Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 645 PM EST Wed Dec 27 2023 Day 1 Valid 01Z Thu Dec 28 2023 - 12Z Thu Dec 28 2023 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID ATLANTIC AND NORTHEAST... ...01Z Update... An area of low pressure organizing off the North Carolina coast is expected to move northeast tonight, reaching near southern New England Thursday. As this low moves up the coast, an impressive and anomalous plume of higher moisture will overspread much of the coastal Mid-Atlantic to southern New England area with PWs reaching 1-1.25", which will be 2-3 standard deviations above normal for this time of year. This will be aided by 850 mb flow of 30-40 kts out of the southeast, overrunning a stationary boundary draped along the coast from eastern VA through southern New England. Aloft, an embedded vort max within the broad/sprawling closed upper low centered over the Midwest and an impressive jet streak over the Southeast will aid further in the large scale forcing for ascent. The latest hi-res guidance and 18Z HREF is in relatively good agreement for a widespread rainfall event through tomorrow morning with most areas seeing additional hourly rain totals between 0.5-0.75" and additional totals through 12Z Thursday of 1-2" with locally higher amounts of 3" most likely from portions of eastern MD, Delaware, eastern PA, and much of central/northern NJ into the NYC metro area. The 18Z HREF shows high probabilities of at least 2" (70-80 percent) with a slight signal (10-20 percent) for 3" totals through 12Z. Much of this rainfall will fall on areas that are already extremely saturated/wet from recent heavy rainfall events over the last couple of weeks. 14-day rainfall departures in the area are between 200-300 percent of normal and the latest Flash Flood Guidance is quite low in the region, particularly from eastern PA and NJ where even 1-hr FFG is likely to be met or exceeded (generally 0.5") as well as the 3-hr and 6-hr FFGs. This is likely to result in excessive runoff and at least scattered instances of flooding through the overnight period. The Slight Risk area was expanded some to account for the trends in the hi-res guidance though the greatest concern (higher end Slight Risk range) is from eastern PA through NJ and portions of southern NY where the combination of the rainfall totals, wet ground conditions, and urbanized area could result in some greater flooding concerns. Taylor Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Comments