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Annual March 1 post - 2010 edition
We've made it - it's the day that is like a national holiday to me and to many expeditioners. The start of meteorological spring today marks the 'beginning of the end' for the 2009-2010 winter season. While "official" spring is based on the date of the equinox, meteorological spring is based on the start of the climatological transition period between winter and summer weather patterns, which lasts from March 1 to June 1. Meteorological spring features an active jet stream across the USA that slowly moves north, bringing warmer temperatures, higher thunderstorm frequencies and the world's most prolific tornado season with it. March 1 is like the cavalry arriving with a trumpet blast, starting the atmospheric battle that we all know will end in victory.
The upcoming storm season will be one of firsts for me in many ways. First and foremost is being based in the St. Louis area, which opens the door for possibilities I've never had before - the ability to chase with greater frequency in more tornado-prone areas. My home chase range now includes part of the Great Plains region, and I'm in a position to pursue virtually any Midwestern event at a lower-than-ever cost. I'm very excited about the upcoming months and what they may bring!
First spring chase forecast
So now that it's March, what's the first week of storm season looking like? In my last post, I discussed the models' suggestion of the first Gulf moisture surge and coincident thunderstorm event for the central US occuring next weekend. For the most part, that is still a possibility - with signs pointing to a strong western troughing configuration. It looks like this is going to be spring's first 'warm surge', but unfortunately short-lived and probably not much of a severe weather maker.
Strong 500mb trough moving in, although too far south to be a big player for severe weather in the Plains and Midwest - very typical for early March. Moisture is definitely coming back, but not much to speak of yet. Only a narrow nose of 50°Fs to work with to start Monday. The precip forecast makes it look like a squall line that starts in the Plains and begins breaking up as it moves into the Midwest. The low is shown likely occluding and keeping its best wind shear influences west of the warm sector. This would suggest a remote cold-core possibility if the low avoids being 'vertically stacked' and any clearing can take place near the low center.
Again, this is still very far out in model range terms, and even now, it doesn't look like much of an event yet. Moisture is surging north, but not quite enough for what I'd consider for something chaseable. Speaking of moisture: the Gulf of Mexico, the fuel source for virtually all Plains/Midwest thunderstorms and severe weather, is still reeling from this brutal winter. Sea surface temps are still very cool, which will slow evaporation rates and attendant low-level moisture depth/quality.
I'm not sure how much the GFS model above takes into account the Gulf SSTs, a question that could have big implications for the upcoming dewpoints situation. We'll just have to watch soundings near the Gulf coast to verify if the air is getting 'juiced up'.
Depending on the position of the upper trough and track of the attendant low, I do think that some lightning from the Plains through parts of the Midwest is likely on Sunday and Monday - as at least meager ingredients will be there (dynamics and at least limited moisture). Temperatures in the warm sector of this system are not shown getting much above the 50s outside of the Plains and north of the I-40 latitudes, however. That's a little disappointing for those north of an I-70 latitude wanting a day to get outside and do something. If the trough slows down a little, allowing for a longer period of southerly flow, temps/moisture/storm chances will improve everywhere.
The lone area that may end up having the best shot for tornadoes/supercells with this system is extreme south Texas into northeastern Mexico. This region is usually where spring tornado season begins first, as it is the first region to see a dryline with the juxtaposition of deep moisture and good upper support.
March storm systems like this have a downside - that is, their 'cold' side. This time of year, these systems usually feature not only thunderstorms and warmth on their leading end, but a winter storm and cold surge on their trailing side. As this trough passes and cold northwest flow resumes, potential for widespread winter weather also returns. However, the higher sun angle will be increasingly working against the longevity and depth of cold spells/snow cover from this point on.
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