DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 262001
SWODY1
SPC AC 261958

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT SUN MAY 26 2013

VALID 262000Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN HIGH PLAINS INTO
PORTIONS OF THE CNTRL AND NRN PLAINS...

...CNTRL PLAINS AREA...

ONLY MINOR CHANGES HAVE BEEN MADE TO THIS PORTION OF THE OUTLOOK.
VISIBLE IMAGERY SHOW CUMULUS INCREASING ALONG N-S CONVERGENCE AXIS
EXTENDING THROUGH WCNTRL NEB FROM A SFC LOW OVER SWRN NEB...AS WELL
AS ALONG THE E-W QUASI-STATIONARY FRONT ACROSS CNTRL NEB. THE
ATMOSPHERE IS BECOMING STRONGLY UNSTABLE WITH MLCAPE APPROACHING
3000 J/KG...BUT STILL APPEARS TO BE CAPPED TO SFC BASED STORMS. AS
THE SFC LAYER CONTINUES TO WARM...HRRR GUIDANCE INDICATE STORMS WILL
DEVELOP OVER WCNTRL NEB BY LATE AFTERNOON. EFFECTIVE SHEAR IS
SUFFICIENT FOR SUPERCELLS...AND 0-2 KM HODOGRAPHS WILL INCREASE IN
SIZE AS THE LLJ STRENGTHENS DURING EARLY EVENING. VERY LARGE HAIL
AND ISOLATED TORNADOES WILL BE THE MAIN INITIAL THREATS...BEFORE
ACTIVITY EVOLVES INTO ONE MORE CLUSTERS LATER THIS EVENING.

...NRN PLAINS...

PRIMARY CHANGE TO THIS REGION WAS TO INTRODUCE A GAP IN THE SIG AND
30% HAIL COVERAGE LINES. A RELATIVE MINIMUM IN STORM COVERAGE MIGHT
OCCUR WHERE CONVECTIVELY MODIFIED AIR HAS BEEN ADVECTED SWWD AND IS
SERVING TO MAINTAIN STRATUS INTO PARTS OF WRN SD. MORE ROBUST
DEVELOPMENT APPEARS MORE LIKELY FARTHER NW WHERE STORMS WILL SPREAD
EWD OFF THE HIGHER TERRAIN OF MT AND NERN WY.

...SRN PLAINS...

WILL MAINTAIN A CONDITIONAL THREAT FOR ISOLATED LARGE HAIL AND
DAMAGING WIND WITH ANY STORMS THAT CAN DEVELOP WITHIN ZONE OF DEEPER
MIXING ON DRYLINE CIRCULATION. ANY STORMS THAT DEVELOP SHOULD REMAIN
ISOLATED.

..DIAL.. 05/26/2013

.PREV DISCUSSION... /ISSUED 1116 AM CDT SUN MAY 26 2013/

...SYNOPSIS...

LITTLE CHANGE TO THE SYNOPTIC PATTERN IS FORECAST THROUGH THE D1
PERIOD WITH UPPER LOWS OVER BC/AB AND OVER NEW ENGLAND INTO THE
CANADIAN MARITIMES. BETWEEN THESE FEATURES...A RIDGE FROM MB/ON
INTO THE MID-MO VALLEY WILL GRADUALLY LOSE AMPLITUDE IN RESPONSE TO
THE EWD PROGRESSION OF A SERIES OF VORTICITY MAXIMA ORIGINATING
WITHIN THE CYCLONIC FLOW REGIME OVER THE WRN STATES. ONE IMPULSE OF
POTENTIAL IMPORTANCE IS APPARENT IN WATER VAPOR IMAGERY OVER THE
GREAT BASIN AS OF MID MORNING. THIS FEATURE IS FORECAST TO
TRANSLATE NEWD INTO THE NRN HIGH PLAINS BY THIS EVENING.

IN THE LOW LEVELS...CONSIDERABLE CONVECTIVE OUTFLOW HAS MASKED THE
SYNOPTIC BOUNDARIES ACROSS THE NRN PLAINS THIS MORNING.
HOWEVER...IT APPEARS THAT A PAIR OF LEE CYCLONES WILL DEEPEN TODAY
OVER CNTRL OR ERN WY AND OVER ERN CO...ALONG A LEE TROUGH/DRY LINE
WHICH WILL EXTEND ALONG THE HIGH PLAINS. A QUASI-STATIONARY
BOUNDARY WILL INTERSECT THE LEE TROUGH OVER ERN WY BEFORE EXTENDING
SEWD THROUGH THE MID-MO INTO MID-MS VALLEYS.

