FOUS30 KWBC 281512 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1112 AM EDT Wed Oct 28 2026 Day 1 Valid 16Z Wed Oct 28 2026 - 12Z Thu Oct 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR EAST-CENTRAL FLORIDA... ...East Coast of Florida... 16Z Update: Inherited forecast and outlook area is in excellent shape with no significant adjustments needed. Taylor ---previous discussion--- An area of low pressure near the Bahamas will shift southeast towards the Straights of Florida while the upper level energy with the system splits off to the northeast. This will result in another day of northeasterly flow with embedded showers and storms moving onshore along the Florida East Coast. Moisture wrapping around the northern side of the low circulation will shift north and increase PWATs to around 2 inches across East-Central Florida. The environment will also become unstable as the surface low shifts southeast and MUCAPE values rise to 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 the prolonged period of northeasterly flow with coastal showers and the sensitivity of the urban I-95 corridor, there is a Marginal Risk of excessive rainfall for portions of East-Central Florida where isolated instances of flash flooding will be possible. Dolan Day 2 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... ...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 well above normal for this time of year. 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 continues to trend north and west with the QPF footprint of this event, which has resulted in a northward expansion of the preexisting Slight Risk area across portions of West and Central Texas. There is good agreement from model guidance showing the heaviest precipitation totals (2-4 inches, locally higher) focusing between the Stockton and Edwards Plateaus and the Midland area, but there is still some uncertainty in the rainfall distribution within this area. For now, there is high-end Slight Risk potential for this area, but a targeted Moderate Risk might not be out of the question for portions of the Stockton and Edwards Plateaus in future updates. However, that decision may not be able to be made until model guidance becomes a bit more clear and when the entire period is within range of the hi-res models. Surrounding the Slight Risk area, there is a broader Marginal Risk area that covers much of the western half of Texas to account for locally heavy rainfall potential extending further north and west. The Marginal Risk also includes southern New Mexico where the combination of Gulf and Pacific moisture will allow for scattered to widespread convection, and there should be sufficient CAPE to allow for locally heavy rainfall rates. Locally heavy rainfall over sensitive terrain and burn scars could cause flash flooding, especially considering how saturated soils are after recent heavy rains in this region. Dolan Day 3 Valid 12Z Fri Oct 30 2026 - 12Z Sat Oct 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND SOUTHERN ARIZONA... ...Southwest... Broad troughing will move into the western U.S. with embedded shortwave energy moving across portions of the Southwest on Friday. Meanwhile, a strong southern stream jet will approach Baja California, placing Arizona under the favorable left exit region with enhanced upper level divergence. Southerly low-level flow will direct Pacific moisture into the area as well, bringing PWATs up to 1-1.4 inches across the southern half of Arizona (2-3 standard deviations above normal). This warm, moist air mass will also increase instability, with MUCAPE values potentially exceeding 1000 J/kg across much of southern Arizona. With favorable conditions throughout the atmospheric column, scattered to widespread convection is expected to develop with the passing of the upper shortwave. Model guidance has been consistently showing elevated precipitation totals along and south of the Mogollon Rim, and there is a Slight Risk of excessive rainfall in place that includes most of central and southern Arizona. The Slight Risk also includes some of the terrain in southwestern New Mexico that should also see scattered convection. Persistent showers/storms with moderate to locally heavy rainfall rates could result in scattered instances of flash flooding, especially near steep terrain and burn scars. The risk of flash flooding is also slightly heightened across portions of Arizona and New Mexico where an anomalously wet pattern has resulted in increased soil moisture. Much of the southwestern U.S. is included in a broader Marginal Risk area due to increased moisture and support for at least isolated to scattered convection, but the flash flood risk is a bit lower since the best moisture and instability will be limited to southern Arizona. ...Texas and Oklahoma... The mid-level circulation associated with the remnants of TC Vance will continue to move north across the southern and central Plains on Friday while becoming more organized, which could support a continued heavy rainfall threat for portions of Texas and Oklahoma. The southern stream jet should shift north, maintaining favorable conditions for convection over the area through Friday afternoon. Anomalous moisture will remain in place across the southern Plains, but instability may become the limiting factor for heavy rainfall. The best instability looks to