Severe Thunderstorm Warning 188, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
301 PM CDT WED AUG 20 1997

TSRA FORECAST TO REMAIN CHALLENGE THROUGH THE PERIOD.

SURFACE ANAL AT 18Z SHOWED SURFACE HIGH EXTENDING SOUTHEAST FROM NWRN
SOUTH DAKOTA INTO NERN KS. TROUGH OF LOW PRESSURE EXTENDING FROM WEST
OF BFF TO SOUTH OF GLD AND THEN EAST ACROSS SRN KS. SOUTHEAST WIND FLOW
RETURNED DWPTS INTO THE 60S IN EXTREME SOUTHWEST FORECAST AREA. VISIBLE
SATELLITE LOOP SHOWS WEAK BOUNDARY ACROSS THE NEB PANHANDLE FROM OVER
AIA TO ABOUT 10 MILES SOUTHEAST OF LBF. OUTFLOW BOUNDARY FROM PREVIOUS
STRONG THUNDERSTORMS EXTEND ACROSS OGA. ACCUS CAN BE SEEN OUT THE
WINDOW ASSOCIATED WITH BOUNDARY AND KLNX 88D SHOWING LONE CELL NOW
MOVING ACROSS NRN GARDEN COUNTY AND ARTHUR COUNTIES ALONG OUTFLOW
BOUNDARY.

MODELS HAVE SHOWN A HISTORY OVER THE LAST COUPLE OF DAYS OF MOVING
SHORTWAVES TOO FAST AND UPPER RIDGE BEING STRONGER THAN ANALYZED. 21/00Z
PROGS INDICATE UPPER RIDGE TO CONTINUE AMPLIFYING AND BUILD EAST TO
ACROSS NORTHWESTERN WYOMING THIS EVENING AND BELIEVE THIS TO BE FAST
PACED WITH REMNANTS OF TS IGNACIO TO INHIBIT STRENGTHENING UPPER RIDGE
TONIGHT. THIS WOULD RESULT IN 500 MB SHORTWAVE PROGGED TO MOVE THROUGH
CENTRAL PORTIONS TONIGHT TO EXTEND FURTHER WEST. CONVECTIVE TEMP
REACHED OVER PORTIONS OF THE PANHANDLE THIS AFTERNOON...HOWEVER FURTHER
EAST ADDITIONAL DYNAMICS ARE NEEDED TO CONTINUE THUNDERSTORM
DEVELOPMENT EAST OF THE ADJACENT COUNTIES TO THE PANHANDLE. GRIDDED
DATA INDICATED A 500 MB THERMAL TROUGH TO MOVE THROUGH THIS EVENING WITH
THE ADDITIONAL COLD AIR ALOFT TO FURTHER DESTABILIZE LAPSE RATES. 200 MB
JETSTREAM AXIS TO CARRY MAXIMUM THROUGH TONIGHT WITH RRQ ENTRANCE
REGION TO MOVE ACROSS AFTER MIDNIGHT. 850 MB CONVERGENCE INCREASES
ALONG THE FRONT RANGE THIS EVENING AND OVERNIGHT...ALONG WITH DIVG
ALOFT AND AN INCREASING MOISTURE SUPPLY AS THE SURFACE HIGH BUILDS
EAST. CAPE VALUES PRESENTLY AROUND 1500 J/KG AT LBF AND GRIDDED DATA
SHOWS THIS TO STEADILY INCREASE OVERNIGHT...THEN DECREASE DURING
MORNING WITH STRONGER RETURN OF THETAE AIR ON THURSDAY. HOWEVER MOST
ACTIVITY SHOULD CEASE AFTER SUNSET ACROSS THE PANHANDLE AND AFTER
MIDNIGHT FURTHER EAST TO A VTN TO LBF LINE.

ACROSS NORTH CENTRAL SECTIONS COOL DRY HIGH PRESSURE SHOULD INHIBIT
THUNDERSTORM DEVELOPMENT EAST WITH POSSIBLY SOME HIGH CLOUDINESS
OTHERWISE PARTLY CLOUDY TONIGHT.

ON THURSDAY A REPEAT WITH 850 MB CONVERGENCE TO SHIFT FURTHER EAST AS
SURFACE RIDGE WEAKENS AND MOVES EAST. LEESIDE TROUGH TO DEVELOP WITH
REDEVELOPMENT OF STORMS OVER THE FOOTHILLS BY LATE AFTERNOON...THEN
CONVECTION MOVING EAST SOUTHEAST INTO WRN NEB. 24 TO 36 HOURS PROGS
VARY WITH POSITION AND STRENGTH OF NEXT WAVE TO TOP THE RIDGE THURSDAY.
BELIEVE A COMPROMISE OF ETA/NGM TO BE BEST COURSE TO TAKE WITH THE
EXPECTATION OF SCATTERED THUNDERSTORM DEVELOPMENT FURTHER EAST INTO
PORTIONS OF NORTH CENTRAL THURSDAY EVENING AND NIGHT.

NORTHWEST UPPER FLOW KEPT COLD AIR ADVECTION INTO WESTERN NEB WITH HIGH
SUN ANGLE AND FEW CLOUDS TO ALOW TEMPS TO GET TO AROUND 80 TO THE LOWER
80S. SLIGHTLY WARMER READINGS EXPECTED ON THURSDAY. ALL MODELS GUIDANCE
ARE CONSISTED AND WILL FOLLOW CLOSE.

CCF
LBF BB 057/086 058/086 056 19312
OGA BB 058/087 060/088 059 19312
IML BB 060/087 060/088 060 19312
VTN BB 055/083 056/085 056 19212
ONL UB 054/082 056/083 056 1900-
BBW UB 054/083 057/085 057 19002

WOOD