Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Tucson, AZ...Casas Adobes, AZ...Catalina Foothills, AZ...Rapid City, SD...Bismarck, ND...
SPC AC 040527
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 AM CDT FRI JUL 04 2014
VALID 041200Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF ERN ND INTO NW MN
THIS AFTERNOON AND EVENING...
...SUMMARY...
SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING ACROSS
PARTS OF NORTHEAST NORTH DAKOTA INTO NORTHWEST MINNESOTA. STRONG
WINDS AND HAIL WILL BE THE MAIN THREAT...BUT A TORNADO OR TWO ALSO
IS POSSIBLE. ISOLATED TO WIDELY SCATTERED THUNDERSTORMS ARE EXPECTED
SOUTHWARD ACROSS THE CENTRAL PLAINS...WHERE A FEW STRONG WIND GUSTS
AND HAIL WILL BE POSSIBLE DURING THE AFTERNOON AND EVENING.
ADDITIONAL STRONG WIND GUSTS WILL BE POSSIBLE ACROSS PARTS OF
SOUTHERN ARIZONA WITH AFTERNOON STORMS.
...SYNOPSIS...
THE UPPER TROUGH OVER THE GREAT LAKES AND APPALACHIANS WILL SHIFT
E/NE TODAY. HURRICANE ARTHUR SHOULD START TO BECOME ABSORBED WITHIN
THE TROUGH BY THE END OF THE PERIOD...WITH IMPACTS MOSTLY REMAINING
OFFSHORE THE EASTERN SEABOARD. SFC HIGH PRESSURE BUILDING IN THE
WAKE OF THE EASTERN TROUGH WILL LEAD TO WIDESPREAD STABLE CONDITIONS
EAST OF THE MISSISSIPPI RIVER.
ACROSS THE WESTERN AND CENTRAL U.S...A BROAD UPPER RIDGE WITH
QUASI-ZONAL FLOW WILL OVERSPREAD THE NRN/CNTRL ROCKIES INTO THE
NRN/CNTRL PLAINS. WEAK SHORTWAVE IMPULSES WILL TRACK EWD THROUGH THE
RIDGE INTO THE PLAINS...AIDING IN THUNDERSTORM DEVELOPMENT IN A
MOIST AND UNSTABLE AIRMASS DURING THE AFTERNOON AND EVENING FROM THE
CNTRL/NRN HIGH PLAINS EASTWARD INTO THE NRN/CNTRL PLAINS. ADDITIONAL
THUNDERSTORMS ARE EXPECTED ACROSS PARTS OF THE ARIZONA DESERTS IN
INCREASING BOUNDARY LAYER MOISTURE ON ELY LOW LEVEL FLOW.
...NRN/CNTRL PLAINS...
SOUTHERLY LOW LEVEL FLOW WILL TRANSPORT LOW TO MID 60S DEWPOINTS
NORTHWARD ACROSS THE PLAINS TO THE EAST OF A SFC TROUGH SITUATED N-S
FROM THE WRN DAKOTAS INTO WRN KS BY LATE AFTERNOON. STRONG SFC
HEATING OF THIS MOIST AIRMASS BENEATH STEEP LAPSE RATES WILL LEAD TO
MODERATE INSTABILITY THIS AFTERNOON. DEEP LAYER SHEAR WILL BE
ENHANCED OVER ERN ND INTO NW MN WHERE A SHORTWAVE IMPULSE WILL
ROTATE THROUGH UPPER RIDGE...AND CLOSER PROXIMITY TO THE SFC LOW
OVER THE S-CNTRL CANADIAN PRAIRIE WILL RESULT IN BETTER LOW LEVEL
CONVERGENCE/BACKED SFC WINDS. 25-35 KT DEEP LAYER SHEAR SHOULD ALLOW
FOR ORGANIZED STORM CLUSTERS CAPABLE OF LARGE HAIL AND STRONG WIND
GUSTS. GIVEN BACKED LOW LEVEL FLOW AND MEAN MIXING RATIOS
APPROACHING 13 G/KG...A BRIEF TORNADO OR TWO MAY BE POSSIBLE AS
WELL.
FARTHER SOUTH AND WEST...THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER
THE HIGHER TERRAIN OF THE NRN/CNTRL HIGH PLAINS AND TRACK EWD IN
CONJUNCTION WITH A SHORTWAVE IMPULSE MOVING OUT OF THE ROCKIES AND
INTO THE CENTRAL PLAINS. DEEP LAYER SHEAR WILL BE WEAKER...GENERALLY
LESS THAN 25 KT...THAN THAT TO THE NORTH...AND WARMING 850-700 MB
TEMPS MAY POSE CAPPING ISSUES. FOR THIS REASON...STORM
LONGEVITY/ORGANIZATION AND COVERAGE ARE ALL IN QUESTION.
HOWEVER...STEEP LAPSE RATES AND STRONG INSTABILITY WILL BE
PRESENT...SO AT LEAST AN ISOLATED/CONDITIONAL SEVERE THREAT WILL BE
PRESENT INTO THE EVENING HOURS. SHOULD STORMS DEVELOP AND BE
MAINTAINED INTO THE NIGHTTIME HOURS OVER PARTS OF NEB/KS...SOME
UPSCALE GROWTH COULD OCCUR AS THE LLJ INCREASES. ANY OVERNIGHT
STORMS SHOULD BE ELEVATED BUT WOULD POSE A HAIL THREAT.
...SE AZ...
BOUNDARY LAYER MOISTURE WILL INCREASE OVER THE SOUTHWEST DESERTS ON
ELY LOW TO MIDLEVEL FLOW AROUND LOW/MIDLEVEL ANTICYCLONE. STRONG SFC
HEATING BENEATH MODEST MIDLEVEL LAPSE RATES /6.5-7.0 DEG C PER KM/
WILL RESULT IN WEAK INSTABILITY /GENERALLY LESS THAN 1000-1500 J PER
KG/ BY AFTERNOON AND WIDELY SCATTERED THUNDERSTORMS ARE EXPECTED.
WEAK DEEP LAYER SHEAR WILL LIMIT OVERALL ORGANIZATION/LONGEVITY OF
STORMS...BUT MARGINALLY SEVERE HAIL AND A FEW STRONG WIND GUSTS WILL
BE POSSIBLE.
..LEITMAN.. 07/04/2014
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