Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 011256
SWODY1
SPC AC 011254

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0654 AM CST SUN FEB 01 2015

VALID 011300Z - 021200Z

...THERE IS A MRGL RISK OF SVR TSTMS FROM PARTS OF SERN TX EWD TO
PARTS OF WRN AL...

...SUMMARY...
A FEW MARGINALLY SEVERE THUNDERSTORMS MAY OCCUR THIS AFTERNOON AND
EARLY EVENING FROM PORTIONS OF SOUTHEAST TEXAS TO THE LOWER
MISSISSIPPI VALLEY REGION.

...SYNOPSIS...
MORNING WATER VAPOR IMAGERY INDICATES A MIDLEVEL SHORTWAVE TROUGH
AMPLIFYING OVER THE CNTRL PLAINS. ASSOCIATED SFC LOW
PRESSURE...ANALYZED ALONG THE KS/MO BORDER...WILL DEVELOP EWD TOWARD
THE OHIO VALLEY AND CNTRL APPALACHIANS IN TANDEM WITH THE
PROGRESSION OF THE SHORTWAVE TROUGH. IN THE WAKE OF A COLD FRONT
TRAILING SW OF THE DEEPENING SFC CYCLONE...SPRAWLING SFC HIGH
PRESSURE WILL REINFORCE CONTINENTAL POLAR AIR OVER THE GREAT PLAINS.
MEANWHILE...AHEAD OF THE COLD FRONT...POLEWARD MASS FLUXES WILL
ENCOURAGE THE INLAND ADVANCE OF PARTIALLY MODIFIED GULF MOISTURE. BY
EARLY MON...THE COLD FRONT IS FORECAST TO EXTEND FROM PORTIONS OF
THE CNTRL APPALACHIANS TO THE ERN GULF COAST.

...PORTIONS OF SOUTHEAST TX TO THE LOWER MS VALLEY REGION...
SFC OBSERVATIONS INDICATE DEWPOINTS FROM THE UPPER 50S TO AROUND 60F
EXTENDING INLAND FROM THE TX COAST TO THE DFW METROPLEX...IN ADVANCE
OF THE COLD FRONT. THIS FRONT IS ANALYZED FROM THE KS/MO-AREA LOW
PRESSURE SWWD TO THE TX S PLAINS. AS MASS FIELDS RESPOND TO SFC
CYCLOGENESIS OCCURRING WELL N OF THE REGION...SIMILAR DEWPOINTS WILL
OVERSPREAD AREAS FARTHER E TOWARD THE LOWER MS VALLEY AHEAD OF THE
FRONT...WHERE 12Z RAOBS INDICATE A DRY/COOL BOUNDARY LAYER PRESENTLY
IN PLACE.

A STEADY SUPPLY OF MOISTURE E OF A NWRN-MEXICO MIDLEVEL
CYCLONE...COUPLED WITH MODEST ISENTROPIC ASCENT IN THE ENTRANCE
REGION OF A SFC-CYCLONE-PRECEDING LLJ...WILL MAINTAIN CLOUDS AND
AREAS OF PRECIPITATION ACROSS THE WARM/MOIST SECTOR. THIS WILL STUNT
DIURNAL DESTABILIZATION. HOWEVER...AS THE STRONGEST LOW-LEVEL MASS
FLUXES BECOME CONCENTRATED OVER THE OHIO AND TN VALLEYS...BREAKS IN
CLOUD COVERAGE/DECREASING CLOUD-OPACITY MAY PROMOTE MARGINAL
PRE-FRONTAL DESTABILIZATION. A CORRIDOR OF 200-500-J/KG MLCAPE WILL
LIKELY MATERIALIZE AHEAD OF THE FRONT BY MID-AFTERNOON...FROM SERN
TX TO CNTRL MS. THIS WILL BE SUFFICIENT FOR THE DEVELOPMENT OF
ISOLATED TO SCATTERED THUNDERSTORMS INVOF THE FRONT DURING THE
AFTERNOON...WITH THIS ACTIVITY SPREADING EWD INTO THE EVENING.
ADDITIONAL CONVECTION MAY MATURE WITHIN THE
PRE-FRONTAL/ISENTROPIC-ASCENT REGIME THROUGHOUT THE DAY FROM CNTRL
LA TO CNTRL/S-CNTRL/ERN MS...WITH THIS ACTIVITY SIMILARLY SHIFTING
EWD.

