Environment
SPC SWODY1 (early morning discussion)
...MS/OH VALLEY...
LATEST MODEL GUIDANCE SUGGEST SHORTWAVE TROUGH OVER CENTRAL ROCKIES WILL SHIFT EWD ACROSS
THE CENTRAL PLAINS EARLY IN THE PERIOD...WITH BAND OF MODERATELY STRONG MID LEVEL FLOW
FORECAST TO EXTEND FROM SRN PLAINS...NEWD INTO THE GREAT LAKES REGION. EARLY THIS MORNING
CONSIDERABLE AMOUNT OF CONVECTION HAS DEVELOPED AHEAD OF THIS FEATURE FROM NWRN TX INTO
GREAT LAKES REGION. THIS ACTIVITY IS SPREADING EWD AND WILL LIKELY BE ONGOING...AT TIMES
SEVERE...AT BEGINNING OF PERIOD. THE MAIN CONCERN WITH THIS CONVECTION IS STABILIZING
EFFECTS AND EWD PROGRESSION AHEAD OF UPSTREAM FEATURE. IT APPEARS SQUALL LINE WILL EXTEND
FROM PORTIONS OF THE SRN GREAT LAKES...SWWD ACROSS IL/MO...INTO NERN OK WHERE STRONG CAP
WILL LIKELY PREVENT SWWD DEVELOPMENT ACROSS THE SRN PLAINS. 17/00Z SOUNDINGS THIS EVENING
SUGGESTED FAIRLY STEEP MID LEVEL LAPSE RATES EXTENDING AS FAR EAST AS IL AND
AR...SUPPORTING THE IDEA THAT SQUALL LINE WILL CONTINUE THROUGH EARLY MORNING.
BY AFTERNOON THE MAIN CONCERN FOR PORTIONS OF THE OH VALLEY IS POST SQUALL LINE
DESTABILIZATION...AND LACK OF SIGNIFICANT DEEP LAYER SHEAR. APPROACHING UPPER TROUGH AND
LOW LEVEL CONVERGENCE ALONG COLD FRONT SHOULD PROVIDE SUFFICIENT LIFT FOR SCATTERED
THUNDERSTORMS. ISOLATED SEVERE THUNDERSTORMS ARE LIKELY WITH LARGE HAIL AND STRONG WINDS
PRIMARY THREAT.
Maps from 1200 UTC:
250 mb
500 mb
700 mb (typical analysis)
Let's look at the 700 mb in a slightly different way...
The dry air was being advected into the storm system.
850 mb
The key to the forecast was the dry air at 700 mb which was not highlighted on the initial analysis.
