Major autumn cold blast possible for eastern U.S., D.C. in 7-10 days


European model shows cold blast approaching the East Coast in 8 days (WeatherBell.com)

Brought to you, in part, by typhoon Wipha, much of the eastern two-thirds of the U.S. is due for a possible taste of late autumn-like or even early winter-like temperatures in just over a week’s time.

Wipha has now transitioned from a typhoon into a mid-latitude storm in the north Pacific. Its presence is helping to build a big ridge of high pressure over the western North America, which – in turn – is going to gradually cause the jet stream to buckle and dive south over the eastern two-thirds of the U.S.  This will open up the floodgates of Arctic Air.

Evolution of high altitude weather pattern, illustrating ridge Wipha (and its remnant low) helping to build a ridge of high pressure (orange and red shades) over western North America, which helps establish lower pressure and colder air over eastern North America (WeatherBell.com GFS model simulation)
Evolution of high altitude weather pattern, illustrating ridge Wipha (and its remnant low) helping to build a ridge of high pressure (orange and red shades) over western North America, which helps establish lower pressure and colder air over eastern North America (WeatherBell.com GFS model simulation)

The pattern change will take about a week to evolve, as the core of chilly air is initially (through early next week) steered more towards the Plains and Midwest (see frames for October 17-20 in above image) October before making its way to the East Coast (October 21-23).

“The key  to the whole pattern is the development of the big LOW pressure area over the Great Lakes that moves up into southeastern Canada [see last two frames of above animation] and the Canadian maritime provinces,” writes Dave Tolleris, meteorologist for WxRisk out of Richmond, on his Facebook page.  “If that LOW  does not do that ….then the northwest winds will be significantly less  and the heart of the cold air will NOT  plunge deep into the eastern half of the country.”

It’s not really a question of whether the cool air will arrive, but rather how cool it will be. All three of the major computer models: the Canadian, the GFS, and European (and the majority of their ensembles) are in reasonable agreement about the gradual infiltration of the cooler weather.

How cold are we talking? Preliminary indications are that by late next week, highs may only be in the 50s, with lows in the 30s and the possibility of a frost or freezing conditions in D.C.’s north and west suburbs.


European model forecast of hi and low temperatures 10 days into the future (WeatherBell.com)

European model forecast for low temperatures on October 25. (WeatherBell.com)

The models suggest that once the cooler air arrives, there may be reinforcements that help it stay around for a while – though this is a lower confidence projection.


Temperature difference from normal simulated by GFS model 8-16 days in the future.  It is  average of 16 different simulations of the GFS model ensemble. Green shades indicate temperatures 4-8 degrees C (or 7-15 degrees F) colder than normal. (WeatherBell.com)

NOAA’s Climate Prediction Center is buying into the model projections and favors cooler than temperatures in the 8-14 day period for the eastern two-thirds of the nation.


Climate Prediction Center 8-14 day outlook (NOAA)

Note that models sometimes overdo cold air outbreaks and confidence in the forecast declines considerably beyond 5-7 days into the future.

Of course, temperatures are in decline, on average, at this time of year without any help from the overall pattern.  Average highs fall from the upper 60s to the low-to-mid 60s over the next 14 days in the D.C. area.

Related: It’s All Connected (Ryan Hanrahan)

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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Jason Samenow · October 16, 2013