Severe Thunderstorm Warning 157, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
226 PM CDT SUN JUL 9 2000

...MAIN FORECAST CHALLENGE TO BE TSRA CHANCES AND CHOICE BETWEEN
AVN AND ETA SOLUTIONS...

MODELS ALL INITIALIZED SIMILAR WITH UPPER RIDGE CENTERED OVER
SOUTHEAST CONUS EXTENDING INTO CENTRAL PLAINS...NARROW TROUGH FROM
WESTERN CANADA TO EASTERN PACIFIC. SUBTLE DIFFERENCES IN EMBEDDED
SHORTWAVES IN MID FLOW MOVING INTO RIDGE...WITH ALL MODELS
INDICATING SHORTWAVE OF CONCERN FROM CENTRAL WYOMING INTO NORTHWEST
COLORADO. AT THE SURFACE...ALL MODELS DID WELL WITH SURFACE LOW IN
SOUTHWEST NEBRASKA WITH NGM A BIT TOO WEAK. COLD FRONT POSITION
OVER SOUTHERN SOUTH DAKOTA ALSO HANDLED WELL. ETA PERHAPS A BIT
UNDERDONE WITH SURFACE RIDGING IN ROCKIES...WITH AVN BETTER IN LINE
WITH OBS.

AT 17Z...AVN APPEARS TO HAVE MUCH BETTER HANDLE ON SURFACE LOW
SITUATED OVER NORTHWEST KANSAS/SOUTHWEST NEBRASKA. ETA TOO DEEP AND
TOO FAR SOUTHWEST WHILE NGM SHOWING TYPICAL NORTHERN BIAS. QPF
FIELDS SHOW THE STORY...WITH NGM ALREADY CRANKING OUT NEARLY
TWO-TENTHS OF AN INCH OF PRECIP OVER ENTIRE NORTHERN CWA THROUGH
18Z. AVN QPF MISSING ONGOING CONVECTION IN SOUTH DAKOTA/NORTHERN
PANHANDLE...WHILE ETA APPEARED IN LINE. AVN HANDLING SURFACE
DEWPOINTS ALONG NEBRASKA/SOUTH DAKOTA BORDER BEST...BUT BOTH ETA
AND AVN UNDERDONE. WITH ALL THIS IN MIND...WILL GO WITH A BLEND OF
THE ETA/AVN SOLUTIONS.

TONIGHT...ONGOING PRECIP IN SOUTH DAKOTA DEPICTED WELL WITH ETA 700
MB HEIGHT/OMEGA FIELDS...WHILE AVN TOO FAR SOUTH AND EAST WITH THESE
FEATURES. PRECIP ALSO IN LINE WITH ETA 850 MB COLD FRONT. AT THE
SURFACE...BY 00Z...SURFACE LOW SHOULD BE SITUATED OVER NORTHWEST
KANSAS WITH TROUGH EXTENDING NORTHEAST. ETA MUCH STRONGER ON 850 MB
COLD FRONT DROPPING INTO NORTHWEST CWA...WHILE AVN NEVER REALLY
BRINGS COLDER AIR INTO REGION. WITH ETA HANDLING SHORTWAVE CURRENTLY
OVER NORTHERN COLORADO A BIT BETTER...WILL LEAN TOWARD ETA
SOLUTION. SHOULD SEE CONVECTION INITIATING OVER NORTHERN CWA AS
SHORTWAVE APPROACHES...SPREADING EAST. SOUTHERN EXTENT OF PRECIP TO
BE TRICKY. WITH SOME FORCING TRAILING SHORTWAVE...CANNOT RULE OUT
PRECIP. HOWEVER...MOST OF VORTICITY CHANNELIZED WITH FLOW...WITH
BEST OMEGA FIELDS MOVING OVER NORTHERN CWA...WITH SOME FORCING TO
SOUTHEAST OF CWA MORE ASSOCIATED WITH LOW LEVEL JET. WILL HIT POPS
HIGHEST IN NORTHERN CWA...LOWER AMOUNTS FURTHER SOUTH AND WEST. WITH
COOLER AIR AND EASTERLY FLOW...ALONG WITH LOWEST LEVEL RELATIVE
HUMIDITY FIELDS HIGH...WILL MENTION AREAS OF FOG/LOW CLOUDS IN
NORTHEAST CWA TOWARD DAYBREAK. CURRENT FORECAST TEMPS APPEAR IN
LINE.

MONDAY...SURFACE LOW AND FRONT TO DROP SOUTH OF CWA...PLACING US IN
UPSLOPE FLOW. WITH EASTERLY FLOW...MOISTURE ADVECTION TO BE
ENHANCED. BOTH ETA AND AVN INDICATING SHORTWAVE TO AFFECT CWA...
WITH AVN SLOWER BUT STRONGER. EITHER WAY...WILL HAVE TO CONTINUE
WITH POPS IN AFTERNOON. WITH 850 MB TEMPS RANGING FROM MID 20S TO
AROUND 30 NORTHEAST TO SOUTHWEST...THIS WOULD EQUATE TO SURFACE
TEMPS IN THE MID 80S TO LOWER 90S. HOWEVER...WITH EASTERLY FLOW...
MAY NOT FULLY REALIZE THESE. WILL BLEND COOLER FWC NUMBERS WITH
WARMER FAN NUMBERS.

