Severe Thunderstorm Warning 171, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
215 PM CDT THU JUL 15 1999

...TSRA CHANCES ARE THE MAIN CONCERN THRU THE PERIOD...

17Z SFC ANALYSIS SHOWS SFC LOW CENTERED ON THE ND AND SD BORDER WITH A
SFC TROUGH EXTENTING SOUTH FROM A VTN TO IML LINE.  SFC LOW ALSO
CENTERED NEAR PUB IN SE CO. THE COLD FRONT HAS REACHED THE EXTREME NW
PANHANDLE OF NEBRASKA SKIES FAIRLY SUNNY BEHIND THE TROUGH AND THE
FRONT.

AT 19Z...KLNX RADAR SHOWS THUNDERSTORMS DEVELOPING ALONG TROUGH AXIS IN
NW KS AND EXTREME SW NEBRASKA NEAR MCCOOK.  DEWPOINTS BEHIND THE TROUGH
ARE IN THE 50S WHILE AHEAD OF THE TROUGH DEPOINTS ARE IN THE MID 60S.

19Z LAPS DATA INDICATES CAPES OF 3500 TO 5000 J/KG JUST EAST OF CWA.
DO EXPECT ORGANIZED THUNDERSTORMS TO FIRE LATE THIS AFTERNOON EAST OF A
BASSETT TO BRADY TO HAYES CENTER LINE. WIDELY SCATTERED SHOWERS AND
THUNDERSTORMS MAY DEVELOP TO THE WEST.

THE NGM AND AVN INITIALIZED THE SFC FEATURES WITH PRESSURE TOO HIGH
SOUTH INTO COLORADO.  THE ETA WAS VERY CLOSE WITH 12Z SFC ANALYSIS.
WILL FOLLOW ETA WITH SFC FEATURES THRU 48 HRS.

IN THE UPPER FEATURES...ALL MODELS ARE IN FAIR AGREEMENT THROUGH 48HRS
SHOWING UPPER RIDGE RETROGRADING BACK WEST INTO THE CENTRAL PALINS IN
RESPONSE TO A DEEPENING TROUGH IN THE PACIFIC NW.  THIS WILL GIVE A
GRADUAL DECREASE IN TSRA CHANCES AS UPPER RIDGE BEGINS TO DOMINATE AND A
STRONGER CAP BUILDS IN. FAIRLY GOOD MOISTURE WILL BE PRESENT THROUGH
THE WEEKEND FOR SOME CHANCE OF LATE DAY TSRA TO DEVELOP.

WILL GENERALLY FOLLOW THE ETA MODEL WITH THE AVN IN THE LATER PERIODS.

TONIGHT...MAIN FOCUS FOR CONVECTION WILL BE ALONG AND AHEAD OF SFC
TROUGH. WILL HAVE THE HIGHEST POPS IN BUB AND ONL AREAS WITH DECREASED
POPS TO THE WEST.
FRIDAY...THE SFC TROUGH SLOWLY MOVES EAST STILL ENOUGH INSTABILITY AN
MOISTURE TO WARRANT LOW POS IN AFTERNOON AND EVENING.
FRIDAY NIGHT AND SATURDAY...NO FORCING INDICATED BY THE ETA MODEL THRU
12Z SATURDAY. A STATIONARY FRONT IS SHOWN FROM SE NEBRASKA INTO SW
KANSAS WILL ALL FOCUS SE OF THE CWA.  AVN SHOWS WEAK SHORTWAVE SLIDING
SE FROM WYOMING INTO THE NEBRASKA PNHDL BY 00Z SUNDAY AND INTO CWA
OVERNIGHT.

IN THE EXTENDED...WILL HAVE CHANCE OF THUNDERSTORMS SUNDAY WITH AVN
SHOWING SFC LOW IN WRN SD AND TROUGH SOUTHWARD INTO WRN KS AND VORT MAX
PASSING THROUGH AREA. MONDAY AND TUESDAY...DESPITE UPPER RIDGE BUILDING
IN...MOISTURE DOES STAY IN AREA. WEAK SHORTWAVES EJECTING OUT OF
SOUTHWEST FLOW WILL GIVE AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS.
WILL KEEP HIGHS IN THE 80S SUNDAY WITH UPPER 80 TO LOWER 90S MONDAY AND
TUESDAY.

.LBF...NONE.

ROBERG