12:45 PM | *Coastal storm threat by the weekend*

12Z GFS forecast map for Saturday evening with low pressure off the Mid-Atlantic coastline; map courtesy tropicaltidbits.com, NOAA

Overview
Here we go again…by the time the weekend begins the upper air pattern will closely resemble the “omega” blocking pattern of a couple weeks ago featuring an impressive upper-level trough over both the east and west coasts and extensive high pressure ridging in the middle of the country.  The upper-level trough in the eastern states will help to intensify low pressure on Saturday as it treks from the Ohio Valley to the Mid-Atlantic coastline.  As a result, rain is likely to push into the DC-to-Philly-to-NYC corridor by late Friday night or early Saturday morning and then continue heavy at times through most of the day in much of the Mid-Atlantic region; especially, to the south of the PA/MD border .  

12Z GFS forecast map of 500 mb height anomalies for Saturday evening indicating upper-level troughs of low pressure over both coasts (blue regions) and high pressure ridging in the middle of the US (orange region); map courtesy tropicaltidbits.com, NOAA

Details
Large high pressure to our northwest will bring some improvement to the I-95 corridor by later today and tonight and then a good deal of sunshine is likely on Thursday and Friday along with milder conditions.  By Saturday, however, this protective high pressure system will push off the coast and lose control of our weather and low pressure will intensify as it treks towards the Mid-Atlantic coastline from the Lower Ohio Valley.  Rain is likely to break out in the I-95 corridor by late Friday night or early Saturday morning and then continue heavy at times during the day with a possible thunderstorm or two mixed into the picture.  By the time early Sunday morning rolls around, rainfall totals could exceed two inches in parts of the Mid-Atlantic region; especially, those areas south of the PA/MD border.  In addition, it should be quite cool and breezy on Saturday as the storm reaches the Mid-Atlantic coastline with a noticeable low-level wind out of the northeast. Sunday will feature some improvement, but a few showers cannot be ruled out.  

12Z GFS total rainfall amounts for upcoming storm (by Sunday morning); map courtesy NOAA

Looking ahead

As is typical with “omega” blocking patterns, upper-level features will be slow to move. Consequently, the upper-level low pressure trough over the eastern states will stick around into early next week and a follow up coastal storm may form by Tuesday.  There is a chance this potential second system stays just far enough off the coast to produce anything significant in the I-95 corridor, but it’ll have to be closely monitored over the next few days. 

Meteorologist Paul Dorian
Vencore, Inc.