Tuesday 11:30 a.m.
The dominant weather story these days remains the wilting heat baking the West. Another handful of records were erased on Monday, including the nation's high of 127 in Death Valley, Calif. Records were tied or broken from California and Arizona to Washington and Idaho, as well as in Montana and Wyoming. The unrelenting heat is the product of a strong upper-level ridge centered over Nevada:
There is SOME relief on the way. One upper-level disturbance moving inland from the Pacific will cross the Northwest this afternoon and tonight. While precipitation will overall be lacking with this feature, it will trim temperatures starting tomorrow in Washington and Oregon. That front will have minimal impact on temperatures farther inland, but a second upper-level trough will follow tomorrow night and Thursday to bring temperatures down even more throughout the region. By the end of Friday, the region that today is under the influence of a strong upper-level ridge will instead be governed more by the presence of an upper-level trough. Look at the 12z July 2 NAM 500mb forecast for Friday evening:
While by no means chilly, the air mass late this week into the weekend will be far more comfortable than anything seen in recent days. And the net effect of these troughs is to flatten the upper-level ridge to some degree, which, in turn, will mean lower temperatures over the Southwest.
If you refer back to the first image, you'll clearly see the deep upper-level trough plopped right in the middle of the country. This full-latitude trough has pushed a rare summer cold front deep into Texas, lowering the dew points into the 50s behind it. This is a rare feat, indeed, for the beginning of July and it's also helping to spread cooler-than-normal air into the southern Plains and parts of the Deep South. Where the sky is nice and clear, the departures from normal are not that large. However, there are many places stuck with clouds and some form of precipitation. Look at the late morning visible satellite image:
From around St. Louis to Chicago into Michigan, as well as from far upstate New York and northern New England, where it is cloudy, it is rather cool for being so close to the peak of typical summer heat. And with some rain in these areas, it's only adding to the departures from normal.
On the eastern flank of the upper-level low, the southerly flow is pulling a lot of tropical moisture northward from the Caribbean and through the eastern Gulf of Mexico into the Southeast, with that tropical plume extending all the way to Syracuse, as well as up to southernmost Vermont and New Hampshire. Dew points are close to if not a bit above 70, and where there are showers and thunderstorms, they tend to let forth a lot of water. That's why there have been a lot of problems with flooding and flash flooding over the past several days up and down the Eastern Seaboard and why flood or flash flood watches remain in effect.
Offshore, though there is a strong upper-level ridge, equal to the one that's over the West. Over the next few days, it will gradually expand westward onto the East Coast. The net impact of this move is to push this band of deep tropical moisture slowly but surely westward as well over the next couple of days.
There's one more thing to touch on. If you go back to that satellite image above, you'll notice in the lower right hand corner of it there appears to be a cluster of thunderstorms over the northwest Caribbean and western Cuba. That's actually a tropical wave that the models have had and seemingly lost since the middle of next week. While that feature is not likely to spend enough time over the eastern Gulf for it to develop a low-level circulation before slamming into the central Gulf Coast region, it will nevertheless have an impact on Florida by pulling the heaviest rains out of the Florida Peninsula.
This area of heavy rain appears to be headed for the Florida Panhandle, Alabama and Mississippi into the Tennessee and Ohio valleys later tomorrow and tomorrow night into Thursday. This will help to keep temperatures below normal in these areas heading through the Independence Day holiday. At the same time, however, the westward expansion of the upper-level ridge will slowly dry things out along the Eastern Seaboard, especially east of the I-95 corridor. The decreased rain activity, warmer and drier air aloft and an increase in sunshine should translate into an increase in temperatures Thursday and beyond. By the weekend proper, much of the mid-Atlantic and New England will be in the midst of a sauna with 90-degree heat and high humidity.
Rain and thunderstorms will pelt the East Coast into the start of the weekend, making it one of many areas around the country with unsettled weather now through Sunday.
Despite the current cool spell in much of the country, summer's heat will return to most of the country as we move forward in August.
A fall-like chill has descended upon the country from the Rockies to the Appalachians, and it will be slow to ease the rest of the week into the weekend.
A deep upper-level trough of low pressure is caught in between two strong upper-level ridges, locking cool weather into Plains to the Appalachians and beyond.
A much cooler air mass will expand from the northern Plains this weekend to the Deep South and into the East by Tuesday, pushing temperatures much below normal.
Intense heat and oppressive humidity surging out of the central Plains will cause severe weather from the Midwest to the Ohio Valley in the next 72 hours, followed by much cooler weather next week.