An active weather pattern will bring a series of passing fronts and upper-level disturbances to the Northeast over the course of this week. These features will bring wide temperature swings and locally heavy thunderstorms, but also the promise of being one step closer to a warmer, more typical summer pattern after their departure.
Easterly winds will circulate around an idle high pressure system situated off the New England coast Monday. The oceanic air will keep the entire region cool. Inland areas of New England and the Northern Mid-Atlantic should warm into the mid 70s as dry air pushes clouds southward. Despite the sunshine, coastal areas of New England and the northern Mid-Atlantic will remain in the low to upper 60s. Clouds and light showers will keep eastern West Virginia, all of Maryland, and northern Virginia in the mid to upper 60s.
Tuesday, temperatures will jump 5 to 15 degrees over Monday. The coastal high pressure system will drift southeastward, allowing New England, western Pennsylvania, and most of New York State to warm to seasonable temperatures between the mid 70s and low 80s. Long Island southward to the Carolinas will still be caught in the onshore flow. Coastal areas will be stuck in the upper 60s whereas inland areas will only warm to the mid 70s.
The forecast becomes more uncertain Tuesday night and Wednesday as showers and thunderstorms develop ahead of two separate features. The stalled frontal boundary that brought Flash Flooding to Philadelphia and other parts of the Mid-Atlantic will return northward as a warm front Tuesday night. Meanwhile, a weakening shortwave trough with an accompanying cold front will slide across New England throughout the day Wednesday.
Scattered showers will develop ahead of the warm front Tuesday night into Wednesday morning in western Maryland, Pennsylvania, and New York, with clouds reaching the coast. Instability will develop as clouds clear behind the warm front away from southern facing shore lines in the Mid-Atlantic during the afternoon and evening. The eastward creeping cold front will trigger showers and thunderstorms in the Mid-Atlantic and southern New England throughout the afternoon and evening from west to east. Storms Wednesday afternoon and evening will have a chance of producing some strong wind gusts, hopefully sun is able to peak through. Closer to the upper-level shortwave in the North Country of New York and northern New England, a broader region of showers will develop throughout the day.
In the warmer sector, ahead of the cold front and where clouds do make room for some sun, temperatures will climb to the low to mid 80s. New York City should be the northward extent of these temperatures. Clouds will also clear in northern Pennsylvania and upstate New York. However, as these areas are far from the core of the air mass, temperatures will only rise to the mid 70s. Clouds will linger over New England Wednesday, keeping temperature in the 70s there as well.
By Thursday morning the cold front will have cleared the coast, making way for a day of full sunshine everywhere except northern New England, where clouds may hang on. The core of the cooler air mass will be trapped west of the Appalachians, allowing the coastal plain to warm to the upper 70s to mid 80s. Along and west of the mountains, temperatures will remain in the 70s.
A passing shortwave may stir one last bout of uncertainty Friday before the first dry weekend since April for parts of the Mid-Atlantic. With limited moisture available, only isolated showers are expected, namely over Pennsylvania and New York. Friday should otherwise be a partly cloudy to mostly sunny day, but with temperatures a few degrees cooler than Thursday.
The passing of the upper-level low on Friday will mark the beginning of a transition in the weather for the entire country. The dome of high pressure infamous for scorching the Plains and the Southwestern US over the past month will finally shift eastward, at least temporarily. As ridging of high pressure builds into the East, a new pattern favoring mostly seasonable to above-average warmth and heat will dominate the weather in the Northeast from Saturday through at least the second half of June. Cold fronts may interrupt the summer warmth, but cooler weather is not likely to be as intense nor as abrupt as those over the last month. With this new pattern, the Mid-Atlantic should finally experience a dry weekend barring a few pop-up thunderstorms, with more likely to follow in the coming weeks.