Perfect summer of 2015? Rain and severe risk tomorrow
Perfect summer?
One thing you learn quickly as a practicing broadcast meteorologist is all weather is subjective. One person's weather trash is another's meteorological treasure.
With that caveat, this may be the "best" summer on record for many Minnesotans. An abundance of warm sunny days. Just the right amount of well spaced but timely rainfall. Yes, the weather quality of life is high in the summer of 2015.
Case in point? Our Summer Glory Index ranking in the top 3 at summer's halfway point.
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Favorable weather trends since mid-July have kept the SGI number high.
Another interesting aspect of this summer's weather has been the persistence of well spaced but timely rainfall events. Check out the interval between soaking rains during July at Minneapolis-St. Paul International Airport for the Twin Cities climate data below.
Our latest weather winning streak comes to and end tomorrow across Minnesota.
8th consecutive day today without measurable rain at MSP Airport
.87 inch Global Forecast System rainfall output for MSP Thursday night into Friday morning
Slight severe risk for southwest Minnesota Thursday
Marginal severe risk for Twin Cities Thursday evening
Air mass destabilization
One more dry day across Minnesota. By tonight, the next low pressure wave gathers to the west. The air mass destabilizes as dew points climb on warm advection and moisture transport from southerly flow.
Translation? The low sucks up Gulf moisture into Minnesota that aids thunderstorm development Thursday.
The likely scenario Thursday includes a cluster of storms developing over eastern South Dakota and rumbling east into southwest Minnesota. Another mesoscale convective system complex will likely produce a few severe storms capable of damaging winds, hail and even a few tornadoes.
The severe risk is highest in southwest Minnesota and storms will likely decrease in intensity by the time they reach the metro Thursday night. But this has been the summer of nocturnal intensity for the Twin Cities so all bets are off.
I get nervous when the NOAA's Storm Prediction Center uses words like "congealing" in the convective outlook.
LIFT ASSOCIATED WITH THE LOW AND WARM FRONT SHOULD BE SUFFICIENT FOR ADDITIONAL STORM DEVELOPMENT IN THE PRESENCE OF ADEQUATE SHEAR FOR STORM ORGANIZATION.
MOST SUPPORTIVE JUXTAPOSITION OF CAPE/SHEAR AND DYNAMIC FORCING WITHIN LEFT EXIT REGION OF MIDLEVEL JET IS FORECAST TO OCCUR DURING LATE AFTERNOON AND EVENING FROM ERN SD INTO SWRN MN AND ADJACENT AREAS OF NEB/IA.
A FEW SUPERCELLS APPEAR POSSIBLE IN THESE AREAS...PERHAPS CONGEALING INTO A FORWARD-PROPAGATING MCS WITH TIME. HAIL AND SOME TORNADO POTENTIAL MAY EVOLVE FROM INITIALLY DISCRETE CONVECTION BEFORE ONSET OF POSSIBLY MORE LINEAR MODE RESULTS IN AN INCREASED CHANCE FOR DAMAGING WINDS.
LACK OF GREATER DESTABILIZATION WITH EWD EXTENT SUGGESTS OVERALL SEVERE WIND RISK MAY BE PRIMARILY CONFINED TO LATE AFTERNOON AND EVENING.
Here's a similar takeaway from the Twin Cities NWS forecast discussion.
CAMS...PARTICULARLY THE WRF-ARW...ARE SHOWING THE POTENTIAL FOR A LINE OF STORMS TO FORM NEAR THE SD/MN LINE DURING THE LATE AFTERNOON AND PROPAGATING EAST DURING THE EVENING. MAIN THREAT WOULD BE WIND DAMAGE...
BUT STRONG LOW LEVEL SHEAR COULD BRING SOME CHANCE OF QLCS TORNADOES AS WELL. THE SEVERE THREAT PROBABLY WON/T LAST TOO LONG INTO THURSDAY NIGHT WITH INCREASING STABILITY TO THE EAST. HOWEVER...
WIDESPREAD RAIN ALONG THE FRONT SHOULD BRING RAINFALL TOTALS TO NEAR 3/4 INCH JUST ABOUT AREA WIDE THROUGH EARLY FRIDAY MORNING.
By the way, the Twin Cities mention of "QLCS tornadoes" above refers to Quasi-Linear Convective System tornadoes. The translation is "Gustnadoes" that form along the leading edge of gust fronts often associated with bow echoes. Think the midnight tornado in Watertown on July 18.
Drier weekend?
After Friday morning, the European Centre for Medium-Range Weather Forecasts model continues the notion of a dry weekend while NOAA's Global Forecast System keeps scattered storms in the Sunday forecast. Here's the European version of events.
