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While the core of US drought remains over the Plains, 2013 is changing the shape with the West becoming more arid with time from San Francisco down to LA across to Phoenix and up to Salt Lake City.
However, it’s been somewhat wetter over the Rockies thanks to recent late season snowstorms. Even in the Plains, despite severe drought holding strong, recent snowstorms have been a help but likely not enough.
As the sun climbs higher and the heat builds as we push towards May, I fear the moisture we’ve seen over parts of Texas, Oklahoma, Kansas may not be enough. Remember that the warmer sun will raise evaporation rates considerably and so as we press through spring, those soils dry out quicker.
The region which has potentially went from one extreme to the other is North Dakota down through Iowa, Missouri, Illinois where last spring was exceptionally dry, this year many areas have seen 200-300% normal rains (incl snow) over the past 6 weeks.
Shipping was significantly impacted by record low Mississippi River levels this time last year, whereas flooding is a growing concern this year as one moist system after another barrels through this region. Couple the big rains of late with the deep snowpack which remains across the Dakotas, Minnesota and Wisconsin, once this melts, there is going to be a strain on the river network which a lot of it drains into the Mississippi.
Not just around Fargo or Des Moines, but areas all the way down the Mississippi could feel the effects of all that Upper Midwest snow melt and the rains over Iowa, Illinois and Missouri all the way to Louisiana.
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Here is the current drought monitor as of April 16.
As for the palmer drought severity index you can see from the latest chart last issued April 13 that the greatest drought impacts are in fact in the Rocky Mountains from Montana to New Mexico despite the recent moisture and not surprisingly across the Southwest with Southern California in bad shape. Note the wet conditions from Minnesota through Missouri to Louisiana.
Let’s not forget Florida, there’s drought here and this may have impacts on the early summer here with heat.
The Pacific Northwest is faring well but I think the PNW dries out as the heights rise in the West. In fact don’t be surprised to see a warmer, drier than normal May which sets the stage for a warmer, drier than normal June-July period.
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Here’s what the latest QPF shows for precipitation over the next 7 days. Lots of water up and down the Atlantic Seaboard. That’s because models see a coastal system pushing north next week. This should increase soil moisture from South Carolina to Maine next week. There’s also an additional .5 to 2 inches of rain from the PNW across the central and northern Rockies, Plains into the heart of the ‘wet zone’. California, much of Nevada, Arizona, New Mexico into West Texas remains bone dry! The feedback of a dry first part of the year has begun and where it remains dry, it’s tougher for the atmosphere to produce rain in these areas, opposite of where it’s wettest.
In recent posts, I have stated the importance of where the biggest rains set up and where those soils are wettest during spring. These wet soils lead to increased dew points which can lead to wetter weather later down the road as the sun heats the ground, releases this moisture into the atmosphere and increases the threat of thunderstorms and therefore additional rain. A feedback can quickly be triggered when you’ve got wetter than normal ground. This can also lead to lower pressure and weak upper level troughiness during the hot season.
The opposite goes for drier than normal soils as less moisture means less moisture drawn out of the ground and into the air. Less moisture for the sun to evaporate means, more energy goes into warming the ground and the lower atmosphere. This can feedback to stronger than normal heights and ultimately hotter weather than normal.
Here’s the May forecast off the CFSv2 for temperature.
I continue to forecast further wet conditions from the Mississippi on east to the Atlantic while drier than normal conditions are set to persist from Colorado west and south over the next 7-10 days but the wet conditions may ease over the East because of a mean trough setting up in the East which will have a persistent feed of cool, DRY air but with rain on the horizon and Western ridge building, you just know where the heat is going given the +PNA, -NAO/AO, a trough is likely to persist through a good chunk of May in the East with those indexes and the help of soil moisture feedback.
In terms of the feedback of soil moisture and influence with atmospheric pressure, it’s not until you get into the summer season when this becomes more of a significant influence when there’s less influence from the PNA/NAO/AO and the mid-latitude ridge becomes the dominant player as it lifts towards it’s most northerly position and that’s over the United States. Even into summer, while heights naturally rise and cold air is pushed way up to the arctic, there should be a tendency for more of a trough from the Great Lakes to Southeast while from the California coast to central Rockies, simply because of where the wettest and driest soils reside.
The Midwest and even East should see a more humid summer thanks to those wetter soils adding greater than normal moisture into the air.
The area to watch for long lived hot spells I think is West Texas into New Mexico. While there’s been a fair amount of rain of late over Texas, it’s West Texas which appears to avoid any real rains and this may lead to a long hot summer here and could be a focus of hottest weather for a time, especially in the early summer where I think it’s going to be a hot May through Mid-July period from Palm Spring, Calif to Lubbock, TX.
Summer should start off fairly damp and cool in the East and where it’s been a soaker of a spring so far.. this summer overall may be fairly cool with frequent thunderstorm days.
Here’s the Jamstec’s latest temperature anomaly forecast. Note it has a warmer than normal summer across most of the country.
[youtube http://www.youtube.com/watch?v=wFpM3seYeG8]
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