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.
SPC AC 181623
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1123 AM CDT THU JUN 18 2015
VALID 181630Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON INTO
TONIGHT ACROSS PARTS OF THE NORTHERN ROCKIES AND ADJACENT NORTHERN
HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON ACROSS PARTS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS PARTS OF THE LOWER
GREAT LAKES AND UPPER OHIO VALLEY INTO THE MID ATLANTIC COAST
REGION...
...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
ROCKIES AND PLAINS...THE OZARK PLATEAU AND MIDDLE MISSISSIPPI
VALLEY...THE LOWER OHIO AND TENNESSEE VALLEYS AND APPALACHIANS...
...SUMMARY...
A FEW SEVERE THUNDERSTORMS ARE EXPECTED LATE THIS AFTERNOON AND
EVENING ACROSS PARTS OF THE NORTHERN ROCKIES AND ADJACENT HIGH
PLAINS...AND PORTIONS OF THE CENTRAL INTO SOUTHERN HIGH PLAINS.
THUNDERSTORM ACTIVITY CAPABLE OF GENERATING LOCALLY DAMAGING WIND
GUSTS AND SOME HAIL IS ALSO POSSIBLE ACROSS MUCH OF THE LOWER GREAT
LAKES REGION...AND THE UPPER OHIO VALLEY INTO THE MID ATLANTIC
COAST.
...SYNOPSIS...
MID/UPPER SUBTROPICAL RIDGING WILL REMAIN PROMINENT ACROSS MUCH OF
THE CENTRAL AND SOUTHERN TIER OF THE U.S. THROUGH THIS PERIOD.
WITHIN THE SOUTHERN BRANCH OF SPLIT MID-LATITUDE WESTERLIES...A
SIGNIFICANT CLOSED LOW IS EXPECTED TO CONTINUE GRADUALLY MIGRATING
INLAND ACROSS THE BRITISH COLUMBIA/PACIFIC NORTHWEST COAST.
DOWNSTREAM SHORT WAVE RIDGING ACROSS THE NORTHERN ROCKIES/PLAINS MAY
BE SUPPRESSED BY THE EASTWARD PROGRESSION OF A SMALLER SCALE
IMPULSE...AND THE SOUTHEASTWARD PROGRESSION OF ANOTHER IN A SERIES
OF NORTHERN STREAM SHORT WAVE TROUGHS DIGGING THROUGH THE CENTRAL
CANADIAN PROVINCES. A MUCH MORE VIGOROUS NORTHERN STREAM
IMPULSE...NOW OVER HUDSON/JAMES BAYS AND ONTARIO...IS FORECAST TO
TURN EAST NORTHEASTWARD ACROSS QUEBEC. AT THE SAME TIME...IN LOWER
LATITUDES...THE REMNANTS OF TROPICAL STORM BILL LIKELY WILL CONTINUE
SLOWLY AROUND THE NORTHWESTERN PERIPHERY OF THE SOUTHWESTERN
ATLANTIC SUBTROPICAL HIGH CENTER...FROM THE LOWER SOUTH CENTRAL
PLAINS INTO THE OZARK PLATEAU.
A COLD FRONT ASSOCIATED WITH THE EASTERN CANADIAN SHORT WAVE TROUGH
HAS ALREADY ADVANCED THROUGH PORTIONS OF THE UPPER GREAT LAKES AND
NORTHERN PLAINS...AND IS EXPECTED TO CONTINUE SOUTHEASTWARD TODAY.
THIS WILL REINFORCE A STALLED SURFACE FRONTAL ZONE NOW ARCING FROM
THE MID ATLANTIC COAST INTO THE SOUTHERN GREAT LAKES/OHIO VALLEY
REGION. THIS FRONT EXTENDS INTO THE MIDDLE MISSISSIPPI VALLEY AND
CENTRAL PLAINS...BUT IS BECOMING INCREASING OBSCURED DUE TO THE
INFLUENCE OF PRECIPITATION ASSOCIATED WITH THE REMNANTS OF
BILL...AND CONVECTIVE OUTFLOW FROM AN OVERNIGHT MCS. THE CONVECTIVE
OUTFLOW IS ADVANCING STEADILY SOUTHWARD THROUGH THE CENTRAL HIGH
PLAINS...AND MAY CONTINUE TO DO SO AS FORCING ALONG ITS LEADING EDGE
SUPPORTS RENEWED CONVECTION.
