High Wind in Nebraska, May 21, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
220 PM CDT TUE MAY 21 2002

...INITIAL FORECAST PROBLEM IS THE WIND AND CHANCE OF
PRECIPITATION IN THE INITIL FORECAST PERIOD...THEN THE CHANCE OF
PRECIPITATION DAYS 3-7...

...18Z SYNOPSIS...
     SURFACE ANALYSIS SHOWED SOME PRETTY IMPRESSIVE CYCLOGENESIS
ALONG THE MONTANA-WYOMING BORDER WITH A VERY TIGHT MSL PRESSURE
GRADIENT. VERY WINDY CONDITIONS WERE PREVALENT ON THE NORTHERN
PLAINS WITH GUSTS APPROACHING 50 MPH ON PARTS OF THE HIGHER PLAINS.
IN THE UPPER LEVELS, A MATURE CYCLONE WAS APPARENT IN THE 6.7U
IMAGERY CENTERED OVER NORTHERN UTAH. THERE WAS ALSO A GOOD MID LEVEL
MOISTURE PLUME FROM THE SOUTHWEST U.S. AND UP ALONG THE HIGH PLAINS
OF COLORADO AND THE NEBRASKA PANHANDLE. THE 750M AGL WIND PROFILERS
WERE SHOWING A GOOD STREAM FROM THE GULF OF MEXICO INTO CENTRAL
NEBRASKA. ALSO, THE BLOCKING PATTERN OF THE LAST 5 DAYS APPEARS TO BE
BREAKING DOWN FINALLY.

..MODELS...
     THERE ARE SOME DIFFERENCES BETWEEN THIS MORNINGS RUN OF THE
GLOBAL AND THE ETA. THE ETA IS FASTER THAN THE AVN/GLOBAL IN BRINGING
COLD AIR ONTO THE NORTHERN PLAINS FROM CANADA. BOTH ARE SHOWING
GOOD CONTINUITY WITH THE PREVIOUS MODEL RUN, SO, THAT DOESNT SHED
ANY MORE LIGHT ON THE SUBJECT. THE NGM IS NEARLY IDENTICAL TO THE ETA
IN THAT REGARD. SO, I WILL GO WITH THE FASTER SOLUTION THROUGH THE
THIRD PERIOD AND AIR BRUSH A COMPROMISE BETWEEN THE GLOBAL AND THE
ETA IN THE FOURTH PERIOD.
     THE WEAKENING OF THE BLOCK HERALDS A CHANGE TO A MORE
PROGRESSIVE PATTERN. SO, I HAVE MODERATE CONFIDENCE IN THE 00Z RUN OF
THE GLOBAL. IN THE MEDIUM RANGE, THE WEIGHTED CONSENSUS ON THE
ENSEMBLE PAGE SEEMS TO FAVOR THE GLOBAL MODELS SOLUTION AS WELL.

