. Moisture wrapping around the circulation will be directed into Southeast Florida, bringing PWAT values up to 1.7-2 inches. The low will trigger scattered showers and storms over the Atlantic that will migrate into the Southeast Florida coast. Instability will be fairly limited, but there should be enough MUCAPE (400-800 J/kg) over the Atlantic waters and the immediate Southeast Florida coast to support a some storms with locally heavy rainfall (rates 1-2 inches per hour). These rainfall rates will generally fall below FFGs, but persistent showers throughout the day and into tonight will allow for isolated higher rainfall amounts that could lead to flash flooding. Hi-res model guidance shows the highest rainfall totals (generally 1-2 inches, locally up to 4 inches) focusing along the Southeast Florida coast, impacting the I-95 corridor, an area that has received several rounds of rainfall over the past few days. Given recent heavy rains and the urban environment, there is a Marginal Risk of excessive rainfall leading to isolated instances of flash flooding in Southeast Florida. Dolan Day 2 Valid 12Z Wed Oct 28 2026 - 12Z Thu Oct 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR EAST-CENTRAL AND SOUTHEAST FLORIDA... 21Z Update.. Similarly to the Day 1 update, very minimal changes were made to the inherited Day 2 ERO. A minor reduction was made to the southern portion of the existing Marginal Risk area in east-central Florida to match the latest suite of guidance of hi-res and global guidance. Otherwise, the previous outlook and discussion remain in good shape. Blanco-Alcala ..Previous Discussion.. ...East Coast of Florida... The area of low pressure near the Bahamas will gain momentum on Wednesday as the upper level energy splits, with a portion of the energy being swept into the Atlantic while another portions shifts southeast across South Florida. This will result in another day of northeasterly flow with showers and storms moving onshore along the Florida East Coast. The band of moisture on the northern side of the system will shift north and increase PWATs to around 2 inches across much of Central and South Florida. The environment will also become more unstable as the surface reflection of the low shifts southeast towards South Florida. MUCAPE values are expected to rise to around 800-1200 J/kg in Central and South Florida, which will support deeper convection capable of producing high rainfall rates (1.5-2.5 inches per hour) at times. Hi-res and global models are in agreement that the highest rainfall totals should materialize near the East-Central Florida Coast, with some earlier convection capable of producing locally heavy rainfall over portions of Southeast Florida as well. Given recent heavy rainfall and the sensitivity of the urban I-95 corridor, there is a Marginal Risk of excessive rainfall for portions of East-Central and Southeast Florida where isolated instances of flash flooding will be possible. Dolan Day 3 Valid 12Z Thu Oct 29 2026 - 12Z Fri Oct 30 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WEST AND CENTRAL TEXAS... 21Z Update.. An expansion to the Slight Risk area was made in this update, with a continued consensus of a heavy QPF core over western Texas to eastern New Mexico among the latest suite of guidance. Remnant moisture from T.C. Vance will move northward into north-central Mexico, before being picked up by a mid-level shortwave trough and moving into Texas and New Mexico. AI/ML guidance (EC-AIFS & AIGFS) has also remained fairly consistent in the placement of the QPF core, but has trended down in terms of rainfall amounts over a 24hr period. Additionally, AI models suggest an increased areal footprint along with the minor downtrend, justifying the expansion of the SLGT Risk area. As such, a higher-end Slight remains, but a potential upgrade could be justified in the coming updates, especially as CAMs guidance becomes available. Blanco-Alcala ..Previous Discussion.. ...Texas and New Mexico... Conditions will be favorable for widespread convection across portions of Texas and New Mexico on Thursday as mid-level energy associated with the remnants of TC Vance move into the region. As the wave approaches, southeasterly low-level flow will bring anomalous Gulf moisture into the south-central U.S., increasing PWATs across Texas to 1.5-2 inches, which is 3 standard deviations above normal and well above the climatological 90th percentile. In addition to mid-level destabilization from the wave, enhanced upper level divergence in the right entrance region of a southern stream jet will support a broad region of ascent across Texas. These ingredients combined with at least modest CAPE (slightly limited due to widespread cloud cover) are expected to support an organized heavy rainfall event. Model guidance has been trending north and west with the QPF footprint of this event during the Day 3 time frame. This has resulted in shifting the Slight Risk area to include more of West and Central Texas. There is good agreement among the deterministic (physical and AI) and ensemble guidance that the highest rainfall amounts will focus between the Edwards Plateau/western Hill Country and the Midland area, which is facing a high-end Slight Risk on Thursday. There is still quite a bit of uncertainty in QPF to the west and north of this region, with some models showing a faster and further north spread with the heavier totals and some showing elevated amounts in the terrain of West Texas. The rest of West Texas and portions of west-Central Texas up to the Panhandle have been included in a Marginal Risk to account for this QPF uncertainty. An isolated flash flood/Marginal risk will likely extend into southern New Mexico as well where locally heavy rainfall over sensitive terrain and burn scars could cause flash flooding, especially considering how saturated soils are after recent heavy rains. Dolan Day 4 and Day 5 Valid 12Z Fri Oct 30 2026 - 12Z Sun Nov 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN AND CENTRAL ARIZONA ON FRIDAY... ..Texas into Oklahoma... 