...NORTHERN ROCKIES/ADJACENT HIGH PLAINS....
BOUNDARY LAYER MOISTENING ON EASTERLY POST-FRONTAL LOW-LEVEL FLOW
PROBABLY WILL CONTRIBUTE TO CAPE ON THE ORDER OF 1000-2000
J/KG...WITH DAYTIME HEATING BENEATH RATHER STEEP MID-LEVEL LAPSE
RATES. IN THE PRESENCE OF STRONG DEEP LAYER SHEAR BENEATH WESTERLY
500 MB FLOW STRENGTHENING TO 40-50+ KT...THE ENVIRONMENT IS EXPECTED
TO BECOME CONDUCIVE TO ORGANIZED SEVERE STORM DEVELOPMENT.
SUPERCELLS MAY INITIATE OVER THE MOUNTAINS OF SOUTHWEST/CENTRAL
MONTANA...BEFORE CONVECTION CONSOLIDATES INTO AN ORGANIZING
MESOSCALE CONVECTIVE SYSTEM ACROSS SOUTH CENTRAL INTO SOUTHEASTERN
MONTANA THIS EVENING. ACTIVITY MAY REMAIN STRONG ENOUGH TO MAINTAIN
THE RISK FOR SEVERE WEATHER ACROSS PARTS OF SOUTHWESTERN NORTH
DAKOTA/WESTERN SOUTH DAKOTA AND NORTHEAST WYOMING OVERNIGHT.
...CENTRAL/SOUTHERN HIGH PLAINS...
THE TENDENCY FOR WARMING MID-LEVEL TEMPERATURES COULD ACT TO
SUPPRESS RENEWED CONVECTIVE DEVELOPMENT...WITH MID/UPPER SUPPORT FOR
CONVECTIVE DEVELOPMENT UNCLEAR. HOWEVER...FORCING ON THE SOUTH
SOUTHWESTWARD SURGING PORTION OF THE CONVECTIVE OUTFLOW MAY BE
SUFFICIENT TO SUPPORT CONVECTIVE RE-INTENSIFICATION ACROSS PARTS OF
SOUTHWEST KANSAS INTO THE TEXAS/OKLAHOMA PANHANDLE REGION...AS IT
ENCOUNTERS A RATHER STRONGLY DESTABILIZING ENVIRONMENT. MID-LEVEL
LAPSE RATES ARE FAIRLY STEEP...AND WITH CONTINUED STEEPENING OF
LOW-LEVEL LAPSE RATES...SEVERE HAIL AND WIND GUSTS PROBABLY WILL
ACCOMPANY STRONGEST STORMS. WEAK TO PERHAPS MODEST SHEAR...DUE TO
PRONOUNCED VEERING WITH HEIGHT OF LOW TO MID-LEVEL WIND
FIELDS...COULD ENHANCE LATE AFTERNOON AND EARLY EVENING ACTIVITY.
...LOWER GREAT LAKES/UPPER OHIO VALLEY INTO MID ATLANTIC...
THE LATEST CONVECTION ALLOWING MODEL OUTPUT DOES NOT ADD ANY MORE
CLARITY CONCERNING POTENTIAL CONVECTIVE EVOLUTION AND THE EXTENT OF
THE SEVERE WEATHER RISK TODAY. IT CURRENTLY SEEMS THAT THE RISK FOR
MAINLY POTENTIALLY DAMAGING WIND GUSTS MAY REMAIN RATHER LOCALIZED
WITH STRONGEST CONVECTION. HOWEVER...CONSIDERABLE THUNDERSTORM
DEVELOPMENT DOES APPEAR PROBABLE AS THE PRE-FRONTAL MOIST BOUNDARY
LAYER BECOMES MODERATELY UNSTABLE THIS AFTERNOON. AND DOWNWARD
MIXING OF 30+ KT LOWER/MID TROPOSPHERIC FLOW MAY CONTRIBUTE TO THE
POTENTIAL FOR PEAK CONVECTIVE GUSTS AT LEAST APPROACHING...IF NOT
BRIEFLY EXCEEDING...SEVERE CRITERIA.
..KERR/PICCA.. 06/18/2015
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