Severe Thunderstorm Warning 206, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
230 PM CDT TUE JUL 21 1998

...FORECAST PROBLEM WITH THIS AFTERNOONS FORECAST CYCLE IS THE
LOCATION OF THUNDERSTORMS...

MODEL PERFORMANCE DISCUSSION...
    THE ETA, AVN, AND NGM SOLUTIONS ARE SIMILAR WITH NEARLY ALL
PARAMETERS THROUGH 24 HOURS. AT 36 HOURS, THE ETA APPEARS TO BE A
LITTLE FASTER WITH SURFACE AND UPPER AIR FEATURES. ETA IS ALSO
SIGNIFICANTLY STRONGER AND FASTER WITH THE VORT MAX PROJECTED INTO
WESTERN NEBRASKA ON THURSDAY. AT 36-48 HOURS, THE NGM AND AVN ARE
NEARLY IDENTICAL. THE NGM HAS DONE WELL WITH TEMPERATURES YESTERDAY AND
THE DAY BEFORE, AND SEEMS TO BE THE CLOSEST THIS MORNING WITH THE
LOCATIONS AND STRENGTHS OF THE SURFACE FRONT AND THE LOW, AND WITH THE
500MB HEIGHT AND VORTICITY FIELDS. SO, HAVE CHOSEN THE NGM FOR EARLY
PERIODS AND THE AVN/MRF FOR LATE PERIODS.

FIRST PERIOD DISCUSSION...
    LAST NIGHT THE CONVECTIVE COMPLEX DEVELOPED NORTH OF THE SURFACE
FRONT AND THE AXIS OF THE 850MB THETA-E RIDGE AND ALONG AND SOUTH OF THE
700MB FRONT. ITS ELEMENTS MOVED NEARLY PARALLEL TO THE THETA-E RIDGE
PRODUCING RAINFALL AMOUNTS OF 2-3 INCHES ALONG A BBW-OGA AXIS. I DONT
REALLY SEE ANY REASON THAT THE SAME CRITERIA WONT WORK TONIGHT. SO A
GOOD INDICATION FOR TONIGHTS FORECAST IS THE LOCATION OF THOSE
FEATURES. AT 00Z, THE NGM HAS BOTH THE 850M AND 700MB THETA-E RIDGE
THROUGH CENTRAL KANSAS WITH THE 700MB FRONT ALONG THE NEB/KANS LINE.
USING THOSE LOCATIONS, THE MOST LIKELY LOCATION FOR THE DEVELOPMENT
TONIGHT IS SOUTH BBW-LBF-OGA LINE (IN THE SPC SLIGHT RISK OUTLOOK
AREA). BECAUSE OF THE CONTINUED INSTABILITY (0 TO -2 850-500MB LIFTED
INDEX) AND ABUNDANT LOW AND MID LEVEL MOISTURE, SOME MENTION OF
THUNDERSTORMS (SAY 30-40 PERCENT) IS APPROPRIATE FOR THE REST OF
SOUTHWEST AND WESTERN NEBRASKA WEST OF A VTN-LBF LINE. COULD PROBABLY
GET BY WITH NO MENTION OF THUNDERSTORMS IN THE THE CENTRAL AND NORTH
CENTRAL ZONES. PROBABLY SHOULD GO 20 PERCENT VALENTINE, MULLEN, AND
MERRIMAN AREAS IN THE TRANSITION BETWEEN 30 PERCENT AND ZERO.
    TEMPERATURES TONIGHT SHOULD BE AT OR SLIGHTLY COOLER THAN THIS
MORNINGS NUMBERS IN THE NORTHERN AND EASTERN PARTS OF THE NORTH PLATTE
FORECAST AREA (WHICH WERE IN THE MID 50S TO LOWER 60S). IN THE SOUTH
CLOUDS WOULD NORMALLY HOLD THEM UP, BUT, WITH COOLING DUE TO
THUNDERSTORMS, MID 60S ARE PROBABLY OKAY.

SECOND PERIOD AND BEYOND...
    THE SURFACE PRESSURE FIELD AND 1000-500MB THICKNESS VALUES INDICATE
THE FRONT AND THE 850MB THETA-E RIDGE CONTINUING THROUGH CENTRAL KANSAS
THROUGH THURSDAY NIGHT WITH THE 700MB FRONT ALONG THE NEB/KANS LINE. AT
700MB, THE 700MB THETA-E RIDGE WILL RUN THROUGH CENTRAL KANSAS AND INTO
CENTRAL COLORADO WITH THE BEGINNINGS OF A RIDGE FROM CENTRAL COLORADO
INTO THE NEBRASKA PANHANDLE, SO THUNDERSTORMS COULD BE EXPECTED SOUTH
AND WEST OF A CDR-LBF LINE THURSDAY AS THE 700MB FRONT WORKS ITS WAY
BACK INTO WESTERN THROUGH SOUTH CENTRAL NEBRASKA. SPREADING TO VTN,
ANW, BBW, (AND POSSIBLY ONL) THURSDAY NIGHT. WITH THE FRONT CONTINUING
THROUGH NORTHERN KANSAS AS THE AVN/MRF INDICATES, A 40 PERCENT
PROBABILITY OF AT LEAST AFTERNOON THUNDERSTORMS IS PROBABLY NEEDED IN
THE WESTERN AND SOUTHWESTERN PARTS OF THE NORTH PLATTE FORECAST AREA
FRIDAY (AND MAYBE BEYOND).
    IN THE OUTLOOK FOR TEMPERATURES, THE NGM THICKNESS DECREASES ABOUT
30M BETWEEN THIS EVENING AND THURSDAY EVENING WITH 850MB TEMPERATURE
FALLS OF ABOUT 5C. IN THE CENTRAL AND NORTH, INCREASSED SUNSHINE SHOULD
COMPENSATE AT LEAST PARTIALLY. ON FRIDAY THE AVN/MRF INDICATES LITTLE
CHANGE IN EITHER THICKNESS OR 850MB TEMPERATURES.

SUGGESTED CCF

PRELIMINARY GUIDANCE FOR COORDINATION ONLY. OFFICIAL FORECAST IS
CONTAINED WITHIN THE PRODUCT OMAZFPLBF.

LBF BB 060/084 058/084 057 49426
VTN BB 058/083 060/084 058 49203

OGA BB 061/085 059/085 058 49426
IML BB 064/086 062/086 060 49646
BBW BB 059/084 058/084 059 49203
ANW BB 064/082 060/082 060 49003
ONL BB 065/081 063/081 062 49003

SPRINGER