FOUS30 KWBC 301558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Fri Oct 30 2026 Day 1 Valid 16Z Fri Oct 30 2026 - 12Z Sat Oct 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF ARIZONA, SOUTHERN UTAH, AND SOUTHWESTERN NEW MEXICO... ..16z Update.. Southwest: The forecast remains on track for a higher end Slight Risk across south, central Arizona focused around the Mogollon Rim. There is reasonably good agreement of 2-3 inches of rainfall across this region with the latest model guidance. HREF probabilities of 3 and 6 hour QPF exceeding flash flood guidance peaks around 40-60% in the late afternoon across this region. The Slight Risk was also extended northward into more of southern Utah and eastward to encompass more of Nevada, but remains outside the Las Vegas metro. This expansion correlates well with EAS 24 hr QPF exceeding 2 inches, as well as covering latest 20-40% probabilities of 3hr and 6hr QPF exceeding flash flood guidance. Urban areas and sensitive terrain such as burn scars and slot canyons will be the most likely to see impacts from flash flooding. Southern to Central Plains: A shield of moderate rainfall continues across much of Texas this morning/early afternoon with hourly rainfall rates generally half an inch of less. Despite the modest rainfall rates, additional rainfall over saturated soils from yesterday's rainfall will maintain a continued isolated flash flood threat. Low water crossings across the Hill Country will be the most susceptible to flooding concerns, where flash flood warnings were issued this morning. Moisture will continue to stream northward through the central Plains where 1-2 inches of rainfall may accumulate through the day. Relatively high flash flood guidance should keep any flooding, if it occurs, isolated. The one exception will be across northern Kansas where rainfall overnight has lowered flash flood guidance to under an inch per hour in some locations; this area will more susceptible to water runoff concerns. Wilder ...Previous Discussion... ...Arizona, Utah, New Mexico, Colorado... Scattered to numerous thunderstorms are expected to develop primarily across central through eastern Arizona during the forecast period. Convection could start as early as 15Z before expanding in coverage an intensity. Many areas of 1.5-3 inch rainfall totals are expected, with highest totals along the Mogollon Rim eastward toward the White Mountains. Scattered convection should also peak during the afternoon across southeastern Arizona and portions of southwestern Utah. A Slight Risk has been maintained in much of this region for the new D1 update, with expansions into southeastern Arizona and southwestern New Mexico to account for scattered convection that should migrate into these areas especially in the 00-06Z timeframe. Several instances of flash flooding are possible given this regime, with typical low spots/slot canyons and other sensitive terrain being most susceptible to impacts. Farther northeast, a Marginal Risk has been maintained into the Four Corners region. While thermodynamic profiles will likely support a few convective cells as far northeast as southwestern Colorado during the afternoon and evening, convective coverage is in question and is varied in the models. More consistent signals for locally heavy precipitation exist in these areas after peak heating hours, which may temper rain rates a bit due to low-level nocturnal stabilization processes. Portions of this region (southeastern UT into southwestern CO) may need an upgrade to Slight in later updates if instability (and resultant convective coverage) is greater than currently forecast -- especially given sensitive ground/riverine conditions in that area. ...Great Plains... An ongoing convective cluster in northeastern KS/northern MO and vicinity should pose a limited/isolated flash flood risk in the morning hours before gradually weakening due to decreasing low-level convergence. Throughout the day, abundant moisture from a substantial mid-level wave (currently over northern Mexico) will help spread moderate to locally heavy rainfall through much of the Plains throughout the day. A few pockets of deep convection may develop, though the extent of heavier rainfall will likely depend on the degree of low-level insolation during peak heating hours. Portions of central/southern Texas appear to have a chance of scattered, slow-moving convection with weakly supercellular wind profiles in place during the afternoon. Isolated instances of flash flooding could occur if these heavier rain rates occur over sensitive/urban locales. A renewed threat of elevated convection could pose a risk of isolated flash flooding across northern Iowa late in the forecast period (06-12Z Saturday morning). Cook Day 2 Valid 12Z Sat Oct 31 2026 - 12Z Sun Nov 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF ARIZONA... ...Southwest... A plume of deep tropical moisture will be drawn northeastward by a longwave positively tilted trough into the Desert Southwest. A Pacific low at the surface will track towards southern California, forced by the abundant divergence aloft in the right entrance region of a 130 kt southwesterly jet. A vigorous shortwave riding the base of this upper level trough will further enhance lift supporting heavy rainfall. The jet will allow IVT values to surge as high as 750 kg/ms. This pattern will advect near record amounts of moisture for this time of year into the Southwest. PWATs between 1 and 1.5 inches are 4-6 sigma above normal for this time of year. The result of this highly unusual amount of moisture racing northeastward will mean the topography of the coastal ranges like the Peninsular Ranges of southern California and the Mogollon Rim, which are roughly oriented perpendicular to that southwesterly flow, will squeeze out ample moisture in the form of heavy rainfall from the atmosphere. Expect 1-2 inches of rain along the Mogollon Rim, much of which occurring after midnight Saturday night. While instability will be nominal, values will remain high enough to support some elevated convection, which will occur in addition to heavier rain in the favored upslope regions. Antecedent soil conditions are also much wetter than normal, which will support fast developing fast flooding in flood-prone areas, especially burn scars, dry washes, slot canyons, and arroyos. ...Lower Mississippi Valley... Return flow behind an area of high pressure over the Northeast will draw abundant Gulf moisture northward up the lower Mississippi Valley into the Ohio Valley on Saturday. While moisture flux and amounts will be well above normal (2-3 sigma), instability will also be limited for areas away from the Gulf. Soils in this