DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 270532
SWODY1
SPC AC 270530

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 AM CDT FRI SEP 27 2013

VALID 271200Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
ACROSS MUCH OF THE CENTRAL INTO SOUTHERN PLAINS...

...SYNOPSIS...
LITTLE CHANGE TO THE LARGE-SCALE MID/UPPER PATTERN IS EXPECTED
THROUGH THIS FORECAST PERIOD ACROSS THE EASTERN U.S...WITH WEAK
TROUGHING LINGERING EAST OF THE ATLANTIC COAST...AND A SHARP UPPER
RIDGE REMAINING PROMINENT NORTH OF A WESTERN GULF OF MEXICO
SUBTROPICAL HIGH CENTER THROUGH THE GREAT LAKES REGION.
HOWEVER...LARGE SCALE MID/UPPER TROUGHING OVER THE WESTERN STATES
APPEARS LIKELY TO BECOME LESS AMPLIFIED...AS A SIGNIFICANT EMBEDDED
SHORT WAVE IMPULSE SHIFTS NORTHEASTWARD OUT OF THE GREAT BASIN/
SOUTHERN PLATEAU REGION...THROUGH THE NORTHERN AND CENTRAL PLAINS BY
12Z SATURDAY. MODELS SUGGEST THAT THIS LATTER DEVELOPMENT WILL
OCCUR AS A STRONG UPSTREAM IMPULSE AND ASSOCIATED JET STREAK DIG
THROUGH THE NORTHEAST PACIFIC.

IN RESPONSE TO THE IMPULSE EMERGING FROM THE INTERMOUNTAIN
REGION...MODELS SUGGEST THAT A SURFACE CYCLONE MAY SLOWLY DEEPEN
OVER THE CENTRAL HIGH PLAINS DURING THE DAY TODAY...BEFORE A SURFACE
FRONT...EXTENDING NORTHEASTWARD THROUGH THE MID MISSOURI AND UPPER
MISSISSIPPI VALLEYS...STRENGTHENS AND BEGINS TO SURGE EASTWARD
ACROSS THE CENTRAL PLAINS TONIGHT. WHILE A RETURN FLOW OF GULF
MOISTURE IS IN THE PROCESS OF DEVELOPING ACROSS THE LOWER RIO GRANDE
VALLEY...SUBSTANTIVE BOUNDARY LAYER MOISTENING FROM THIS SOURCE
REGION MAY NOT REACH THE CENTRAL PLAINS UNTIL LATE THIS AFTERNOON OR
EVENING. HOWEVER...MOISTENING ACROSS THE SOUTHERN INTO CENTRAL HIGH
PLAINS DOES APPEAR LIKELY TO BE AUGMENTED BY AN INFLUX OF MOISTURE
OF LOWER LATITUDE EASTERN PACIFIC ORIGINS...ON SOUTHWESTERLY FLOW AT
LOWER/MID-LEVELS...AHEAD OF THE UPPER TROUGH.

...CENTRAL AND SOUTHERN PLAINS...
WHILE IT DOES APPEAR LIKELY THAT CONSIDERABLE LOW/MID-LEVEL
MOISTENING WILL OCCUR TODAY ALONG A PRE-FRONTAL SURFACE TROUGH
ACROSS THE SOUTHERN INTO CENTRAL HIGH PLAINS...AND ALONG THE FRONT
ACROSS NORTHEAST COLORADO THROUGH CENTRAL NEBRASKA...INITIALLY
MODESTLY STEEP MID-LEVEL LAPSE RATES MAY NOT BE MAINTAINED. AND
MODELS SUGGEST THAT SURFACE HEATING TODAY WILL BE MORE MODEST THAN
YESTERDAY...SO UNCERTAINTY EXISTS CONCERNING HOW FAVORABLE
THERMODYNAMIC PROFILES WILL BE FOR SEVERE WEATHER POTENTIAL.
STILL...GIVEN THE STRENGTHENING OF THE DEEP LAYER MEAN FLOW FIELDS
AND SHEAR AS THE UPPER IMPULSE PROGRESSES ACROSS THE ROCKIES LATE
THIS AFTERNOON AND EVENING... FAIRLY DEEP BOUNDARY LAYER
MIXING...AND THE EVOLUTION OF SIZABLE SUB-CLOUD TEMPERATURE/DEW
POINT SPREADS...SHOULD BE SUFFICIENT TO SUPPORT SEVERE WIND GUST
POTENTIAL.

ACROSS THE TEXAS PANHANDLE AND PARTS OF WESTERN OKLAHOMA INTO
WESTERN KANSAS...CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS ARE FORECAST
TO BE LARGE ENOUGH TO SUPPORT POTENTIAL FOR TORNADOES...
PARTICULARLY IN DISCRETE STORM DEVELOPMENT. SOUTH OF THE COLD
FRONT...THIS COULD BE THE PRIMARY STORM MODE INITIALLY.
HOWEVER...AS FRONTOGENETIC FORCING INCREASES ALONG THE EASTWARD AND
SOUTHEASTWARD SURGING COLD FRONT...AN ORGANIZING LINE OF STORMS
APPEARS POSSIBLE JUST AHEAD OF IT...FROM PARTS OF CENTRAL AND
SOUTHERN NEBRASKA SOUTHWARD THROUGH THE TEXAS PANHANDLE THIS
EVENING.

CONVECTION MAY PERSIST AHEAD OF THE FRONT ADVANCING TOWARD THE LOWER
PLAINS OVERNIGHT. HOWEVER...AS IT PROGRESSES THROUGH THE RELATIVELY
NARROW CORRIDOR OF PEAK LATE AFTERNOON BOUNDARY LAYER
DESTABILIZATION /CHARACTERIZED BY CAPE ON THE ORDER OF 1000 J PER
KG/...SEVERE WIND POTENTIAL IS EXPECTED TO DIMINISH EAST OF THE HIGH
PLAINS.

..KERR/PETERS.. 09/27/2013

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