Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 181226
SWODY1
SPC AC 181224

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0724 AM CDT THU SEP 18 2014

VALID 181300Z - 191200Z

...NO SVR TSTM AREAS FORECAST...

...SUMMARY...
A FEW SEVERE STORMS ARE EXPECTED TO DEVELOP LATER TODAY FROM
PORTIONS OF THE OZARK PLATEAU TO RED RIVER VALLEY...AS WELL OVER
PARTS OF THE GREAT BASIN INTO NORTHERN ROCKIES. ELSEWHERE...ISOLATED
STRONG TO MARGINALLY SEVERE STORMS ARE POSSIBLE ALONG THE SOUTHEAST
ATLANTIC COAST. GUSTY WINDS AND HAIL ARE THE PRIMARY THREATS.

...SYNOPSIS...

THE LARGE-SCALE PATTERN WILL UNDERGO DE-AMPLIFICATION THIS
PERIOD...LARGELY DUE TO THE FLATTENING OF THE CNTRL U.S. RIDGE BY A
STRENGTHENING ZONAL FLOW REGIME BECOMING ESTABLISHED FROM THE NERN
PACIFIC TO S-CNTRL CANADA. TROUGHS WILL CONTINUE TO BRACKET THE
DAMPENING RIDGE...ONE OVER THE WRN STATES AND OTHER SITUATED
GENERALLY E OF THE MS VALLEY.

AT THE SURFACE...A WEAK COLD FRONT WILL DRIFT SLOWLY SWD THROUGH THE
SERN U.S. WHILE THE NWRN EXTENSION OF THIS BOUNDARY PIVOTS EWD
THROUGH THE NRN AND CNTRL PLAINS IN TANDEM WITH A MIGRATORY SURFACE
LOW TRACKING ACROSS S-CNTRL CANADA. TRAILING SWWD FROM THIS LOW
PRESSURE...A COLD FRONT WILL MOVE THROUGH THE NRN HIGH PLAINS.

...INTERMOUNTAIN WEST THIS AFTERNOON/EVENING...

DESPITE BECOMING INCREASINGLY CUT OFF FROM THE PRIMARY BELT OF POLAR
WESTERLIES DEVELOPING ACROSS WRN CANADA...A BELT OF 35-50 KT
MID-LEVEL FLOW AND WEAK HEIGHT FALLS WILL ATTEND THE WRN U.S. TROUGH
AS IT SLOWLY EDGES SEWD. THIS HIGHER-MOMENTUM FLOW WILL ALIGN WITH A
CORRIDOR OF STEEP LOW TO MID-LEVEL LAPSE RATES AND RESULTANT SBCAPE
OF 500-1000 J/KG RESIDING AHEAD OF A WEAK SURFACE FRONT/TROUGH.
CONVERGENCE ALONG THIS BOUNDARY COUPLED WITH DEEPENING OROGRAPHIC
CIRCULATIONS ARE EXPECTED TO FOSTER WIDELY SCATTERED TSTMS BY
AFTERNOON...A FEW OF WHICH COULD BE STRONG TO MARGINALLY SEVERE AND
CAPABLE OF LOCALLY STRONG WIND GUSTS AND/OR HAIL.

...SERN KS INTO THE RED RIVER VALLEY/ARKLATEX THIS
AFTERNOON/EVENING...

A SWWD-PROPAGATING MCS IS ONGOING AS OF 12Z ACROSS PORTIONS OF SERN
KS AND NERN OK...AIDED BY WEAK WAA/ISENTROPIC ASCENT ALONG A WSWLY
LLJ AND DCVA ASSOCIATED WITH A WEAK MID-LEVEL PERTURBATION
PROGRESSING SEWD THROUGH THE LOWER MO VALLEY. THOUGH A TEMPORARY
DECREASE IN STORM COVERAGE MAY OCCUR THROUGH MID MORNING OWING TO
THE DIURNAL WEAKENING OF THE LLJ...AN UPTICK IN STORM COVERAGE AND
INTENSITY IS ANTICIPATED BY AFTERNOON ALONG THE RELATED COLD POOL AS
IT INTERACTS WITH A MOIST AND MODERATELY UNSTABLE AIR MASS WHERE
MLCAPE COULD APPROACH 1500-2500 J/KG.

EFFECTIVE BULK SHEAR MAGNITUDES ARE FORECAST TO REMAIN GENERALLY
BELOW 30 KT WHICH SHOULD LIMIT THE POTENTIAL FOR HIGHER-ORDER STORM
MODES AND A RISK FOR AN ORGANIZED SEVERE WEATHER EPISODE.
NONETHELESS...THE DEGREE OF INSTABILITY WILL BE SUPPORTIVE OF STRONG
STORM CLUSTERS OR WEAKLY BOWING LINE SEGMENTS WITH A THREAT FOR
ISOLATED DAMAGING WIND GUSTS AND HAIL SPREADING SWD THROUGH THE RED
RIVER VALLEY LATER TODAY.

...SERN ATLANTIC COAST THIS AFTERNOON...

LOW-LEVEL CONVERGENCE/UPLIFT ALONG THE SYNOPTIC COLD FRONT AND
DEVELOPING SEA BREEZE BOUNDARIES WILL PROMOTE THE DEVELOPMENT OF
WIDELY SCATTERED AFTERNOON TSTMS AMIDST A MOIST AND AT LEAST
MODESTLY UNSTABLE AIR MASS. STEEP LOW-LEVEL LAPSE RATES AND 25-30 KT
OF DEEP-LAYER SHEAR MAY SUPPORT A FEW VIGOROUS STORMS WITH AN
ATTENDANT RISK FOR MAINLY GUSTY WINDS.

..MEAD/BOTHWELL.. 09/18/2014




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