Severe Thunderstorm Warning 13, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
232 PM CDT THU MAY 13 1999

...FORECAST CHALLENGE IS THUNDERSTORM CHANCES THROUGH SATURDAY...

SURFACE ANALYSIS SHOWS LEE SIDE LOW DEVELOPING IN NE CO RESULTING IN
TIGHT PRESSURE GRADIENT ACROSS WESTERN NE AND KS. WINDS ACROSS CWFA
REMAINING BELOW ADVISORY CRITERIA AT 20 TO 30 KTS THIS AFTERNOON.
VISIBLE SATELLITE IMAGERY SHOWS DENSE CU FIELD ASSOCIATED WITH
HIGHER SURFACE DEWPOINTS SPREADING INTO W CENTRAL KS AND MAINLY MTN
CI OVER THE PANHANDLE AND WESTERN NE. FEW MID LEVEL CLOUDS AND
POSSIBLE SPRINKLES SHOWING UP ON 88D IN FAR NW.

ETA IS MODEL OF CHOICE WITH BEST HANDLE ON LOCATION OF DEVELOPING
LOW AT 18Z. NGM WAS TOO FAR NORTH...DEPICTING MAIN LOW CENTER IN NE
WY TODAY AND THEN TRACKING IT INTO WESTERN NE WHILE ETA HOLDS LOW
BACK OVER CO UNTIL MOVING INTO NEB LATE FRIDAY NIGHT AND SATURDAY
AS A TROUGH.  MODELS SIMILAR AT UPPER LEVELS WITH OVERALL PATTERN OF
OMEGA BLOCK OVER CANADA BREAKING DOWN THROUGH 48 HOURS AND DEEPENING
TROUGH IN THE WEST.

INITIAL FORECAST PROBLEM IS POTENTIAL FOR THUNDERSTORMS TONIGHT. MAIN
FOCUS LOOKS TO BE SW AND EASTERN PANHANDLE WHERE UPPER LEVEL
DIVERGENCE ASSOCIATED WITH H3 JET COUPLES WITH H7 OMEGA FIELD AND
MODEL COMPUTED LI/S FROM -2 TO -4 C. CAPE ALSO HIGHEST IN THIS AREA
WITH VALUES GENERALLY FROM 800 TO 900 BETWEEN 00 AND 06Z THIS
EVENING. WILL GO WITH 50 PERCENT POPS IN EASTERN PANHANDLE ZONES AND
40 PERCENT IN ADJACENT ZONES. SHOULD REMAIN BREEZY OVER ENTIRE CWFA
AS WELL WITH LOW LEVEL JET FORMING AT 850 MB.

POTENTIAL FOR THUNDERSTORMS LOOKS MORE IMPRESSIVE FOR LATE FRIDAY
AND FRIDAY NIGHT AS GULF OPENS UP AND LOW LEVEL JET USHERS HIGH
SURFACE THROUGH 850 MB DEWPOINTS INTO FORECAST AREA. LATE AFTERNOON
TIMING OF H5 SHORTWAVE COMBINED WITH UPPER LEVEL DIVERGENCE AND
FORECAST CAPES FROM 1000 TO 2000 J/KG AND LI/S AS LOW AS -3 TO -7
DEG C INDICATE POTENTIAL FOR SEVERE THUNDERSTORMS BY LATE AFTERNOON
AND EVENING AS PER SPC 2ND DAY OUTLOOK. APPEARS BIGGEST THREAT MAY
BE IN THE SOUTH WITH POSSIBLE MCS THEN DEVELOPING DURING EVENING
INTO THE N AND NE.

IN LATER PERIODS...MRF SHOWS MAIN SURFACE LOW DEVELOPING AND
LINGERING IN TX PANHANDLE REGION EARLY NEXT WEEK FEEDING LOW LEVEL
MOISTURE INTO MUCH OF FORECAST AREA. WILL NEED AT LEAST CHANCE OF
THUNDERSTORMS THROUGH EXTENDED FORECAST WITH TEMPERATURES NEAR OR
JUST BELOW GUIDANCE FOR HIGHS DUE TO CLOUD COVER AND PRETTY CLOSE
FOR LOWS.

.LBF...NONE.

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