Severe Thunderstorm Warning 104, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
300 PM CDT MON JUN 19 2000

...FORECAST PROBLEM...THUNDERSTORMS THIS EVENING AND TONIGHT

...SYNOPSIS...
   A CONVERGENCE BOUNDARY WITH 45-50F DEWPOINTS COULD BE FOUND IN
WESTERN NEBRASKA FROM ABOUT MERRIMAN...THROUGH WESTERN LINCOLN
COUNTY...TO IMPERIAL. BEHIND THAT BOUNDARY...DEWPOINTS WERE 55-60F.
THERE WAS ALSO A PAIR OF SURFACE CYCLONES IN SOUTHWEST AND NORTHWEST
SOUTH DAKOTA WITH A FRONT TRAILING INTO WYOMING.
...MODEL CHOICE AND DISCUSSION...
    THE ETA IS THE MODEL OF CHOICE. THE 19/12Z RUN WAS VERY CLOSE
WITH THE LOCATION OF THE UPPER LEVEL VORTEX IN SOUTHEAST IDAHO. IT
ALSO DID WELL WITH THE LOCATION OF THE SURFACE FRONT AND CYCLONE.

...THIS EVENING AND TONIGHT...
    AT 19Z...CONVECTION IS DEVELOPING ALONG A CHADRON-SIDNEY LINE.
THE SURFACE LAPS SBCAPES INDICATE VALUES OF 3000-5000 J/KG FROM
MERRIMAN TO OGALLALA AND EAST. THE 5000 J/KG IS UP IN WESTERN CHERRY
COUNTY AND MAY NOT BE ACCURATE. THE RUC HAS VALUES OF 1500-2500
J/KG. THE 12Z ETA INDICATES 2000-2500 J/KG BETWEEN MERRIMAN AND
VALENTINE WITH 1500-2000 J/KG IN THE SOUTHWEST. THE GOES DERIVED CAPE
SUPPORTS THE RUC SOLUTION WHERE IT ISN'T BLOCKED OUT BY THE CLOUDS. I
WILL MAKE ADJUSTMENTS AS DICTATED BY THE EVOLUTION OF THE CONVECTION
AND ACTION BY SPC. THE CONVERGENCE LINE IS MOST LIKELY TO BE THE
FOCUS OF CONVECTION. SO ITS LOCATION IS CRITICAL. I WILL MAKE LAST
MINUTE ADJUSTMENTS AS DICTATED BY SATELLITE AND RADAR INDICATIONS
AND ON ACTION BY SPC.
...TUESDAY...
    LAYER MEAN RH PROGS INDICATE THAT CLOUDS SHOULD CONTINUE OVER
THE NORTHERN PART OF THE FORECAST AREA THROUGH MOST OF THE DAY...
CLEARING DURING THE NIGHT. THE 700-500MB DCVA WITH THE UPPER LEVEL
TROUGH IS REALLY THE ONLY FORCING APPARENT. SO...WILL KEEP
PROBABILITIES LOW. IN THE CENTRAL AND SOUTHWEST FORECAST ZONES...
DRYING SHOULD CLEAR CLOUDINESS OUT. THE 850MB 24 HOUR TEMPERATURE
CHANGES INDICATE DECREASES FROM 5C IN THE SOUTHWEST TO 10C IN THE
NORTH CENTRAL ZONES. SO...TEMPERATURES WILL BE SIGNIFICANTLY COOLER.
...TUESDAY NIGHT AND WEDNESDAY...
    THERE IS VERY LITTLE MOISTURE OR FORCING INDICATED THROUGH
WEDNESDAY AFTERNOON...AND THE 850MB 24 HOUR TEMPERATURE INCREASES
RANGE FROM 2C IN THE NORTHEAST PART OF THE FORECAST AREA TO 10C IN
THE SOUTHWEST. SO...WARMER WEATHER IS LIKELY WITH FEW CLOUDS.

    IN THE MEDIUM RANGE...THE MRF SEEMS TO BE AS GOOD AS THE OTHERS.
COMPARING IT TO THE 12Z WV IMAGERY AND WIND PROFILERS...THE 17/00Z
RUN OF IT DID WELL WITH THE RH, VORTICITY, AND WIND IN THE UPPER
LEVELS. IT WAS ALSO VERY CLOSE WITH THE SURFACE PRESSURE FIELD AND
FRONTAL POSITIONS. AT 500MB...IT WAS A LITTLE TOO WARM WITH
TEMPERATURES...BUT THE HEIGHTS WERE GOOD.
    ALL INDICATIONS ARE THAT TEMPERATURES SHOULD WARM INTO THE 80S
TO LOW 90S THURSDAY AND INTO THE 90S FRIDAY AND SATURDAY OVER MUCH OF
THE FORECAST AREA.
    ACCORDING TO THE FORECAST...LOW LEVEL CONVERGENCE...DCVA...AND
LOW LEVEL WARM ADVECTION SHOULD COMBINE TO PRODUCE SIGNIFICANT
FORCING. HOWEVER...WITH LOW LEVEL CONDENSATION DEFICITS OF 50MB TO
100MB...MOISTURE IS MARGINAL. THE STRONGEST FORCING APrPEARS TO BE
SATURDAY WHILE THE MORE FAVORABLE CONDENSATION DEFICITS ARE FRIDAY.
SO...WILL MAINTAIN DRY FORECAST THURSDAY AND PUT A CHANCE OF
THUNDERSTORMS FRIDAY AND SATURDAY.

.LBF...NONE

SPRINGER

NEZ004>010-022>029-035>038-056>059-069>071-192045-

SEVERE WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1100 AM CDT MON JUN 19 2000

...STORM SPOTTER ACTIVATION MAY BE NEEDED ACROSS PORTIONS OF WESTERN
AND NORTH CENTRAL NEBRASKA THIS AFTERNOON AND EVENING...

THERE IS A CHANCE OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING
ACROSS PORTIONS OF THE OUTLOOK AREA. THE GREATEST RISK IS EAST OF A
LINE FROM MERRIMAN...TO SUTHERLAND...TO HAYES CENTER. THUNDERSTORMS
ARE EXPECTED WEST OF THIS LINE...BUT THESE ARE NOT AS LIKELY TO
BECOME SEVERE.

SOUTH WINDS WILL CONTINUE TO TRANSPORT LOW LEVEL MOISTURE INTO THE
OUTLOOK AREA THIS AFTERNOON. ENOUGH GAPS IN THE HIGH CLOUDINESS ARE
EXPECTED TO ALLOW SURFACE HEATING TO TAKE PLACE. THE COMBINATION OF
SURFACE HEATING AND LOW LEVEL MOISTURE WILL CAUSE THE ATMOSPHERE TO
BECOME INCREASINGLY UNSTABLE. THUNDERSTORMS ARE EXPECTED TO DEVELOP
ALONG A SURFACE DRYLINE IN THE NEBRASKA PANHANDLE AROUND MID
AFTERNOON AS AN UPPER LEVEL DISTURBANCE MOVES OUT OF THE ROCKIES.
THESE STORMS MAY BECOME SEVERE AS THEY MOVE INTO THE AREA OF GREATER
INSTABILITY. THE PRIMARY SEVERE WEATHER THREAT IN THE OUTLOOK AREA
WILL BE LARGE HAIL AND STRONG GUSTY WINDS FROM MID TO LATE
AFTERNOON. AS THE STORMS MOVE EAST THIS EVENING...THE MAIN THREAT
WILL BE DAMAGING WINDS ALONG WITH BRIEF HEAVY RAINFALL.

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