Severe Thunderstorm Warning 150, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
340 AM CDT WED JUL 5 2000

FORECAST PROBLEM...
    LOCATION...COVERAGE...AND TIMING OF THUNDERSTORMS.

...SYNOPSIS...
    AT 06Z...THE 11U-3.9U IMAGERY INDICATED A BOUNDARY IN
SOUTHWEST SOUTH DAKOTA ALONG A PIERRE...PHILIP...CUSTER LINE. IT WAS
THE FOCUS OF THE THUNDERSTORM DEVELOPMENT IN NORTHWEST SOUTH
DAKOTA...AND NOW APPEARS TO BE ENHANCED BY OUTFLOW FROM THE ONGOING
SOUTH DAKOTA/NORTH DAKOTA CONVECTION. A 06Z SURFACE HAND ANALYSIS
SHOWS A CLOSED LOW IN SOUTHEAST COLORADO WITH A STATIONARY FRONT
ALONG THE KANSAS-NEBRASKA BORDER. SEVERAL BOUNDARIES CAN BE SEEN IN
THE PRESSURE FIELD PIN-WHEELING ABOUT THE LOW CENTER. A LARGE POOL OF
70+ SURFACE DEWPOINTS WAS IN CENTRAL AND EASTERN NEBRASKA WITH 75 IN
SOUTH CENTRAL NEBRASKA. GOES DERIVED PRECIPITABLE WATER RANGED FROM
ABOUT 30MM IN SOUTHWEST NEBRASKA TO NEARLY 50MM IN SOUTHEAST
NEBRASKA. RADAR COMPOSITES SHOW CONVECTION IN THE NEBRASKA
PANHANDLE.
...MODEL CHOICE DISCUSSION...
    THE AVN AND ETA SOLUTIONS ARE SIMILAR. THE ETA AND AVN SURFACE
AND 850MB TEMPERATURE PROGS BOTH INDICATE A COOL MESOSCALE BOUNDARY
ALONG THE NEBRASKA/SOUTH DAKOTA BORDER BY 18Z. THIS IS APPARENTLY
A REFLECTION OF THE DAKOTA BOUNDARY INDICATED BY THE SATELLITE
LOOP. FOR THE FIRST PERIOD...I WILL TRY TO BLEND THE ETA WITH
OBSERVED CONTINUITY TO DETERMINE THE LOCATION AND TIMING OF
THUNDERSTORM DEVELOPMENT...AND USE THE ETA FOR THE SECOND PERIOD.

