Hail in Nebraska, June 25, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
220 PM CDT MON JUN 25 2001

THE CHANCES OF PRECIPITATION WITH THE STALLING SURFACE FRONT WILL BE
THE MAIN FORECAST PROBLEM FOR THE NEXT SEVERAL DAYS.

...18Z SYNOPSIS...
    SURFACE ANALYSIS SHOWED A CLOSED LOW ALONG THE SOUTH DAKOTA-
NORTH DAKOTA BORDER WITH A COLD FRONT TRAILING OFF THROUGH WYOMING
INTO NORTHERN UTAH. WITH UPPER FLOW PARALLEL TO THAT FEATURE...I
WOULD EXPECT THE FRONT TO STALL BEFORE IT GETS INTO NEBRASKA. THERE
WAS ALSO A SURFACE TROUGH IN WESTERN KANSAS AND WESTERN NEBRASKA
ACROSS WHICH DEWPOINTS DROP FROM THE LOWER 60S TO AROUND 50. WATER
VAPOR IMAGERY INDICATED A DEVELOPING WAVE IN SOUTHERN CALIFORNIA.
ACCORDING TO THE ETA/AVN OUTPUT...THIS FEATURE WILL BE FORCED INTO
THE FAST SOUTHWEST FLOW NORTH OF NEBRASKA. IT SHOULD ALSO WEAKEN AS
IT TRIES TO ROUND THE CREST OF THE RIDGE. THERE WAS ALSO A DEVELOPING
WAVE IN THE PACIFIC NORTHWEST. TEMPERATURES FIELDS IN THE 12Z UPPER
AIR ANALYSIS SHOWED THAT THIS FEATURE WAS STEEPLY BAROCLINIC.
...MODELS...
    THE AVN AND ETA ARE NEARLY IDENTICAL IN THEIR TREATMENT OF BOTH
THE SURFACE AND UPPER FEATURES. THEY SHOW GOOD CONTINUITY BETWEEN
RUNS AND DID WELL WITH THE INITIAL CONDITIONS.
    IN THE EXTENDED...THE LATEST ECMWF AND MRF SOLUTIONS ARE NEARLY
IDENTICAL IN THEIR TREATMENT OF THE UPPER HIGH IN THE SOUTHWEST AND
THE UPPER LOW IN THE NORTHEAST PACIFIC. THEIR SURFACE SOLUTIONS ARE
SIMILAR AS WELL. BOTH SHOW GOOD CONTINUITY WITH THE PREVIOUS MODEL
RUN. THIS MORNINGS AVN SUPPORTS THE MRF SOLUTION. SO...THE ETA AND
THE AVN ARE PREFERRED FOR DAYS 1-3...AND THE AVN AND MRF FOR DAYS
3-7.

