071 FOUS30 KWBC 161921 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 321 PM EDT Fri Oct 16 2026 Day 1 Valid 16Z Fri Oct 16 2026 - 12Z Sat Oct 17 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL/SOUTH FLORIDA... Seasonably high moisture combined with afternoon heating will lead to sufficient instability for scattered thunderstorms across central to south Florida. Efficient downpours with rain rates upwards of 2-3" per hour are expected with localized heavier totals in the 4-5" range. This may lead to some isolated instances of flooding particularly for urban areas. Elsewhere, a line of thunderstorms is expected to develop along a cold front moving through the Northeast this evening. The progressive nature of the front should limit rain totals overall, though the chance of a quick 1-2" particularly with southern extent along the I-95 corridor through the Mid-Atlantic could cause some minor ponding on urban streets. Putnam Day 2 Valid 12Z Sat Oct 17 2026 - 12Z Sun Oct 18 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE FLORIDA EAST COAST... Similar to Friday, seasonably high moisture will be in place across portions of central/south Florida on Saturday with afternoon heating leading to sufficient instability for scattered thunderstorms. However, overall forcing will be increased to do an approaching cold front leading to more intense downpours with hourly rain rates of 3"+ possible. Veering onshore flow with the passing front will also help to support convergence along the east/Atlantic coast with the potential for repeated and persistent, slow-moving thunderstorms and longer-duration rainfall. The now available hi-res guidance shows the potential for locally heavy totals in the 6-10", and both the HREF and RRFS show high probabilities (70-90%) of totals exceeding 5 inches and moderate probabilities (40-70%) of totals exceeding 8 inches. Therefore, a Slight Risk has been introduced due to an expectedly more scattered threat of flooding particularly for the I-95 urban corridor. Putnam Day 3 Valid 12Z Sun Oct 18 2026 - 12Z Mon Oct 19 2026 ...MARGINAL RISKS OF EXCESSIVE RAINFALL EXIST FOR SOUTH FLORIDA AND THE OUTER BANKS OF NORTH CAROLINA SUNDAY... ...2030 UTC Update... A developing Nor'easter off the coast of the Carolinas will begin to lead to increasing heavy rain chances along the coast over the next few days. While there remains some uncertainty with the details of how fast the low develops/strengthens and then meanders relative to the coast, and thus storm chances, the latest guidance indicates showers and thunderstorms will begin for at least the Outer Banks over the weekend. There is greater confidence in modestly heavy totals in the 1-3" range by Sunday and a Marginal Risk for isolated flooding concerns has been added. Otherwise, the forecast for South Florida below remains on track. Putnam ...Previous Discussion... A well defined cold front is expected to press southward before stalling south of Florida on Monday. Moderate to strong post- frontal on-shore flow Low level flow will focus moisture flux convergence in proximity of the front. Strong boundary layer convergence maxima likely along the east central coast of Florida, which would be strongest overnight will support potential for locally heavy rains from well defined rain bands that may train for periods early Sunday. There has been a subtle southward shift in the placement of the rainfall compared with previous model runs...but spaghetti plots from the ECMWF Ensembles and the GEFS ensembles still indicate that some potential lingers for 3+ inch amounts during the period. Consequently...shrunk the Marginal risk area somewhat but did not remove it. Bann Day 4 and Day 5 Valid 12Z Mon Oct 19 2026 - 12Z Wed Oct 21 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE NORTH CAROLINA OUTER BANKS MONDAY INTO TUESDAY NIGHT... 20z Update: No changes to the Marginal risks across portions of the Outer Banks. While there will be an area of low pressure offshore, model guidance continues to show high run to run variability in the location, which will impact whether heavy rain makes it onshore or not. The latest 12z ECMWF and AIFS have shifted more offshore, limiting the threat of heavy rainfall along the coast. However, with this being just one run, and there being high run to run variability and ensemble spread, we will not make any changes to the risks at this time. Chenard ...Previous Discussion... ...Eastern NC/Southeast VA... The guidance is trending more towards an occluded low not far off the Southeast Coast, which could have some 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. Wet solutions are now shown on the 00z Canadian and 00z ECMWF, with the 00z GFS barely off the coast with its heavy rain signal Monday/Monday night before it ejects the cyclone northeast due to a slightly stronger shortwave moving through Atlantic Canada. The 00z ECMWF AIFS and 00z AIGFS are supportive of their control/operational runs respectively. Since support appears to be slowly increasing and spread generally decreasing. left the Marginal Risk from continuity for coastal NC/VA for Monday/Monday night and introduced a new MRGL for a similar locale Tuesday/Tuesday night. ...Southwest... There was consideration for a Marginal Risk for portions of southeast and central AZ to the southeast and eventually east of a deep layer cyclone/"outside slider" moving west of CA, but the atmosphere didn't appear to be sufficiently saturated with 0.75-1" precipitable water values in an environment with 5640-5670 decameter 1000-500 hPa thickness. MU CAPE also appears skimpy, with only small pockets of 250 J/kg forecast by the 00z GFS and 100 J/kg by the 00z ECMWF. While the threat for flash flooding/ excessive rainfall may be non-zero, did not feel it was up to the Marginal Risk threshold so left risk areas out, for the time being. This can be re-evaluated in later cycles. 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 $$