area are bone dry, and well below normal for this time of year. Thus, the Marginal Risk is a low-end one, to cover urban and particularly flood prone areas. ...Florida... The Marginal Risk along the east coast of Florida from Cape Canaveral through Miami is unchanged with this update. Portions of the Treasure Coast have soils that are water-logged from multiple days of rainfall. However, as on previous days, robust convection will struggle to make it too far inland before falling apart, so the flooding threat remains confined to urban and coastal areas where soils remain near saturation. Wegman Day 3 Valid 12Z Sun Nov 01 2026 - 12Z Mon Nov 02 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE FOUR CORNERS REGION... ...Southwest... A high-impact heavy rainfall event is likely to unfold across the Four Corners region on Sunday. Abundant moisture to 4-5 sigma above normal will move northeast ahead of a deep and vigorous longwave trough over the West. As that moisture runs into the 14,000 ft peaks of the San Juans of southwest Colorado, it will very effectively be wrung out by the terrain as that moisture uplifts across the mountains. This will make for an 18 hour or so period of steady heavy precipitation across those ranges. The San Juans will be particularly targeted with heavy precipitation due to the tall peaks of many of the mountains that are aligned perpendicular to the mean southwesterly flow. Snow levels will rise above 11k feet, meaning only the highest peaks will see significant snowfall. Meanwhile the mid-mountains down to the valleys will all see heavy rain, that will be quickly funneled into the headwaters of the San Juan river. In a near-repeat of last week's heavy rain event, the still saturated soils will quickly convert nearly all of the rain into runoff, resulting in fast and steep rises along area streams and creeks as well as the larger San Juan river. The Moderate Risk was hoisted with this update due not only to the very favorable meteorological and hydrologic conditions for flash flooding, but also for the very short period of time in between this area's big rainfall events. The Moderate was coordinated with the ABQ/Albuquerque, NM forecast office. Elsewhere across the Southwest, a large Slight covers all of Arizona and portions of each of the neighboring states. Much of Arizona is in a higher-end Slight as the flood prone deserts and numerous canyons will also effectively funnel the heavy rains into small and fast-reacting river basins. Much like in the San Juans, back-to-back major rainfall events could have outsized impacts across Arizona. While the Mogollon Rim area is generally able ot handle heavier rains as compared with the other topography, multiple days of heavy rain could lead to more widespread flooding impacts. It remains possible that another Moderate Risk upgrade may be needed for portions of this area, particularly in central Arizona. ...Florida... A vigorous tropical wave tracking east across the Gulf will impact the Florida Peninsula on Sunday. A notable increase in instability will accompany PWATs over 2 inches in some areas. Unlike previous days where the heaviest rains were confined to the immediate east coast, on Sunday essentially all of the Florida Peninsula will see over an inch, and in many areas over 2 inches of rain. Areas such as the Treasure Coast already have saturated soils, and will be much more prone to developing flooding as compared to much of the west coast of Florida. Nonetheless, given the abundant moisture and weak flow that will keep any storm motions slow, all of the Peninsula will at least have an isolated risk of flash flooding. A Slight Risk upgrade is probable with future updates, especially around the Treasure Coast, once the CAMs guidance can add more detail to the forecast. ...Elsewhere... The Marginal Risk for the lower Tennessee and Ohio Valleys follows ongoing rain from Saturday night continuing into Sunday morning in the form of slow-moving convection. With daytime heating, this too should weaken with time. Across the central Plains, the flooding threat will come Sunday night as the heavy rains with the storm impacting the Southwest during the day eject east into the Plains. Wegman Day 4 and Day 5 Valid 12Z Mon Nov 02 2026 - 12Z Wed Nov 04 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GREAT PLAINS, MIDWEST, MISSISSIPPI VALLEY, AND EASTERN FLORIDA PENINSULA... ...Great Plains & Mississippi Valley... Deep upper trough enters the central U.S. by Monday (Day 4) and spreads ample moisture northward throughout the Great Plains and into the Upper Midwest. The most impressive moisture anomalies when compared to climatology are expected to be located across the northern Plains (+5.0 standard deviations) and more specifically from NE/SD to MN. However, instability will be limited here and lead to more moderate rainfall over a long duration rather than the intense rainfall rates >1-2"/hr necessary for flash flooding. Heaviest rainfall amounts may also be tied to the location of the synoptic low as it tracks across the region, which remains somewhat uncertain at this range. However, given the probabilities for >2" in 24-hrs from the NBM are greater than 50% as far north as eastern SD and southern MN, a MRGL risk was maintained this far north for now. Farther south, greater instability and potential for isolated instances of flash flooding exists along and ahead of the sweeping cold front as it tracks across the central/southern Plains on Monday before entering the Lower Mississippi Valley on Tuesday (Day 5). Additionally, a separate area of low pressure may develop on the southern end of the related upper trough and provide a focus for moderate to locally heavy rain. Uncertainty with regards to impacts associated from excessive rainfall remains highly tied to the progressiveness of this system as it could lead to limited duration of moderate to heavy rainfall rates. Thus, a MRGL risk was maintained, with much of this region also experiencing dry antecedent conditions between eastern OK and northeastern TX to central MS. ...Florida... Shortwave energy spilling into Florida on Sunday will linger into Monday (Day 4) could promote increased convective coverage. PWs should be near the 90th climatological percentile while global models show MUCAPE reaching around 1500 J/kg at times. While much/all of Florida could see scattered thunderstorms with locally heavy rain along the draped stationary boundary, will show a MRGL risk for the east coast in particular, because of easterly low level flow for increased convergence, and the urban centers that are more sensitive to heavy rain. Snell 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 $$