...FORECAST...
     WIND WILL CONTINUE AT ADVISORY LEVEL UNTIL AT LEAST SUNSET, SO,
I WILL KEEP THE ADVISORY GOING IN ALL ZONES THIS EVENING. BY
MIDNIGHT, IT SHOULD BE DOWN TO 20 TO 30 MPH.
     THE NEXT PROBLEM WITH TONIGHTS FORECAST IS THE CHANCE OF
PRECIPITATION. WITH DECENT LOW LEVEL WARM ADVECTION AND CONVERGENCE
COUPLED WITH ELEVATED 2D-FRONTOGENESIS 800-650MB AND 700-500MB
DCVA, THERE IS PLENTY OF FORCING THIS EVENING IN WESTERN NEBRASKA.
THERE IS ALSO SOME INSTABILITY. THE GOES DERIVED TPW IS NOT MUCH USE
FOR WESTERN NEBRASKA BECAUSE OF CLOUDINESS, BUT WHAT IS AVAILABLE
SHOWS A MOISTURE PLUME FROM THE GULF INTO SOUTH CENTRAL NEBRASKA.
HOWEVER, EVEN AT 750MB THE CONDENSATION DEFICITS ARE GREATER THAT
50MB. SO, CONVECTION WILL BE HIGH-BASED AND IS NOT LIKELY TO PRODUCE
MUCH IN THE WAY OF RAIN AMOUNTS. EVEN THE ETA QPF MAY BE OVERDONE.
STILL, I WILL GENERALLY FOLLOW THE ETA IN THE FORECAST GRIDS WITH
SOME ADJUSTMENTS POSSIBLE. THEN, IT REALLY ISNT UNTIL FRIDAY THAT
ANY FORCING IS EXPECTED IN NEBRASKA, AND THEN IT IS ONLY IN THE
SOUTH.
     THE GULF FLOW DOESNT REACH INTO NEBRASKA AGAIN BEFORE LATE
SATURDAY NIGHT. THEN, A GOOD FLOW TRAJECTORY BECOMES ESTABLISHED BY
EARLY SUNDAY. SO, THE CHANCES OF PRECIPITATION ARE SMALL UNTIL THEN.
BY LATE SUNDAY, CONVERGENCE ALONG A SURFACE TROUGH WILL INITIATE THE
LIFT, BUT, ELEVATED 2D-FRONTOGENESIS AND DCVA IS NOT VERY STRONG
UNTIL TUESDAY NIGHT. STILL, EVEN WITH MINIMAL LOW LEVEL FORCING LATE
SUNDAY, THE 850MB CONDENSATION DEFICITS IN CENTRAL AND EASTERN
NEBRASKA DECREASE TO 50MB OR LESS WITH SPECIFIC HUMIDITY ABOUT 8G/KG
IS ENOUGH TO WARRANT A MENTION OF PRECIPITATION. INCREASING ELEVATED
2D-FRONTOGENESIS AND DCVA SHOULD ALLOW THE PRECIPITATION TO DEVELOP
AGAIN MONDAY AND TUESDAY. THE 850-500MB LI DECREASES TO -2C TO -4C IN
ALL BUT THE WESTERN QUARTER OF THE NORTH PLATTE FORECAST AREA.

.LBF...ZONES 004>010-022>029-035>038-056>059-069>071-094
       WIND ADVISORY TIL LATE EVENING.

SPRINGER

NEZ004>010-022>029-035>038-056>059-069>071-094-212045-

HAZARDOUS WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1145 AM CDT TUE MAY 21 2002

...SEVERE WEATHER IS NOT EXPECTED TODAY OR TONIGHT...

THERE IS A CHANCE OF THUNDERSTORMS TONIGHT OVER PORTIONS OF WESTERN
AND NORTH CENTRAL NEBRASKA.  ANY THUNDERSTORMS WHICH FORM ARE NOT
EXPECTED TO REACH SEVERE LEVELS.

AN INTENSE UPPER LEVEL STORM SYSTEM WILL LIFT NORTHEAST INTO THE
NORTHERN HIGH PLAINS TONIGHT. AS THIS SYSTEM LIFTS NORTHEAST OUT OF
THE CENTRAL ROCKIES...A DEEP TROUGH OF LOW PRESSURE AT THE SURFACE
WILL MOVE EAST OFF THE HIGH PLAINS OF COLORADO AND WYOMING...
REACHING CENTRAL NEBRASKA BY WEDNESDAY MORNING.

SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG THE FOOTHILLS
OF THE ROCKIES LATE THIS AFTERNOON...MOVE NORTHEAST INTO NORTHWEST
NEBRASKA THIS EVENING...AND CONTINUE EAST AND WEAKEN OVER WESTERN
AND NORTH CENTRAL NEBRASKA TONIGHT.

LOW-LEVEL MOISTURE WILL REMAIN VERY LIMITED OVER ALL OF WESTERN AND
NORTH CENTRAL NEBRASKA THROUGH TONIGHT. THEREFORE...ANY
THUNDERSTORMS WHICH FORM WILL REMAIN WIDELY SCATTERED...HAVE LIMITED
RAIN...AND ARE NOT EXPECTED TO PRODUCE LARGE HAIL OR DAMAGING WINDS.
BECAUSE OF THE WIDELY SCATTERED NATURE OF THE STORMS...MOST AREAS
WILL REMAIN DRY.