1:10 PM | *Heavy rainfall coming to the DC, Philly, NYC metro regions*
Paul Dorian
12Z GFS forecast map for Sunday morning with heavy rainfall (yellow) along the DC-to-Philly-to-NYC corridor; map courtesy NOAA/EMC; tropicaltidbits.com
Overview
It has been very dry in recent months in the DC metro region and drier-than-normal in the Philly and New York City metro regions, but heavy rain is headed this way for the upcoming weekend and that, combined with rains earlier this week, should help alleviate some of the dry conditions in the area. Multiple waves of moisture-laden low pressure will slowly ride up along a frontal boundary zone this weekend from southwest-to-northeast and by the time the weekend ends, many spots in the DC-to-Philly-to-NYC corridor will have received 1.50-2.50 inches of rainfall. Even heavier amounts of rainfall may pile up in the Tennessee Valley from this weekend system where some spots could receive 6+ inches by early Monday morning.
12Z GFS forecast map for late Sunday night with additional heavy rain in the I-95 corridor; map courtesy NOAA/EMC, tropicaltidbits.com
Details
In the latest weekly "drought monitor" report from NOAA, moderate-to-severe conditions are being reported in the DC metro region and "abnormally-dry" conditions are highlighted in the Philly and New York City metro regions. These overall dry conditions have already improved slightly this week with some prior rainfall and there will be considerably more improvement this weekend as heavy rain moves into the region. In fact, I wouldn't be surprised to see NOAA/National Weather Service issue "flash flood watches" for at least parts of the Mid-Atlantic region as the event time approaches given the potential of this developing pattern.
12Z GFS forecast map of total accumulated rainfall as of Monday morning; map courtesy NOAA/EMC, tropicaltidbits.com
High pressure is pushing offshore today and this will open the door for Gulf of Mexico moisture to move in our direction from the Deep South. In addition, as low-level winds turn to an east-to-southeast direction on Saturday, moisture from the Atlantic Ocean will feed into this overall pattern. One low pressure system will emerge from Texas on Saturday and move northeastward over the Appalachians and towards this part of the country and then another system will follow closely on Sunday in the same general path along a frontal boundary zone.
Latest surface map showing high pressure now off the Mid-Atlantic coastline and this opens the door for both Gulf of Mexico and Atlantic Ocean moisture to feed into this developing system; courtesy NOAA/SPC, twitter (crankyweatherguy)
Rain will spread into the DC-to-Philly-to-NYC corridor late in the day on Saturday from the southwest-to-northeast and continue heavy at times Saturday night, Sunday and perhaps even well into Sunday night. This will be a long precipitation event with genuine drying not likely to occur until early Monday. As far as temperatures are concerned, it’ll turn milder on Saturday with highs approaching the 50 degree mark in much of the I-95 corridor and then temperatures are likely to climb well into the 50’s on Sunday and perhaps even top the 60 degree mark south of the PA/MD border.
Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com
Morning video discussion on the upcoming long-lasting heavy rain event for the DC-to-Philly-to-NYC corridor: