Tornado and Hail in Nebraska, June 12 to 13, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
313 PM CDT TUE JUN 12 2001

...CONVECTION TONIGHT AND 3RD PERIOD POPS ARE THE CHALLENGE...

UPPER PATTERN FEATURES A SHARP TROF OVER THE WESTERN U.S....FLAT
RIDGING THROUGH THE CENTRAL STATES AND WEAK TROFING EAST. AT THE
SURFACE...LOW PRESSURE IS CENTERED IN EASTERN WYOMING WITH A WAVY
WARM FRONT THAT EXTENDS DOWN TO SOUTHWESTERN NEBRASKA AND
NORTHEASTWARD THROUGH CENTRAL AND EASTERN NEBRASKA.

ENVIRONMENT RAPIDLY BECOMING FAVORABLE FOR A SEVERE WEATHER EVENT
IN THE CWA. WARM FRONT EXTENDS THROUGH THE SOUTHERN HALF OF
CWA. WHERE CLOUDS HAVE CLEARED SOUTH OF FRONT CAPE VALUES OF 3000 TO
5000 EXIST. ALTHOUGH THE CAP IS STRONG IN THIS AREA...THE DRYLINE
IS MAKING PROGRESS IN EASTERN COLORADO AND THE CAP HAS WEAKENED
CONSIDERABLY ACCORDING TO LATEST LAPS ANALYSIS. UPPER WAVE IS ALSO
BEGINNING TO EJECT THROUGH EASTERN WYOMING...TAIL END OF WHICH
COULD PROVIDE SUPPORT FOR INITIATION IN COLORADO. GREATER CONFIDENCE
IN CONVECTIVE COMPLEX OVER NORTHERN ZONES TONIGHT WHERE ALL
PARAMETERS ARE EXPECTED TO COME TOGETHER. HIGHEST AXIS OF
INSTABILITY WILL EXTEND INTO NORTHWESTERN ZONES AND CONVERGE IN
VICINITY OF SURFACE LOW AND WARM FRONT...ALL AHEAD OF AFOREMENTIONED
EJECTING WAVE. SUFFICIENT SPEED AND DIRECTIONAL SHEAR WILL EXIST FOR
TORNADIC SUPERCELLS AND A LLJ WILL DEVELOP TONIGHT TO MAINTAIN
COMPLEX THROUGH THE NIGHT. MODELS FORECAST THIS FEATURE TO TRAVEL
NORTHEAST BUT STRENGTH OF LLJ SUGGEST SOME PROPAGATION INTO THE LOW
LEVEL INFLOW MAY OCCUR. HIGH POPS WILL BE CARRIED IN NORTHERN ZONES
FOR THIS REASON...LOWEST POPS SOUTH.

BY 12Z WEDNESDAY SURFACE FRONT SHOULD BE ALONG EASTERN FRINGE OF
CWA AND UPPER WAVE WELL NORTH INTO ND/MN. DIRECTIONAL SPREADING OF
LAYER Q-VECS SUGGESTS LARGE SCALE SUBSIDENCE FOR MUCH OF THE CWA
SUPPORTING GUIDANCE IDEA OF DRY. A WIDELY SCATTERED AFTERNOON STORM
IS STILL POSSIBLE ALONG THE FRONT IN FAR NORTHEAST ZONES WHERE
INSTABILITY AND MOISTURE CONVERGENCE WILL REMAIN FAVORABLE. H85 24HR
CAA OF NEARLY 10 DEGREES WILL YIELD MUCH COOLER AFTERNOON HIGHS
ESPECIALLY SOUTHERN ZONES.

WILL REINTRODUCE POPS WEDNESDAY NIGHT AS THE ETA HAS MOVED CLOSER TO
RECENT AVN SOLUTIONS. STRONG WAVE EXPECTED TO EJECT FROM TROF WHICH
WILL STILL BE WEST OF THE AREA. MODELS HAVE RESOLVED A SIGNIFICANT
COUPLET OF PV ADVECTION/UPPER DIVERGENCE/FRONTOGENESIS. DESPITE
SIGNIFICANT DRYING OF LOWER LEVELS...FORCING APPEARS SO STRONG THAT
SCATTERED SHOWERS WILL BE A GOOD BET.

WAVE WILL CONTINUE TO MOVE ACROSS NORTH CENTRAL ZONES EARLY
THURSDAY AND MAIN AXIS OF UPPER WAVE WILL SWING THROUGH. HERE AGAIN
PV ADVECTION/DIVERGENCE/FRONTOGENESIS WILL REMAIN SUFFICIENT TO
CONTINUE A SCATTERED POP. DRY SOUTH WITH LARGE SCALE SUBSIDENCE.
APPROXIMATELY ANOTHER 5 DEGREES OF CAA WITH EVEN COOLER MAXES...SOME
NORTHERN ZONES NOT REACHING 70.

FINALLY QUIET ON THURSDAY NIGHT IN WAKE OF EXITING TROF AS LARGE
SCALE SUBSIDENCE AND STRONG LOW LEVEL DRYING CONTINUES IN WESTERLY
FLOW. RATHER COOL AS MOST AREAS ARE LIKELY TO DECOUPLE WITH SURFACE
HIGH DIRECTLY OVER THE AREA.

IN THE EXTENDED...DRY CONDITIONS TO CONTINUE RIG`HT THROUGH THE
WEEKEND WITH ZONAL FLOW EXPECTED TO DEVELOP. NEXT SIGNIFICANT WAVE
IN MEDIUM RANGE MODELS ON MONDAY WITH NEXT CHANCE OF CONVECTION.
DRY AGAIN TUESDAY IN WAKE OF WAVE.

.LBF...NONE.

DJB