THE PRESENCE OF 55-60-KT H5 WSWLYS WILL OFFER SUFFICIENT DEEP SHEAR
FOR ORGANIZED CONVECTIVE STRUCTURES. SMALL BOWING SEGMENTS MAY YIELD
A FEW INSTANCES OF MARGINALLY SVR WIND GUSTS. LOW-LEVEL FLOW WILL BE
SLIGHTLY BACKED RELATIVE TO THE FLOW ALOFT IN PROXIMITY TO A
LOW-LEVEL CONFLUENCE AXIS EXTENDING SSW OF THE CYCLONE TO THE CNTRL
GULF COAST THIS AFTERNOON. PRE-FRONTAL CONVECTION EVOLVING IN THIS
REGIME MAY OCCASIONALLY EXHIBIT MIXED CONVECTIVE MODES...PERHAPS
INCLUDING SEMI-DISCRETE SUPERCELLS. THIS WOULD PARTICULARLY BE THE
CASE ACROSS PORTIONS OF CNTRL/SRN/ERN MS AND ADJACENT SECTIONS OF
NERN LA AND WRN AL. CURVED...ELONGATED LOW-LEVEL HODOGRAPHS
SUPPORTING 100-250 M2/S2 OF 0-1-KM SRH SUGGEST THAT A BRIEF/WEAK
TORNADO CANNOT BE RULED OUT IN THESE AREAS.

HOWEVER...THE DEARTH OF BUOYANCY WILL BE A MITIGATING FACTOR FOR
MORE ROBUST SVR-TSTM POTENTIAL...ESPECIALLY GIVEN INCOMPLETE
MODIFICATION OF THE AIR MASS OVERLYING THE GULF OF MEXICO AND THE
PRESENCE OF ONLY MODEST MIDLEVEL LAPSE RATES. FURTHERMORE...THE
SPATIAL DISPLACEMENT BETWEEN THE STRONGER DEEP ASCENT/SFC
CYCLOGENESIS AND GREATER BOUNDARY-LAYER THETA-E WILL BE A MITIGATING
FACTOR FOR A MORE SUBSTANTIAL SVR-TSTM POTENTIAL. AS SUCH...ONLY
MARGINAL-SVR-TSTM DELINEATION IS IN EFFECT. ANY SVR-TSTM RISK WILL
DIMINISH AS CONVECTION SPREADS E OF WRN AL THIS EVENING...AND
NOCTURNAL COOLING BREEDS AN INCREASE IN BOUNDARY-LAYER STATIC
STABILITY.

...EXTREME ERN NC INCLUDING THE OUTER BANKS...
STRENGTHENING LOW-LEVEL SLYS AHEAD OF THE SHORTWAVE TROUGH WILL
FOSTER AN INFLUX OF LOW-LEVEL MOISTURE FROM THE SWRN NORTH ATLANTIC
LATE TONIGHT...ALONG WITH SOME UPTICK IN CONVECTION. DESPITE STRONG
FLOW JUST ABOVE THE SFC...FORECAST SOUNDINGS INDICATE A PAUCITY OF
BUOYANCY OWING TO STATICALLY STABLE THERMODYNAMIC PROFILES IN THE
LOW LEVELS. THE NOCTURNALLY ENHANCED STABLE LAYER WILL MINIMIZE THE
OPPORTUNITY FOR DOWNDRAFTS TO MANIFEST STRONG WINDS AT THE SFC.
THEREFORE...NO SEVERE PROBABILITIES HAVE BEEN INCLUDED.

..COHEN/CARLAW/MEAD.. 02/01/2015




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