High Wind in Nebraska, April 11, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
325 AM CDT WED APR 11 2001

THE FOCUS OF THIS FORECAST IS TYPE AND EXTENT OF PRECIPITATION WITH
THE PASSING CYCLONE TODAY. ALSO...WIND SPEED IS A CONCERN.

...06Z SYNOPSIS...
    HAND ANALYSIS OF THE SURFACE INDICATES THE COLORADO LOW IS
STILL IN SOUTHEAST COLORADO WITH CENTRAL PRESSURE OF 987MB. A WARM
FRONT WAS DRAPED ACROSS SOUTHEAST NEBRASKA AND THROUGH KANSAS TO THE
LOW IN COLORADO. WATER VAPOR IMAGERY SHOWED THE UPPER VORTEX ON THE
COLORADO/NEW MEXICO LINE SOUTH OF ALAMOSA.
...MODELS...
    SMALL DIFFERENCES BETWEEN THE ETA AND THE AVN IN THE SPEED OF THE
CYCLONE WILL RESULT IN LESS THAN 6 HOURS DIFFERENCE. THE LATEST TWO
RUNS OF THE ETA SEEM TO HAVE A HANDLE ON THE LOCATION OF THE COLORADO
SURFACE LOW, THOUGH THE ETA ON BOTH COUNTS IS TOO HIGH WITH THE
CENTRAL PRESSURE. THE AVN IS MOVING THE SYSTEM OUT OF THE LEESIDE A
LITTLE TOO QUICKLY (MAYBE ON THE ORDER OF ABOUT THREE HOURS)...SO
LAST NIGHTS RUN HAS IT ALREADY IN SOUTHWEST KANSAS NEAR DDC. THE
PROJECTED PATH OF THE UPPER VORTEX SHOULD BRING IT OVER THE MOUNTAINS
AND INTO SOUTHEAST COLORADO ABOUT 12Z. SO, THE SURFACE LOW SHOULD
BEGIN TRACKING TO THE NORTHEAST JUST AHEAD OF THE UPPER SYSTEM BY
THAT TIME. THIS FITS THE ETA SCENARIO WELL. SO THE ETA IS THE MODEL
OF CHOICE AT LEAST FOR THE FIRST TWO PERIODS. AFTER THAT...BOTH THE
ETA AND THE AVN ARE SHOWING GOOD CONSISTENCY WITH THEIR 12Z MODEL
RUN. HOWEVER...THERE ARE MAJOR DIFFERENCES BETWEEN THE TWO IN THEIR
HANDLING OF THE NEXT SURFACE LOW DIVING IN FROM THE NORTHWEST
THURSDAY. LOOKING AT THE UPPER SYSTEM...THE NGM SUPPORTS THE ETA
SOLUTION. SO, WITH A LITTLE LESS CONFIDENCE, I WILL STILL USE THE ETA
FOR THE THIRD AND FOURTH PERIOD. BEYOND THAT, THERE ISNT MUCH
DIFFERENCE ANYWAY BETWEEN THE ETA AND AVN.

