Cooling In East, Heating Up In West & Plains, Severe Threat Increases

Written by on July 8, 2013 in United States of America with 0 Comments

It’s been a hot, steamy second half to last week and of course through this weekend from DC to Boston with low to mid-90s but this heat is about to break as a system pushes in and a trough gets recarved. By late this week, temperatures may stay in the 70s in New York, low 80s Philly down to DC with an increasing severe threat. An upper disturbance will push through Washington state tomorrow (having little impact on the ground) and will ride the northern periphery of the ridge, enhancing unsettled weather across the Dakotas where hot, humid air lifts north, colliding with cooler air along the US-Canada border. As this system tracks east, so the ridge intensifies over the Four Corners east into the Plains while heights below lowering over the East once again and so the shower and thunderstorm activity increases as we see cooling in the upper levels and the lapse rate increases.

Here’s the GFS 500mb for Monday

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

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Note an upper disturbance floating into the Northeast, allowing added lift. With still hot, juicy air at the surface with highs near 90, Monday afternoon will see storms develop from Erie, PA to DC. Also note the next system arriving into the PNW which will be over the Great Lakes by midweek. Ahead of that system, temps return to the 110 range for Phoenix and Las Vegas, then trim briefly before the ridge surges up into the Northern Rockies on the backside of the system during Tuesday. 100s return to Salt Lake City and Boise while the heat pump extends into the Central and Southern Plains.

Enhanced shower and thunderstorm activity Tuesday across the Dakotas and then from Minneapolis to Chicago Wednesday with an increased severe potential as dynamics merge while in the Plains, the heat remains on with 100s back into Dallas, perhaps as far south as Houston. Once that upper low gets east of the Dakotas, expect 100s to surge northeast.

Here’s the 500mb and surface chart for Wednesday.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Surface

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Note the front spreading thunderstorms and heavy rains from N Missouri up to southern Ontario, including impact on St Louis, Chicago, eventually Detroit and Toronto.

This mess transfers east, eventually reaching the Big Cities of the Mid-Atlantic and Northeast later Thursday, Friday and on the backside of that front. much cooler, drier air comes down out of Canada with highs slashed by 25 degrees between today and Friday.

Here’s Friday’s upper and surface charts.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Surface

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

As the trough recarves over the Northeast, the front drops back into the Southeast, bringing the return of heavy rains once again to saturated areas.

Let’s not forget the exceptionally wet pattern we’ve seen over the Florida Panhandle and Alabama. Check out these rain totals since last Wednesday.

Source: weather.com

Source: weather.com

The ECMWF is showing a surface low riding around the Bermuda high this week and by next weekend, it’s pushing onto the Gulf Coast near Mobile. With the MJO into phase 2 and an enhanced phase for tropical development in the Atlantic, we should keep a close eye on this feature which crosses South Florida midweek bringing enhanced rains. With SST’s well into the 80s now, this MAY develop in the Gulf late week into the weekend. Something worth keeping a close eye on.
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