N Plains Heatwave, Gulf Coast & Desert Southwest Tropical Flood Threat

Written by on August 23, 2013 in United States of America with 0 Comments

While a lot of focus shifts towards the building heat over the Plains in coming days, we also want to watch carefully the tropics and not one but two features may present big rains and an increased flood potential.

While the upper pattern has changed in recent days which is helping ease the prolific Southeast rains where the focus has been from Alabama to North Carolina, we currently have a weak low pressure feature drifting west over the northern Gulf of Mexico which bears watching and not so much because it may develop but it’s likely to bring flooding rains from New Orleans to Corpus Christi however heavy downpours are likely to extend all the way from Florida.

The below AccuWeather graphic shows the Gulf Coast system well.

Source: AccuWeather

Source: AccuWeather

As for the Northeast and Mid-Atlantic, after another surge of summer heat and humidity, yet another cool, dry and cloud free Canadian high drops south thanks to the ridge axis positioned over the Plains. So, while hot air lifts north into the Dakotas, Minnesota, Manitoba and western Ontario, cooler air with low humidity drops south on the other side of the same high.

Source: AccuWeather

Source: AccuWeather

Another system well worth watching is tropical storm Ivo which is positioned south of Baja California and this is expected to drift north along the Baja coast and weaken but the upper pattern suggests the system’s rich tropical moisture pushes north into northwest Mexico and the US Desert Southwest late this weekend into early next week.

Both tropical features look likely to present a flood threat.

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As for the heat building into the Northern Plains and Upper Midwest, well we’re about to see the hottest weather of the entire summer in such cities as Rapid City, Fargo, Minneapolis and possibly Toronto.

Below is the 500mb charts off the ECMWF which shows the ridge building over the heart of the nation with 592 heights covering a broad area and this ridge will stand firm well into next week.

Expect 100s over parts of North and South Dakotas as well as western Minnesota, possibly Iowa on 3 or 4 days in a row,

Here’s Sunday’s upper chart.

Courtesy/Owned by AccuWeather pro

Courtesy/Owned by AccuWeather pro

Monday

Courtesy/Owned by AccuWeather pro

Courtesy/Owned by AccuWeather pro

Wednesday

Courtesy/Owned by AccuWeather pro

Courtesy/Owned by AccuWeather pro

Minneapolis looks likely to see 2 or 3 straight days of 95+ with a chance at pushing 100 perhaps Tuesday or Wednesday and even Chicago may get up into 96-98 degree territory mid next week. Des Moines, IA is another city which could get close to 100 on 2 or 3 out of 5 days.

It’s worth pointing out pockets of upper level energy may ride the outer periphery of the hot dome, producing MCS’s or mesoscale convective systems over the Northern Plains and Canadian Prairies.

Also note the weak trough which drops down over the Northeast bringing comfortable days with low humidity and plenty of sunshine as well as cool nights.

Check out the ECMWF projected rains by Monday. We could see an unusual ‘widespread heavy rain event’ over the Southwest which brings flooding, localized flash flooding. Cities such as Tucson, Phoenix, Las Vegas and Palm Springs as well as all the way up through Salt Lake City, perhaps Cheyenne may all see persistent heavy rain which tallies 1-2 inches. This is most certainly unusual for this region.

Courtesy/Owned by AccuWeather pro

Courtesy/Owned by AccuWeather pro

The below AccuWeather graphic shows the situation well.

Source: AccuWeather

Source: AccuWeather

Here’s a spray of all the various model tracks for tropical storm Ivo. While most point towards the Southwest US, keep in mind the actual storm weakens but it’s effects in terms of rainfall unfortunately won’t. This has the potential to be a major weather event for this region in coming days.

Source: Wunderground

Source: Wunderground

As for rains from now through next Wednesday, the ECMWF prints out healthy amounts down along the Gulf Coast along with NW Mexico up into the Desert Southwest and Rockies. Notice there’s plenty of moisture which circles the hot dome with a lack of precip beneath the ‘capped’ centre.

Courtesy/Owned by AccuWeather pro

Courtesy/Owned by AccuWeather pro

Here’s the same chart only extending out to next Friday. That’s a heck of a lot of rain expected over Mexico. That sure would present flash flooding.

Courtesy/Owned by AccuWeather pro

Courtesy/Owned by AccuWeather pro

More tomorrow, including video!

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