...FORECAST...
    THE ELEVATED (750-700MB) WARM ADVECTION IN THE WRAPAROUND
CONTINUES THROUGH 18Z IN ALL BUT THE PANHANDLE...AND SO DOES THE
PETTERSON FRONTOGENESIS AT 800-650MB. THE FRONTOGENESIS SLOPES INTO
THE PANHANDLE. BY 00Z...THE FRONTOGENESIS WEAKENS. THE FORCING IN
THE WRAPAROUND AREA IS ENHANCED WITH 700-500MB DCVA AND 300-250MB
DIVERGENCE THROUGH THE AFTERNOON. I GO ALONG WITH THE SIGNIFICANT
(0.1 INCH AND GREATER) PRECIPITATION AREA SHOWN BY THE ETA...BUT 12
HOUR TOTALS OF 2 INCHES MIGHT BE OVERDONE, ESPECIALLY WITH LAYER PW
OF LESS THAN 1 INCH. CROSS-SECTIONS ACROSS CENTRAL AND NORTHERN
NEBRASKA INDICATE THAT THE UPWARD MOTION IN THE WRAPAROUND GETS
THROUGH THE DENDRITIC LAYER OVER ALL OF NEBRASKA TODAY, SO SNOW WILL
FORM. HOWEVER...IT APPEARS THAT THE DEPTH OF ABOVE FREEZING
TEMPERATURES IS LOW ENOUGH ONLY WEST OF A MERRIMAN-OGALLALA LINE.
THIS CORRESPONDS WELL WITH THE 1536 850-700MB THICKNESS. ALSO...THE
MEAN TEMPERATURE IN THE 900-800MB LAYER IS 0C OR COLDER ACCORDING TO
THE 06Z ETA. THE BIG QUESTION, THEN, IS IF THE SNOW WILL ACCUMULATE.
IF IT DOES...CONSIDERABLE BLOWING AND DRIFTING IS LIKELY. ITS REALLY
A CLOSE CALL EITHER WAY. AT THIS TIME, I WILL GO WITH AN ADVISORY
FOR SNOW AND/OR BLOWING SNOW FOR THE EASTERN PANHANDLE WITH TOTAL
ACCUMULATIONS OF 2-4 INCHES. CHEYENNE REPORTS THAT KIMBALL IS GETTING
ACCUMULATIONS AT THIS TIME. THE BEST CHANCE OF ACCUMULATION MAY BE IN
GARDEN AND DEUEL COUNTY. HOWEVER, I WILL PUT THE ADVISORY IN SHERIDAN
COUNTY AS WELL SINCE WE ALREADY HAVE A WINTER WATCH THERE.
    THE 06Z ETA IS SHOWING THE GRADIENT TIGHTENING BY 18Z WITH
BOUNDARY LAYER WIND RANGING FROM 20KT IN ONL TO 45KT JUST EAST OF
AIA. SO...WIND IN THE WEST WILL PROBABLY BE SUSTAINED AT LEAST 35
MPH WITH GUSTS TO 45 MPH TODAY OVER ALL BUT THE ONL-BBW-ANW AREAS.

.LBF...WINTER WEATHER ADVISORY FOR SNOW/BLOWING SNOW NEZ005-022-056.
       WIND ADVISORY NEZ006-023>025-035>037-057>059-069>071

SPRINGER

NEZ004>010-022>029-035>038-056>059-069>071-111630-

SEVERE WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
547 AM CDT WED APR 11 2001

...STORM SPOTTER ACTIVATION IS NOT ANTICIPATED THROUGH THURSDAY
MORNING...

THERE IS A CHANCE OF THUNDERSTORMS TODAY OVER PORTIONS OF WESTERN
AND NORTH CENTRAL NEBRASKA. THE GREATEST RISK FOR THUNDERSTORM
DEVELOPMENT IS SOUTH AND EAST OF AN OGALLALA TO VALENTINE LINE.
MOST OF THESE THUNDERSTORMS ARE NOT EXPECTED TO REACH SEVERE LIMITS.
HOWEVER A FEW ISOLATED THUNDERSTORMS MAY APPROACH SEVERE THUNDERSTORM
LIMITS EAST OF A BROKEN BOW TO ONEILL LINE. LITTLE OR NO THUNDERSTORM
DEVELOPMENT IS EXPECTED ACROSS THE NORTHWEST PORTION OF THE OUTLOOK
AREA.

AN INTENSE LOW PRESSURE SYSTEM WILL MOVE NORTHEAST THROUGH NEBRASKA
TODAY. A WARM FRONT ASSOCIATED WITH THE LOW PRESSURE SYSTEM
WILL ALSO LIFT NORTHWARD ACROSS NEBRASKA...AND SHOWERS AND
TnHUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG AND NORTH OF THE FRONT
ACROSS EASTERN AREAS OF THE OUTLOOK AREA. HOWEVER THESE STORMS ARE
NOT EXPECTED TO BECOME SEVERE ACROSS WESTERN OR NORTH CENTRAL
NEBRASKA.

DP