SWODY1
SPC AC 291221
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0721 AM CDT SUN APR 29 2007
VALID 291300Z - 301200Z
..THERE IS A SLGT RISK OF SVR TSTMS OVER SWRN TX...
..SOUTHWEST TX...
SLOW MOVING UPPER LOW WILL CONTINUE TO SUPPORT SCATTERED TO NUMEROUS
THUNDERSTORMS ACROSS THIS AREA AS IT SLOWLY SHIFTS ENEWD AND BEGINS
TO EVOLVE INTO AN OPEN TROUGH OVER WRN TX THROUGH THE PERIOD.
INFLUX OF RELATIVELY RICH GULF MOISTURE REMAINS EVIDENT THIS MORNING
ON SOUNDINGS AND SURFACE DATA INTO THE BIG BEND REGION...WHERE
SURFACE DEW POINTS AOA 65F WILL LIKELY REMAIN IN PLACE. IN
ADDITION...MID LEVEL LAPSE RATES ARE EXPECTED TO REMAIN STEEP WITHIN
PERSISTENT FEED OF WARM/DRY ELEVATED MIX LAYER OUT OF N-CENTRAL
MEXICO. THIS WILL SUSTAIN AXIS OF MODERATE TO STRONG INSTABILITY IN
A NARROW AXIS NEAR AND SOUTH OF SURFACE WARM FRONT NOW EXTENDING
WSWWD ACROSS THE HILL COUNTRY TO WEAK LOW CENTER SE OF MRF. THIS
BOUNDARY WILL LIKELY BECOME MORE DIFFUSE THROUGH THE DAY...THOUGH
STRONGER STORMS ARE EXPECTED TO WEAKEN AS THEY LIFT NNEWD INTO MORE
STABILITY AND WEAKER LAPSE RATES. SHEAR WILL REMAIN STRONGEST EAST-
SOUTHEAST OF THE MID LEVEL LOW WITHIN 40-50 KT SWLY H5 JET FORECAST
TO OVERSPREAD THE BIG BEND REGION LATER TODAY. GIVEN PERSISTENT
SELY LOW LEVEL WINDS...DEEP LAYER SHEAR WILL REMAIN MORE THAN
ADEQUATE FOR SUPERCELLS. ACTIVITY WILL LIKELY EVOLVE INTO A
LARGER...SLOW MOVING CONVECTIVE SYSTEM AND PERSIST WELL AFTER DARK
TOWARDS CENTRAL TX. THOUGH LARGE HAIL WILL REMAIN PRIMARY SEVERE
THREAT...SOME POTENTIAL FOR DAMAGING WINDS AND EVEN A TORNADO OR TWO
WILL EXIST OVER THE REGION THROUGH MUCH OF THE PERIOD.
..CENTRAL/NRN MT...
COMPLICATED FORECAST ACROSS THIS REGION WITH STRONG MID/UPPER LEVEL
WLY FLOW AND STEEP LAPSE RATES SUPPORTING AT LEAST A CONDITIONAL
THREAT OF SEVERE THUNDERSTORMS AS LARGE SCALE ASCENT INCREASES AND
SPREADS QUICKLY EWD LATER TODAY AND TONIGHT. EARLY MORNING ANALYSES
INDICATE A VERY DRY BOUNDARY LAYER IN PLACE WITH SURFACE DEW POINTS
AOB 35F ACROSS MUCH OF MT. HOWEVER...OVERNIGHT NAM/NAMKF/GFS MODELS
CONTINUE TO INCREASE SURFACE DEW POINTS ALMOST 10 DEGREES DURING THE
AFTERNOON AHEAD OF DEVELOPING LEE TROUGH/FRONT EXPECTED TO SHIFT EWD
ACROSS THE STATE LATER TODAY AND TONIGHT. UNSURE WHAT IS DRIVING
THIS MOISTURE INCREASE GIVEN LACK OF ADVECTIVE SOURCE AND DEARTH OF
VERTICAL MOISTURE FOR DOWNWARD MIXING ON MORNING SOUNDINGS. 09Z RUC
MAY BE MORE REASONABLE IN ACTUALLY DROPPING SURFACE DEW POINTS
WITHIN STRONG DIURNAL MIXING AND WLY DOWNSLOPE FLOW REGIME TODAY.
SHOULD THIS SCENARIO UNFOLD...DEEP CONVECTION /ESPECIALLY ANY
SUPPORTIVE OF SEVERE WEATHER/ WILL BE MUCH LESS LIKELY ACROSS THIS
REGION. GIVEN LARGE UNCERTAINTY AND HIGHLY CONDITIONAL NATURE OF
ANY THREAT...WILL MAINTAIN ONLY LOW SEVERE PROBABILITIES WITH THIS
FORECAST.
..NRN IA/SRN MN INTO SRN WI...
AS MENTIONED IN ABOVE SECTION OVER MT...CONSIDERABLE UNCERTAINTIES
HAVE UNFOLDED OVERNIGHT REGARDING AVAILABLE MOISTURE/INSTABILITY
OVER THIS REGION AHEAD OF SEWD MOVING SURFACE TROUGH/MID LEVEL JET.
APPEARS DEEP MIXING THROUGH THE AFTERNOON WILL TEND TO OFFSET ANY
ADVECTIVE MOISTENING WITHIN THE BOUNDARY LAYER AND HINDER MUCH IF
ANY CONVECTIVE INSTABILITY TODAY. DEEPLY MIXED BOUNDARY LAYER AND
STRONG SHEAR WILL BE MORE THAN ADEQUATE FOR SUSTAINED
SEVERE...LIKELY IN THE FORM OF DAMAGING WINDS...SHOULD SUFFICIENT
INSTABILITY/STORMS DEVELOP. HOWEVER...AREA APPEARS TOO CONDITIONAL
TO WARRANT MORE THAN LOW SEVERE PROBABILITIES ATTM.
.EVANS/CROSBIE.. 04/29/2007
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