SWODY1
SPC AC 190058
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0758 PM CDT SAT AUG 18 2007
VALID 190100Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS THIS EVE ACROSS PARTS OF THE
NRN INTERMOUNTAIN REGION INTO MONTANA....
..THERE IS A SLGT RISK OF SVR TSTMS THIS EVENING...PERHAPS INTO THE
OVERNIGHT HOURS...ACROSS PARTS OF THE N CNTRL PLAINS INTO UPR MS
VLY....
..NRN INTERMOUNTAIN REGION/ROCKIES/PLAINS...
A LARGE SEASONABLY COLD MID/UPPER LOW AND ASSOCIATED TROUGH CONTINUE
TO PROGRESS INLAND...INTO THE NORTHWESTERN STATES. AND...
DESTABILIZATION/STRENGTHENING DEEP LAYER SHEAR...ALONG FRAGMENTED
LEADING EDGE OF 500 MB COOLING...APPEAR TO BE PROVIDING THE SUPPORT
FOR A COUPLE OF BROKEN LINES OF STRONG/SEVERE STORMS. ONE OF THESE
LINES IS STILL INTENSIFYING IN AN ENVIRONMENT WITH MOST UNSTABLE
CAPE IN EXCESS OF 1000 J/KG...EAST OF THE HIGHER TERRAIN...ACROSS
EAST CENTRAL/SOUTHEAST MONTANA. THE OTHER LINE HAS SHOWN RECENT
SIGNS OF WEAKENING...FROM THE MOUNTAINS OF SOUTHWESTERN MONTANA INTO
NORTHERN UTAH...BUT MAY STILL BE CAPABLE OF PRODUCING LOCALLY
DAMAGING WIND GUSTS/HAIL ANOTHER COUPLE OF HOURS. THE BULK OF THIS
THUNDERSTORM ACTIVITY PROBABLY WILL WEAKEN/DIMINISH BY 03/04Z...AS
THE BOUNDARY LAYER COOLS WITH LOSS OF DAYTIME HEATING.
HOWEVER...IN A MORE MOIST REGIME ASSOCIATED WITH LOW-LEVEL EASTERLY
FLOW TO THE NORTH OF SURFACE FRONTAL ZONE ACROSS PARTS OF NORTH
CENTRAL/NORTHEAST MONTANA...NEAR THE INTERNATIONAL BORDER
..POTENTIAL STILL EXISTS FOR INCREASING CONVECTIVE DEVELOPMENT
DURING THE 03-06Z TIME FRAME. LATEST RUC GUIDANCE INDICATES MIXED
LAYER CAPE IS IN EXCESS OF 2000 J/KG ACROSS THIS REGION.
AND...STRENGTHENING LOW-LEVEL WARM ADVECTION/DIVERGENT UPPER FLOW
..ASSOCIATED WITH A WEAK IMPULSE LIFTING OUT OF UPSTREAM TROUGH
INTO DOWNSTREAM RIDGE...MAY PROVIDE SUFFICIENT LIFT FOR THE
DEVELOPMENT OF A STORM CLUSTER CAPABLE OF PRODUCING A FEW STRONG
WIND GUSTS AND SOME LARGE HAIL.
..N CNTRL PLAINS INTO THE UPPER MS VLY...
A WEAK IMPULSE NEAR 700 MB CONTINUES TO PROGRESS EASTWARD THROUGH
BROADER SCALE UPPER RIDGE ACROSS THE NORTHERN PLAINS. HOWEVER...A
RATHER WARM LOWER/MID TROPOSPHERIC AIR MASS ACCOMPANIES THIS FEATURE
AND IS CAPPING MOIST BOUNDARY LAYER NEAR WARM FRONTAL ZONE ACROSS
MUCH OF THE NORTH CENTRAL PLAINS. POTENTIAL FOR WIDESPREAD BOUNDARY
LAYER BASED CONVECTIVE DEVELOPMENT NEAR THE FRONT NOW APPEARS
REMOTE. BUT...STORMS ARE INCREASING AGAIN IN A ZONE OF STRONG WARM
ADVECTION TO THE NORTH OF THE SURFACE FRONT...AND MODERATELY STRONG
CAPE/WEAK TO MODERATE SHEAR MAY BE SUPPORTIVE OF HAIL...PERHAPS
GUSTY WIND...POTENTIAL THROUGH AT LEAST THE 03-06Z TIME FRAME.
.KERR.. 08/19/2007
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