Tuesday, 11:55 a.m.
We've closed the books on the month of April and, surprisingly, it was a month that was near to even a little below normal across upstate New York and much of Pennsylvania into parts of the Great Lakes and Ohio Valley. Still, the month as a whole has to be considered a warm one for a good part of the country from the Rockies on east.
Picking up where we left off, another surge of warmth is fanning out across the Mississippi Valley today. A piece of that warmth is coming eastward over the Appalachians into the mid-Atlantic. The combination of some sunshine and a west wind is spelling the difference between 70s and above and 50s or low 60s, which will be the case in most of New England (assuming everyone gets that high, which isn't a lock). Take a look at the latest pressure analysis:
What you're seeing there is a weak low over Watertown, N.Y., and another near Atlantic City, N.J. North and east of these lows, the wind is at best out of the south and in most cases is more easterly in nature. With a warm air mass trying to budge in from the west and southwest, it's helping to lead to an overcast, gray sky in all of this region, along with some rain and drizzle.
To the west is a 'bubble' high pressure area over northern Ohio. The flow in between the two is out of the west and northwest, including much of Pennsylvania down into Virginia. That is a drying, downsloping wind, one that helps to create a well-mixed atmosphere. And in most cases, there is some sunshine, or will be for a few hours this afternoon, and that's enough to push temperatures into the 70s or better.
Farther west is another low pressure area over the Dakotas, and that's helping to draw very warm air steadily northward from the southern Plains and lower Mississippi Valley. When you combine that with an upper-level flow from the southwest, and you can envision the groundwork being laid to carry this warmth downstream into the Lakes and Ohio Valley in the next 24 hours. Here's the latest 500 mb NAM forecast for tomorrow evening:
High pressure will rebuild across New England tonight and tomorrow, and that will put a roadblock in the way of this surging warmth. Once again tomorrow and into Thursday, the flow around that high will have an easterly component to it across New England down into the mid-Atlantic states, and that will limit in the short term just how much of the warmth out west of the Appalachians can come east. It will still be warmer than average, but the real huge temperature anomalies will be west of the mountains, where sunshine and no marine air can get in the way of the warming.
Around the rim of the warmth there will undoubtedly be some showers and thunderstorms. Any little ripple in the jet stream will help trigger some of these thunderstorms. And that's why the models stick the heaviest precipitation between now and late Friday around the periphery of the heart of the warmth. Here's the NAM forecast of total precipitation from this morning through the day Friday:
Basically, the farther south you go, the drier it will be, with very little moisture over South Carolina and Georgia into northeast Florida, and not necessarily a lot in North Carolina and much of Virginia. The same is true from Kansas to Texas and across Arkansas and Louisiana.
There is a corridor in between these two that will get some rain. If you recall from last week, the feature drifting northward away from Panama through the central Caribbean. Well, that has maintained some structural identity into this morning, and it has brought some rain to South Florida. The large piece of this feature will drift east and northeast across the Bahamas, but there will be a piece that will be pulled northwestward across the eastern Gulf of Mexico toward the central Gulf Coast tomorrow and Thursday. It won't be a developed system, but it can be a locally wet area in the midst of a broadly dry weather pattern throughout the South.
This surge of warmth will fade this weekend as a cold front drops across the Great Lakes into the Northeast Saturday and Saturday night into Sunday. Next week should feature no such surges of warmth if everything comes out according to plan. Look at the GFS seven-day ensemble means for next Monday, May 7, through the following Sunday, May 13:
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