High Pressure Dictating US Pattern Right Now

Written by on August 28, 2013 in United States of America with 0 Comments

At the moment, the main and obvious dominant factor to the US pattern right now is the Plains ridge which is making it rather hot across most of the US. Each day we’re seeing record highs and record high maximums and through the rest of this week and into early next week, there is no real sign this ridge is going to deflate as surrounding features aren’t strong enough to weaken this broad 596dc core.

Notice how features, which are weaker, ride around this wheel. We have an upper disturbance now dropping through the Great Lakes and has the Mid-Atlantic up into NYC in it’s sights Wednesday while moisture continues to stream north over the Southwest up into the Great Basin. With the heat and humidity feeding these features, these are packing a punch and the low dropping into the Mid-Atlantic looks as though it could bring quite a soaking to DC, Baltimore, Philadelphia perhaps as far down as Richmond. More of these types of upper air disturbances will drop into the Northeast and Mid-Atlantic next week given the position of the ridge back west.

We also have more moisture pouring up into the Desert Southwest while a Pacific Storm comes into Washington and British Columbia but while it brings wind and rain to the coast and mountains, it has little effect further inland simply because heights are too strong.

Here’s the ECMWF surface/precip setup through the next 48 hrs.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

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24 hrs

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

36 hrs

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By Saturday there is very little happening.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

However, by Sunday we have two waves of energy dropping down the eastern flank of the ridge which could be strong enough to push the ridge west, allowing a trough and cool down over the East. That trough the ECMWF showed earlier today for next week is now weaker.

Old run for next Wed

Geopotential3250032hPa32and32Temperature32at3285032hPa_North32America_192

New run

Geopotential3250032hPa32and32Temperature32at3285032hPa_North32America_192

Weaker or not, the model has a fairly substantial low which drops a front down the East Coast bringing heavy rain, potentially strong winds. This could be a flood threat to the Northeast Sunday into Monday.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Given the activity over eastern Asia, my hunch is the models will pick up on more of a ridge-trough connection across the Pacific which drops a few fairly deep troughs in the East over the next 1-3 weeks.

We have system one Wednesday-Thursday then system two Sunday-Monday with a refreshing shot of cool behind from Buffalo to Baltimore. But what happens after that? A lot may depend on the recurvature of systems over the western Pacific.

As for the CFSv2.

Week 1-2 holds the blowtorch over the heart of the continent with upper level features riding around it but it’s the system crossing Ontario this weekend which will be strong enough to force the ridge west bringing bigger and more widespread rains.

wk1_wk2_20130826_NAsfcT

Interestingly, while week 3 shows the cool down across the country and the deflation of the ridge, it appears to come back somewhat week 4.

wk3_wk4_20130826_NAsfcT

NAO and AO trend towards the positive side of neutral… Zonal pattern for Sept?

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