FOUS30 KWBC 180036 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 836 PM EDT Sat Oct 17 2026 Day 1 Valid 01Z Sun Oct 18 2026 - 12Z Sun Oct 18 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA GOLD COAST... A Slight risk remains in effect for the southeast FL urban corridor through the overnight hours. Strengthening low level convergence within northeasterly post frontal flow may serve as a focus for slow moving low topped convective cells near the immediate coast. While instability will be limited, strong boundary layer convergence paired with anomalous PW values around 2.3" will support highly efficient warm rain processes in any heavier cells. Several recent HRRR runs have signaled this potential, showing localized rainfall totals exceeding 6" somewhere between Boynton Beach and Miami. Overall, this remains a tricky low confidence setup. The heaviest convective cores could remain offshore, and any heavier rain that does push inland will likely be localized. However, a conditional flood threat exists...should convective cells anchor along the immediate coast, localized extreme rainfall rates could result in a locally significant urban flash flood threat. Chenard Day 2 Valid 12Z Sun Oct 18 2026 - 12Z Mon Oct 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR A PORTION OF SOUTH FLORIDA... South Florida... A well defined, but weakening cold front pushes through south Florida late tonight, with a secondary front Sunday morning. Redevelopment of thunderstorms is expected with the secondary front which should produce heavy downpours over the Miami metro. Given the potential for flash ponding and excessive rain this afternoon/evening, conditions should be somewhat vulnerable Sunday morning. Hence the Marginal Risk is maintained. North Carolina Outer Banks... Confidence is now with an farther offshore solution to the coastal low for Sunday and Monday. Little to no rain is expected over easter North Carolina, so the Marginal Risk has been removed. Jackson Day 3 Valid 12Z Mon Oct 19 2026 - 12Z Tue Oct 20 2026 ...Eastern North Carolina... In coordination with WFOs MHX and AKQ, the Day 3 Marginal Risk has been removed. The 12Z consensus is for the coastal low to be far enough offshore to not warrant an excessive rainfall outlook. Some guidance such as the 12Z AIGFS remain close enough to produce moderate rainfall Monday over the Outer Banks. However, consensus is now for any rainfall to be remain well below excessive levels through Monday night. Jackson Day 4 and Day 5 Valid 12Z Tue Oct 20 2026 - 12Z Thu Oct 22 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST WEDNESDAY/WEDNESDAY NIGHT... 19z Update: The Marginal risk across the Southwest on day 5 still look in good shape. It does appear that a Slight risk upgrade is likely over a portion of this region as the event nears. However still enough model spread with the timing of the approaching mid/upper low to keep the risks at Marginal for now. This event likely continues into day 6 (Thursday), with uncertainty regarding which of the two days ends up having the greater flood risk. The one change to the inherited Marginal risk area was an expansion into southern/central NV, and an expansion into southwest UT. These changes are based on model trends supporting some weak instability getting into these areas, combined with high PWs and some convective rainfall from the global models. Chenard ...Previous Discussion... ...Southwest... For Tuesday/Tuesday night, the Southwest is on the eastern periphery of a deep layer cyclone/"outside slider" moving west of CA. The atmosphere still doesn't appear to be sufficiently saturated with 0.75-1" precipitable water values in an environment with mild 1000-500 hPa thickness values. MU CAPE also appears skimpy, with only small pockets of 250 J/kg forecast by the 00z GFS. Continue not to carry a Marginal Risk since guidance is maintaining serve over its past day of runs. The situation changes markedly on Wednesday/Wednesday night, as the deep layer cyclone approaches SoCal and scoops up moisture from a dying Trudy and flings it into the Southwest. Near the cold low itself, MU CAPE of 250-500 J/kg and precipitable water values of 1-1.3" with up to 30 kts of onshore flow at 850 hPa is forecast. There's enough of a heavy rain signal for a Marginal Risk for the Transverse and Peninsular Ranges, which is there to help cover burn scar concerns. In and near the Four Corners, MU CAPE is forecast to rise above 1000 J/kg, precipitable water values of 0.75-1.25" are anticipated, and a few pieces of deterministic guidance are definitely wet enough for a Marginal Risk with local 3-5" totals. Hourly rain amounts to 2" would be possible across portions of AZ, NM, and the Four Corners. It is possible that this area could carry a greater risk as we move closer to this weather setup. ...Eastern NC/Southeast VA... The guidance advertises a Nor'easter whose center is offshore North Carolina, with an increasing signal for interior convection as -18C air at 500 hPa moves over 28-29C sea surface temperatures during the short range period and perhaps a convective comma head/TROWAL which feeds off additional instability from the western subtropical North Atlantic and tries to brush the NC coast. The guidance has almost completely trended away from heavy rainfall with the system Tuesday/Tuesday night, so removed the Marginal Risk. Wednesday/Wednesday night is a question mark, as the 00z Canadian guidance brings heavy rain back into eastern NC at that time range. As most other guidance has left heavy rainfall offshore, left any Marginal Risks out of the EROs for this system for days 4-5. There is a non-zero chance of excessive rainfall/ flash flooding should a solution like the 00z Canadian come to pass or the guidance tries to slosh/waver back westward in later runs. Stay tuned. Roth 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 $$