...THUNDERSTORM DISCUSSION...
    IT SEEMS THAT THERE WILL BE TWO AREAS OF CONVECTIVE INITIATION
TODAY AND TONIGHT. THE NORTH CENTRAL ZONES WILL BE THE AREA OF
INTEREST TODAY WHILE THE SOUTHWEST WILL BE THE AREA TO WATCH
TONIGHT.
    WITH THE OBSERVED DEWPOINTS IN THE 70S AND HIGH PRECIPITABLE
WATER...THE SITUATION IS CERTAINLY VOLATILE ENOUGH FOR A CONVECTIVE
OUTBREAK. THE 06Z ETA OUTPUT SHOWS SBCAPES OF 3000 TO 4000 J/KG BY
LATE AFTERNOON OVER ALL BUT THE NORTH CENTRAL PART OF THE AREA. THAT
STABLE POOL APPEARS TO BE A MANIFESTATION OF A MESOSCALE BOUNDARY.
SO...THE FORECAST BOILS DOW TO LOCATING THE MECHANISM NEEDED FOR
CONCENTRATION OF CONVECTIVE INITIATION.
    WIND PROFILERS SHOWED A 30-40KT 850MB SOUTHWESTERLY JET BEYOND
MCCOOK AND THE MOTION OF THE LOW CLOUDS WOULD INDICATE WIND TURNING
AND BECOMING EAST TO SOUTHEAST BEFORE REACHING THE SOUTH PLATTE
VALLEY. THE ETA KEEPS AN EAST WIND OVER THE NORTHERN PART OF THE
NORTH PLATTE FORECAST AREA THROUGH THE DAY WITH GOOD CONVERGENCE
INDICATED ALONG A VTN-OGA-SNY LINE BY 18Z.     PROJECTION OF THE
MOTION OF THE SOUTH DAKOTA BOUNDARY BRINGS IT TO THE SOUTH DAKOTA-
NEBRASKA BORDER BY 0900Z. WITH THE PROFILERS INDICATING A TRANSITION
FROM A SOUTH WIND IN SOUTHWEST NEBRASKA TO AN EAST WIND IN NORTH
CENTRAL AND NORTHEAST NEBRASKA...I WOULD NOT EXPECT THE MOMENTUM TO
CARRY THE BOUNDARY MUCH PAST THAT PROJECTED POSITION UNTIL IT IS
REINFORCED BY NEW CONVECTIVE DEVELOPMENT. ONGOING CONVECTION IN THE
PANHANDLE IS LIKELY TO GENERATE OTHER BOUNDARIES TO INTERACT WITH
THE ONE COMING OUT OF SOUTH DAKOTA. THE ETA SOUNDING FOR THE EASTERN
PANHANDLE SHOWED THE NEGATIVE ENERGY APPROACHING ZERO BY 18Z. SO...I
WOULD EXPECT CONVECTION TO FIRE THEN. WITH THE BLEND OF THE ETA
FORECAST AND THE CONTINUITY FROM OBSERVED CONDITIONS...THE LOCATION
OF CONVECTIVE INITIATION WOULD BE NORTH AND WEST OF A BBW-LBF-OGA
LINE AND SOUTH AND EAST OF A VTN-MHN-AIA LINE. THE AREAS SOUTH OF THE
CONVERGENCE LINE WILL PROBABLY BE DRY AS HAS BEEN THE CASE. THE
STRONGEST DIVERGENCE ALOFT AND DCVA IS EXPECTED TO BE IN NORTHWEST
AND NORTH CENTRAL NEBRASKA. THAT MOVES INTO NORTHEAST NEBRASKA BY
LATE AFTERNFOON...BUT ANOTHER PULSE COMES ACROSS NORTHERN NEBRASKA
THIS EVENING AND TONIGHT. IN THE SOUTHWEST...DCVA AND WARM ADVECTION
COMBINE TO PROVIDE GOOD LIFT TONIGHT.

.LBF...NONE

SPRINGER

NEZ004>010-022>029-035>038-056>059-069>071-051630-

SEVERE WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
540 AM CDT WED JUL 5 2000

...STORM SPOTTER ACTIVATION MAY BE REQUIRED TODAY AND TONIGHT IN
WESTERN AND NORTH CENTRAL NEBRASKA...

A STATIONARY FRONT ALONG THE KANSAS...NEBRASKA BORDER AND OTHER
BOUNDARIES FROM THE NORTH AND THE WEST WILL ALL COMBINE WITH THE
VERY WARM HUMID CONDITIONS TO PRODUCE THUNDERSTORMS TODAY AND
TONIGHT. A THUNDERSTORM COMPLEX IS EXPECTED TO DEVELOP BY MIDDAY FROM
THE STORMS IN THE PANHANDLE AND TRACK ACROSS THE NORTHERN PART OF THE
AREA THIS AFTERNOON AND EVENING. WITH THE EXTREME INSTABILITY IN
WESTERN AND NORTH CENTRAL NEBRASKA...THUNDERSTORMS MAY PRODUCE LARGE
HAIL AND DAMAGING WIND. THE GREATEST RISK OF SEVERE WEATHER IS ALONG
AND NORTH OF A LINE FROM ONEILL...THROUGH BROKEN BOW...TO OSHKOSH.

SPRINGER