...FORECAST...
    THE SHORT WAVE TROUGH IN THE PACIFIC NORTHWEST WILL BE STEERED BY
THE FAST NORTHERN STREAM THROUGH SOUTHERN CANADA. AS IT PASSES
THROUGH THE GREAT LAKES REGION...THE UPPER HIGH ON THE SOUTHERN
PLAINS WILL SLIP TO THE NORTH TOWARD THE WARMER AIR. THIS WILL ALLOW
THE SOUTHEAST LOW TO RETROGRADE TO THE WEST AS THE ETA AND AVN/MRF
INDICATE. IT DOESNT APPEAR THAT THE SOUTHEAST LOW WILL HAVE MUCH
INFLUENCE ON THE WEATHER FOR CENTRAL AND WESTERN NEBRASKA.
    AT 12Z...THE 700-500MB DELTA-T INDICATED THE STRONGEST ELEVATED
INSTABILITY ALONG AN INL-FSD-CYS LINE WHERE THE VALUES WERE 22C OR
HIGHER. SO...THE STRONGEST ELEVATED INSTABILITY IS IN SOUTHERN SOUTH
DAKOTA AND NORTHERN NEBRASKA. THE FORECAST 850MB BASED LIS ARE -6C
OR LOWER FROM NORTHEAST SOUTH DAKOTA TO SOUTH CENTRAL NEBRASKA...BUT
THE 850-700MB LAYER MEAN RH IS 50 PERCENT OR LESS OVER ALL BUT THE
NORTHERN AND EASTERN MOST PARTS OF THE LBF FORECAST AREA. FOR
TONIGHT...THE UPPER TROPOSPHERIC FLOW SHOWS A DIFFLUENT AXIS
APPROXIMATELY ALONG A SUX-BFF LINE EARLY THIS EVENING SHIFTING NORTH
INTO SOUTH DAKOTA BY 06Z. THE 300MB DIVERGENCE IS NOT REAL STRONG.
THAT, IN ADDITION TO SOME WEAK 700-300MB DCVA, IS ABOUT ALL OF THE
UPPER SUPPORT THERE IS. IN THE LOWER LEVELS...THERE IS FAIRLY STRONG
CONVERGENCE ALONG AN ABR-LXN LINE AND SOME 800-700MB 2D-FRONTOGENESIS
FROM FSD TO BFF. WITH HIGHER LOW LEVEL RH AND NEARLY ALL OF THE LOW
LEVEL FORCING ALONG THE NEBRASKA-SOUTH DAKOTA BORDER...I WOULD EXPECT
THUNDERSTORMS TO DEVELOP IN THE NORTHERN ZONES TONIGHT. UNLESS THERE
IS SOME STRONG INDICATION OTHERWISE BEFORE THE FORECAST GOES OUT...I
WILL KEEP ONLY SMALL POPS IN THE SOUTHWEST AND INCREASE THEM IN THE
NORTH FROM THE CURRENT FORECAST, AIR-BRUSHING THE TRANSITION ZONES.
    ON TUESDAY...THERE WILL BE ENOUGH INSTABILITY AND MOISTURE
AVAILABLE TO CAUSE THUNDERSTORMS TO FIRE IN CENTRAL AND EASTERN
NEBRASKA IF THERE IS A BOUNDARY FOR FORCING. OTHERWISE...ONLY 700MB
CONVERGENCE INDICATES A FOCUS FOR THE DEVELOPMENT. SINCE ITS LIKELY
THAT THERE WILL BE AN OUTFLOW BOUNDARY FROM TONIGHTS CONVECTION...I
WILL PUT A MENTION OF THUNDERSTORMS IN THE EASTERN CWA TUESDAY. AFTER
THAT...THERE IS ANOTHER CHANCE OF CONVECTION LATE WEDNESDAY WHEN THE
LOW LEVEL CONVERGENCE AND WEAK 2D-FRONTOGENESIS SHOW UP AGAIN IN THE
WESTERN HALF OF THE FORECAST AREA.
    IN THE EXTENDED...THE 850-700MB MEAN LAYER RH INCREASES TO 60
PERCENT OR HIGHER IN ALL BUT THE NORTHEAST FORECAST AREA WEDNESDAY
EVENING. BY LATE WEDNESDAY NIGHT THE CONVERGENT AND FRONTOGENETIC
FORCING DIMINISH...BUT IT PICKS UP AGAIN THURSDAY EVENING AND AGAIN
SATURDAY AND TUESDAY.
    TURNING TO TEMPERATURES...THE FRONT AND ASSOCIATED CLOUDINESS
WILL MODERATE THE TEMPERATURES AFTER TODAY. SO...THAT SHOULD BE THE
END OF THE TRIPLE DIGIT HIGHS THROUGH THE EXTENDED PERIOD...THOUGH
MID 90S ARE AGAIN LIKELY IN THE WEST ON MONDAY WHEN THE 850MB
TEMPERATURES APPROACH 30C ONCE AGAIN.

.LBF...NONE.

SPRINGER