MONDAY NIGHT...ETA INDICATING DECENT SUBSIDENCE...WHILE AVN VERY
SLOW WITH PROGRESSION OF SHORTWAVE. WILL KEEP POPS IN FORECAST...
HIGHEST IN SOUTHWEST. OTHERWISE...RELATIVE HUMIDITY FIELDS WOULD
INDICATE PARTLY CLOUDY/MOSTLY CLEAR. LOWS GENERALLY IN THE MID 60S.

TUESDAY...AVN INDICATING SURFACE LOW OVER NORTHWEST KANSAS...WITH
COLD FRONT DROPPING THROUGH CWA BY LATE AFTERNOON. POSITION OF
SHORTWAVES AND OMEGA FIELDS WOULD INDICATE BEST POPS IN EASTERN
CWA...WITH 850 MB FRONT FROM SOUTHWEST TO NORTHEAST NEBRASKA. 850
MB TEMPS WOULD INDICATE AFTERNOON HIGHS NEAR GUIDANCE...IN THE UPPER
80S TO LOWER 90S. SEE NO REASON AT TIME TO DEVIATE.

EXTENDED...AS SHORTWAVES CONTINUE TO TRANSGRESS THE UPPER RIDGE...
VERY DIFFICULT TO DETERMINE WHICH ONES TO GIVE US PRECIP...THUS VERY
LOW CONFIDENCE IN MODEL PERFORMANCE. WITH PERSISTENT LEE-SIDE
CYCLONE/TROUGH...WILL KEEP SLIGHT CHANCE OF THUNDERSTORMS THROUGH
EXTENDED PERIOD. SEE NO REASON TO DEVIATE FROM FMR TEMPS...WITH
HIGHS IN THE 90S...LOWS IN THE 60S.

.LBF...NONE

M. MUTCHLER

NEZ004>010-022>029-035>038-056>059-069>071-092045-

SEVERE WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1114 AM CDT SUN JUL 9 2000

...STORM SPOTTER GROUPS IN WEST CENTRAL AND NORTH CENTRAL NEBRASKA
SHOULD BE ALERT AND READY FOR ACTIVATION THIS AFTERNOON AND THIS
EVENING...

THERE IS A CHANCE OF SEVERE THUNDERSTORMS THIS AFTERNOON AND THIS
EVENING OVER PORTIONS OF WEST CENTRAL AND NORTH CENTRAL NEBRASKA.
THE GREATEST RISK OF SEVERE WEATHER IS NORTH OF A LINE EXTENDING
FROM BIG SPRINGS...TO NORTH PLATTE...TO BROKEN BOW.  OTHER
THUNDERSTORMS...WHICH ARE NOT EXPECTED TO REACH SEVERE LEVELS...ARE
POSSIBLE SOUTH OF THIS LINE OVER THE REST OF WEST CENTRAL AND
SOUTHWEST NEBRASKA.

A COLD FRONT WILL MOVE SOUTHEAST THROUGH WESTERN AND NORTH CENTRAL
NEBRASKA THIS AFTERNOON INTO TONIGHT.  THUNDERSTORMS ARE EXPECTED TO
DEVELOP ALONG THE FRONT BY EARLY AFTERNOON AS TEMPERATURES RAPIDLY
RISE.  THUNDERSTORMS MAY BECOME SEVERE BY MID AFTERNOON OVER
NORTHWEST NEBRASKA AS THE FRONT ENCOUNTERS AN INCREASINGLY UNSTABLE
ATMOSPHERE.  STORMS ARE THEN EXPECTED TO MOVE SOUTH AND EAST WITH
THE FRONT FOR THE REST OF THE AFTERNOON INTO TONIGHT.

THE GREATEST SEVERE WEATHER THREAT FROM THESE STORMS WILL BE FROM
DAMAGING WINDS AND LARGE HAIL.  HEAVY RAIN IS ALSO POSSIBLE BY EARLY
TONIGHT ACROSS PORTIONS OF NORTH CENTRAL NEBRASKA.

FURTHER SOUTH ACROSS SOUTHWEST NEBRASKA...LIMITED LOW LEVEL MOISTURE
WILL BE IN PLACE WHICH WILL LIMIT THE STRENGTH AND COVERAGE OF THE
THUNDERSTORMS.  ALTHOUGH ISOLATED DAMAGING WINDS ARE POSSIBLE WITH
SOME OF THE STRONGEST STORMS...WIDESPREAD SEVERE WEATHER IS NOT
EXPECTED.

EASTERLY UPSLOPE FLOW BEHIND THE COLD FRONT...AND INCREASING
TEMPERATURES DURING THE DAY ON MONDAY MAY RESULT IN ANOTHER ROUND OF
SEVERE WEATHER.  THE GREATEST THREAT FOR SEVERE WEATHER ON MONDAY
APPEARS WILL BE DURING THE LATE AFTERNOON INTO THE EARLY EVENING
HOURS...MAINLY OVER THE EASTERN NEBRASKA PANHANDLE...AND SOUTH OF
INTERSTATE 80 IN SOUTHWESTERN NEBRASKA.

JWS