...NRN/CNTRL PLAINS THIS AFTERNOON AND TONIGHT...

THE COLOCATION OF STEEP MIDLEVEL LAPSE RATES AND MODEST BOUNDARY
LAYER MOISTURE CONTENT WILL COMBINE WITH DAYTIME HEATING TO YIELD A
MODERATELY UNSTABLE AIR MASS BY AFTERNOON ALONG AND EAST OF THE LEE
TROUGH WHERE MLCAPE VALUES WILL APPROACH 1000-1500 J/KG OVER ERN
MT...TO AS HIGH AS 2000-3000 J/KG ACROSS PARTS OF WRN NEB INTO WRN
AND CNTRL KS. IN THE WAKE OF THE INITIAL ELEVATED STORMS CURRENTLY
MOVING THROUGH THE MID-MO VALLEY...LATEST MODEL GUIDANCE SUGGESTS
THAT SURFACE-BASED STORM DEVELOPMENT WILL BE MOST PROBABLE BY MID TO
LATE AFTERNOON INVOF THE LEE TROUGH AND FAVORED TERRAIN OVER ERN
PARTS OF MT AND WY...AS WELL AS TO THE NORTHEAST OF THE ERN CO LEE
CYCLONE. ANOTHER AREA OF POTENTIAL STORM INITIATION WILL BE ALONG
OR JUST NORTH OF THE OUTFLOW BOUNDARY/SYNOPTIC FRONT OVER CNTRL OR
N-CNTRL/NERN NEB LATE THIS AFTERNOON INTO EVENING WHERE
CONVERGENCE/UPLIFT IS AUGMENTED AT THE TERMINUS OF A DEVELOPING
LLJ.

ELY/SELY LOW-LEVEL WINDS VEERING TO SWLY AT 25-35 KT IN THE
MIDLEVELS WILL RESULT IN SUFFICIENT VERTICAL SHEAR FOR SUPERCELLS AS
THE INITIAL STORM MODE. LARGE HAIL /SOME SIGNIFICANT/ WILL BE THE
PRIMARY HAZARD WITH THESE STORMS...THOUGH A FEW TORNADOES WILL BE
POSSIBLE. THIS IS ESPECIALLY THE CASE THIS EVENING OVER WRN NEB
WHERE THE STRONGEST BUOYANCY AND DEEP-LAYER SHEAR WILL ALIGN WITH A
CORRIDOR OF ENHANCED LOW-LEVEL SHEAR. BY TONIGHT...STORMS MAY GROW
UPSCALE INTO ONE OR MULTIPLE MCS/S WITH A CONTINUED RISK FOR HAIL
AND DAMAGING WINDS SPREADING EWD INTO THE LOWER ELEVATIONS OF THE
PLAINS.

...SRN HIGH PLAINS THIS AFTERNOON AND EVENING...

STRONG DAYTIME HEATING WILL COMBINE WITH STEEP MIDLEVEL LAPSE RATES
AND BOUNDARY LAYER DEWPOINTS IN THE UPPER 50S TO LOW TO MID 60S TO
YIELD AFTERNOON MLCAPE VALUES OF 1500-3000 J/KG AHEAD OF THE
DRYLINE. MORNING WATER VAPOR IMAGERY SHOWS A LOW-AMPLITUDE
SHORT-WAVE TROUGH MOVING THROUGH THE LOWER-CO VALLEY WHICH WILL
LIKELY REMAIN TO THE WEST OF THE REGION THROUGH TODAY. THUS...WHILE
THE UPPER-LEVEL PATTERN WILL BECOME SLIGHTLY DIFFLUENT BY
27/00Z...LARGE-SCALE FORCING FOR ASCENT WILL REMAIN NEGLIGIBLE. AS
SUCH...STORM INITIATION WILL BE STRONGLY TIED TO THE DEVELOPING
DRYLINE CIRCULATIONS WITH ONLY ISOLATED COVERAGE ANTICIPATED.

THE COMBINATION OF THE MODERATE TO STRONG INSTABILITY AND DEEP-LAYER
SHEAR INCREASING TO 30-35 KT WILL PROMOTE INTENSE STORMS...INCLUDING
THE POSSIBILITY OF SUPERCELLS...WITH THE PRIMARY HAZARDS BEING LARGE
HAIL AND LOCALLY DAMAGING WINDS. STORMS SHOULD TEND TO WEAKEN BY
LATE EVENING INTO TONIGHT AS THE BOUNDARY LAYER COOLS AND
STABILIZES.

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