Hail in Nebraska, May 9, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
225 PM CDT WED MAY 9 2001

...BIG CHALLENGES WITH THIS AFTERNOON'S FORECAST ARE THE LOCATIONS
OF THE STRONGEST CONVECTIVE POTENTIAL TONIGHT AND THURSDAY EVENING...

...18Z SYNOPSIS...
     THE SURFACE ANALYSIS SHOWED THE TROUGH/DRYLINE FROM JUST
EAST OF VALENTINE TO NEAR NORTH PLATTE AND IMPERIAL. SOUTH AND EAST
OF THE TROUGH...SURFACE TEMPERATURES AT OR ABOVE 80F AND DEWPOINTS
AOA 55F HAD CAUSED THE SB-CAPES IN THE LAPS TO EXCEED 2000J/KG OVER
CENTRAL AND SOUTHWEST NEBRASKA. VISIBLE IMAGERY SHOWED DEVELOPING
CUMULUS CLOUDS ALONG A LINE FROM NEAR AINSWORTH THROUGH TRYON TO
NEAR OGALLALA. ANOTHER BOUNDARY WAS INDICATED FROM ORD THROUGH OCONTO
TO HAYES CENTER. WATER VAPOR IMAGERY INDICATED A PLUME OF MOISTURE
FROM THE NORTH PACIFIC CROSSING THE ROCKIES AND OVER THE NORTHERN
PLAINS. AN UPPER TROUGH COULD BE DISCERNED ACROSS WESTERN MONTANA AND
SOUTHERN IDAHO. THE STRONGER COLD FRONT WAS STILL ACROSS WESTERN
NORTH DAKOTA AND SOUTHEAST MONTANA.
    THE 17Z DERIVED PRECIPITABLE WATER AND LIFTED INDICES SHOWED THE
STRONGEST INSTABILITY AND HIGHEST MOISTURE SOUTH AND EAST OF A
NORFOLK-MCCOOK LINE WHERE LI'S WERE -3C TO -7C.
...MODELS...
    THERE ARE ONLY SMALL DIFFERENCES BETWEEN THIS MORNING'S ETA AND
AVN. SO, THE ETA IS THE MODEL OF CHOICE THROUGH FRIDAY. THE AVN WILL
BE USED FOR THE REST OF THE FORECAST AS FAR AS IT GOES.
    THE ECMWF, UKMET, AND MRF SOLUTIONS ARE SIMILAR IN THEIR
TREATMENT OF THE NEXT MAJOR FRONT. HOWEVER, THE UKMET IS
CONSIDERABLY FARTHER NORTH WITH THE MOTHER CYCLONE THAN EITHER THE
ECMWF OR THE MRF. ALL THREE OF THEM KEEP THE CYCLONE OUT OF
NEBRASKA; SO, THE DIFFERENCES ARE NOT CRITICAL. DIFFERENCES BETWEEN
THE MRF AND AVN TO MON/12Z ARE SMALL AS WELL. THE CONTINUITY BETWEEN
RUNS FOR THE MRF IS NOT REAL STRONG, BUT THE TREND IS DISCERNIBLE. IT
HAS BEEN ADJUSTING THE TRACKS OF THE SYSTEMS SOUTHWARD WITH EACH RUN.
SO, ALTHOUGH CONFIDENCE IS NOT HIGH, THE MRF IS THE CHOICE FOR THE
EXTENDED BEYOND THE REACH OF THE NEW AVN WITH ADJUSTMENTS OF 2-5
DEGREES LATITUDE FOR THE SOUTHWARD TREND BETWEEN THE CYCLES.

...FORECAST...
    THE GOES DPI OF PW AND LI SUPPORTED THE MODERATE RISK AREA GIVEN
BY SPC. THE DRY LINE WILL PROBABLY GENERATE THE INITIAL CONVECTIVE
DEVELOPMENT...WHILE OTHER CONVECTION WILL DEVELOP ALONG THE
BOUNDARIES DISCUSSED ABOVE. SOUTH AND EAST OF A BBW-LBF-IML LINE.
LATE TONIGHT...SOME LOW LEVEL 2D-FRONTOGENESIS DEVELOPS WITH A LOW-
LEVEL CONVERGENCE-UPPER LEVEL DIVERGENCE COUPLET ALONG THE SOUTH
DAKOTA BORDER. THERE IS AN AREA OF ENHANCED THETA-E THAT AREA AND
FAIRLY LOW CONVECTIVE INITIATION VALUES. SO A SECOND AREA OF
CONVECTION WILL PROBABLY DEVELOP AND TRACK ALONG THE BORDER TO ABOUT
VALENTINE BEFORE THE FORCING DISSIPATES. SO...WILL GO WITH THE 50
PERCENT PROBABILITY IN CUSTER COUNTY AND FRONTIER COUNTY, 30 TO 40
PERCENT IN THE REST OF THE SOUTHWEST AND IN THE NORTHWEST, AND 20
PERCENT OVER THE BALANCE OF THE FORECAST AREA.
    FROM THERE, THE FORCING IS GONE UNTIL LATE THURSDAY WHEN 2D-
FRONTOGENESIS, LOW-LEVEL CONVERGENCE, AND UPPER LEVEL DIVERGENCE COME
TOGETHER WITH EXTREME INSTABILITY IN THE SOUTHERN HALF OF THE
FORECAST AREA. THE FORCING THEN DISSIPATES DURING THE NIGHT.
    UPSLOPE EAST WIND WILL PROBABLY GENERATE SOME LOW CLOUDINESS
FRIDAY NIGHT IN THE SOUTHWEST WHICH SHOULD ERODE FAIRLY QUICKLY
SATURDAY AS THE WIND COMES AROUND TO THE SOUTH.
     A VERY WARM PERIOD IS LIKELY SUNDAY AND MONDAY WITH THE
POTENTIAL FOR 90S IN THE WESTERN FORECAST AREA. THEN A FRONT LATE
MONDAY WILL BEGIN TO BRING COOLING TO THE AREA FOR TUESDAY AND
WEDNESDAY. SINCE THE ANTICYCLONIC CIRCULATION IN THE SOUTHEAST U.S.
WILL PULL THE GULF MOISTURE TO THE EASTERN PART OF THE STATE, THE
CHANCES OF SIGNIFICANT PRECIPITATION IN CENTRAL AND WESTERN NEBRASKA
ARE SLIM THIS WEEKEND AND EARLY NEXT WEEK. HOWEVER, BECAUSE OF WEAK
CONFIDENCE IN THE MEDIUM RANGE SOLUTIONS, I AM NOT READY TO DROP THE
MENTION OF PRECIPITATION ALREADY IN THE FORECAST FOR TUESDAY. FOR NOW
THOUGH, I WILL NOT INTRODUCE PRECIPITATION WEDNESDAY.

.LBF...NONE.

SPRINGER