Yesterday’s update mentioned uncertainty with the exact axis of heavy rainfall with model differences, as the ECM, CMC and UKMET were on the southern end with temperatures in the 50s-low 60s with 2-4 inches of rain, and the GFS and NAM were further north with 1-3 inches of rain and slightly warmer temperatures. As of this morning, the GFS and NAM shifted south, and were aligned closer to the ECM scenario of chilly temperatures, wind gusts up to 40-50 mph, and 2-4 inches of rain, locally up to 5 inches.
At this time, other than slightly increasing rain totals for the southern half of the area and increasing wind speeds, little changes were made to the 5-day forecast, with the outlook for 2-4 inches across the area resulting in flash flooding, wind gusts up to 35-50 mph, and temperatures peaking in the low to mid 60s before falling into the 50s by the evening and overnight hours. For more localized forecasts, please refer to the 5-day forecast page.
A new scenario is showing up with some of the latest models, however; the latest GFS and UKMET runs, which just came within the last hour, show a different outcome less than 24 hours before the storm starts, now showing a much weaker low pressure around 1000mb tracking into southern Pennsylvania, then southeast into Delaware and SE Maryland before weakening and quickly exiting offshore. In that scenario, rainfall amounts would be much lower, only around 3/4 to 1.5 inch, locally higher, winds would be weaker, the Mid Atlantic severe weather risk would be lower and further south, and the rain would end much earlier than expected, around Thursday evening as opposed to Friday morning. As this is only a scenario shown very recently and does not have model support at this time, it was not taken into consideration for this morning’s updated forecast, although I will continue to monitor the latest model runs through the day and should the rest of the afternoon model guidance trend in this direction, changes may be made to the forecast. Stay tuned for more information on tomorrow’s outlook with a forecast discussion this evening.