Severe Thunderstorm Warning 7, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
256 PM CDT SUN MAY 9 1999

SEVERE THREAT MAIN CONCERN TONIGHT...

18Z SFC ANALYSIS SHOWED SFC LOW CENTER BETWEEN DEN AND CYS WITH WARM
FRONT EXTENDING SE FROM LOW CNTR TO NE OF AKO TO ALONG THE NEB/KS
STATELINE TO NEAR TOP. DRYLINE LOCATED EAST OF AKO...S INTO EXTREME
SERN NM. VISIBLE SAT LOOP INDICATES MAINLY HIGH CIRRUS SHIELD
PRESENTLY OVER WESTERN NEB ASSOCIATED WITH WEAK 5H S/W LIFTING NE
WITH A SERIES OF WAVES INDICATED ON WV IMAGERY TO MOVE THROUGH
DURING THE NEXT 24 HOURS. ACCUS WHICH WAS OVER THE W THIS MORNING
NOW EXTENDING N TO S OVER PORTIONS OF CNTRL NEB.

12Z MODEL RUNS WERE COMPARATIVE THROUGH 36 HOURS WITH VARIATIONS
DEVELOPING BEYOND. OVERALL PREFERRED THE ETA SOLUTION THROUGH 36
HOURS WITH MAIN COLD FRONT TO MOVE THROUGH MONDAY. MODEL
TEMPERATURE GUIDANCES CLOSE AND BLEND USED.

THIS EVENING WARM FRONT TO THE SOUTH WILL CONTINUE TO LIFT N AND BE
AT LEAST ONE FOCUS FOR TSTM DEVELOP. 8H SLY LLJ STRENGTHENS TO 65
KTS BY MIDNIGHT WITH THE ATMOSPHERE TO CONTINUE TO MOISTEN
OVERNIGHT. THIS EVENING ACROSS THE W LIS WILL BE -6 TO -8 WITH CAPE
VALUES USING ETA TO 3200 J/KG. WEAK CAP IN PLACE SHOULD QUICKLY
ERODE LATE THIS AFTN WITH SCATTERED TSTMS IN THE W...THEN ACTIVITY
INCREASING WHILE MOVING FURTHER E INTO BETTER MOISTURE AXIS WITH
DWPTS RANGING FM THE LOWER 50S OVER THE ERN PANHNDLE TO 60 AT MCK
ATTM.

MAIN TSTM ACTIVITY EXPECTED ACROSS THE WEST THROUGH MIDNIGHT THEN
THUNDERSTORMS CONTINUING INTO THE OVERNIGHT HOURS AS UPPER LEVEL
DIVERGENCE AIDS IN PROVIDING LIFT. THE SFC LOW WILL MOVE TO NEAR
OGA BY MIDNIGHT WITH THE APEX OF WARM FRONT EXTENDING E-NE ACROSS
NRN NEB. DRIER AIR WILL BEGIN TO FILTER INTO THE SW AS THE DRYLINE
PUSHES EAST.

MONDAY MORNING THE FRONT WILL MOVE SLOWLY EAST ACROSS WESTERN
NEBRASKA WITH STRONGER 5H S/W TO MOVE THROUGH. BY AFTN THE FOCUS
FOR SEVERE STORMS WILL BE ACROSS THE NCNTRL FA AS THE 8H SLY LLJ
CONTINUES TO PULL MOISTURE NWD WITH HIGH PW RATES FOR SOME
THUNDERSTORMS TO PRODUCE VERY HEAVY RAIN. DECENDING MOTION INCREASES
IN THE W ON MONDAY AFTN WITH SHOWERS POSSIBLE.

MONDAY NIGHT THE FRONT WILL BE E OF THE FA AS THE MAIN 5H LOW
MOVES NE INTO SCNTRL SD. THE COLD POOL ASSOCIATED WITH THIS
FEATURE MAY BE SUFFICIENT TO PRODUCE SCATTERED SHOWERS AND
THUNDERSTORMS IN THE WEST AND WILL REINTRODUCE THUNDERSTORMS FOR
THE OVERNIGHT PERIODS MAINLY ACROSS THE NRN FA.

MONDAY NIGHT INTO TUESDAY THE MODELS SOLUTIONS DIVERGE WITH TRACK OF
THE 5H LOW WITH BLEND OF ETA/AVN MODELS USED. WEAK RIDGING WILL BE
IN PLACE AT THE SFC AS WAVES OF ENERGY CONTINUE TO ROTATE THROUGH
THE UPPER LEVEL FLOW. KEPT WITH MAINLY DRY WITH SOME HIGH
CLOUDINESS FOR THE DAY ON TUESDAY.

FOR THE EXTENDED ZONAL FLOW DEVELOPS ALOFT WED AND THU WITH THE
UPPER FLOW BECOMING MORE SOUTHWEST THURSDAY NIGHT INTO FRI. HIGH
PRESSURE WILL DOMINATE AT THE SFC ON WED INTO THU BEFORE LEESIDE
LOW REFORMS OVER ERN CO. WILL MODIFY WED FOR MAINLY DRY THEN CHANCE
OF SHOWERS OR THUNDERSTORMS THU AND FRI. TEMPERATURES CLOSE TO MRF
BASED GUIDANCES.

.LBF...NONE

KECK