be displaced to the north across the central Plains and into the Midwest while cloud cover limits instability to the south. If convection can tap into enough instability, there will still be at least an isolated risk of flash flooding across Texas and Oklahoma and even into southern Kansas, and there is a Marginal Risk in place. Another question will be the speed of the system. There is quite a bit of uncertainty among the models on how fast this system will progress, resulting in location and magnitude differences in the QPF. A smaller Slight Risk area may eventually be needed across portions of Texas and Oklahoma if conditions align and rain falls over areas that are forecast to receive heavy rainfall on Thursday. Dolan Day 4 and Day 5 Valid 12Z Sat Oct 31 2026 - 12Z Mon Nov 02 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST THIS WEEKEND... ...Southwest... An anomalous and potentially high impact setup is taking shape for the Southwest as a longwave trough moves into the West Coast this weekend. The depth of the trough over the eastern Pacific may drop below the climatological 1st percentile for the time of year. Deep, broad southwesterly flow downstream of the trough will tap into subtropical and tropical moisture, driving PW values to near or even above record values for the time of year. The combination of strong dynamic forcing and wind fields, and near record caliber moisture will support a broad swath of moderate to heavy precipitation, maximized across orographically favored slopes. Given lingering hydrologic sensitivity from preceding rainfall across the region, runoff issues and some flooding appears likely even without significant convective enhancement. Widespread cloud cover should generally limit destabilization, but if and where pockets of CAPE are able to develop, a more pronounced flash flood threat could evolve. Forecast guidance exhibits some convergence, with the 00z ECMWF and AIGFS tending towards the consistent AIFS solution. Our preference is in this direction, with less weight given to the GFS. This model preference paints an overall wetter and more impactful scenario for the Southwest. While Saturday (day 4) sits ahead of the strongest synoptic scale forcing, the anomalous moisture axis will be established. A Slight risk has been introduced centered across central AZ into southern NV. Many of these areas will have seen heavy rain and convection on Friday (day 3), leaving hydrologic conditions more primed. Although large scale forcing and instability may dip compared to Friday, persistent 850mb moisture transport and modest instability should be sufficient to sustain some convection and a continued isolated to scattered flash flood risk. Stronger large scale forcing overspreads the region on Sunday (day 5) as the main trough axis approaches, resulting in more widespread precipitation. While cloud cover will hinder destabilization, cooling aloft and some cloud breaks should support some destabilization as the trough axis approaches. The greatest overlap of forcing, moisture and instability is forecast across portions of AZ into southern NV and southern UT, where a day 5 Slight risk has been issued. An expansive Marginal risk surrounds this corridor to account for the broad stratiform rain and lower rain rates falling over a saturated region. Given the magnitude of moisture, dynamics and terrain enhancement, the setup has the potential to produce Moderate risk level impacts if adequate instability materializes. Trends will be closely monitored over the coming days. Confidence is a bit lower over southern CA. Model guidance indicates that an area of low pressure could enhance the convective threat and rain rates late Saturday night into Sunday morning. Because this straddles the day 4 and 5 forecast periods and mesoscale details remain fluid, southern CA will remain within a Marginal risk for now. However, an upgrade to a Slight risk on day 4 and/or day 5 remains a distinct possibility on subsequent forecast updates. ...Central Gulf Coast into the Lower MS Valley... The system responsible for the Southern Plains heavy rainfall on day 2 and 3 will shift into the lower and mid MS Valley on day 4 (Sat). The mid level shortwave and left exit of an impressive jet will provide synoptic ascent for convection. Limiting factors for flooding will be a fairly quick progression of the system, questionable instability, and very dry antecedent conditions. Overall, the model signal for flash flooding is not as robust as it was yesterday and considerable model spread remains. We continue to not prefer the quicker GFS solution, instead favoring something closer to a consensus of the ECMWF/AIFS/AIGFS. Given the dry antecedent conditions, any flash flood threat will likely be high rain rate driven over urban areas or other sensitive basins. Based on our model preferences mentioned above, the best chance of this occurring is pretty far south, from the central Gulf Coast into portions of the lower MS Valley. Thus the Marginal risk was confined to just these areas with this update. Too much model spread to introduce a risk on day 5. The GFS is an outlier and not preferred. If there is a flash flood risk this day it is probably centered over FL, where the EC/AIFS/AIGFS show an axis of more concentrated convective potential. 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 $$