Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
000
ACUS02 KWNS 031726
SWODY2
SPC AC 031725

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1225 PM CDT THU SEP 03 2015

VALID 041200Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF ERN ND AND
WRN MN...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLGT ACROSS
PARTS OF THE NRN HIGH PLAINS AND UPPER MIDWEST...

...SUMMARY...
ISOLATED TO WIDELY SCATTERED SEVERE THUNDERSTORMS WILL BE POSSIBLE
FRIDAY AFTERNOON AND EVENING ACROSS PORTIONS OF EASTERN NORTH DAKOTA
AND WESTERN MINNESOTA.

...SYNOPSIS...

A DEEP TROUGH OVER THE NWRN CONUS WILL UNDERGO SLIGHT AMPLIFICATION
AS A MIDLEVEL SPEED MAX ON ITS WRN FLANK ADVANCES THROUGH FLOW ON
THE SRN RIM OF A CYCLONE ACCOMPANYING THE TROUGH. DOWNSTREAM...A
BROAD AREA OF ANTICYCLONIC FLOW WILL EXTEND FROM THE S-CNTRL CONUS
TO THE GREAT LAKES AND NORTHEAST...WITHIN WHICH SMALL
CYCLONIC-VORTICITY PERTURBATIONS WILL BE EMBEDDED. THE INTERVENING
SWLY FLOW BETWEEN THE DEEPER-TROUGHING AND ERN-RIDGING PATTERNS WILL
ENCOURAGE THE NEWD PROGRESSION OF A SHORTWAVE IMPULSE CURRENTLY
MOVING NEWD OVER THE CNTRL ROCKIES VICINITY...WHICH IS PRESENTLY
SUPPORTING SPORADIC LIGHTNING OVER PARTS OF CO. THIS IMPULSE IS
PROJECTED TO BE MOVING NEWD ACROSS PORTIONS OF THE NRN PLAINS/RED
RIVER VALLEY OF THE NORTH THROUGH THE D2/FRI PERIOD.

AT THE SFC...A FRONT WILL BE DRAPED FROM SRN MB SWWD THROUGH ND TO
THE VICINITY OF THE BIG HORN MOUNTAINS...WITH A LEE TROUGH EXTENDING
SWD OVER THE HIGH PLAINS FROM ITS INTERSECTION WITH THE FRONT OVER
THE NRN HIGH PLAINS. THESE FEATURES WILL MOVE LITTLE THROUGH THE
PERIOD IN ASSOCIATION WITH THE PSEUDO-BLOCKING NATURE OF
SYNOPTIC-SCALE PERTURBATIONS IN THE MID/UPPER LEVELS.

...PORTIONS OF ERN ND/WRN MN...

MODEST LARGE-SCALE ASCENT OFFERED BY THE SHORTWAVE IMPULSE...WAA
ALONG AN IMPULSE-PRECEDING 20-30-KT LLJ...AND FRONTAL CIRCULATIONS
ARE EXPECTED TO SUPPORT AN INCREASE IN TSTM COVERAGE THROUGH THE
AFTERNOON. TSTMS MAY BE ONGOING AHEAD OF THE IMPULSE EARLY IN THE
PERIOD ACROSS SD AND SPREAD NEWD WHILE INTENSIFYING -- PERHAPS BEING
PRECEDED BY ADDITIONAL TSTM DEVELOPMENT IN THE MODEST-ASCENT/
DIURNAL-HEATING REGIME. WITH OBSERVATIONS INDICATING RELATIVELY RICH
NEAR-SFC MOISTURE ALREADY IN PLACE ACROSS THE SLGT -- DEWPOINTS IN
THE UPPER 60S AND LOWER 70S -- THERE SHOULD BE OPPORTUNITIES FOR
INSOLATION TO SUPPORT MODERATE TO LOCALLY STRONG DESTABILIZATION.
UPSTREAM 12Z RAOBS FROM THE CNTRL ROCKIES TO THE ADJACENT HIGH
PLAINS /E.G. RIW...RAP...AND BIS/ ALL SAMPLED A STOUT EML REFLECTED
BY 8.5-9.0-C/KM H7-H5 LAPSE RATES. THIS EML WILL BE ADVECTED OVER
THE RICH PBL MOISTURE TO FACILITATE MLCAPE AROUND 1500-3000
J/KG...YIELDING THE POTENTIAL FOR INTENSE UPDRAFTS. GIVEN THE
AUGMENTATION TO THE MID-LEVEL HEIGHT GRADIENT OFFERED BY THE
MIGRATORY IMPULSE...H5 FLOW AROUND 25-40 KT WILL SUPPORT SUFFICIENT
DEEP SHEAR FOR ORGANIZED CONVECTIVE STRUCTURES CAPABLE OF ISOLATED
TO WIDELY SCATTERED LARGE HAIL AND DMGG WIND GUSTS INTO THE EVENING
HOURS ACROSS THE SLGT. SVR COVERAGE SHOULD BE LESS IN AREAS
SURROUNDING THE SLGT.

...OTHER AREAS OF STRONG-THUNDERSTORM POTENTIAL...

STRONG TSTMS WILL ALSO BE POSSIBLE IN THE FOLLOWING REGIMES:

/1/ THE OVERLAP OF SUBTLE ASCENT ON THE SRN PERIPHERY OF A DECAYING
LOWER-GREAT-LAKES-AREA MIDLEVEL PERTURBATION AND STEEPER LOW-LEVEL
LAPSE RATES MAY SUPPORT TSTMS WITH AN ISOLATED STRONG WIND GUST OR
TWO IN OHIO AND INDIANA. POOR MID-LEVEL LAPSE RATES AND WEAK
VERTICAL SHEAR WILL MITIGATE THE SVR RISK.

/2/ ENHANCED MID-LEVEL FLOW ON THE SERN SIDE OF DEEPER TROUGHING MAY
ENCOURAGE CONVECTIVE MOMENTUM TRANSPORT AND THE RISK FOR A FEW
STRONG WIND GUSTS WITH CONVECTION ACROSS PARTS OF THE GREAT BASIN.
WEAK INSTABILITY WILL MITIGATE THE SVR RISK.

/3/ WATER-LOADING PROCESSES WILL BOLSTER DOWNDRAFT POTENTIAL WITH
SEA-BREEZE-CIRCULATION/REMNANT-OUTFLOW-BOUNDARY-ENCOURAGED TSTMS
DIURNALLY DEVELOPING OVER FL AND SRN GA...THOUGH WEAK DEEP SHEAR
WILL MINIMIZE THE SVR RISK.

..COHEN.. 09/03/2015



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.