Last week I warned that the upper-level pattern was showing signs of becoming blocked and a pattern change to below- average temperatures is likely the second half of April across much of the eastern United States.
Potent Nor’easter May Impact Mid-Atlantic and New England Friday and Saturday
A very potent upper-level low pressure system depicted in the forecast model above (courtesy pivotal weather) will slide across the northern Mid-Atlantic states on Thursday, likely spawning the development of a coastal storm (Nor’easter) on Friday.
Depending upon the exact track of this system wet snow may accumulate in spots from the Alleghenies to the Poconos with a cold rain, gusty winds, and temperatures running twenty degrees below average (or more) for the lower elevations.
Enjoy the above average temperatures this week because the medium range forecast models continue to suggest The Mid-Atlantic may experience below average temperatures the second half of April.
The North Atlantic Oscillation (image below, courtesy The Weather Channel) continues to trend negative, meaning that an upper-level ridge of high pressure is forecast to build across Greenland and the Canadian Maritime.
This upper-level ridge of high pressure acts as a block causing the jet stream to buckle further south into the eastern United States bringing below-average temperatures.
The next image (courtesy Pivotal Weather) shows the 500 millibar (mb) height anomalies through April 15. You’ll notice the bright red and orange colors holding strong from the eastern Hudson Bay of Canada toward Greenland, indicative of the upper-level blocking that I just mentioned.