20Z Update: No change to the previous forecast as the current progs for heavy rainfall extending beyond D3 into the Southern Plains remains on track. Will need to assess the magnitude in the future for the initial D4 period (Friday morning into the afternoon) for a smaller SLGT in the carryover process, but for now, will wait until we get closer to refine those details. Kleebauer ..Previous Discussion.. We will maintain a Marginal risk on day 4 (Fri) across portions of TX into OK. Some threat of flash flooding will persist as the features responsible for the day 3 risk shift northward. However the signal becomes a bit more muted by day 4 and uncertainty on the details become higher. Still will have impressive synoptic support with mid level shortwave energy, upper level divergence and a strong low level jet/moisture transport axis. However the system should be rather progressive by this time, and there is a more of a question regarding the degree of destabilization by this time. So while an area of locally heavy rainfall should be moving north across TX and into OK, rainfall rates and the extent of the flash flood potential become less clear with northern extent. Thus we will stick with a Marginal for now and continue to monitor trends. Chenard ...Southwest... 20Z Update: The D4 period remains consistent with run to run continuity, highlighting AZ as the primary target of opportunity for scattered convection and heavy rain prospects. Models are keen on the Mogollon Rim as the focal point for the heaviest precipitation, in agreement with both the global ensembles and ML guidance. The consistency and overlap in their signals allowed for a maintenance of the SLGT risk on D4 with the best threat occurring that Friday afternoon and evening. As for D5, the setup shifts further west into Southern California with the next potential atmospheric river (AR) setting up for areas along the southern CA coast into the coastal terrain adjacent. The setup calls for the beginning of the threat to occur on Saturday with a crescendo of the precip magnitude beyond the current D5. That said, will monitor the progression of the trough evolution and any subsequent shortwave ejections into the region as the timing of these features and their overall evolutions will play a pivotal role in the timing of the AR, and eventual impacts. For now, just expanded the MRGL a bit further up the coast to encompass all of the Transverse Range to the northwest of Santa Barbara, stopping short of the Big Sur region as the heaviest precip is progged just south of the central CA coastal plain. Kleebauer ..Previous Discussion.. Still good model agreement on day 4 with broad troughing progressing into the western United States. While some timing uncertainty persists regarding individual embedded shortwaves, the overall environmental ingredients are coming together to support a robust convective and heavy rainfall threat centered over AZ on Friday. This is particularly true in the non-ncep models such as the ECMWF/AIFS/UKMET. Dynamic forcing will be impressive, featuring a very strong southern stream upper level jet that will place AZ within its favored left exit region, promoting strong upper level divergence. Mid level shortwave energy ejecting east will interact with a rather strong southerly low level jet resulting in impressive low level moisture transport and PWs across the region. This strong low level flow should help organize and sustain some training/backbuilding convective cells. While thermodynamic details carry inherent uncertainty at this lead time, current model guidance suggests that corridors of 1000+ J/kg of CAPE are probable. Much of the region has been anomalously west of late, which has notably increased the hydrologic sensitivity across the area. While the exact placement and magnitude of the heaviest rainfall axis remains subject to adjustments as we get closer, confidence is high enough in an isolated to scattered flash flood threat to warrant a Slight risk. More spread and greater uncertainty exists across the Southwest on day 5 (Sat). One thing that is certain is that there will be an anomalous amount of deep moisture moving into much of the Southwest. Troughing moving into the West will pull an impressive amount of moisture northward with PWs near or even above record values for the time of year. What is uncertain is the exact timing of the trough axis and an area of low pressure moving towards southern CA, and the degree of instability over the region. With this amount of moisture there is likely to be abundant cloud cover, and model instability fields are currently pretty meager on Saturday. Thus we could be looking at showers and orographically enhanced rain instead of heavier convective rates. This is uncertain though, and even limited instability may result in flood impacts given the saturated conditions over portions of this region. In addition, a quicker low (like the AIFS has been showing), could bring heavier rainfall into southern CA on day 5. All this to say we will start with a broad Marginal risk and fine tune as we get closer. Chenard ...Lower to Mid MS Valley... 20Z Update: The general forecast for the increasing risk of heavy rainfall across the Lower Mississippi Valley into the Southeast U.S. on D5 remains viable. The setup is leaning towards a future upgrade, but the ensembles/ML and deterministic are not in agreement on the exact placement of the heavy rain focus. The MRGL was expanded eastward to account for many of the deterministic and ensemble members sneaking heavy rainfall east of the Mississippi leading to at least a low-end threat for flash flooding in any urbanized zones within the areas of TN/AL/MS. Adjustments were limited for areas west of the Mississippi, although we'll have to watch in future updates if the threat becomes more confined to a specific area, or will the convective coverage become more expansive as suggested by some of the ensemble and global deterministic members. Kleebauer ..Previous Discussion.. The system responsible for the Southern Plains heavy rainfall on day 3 and 4 will shift into the lower and mid MS Valley on day 5 (Sat). The mid level shortwave and left exit of an impressive jet will provide plenty of synoptic ascent for convection. Limiting factors for flooding will be a fairly quick progression of the system, questionable instability, and very dry antecedent conditions. However given the degree of forcing in play and PWs forecast over the 97th percentile for the time of year, at least a localized flash flood risk seems in play from the central Gulf Coast into southern MO. Given the orientation/progression of forcing, could envision a scenario where the front tries to slow across the southern half of the Marginal risk, which is also where the greater chances of higher instability will reside. This could allow for some training/backbuilding component to convection over these areas. Model preference at this time is non-GFS, which seems too quick progressing things off to the east. The ECMWF, AIFS and UKMET are better clustered and align with the Marginal risk area. Given the dry antecedent conditions, this is probably only a urban flash flood risk, where high rainfall rates and brief training could locally result in flash flooding. Chenard 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 $$