Flash Flood and Hail in Nebraska, August 14, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
304 PM CDT TUE AUG 14 2007

.SYNOPSIS...
SFC BOUNDARY LOCATED FROM NEAR OAX TO GRI TO BETWEEN BBW AND
LBF...THEN INTO THE CENTRAL PANHANDLE. MSAS SFC CONVERGENCE
INCREASING ALONG THE FRONT ATTM AND CONVECTION ALREADY FIRING IN
GARDEN COUNTY...AND LEFT OVER FROM  MORNING CONVECTION IN BOYD
COUNTY. FAIRLY SIGNIFICANT UPPER CIRCULATION OVER ERN CO ROTATING
NWD AND BEGINNING TO FIRE TSRA IN THE CENTRAL ROCKIES.
INTERESTINGLY...SOME PV...THOUGH SMALL AMOUNTS...SHOW UP IN THE
500-300MB LAYER VIA MODELS AND ROTATE INTO THE AREA THROUGH WED. NAM
BUFR SOUNDINGS WOULD INDICATE TSRA IN GARDEN COUNTY STILL LIKELY NOT
SFC BASED YET...BUT OF CONCERN IS THE INCREASING VGP/EHI VALUES N OF
BOUNDARY. ONCE TSRA BECOMES SFC BASED THIS COULD YIELD TOR
THREAT...ESPECIALLY NEAR THE BOUNDARY WHERE LCLS ARE LOWEST. THE
WRENCH IN THE MIX IS THE UNDULAR BORE TYPE GRAVITY WAVE ASSOCIATED
WITH THE OUTFLOW FROM CONVECTION IN NERN NEB/SERN SD. THIS WILL
LIKELY ENHANCE CONVERGENCE ALONG THE BOUNDAY...BUT MAY INCREASE
INHIBITION N OF THE FRONT FOR A TIME. THESE FINE LINES ALSO INDICATE
THE AMOUNT OF SHEAR IN THE LOW LAYERS..BELOW WHERE CAP RESIDES.

&&
.SHORT TERM DISCUSSION (TONIGHT THROUGH WEDNESDAY NIGHT)...
OBVIOUSLY CONVECTION IS THE BIGGEST CONCERN TONIGHT. THE EXTENT OF
WHICH WILL DETERMINE FURTHER CONVECTION WED. NAM TOO LATE ON
DEVELOPING CONVECTION IN NERN NEB THIS MORNING...BUT SEEMS TO BE
HINTING AT WRN DEVELOPMENT OK...BUT AGAIN TOO LATE. HAVE GONE WITH
THE IDEA THAT ENTIRE CWA COULD GET TSRA...BUT STRONGEST MOST
ORGANIZED CONVECTION SHOULD BE ALONG AND N OF I-80. PROGGED BFR
SOUNDINGS INDICATE STEEP LAPSE RATES THROUGH THE NIGHT...LIKELY
INDICATIVE OF THE INSTABILITY ASSOCIATED WITH PREVIOUSLY MENTIONED
PV ROTATING THRU AND EVIDENCED ON WV IMAGERY. GUIDANCE GENERALLY
CLOSE FOR MINS AND STAYED ALONG THOSE LINES - SIMILAR TO ONGOING
FCST. MAXES WED WILL BE DEPENDENT ON CLOUD COVER FROM RESIDUAL
CONVECTION AND NEW CONVECTION...BUT HAVE GENERALLY SIDED WITH
GUIDANCE VALUES. SHOULD BE ENOUGH REMAINING OF OLD BNDRY/NEW ONES TO
GENERATE TSRA AGAIN WED.

.LONG TERM DISCUSSION (THURSDAY THROUGH TUESDAY)...
GUIDANCE VALUES FOR THURSDAY A WAYS APART YET...DUE MAINLY TO CLOUD
COVER POSSIBILITIES. THOUGH NAM DOESNT KEEP CLOUD COVER UP NORTH
THROUGH THE ENTIRE DAY...2M TEMPS ONLY IN THE UPPER 70S. ONLY WAY
VTN WILL STAY THAT COOL IS IF CLOUDS STAY IN ALL DAY. THEREFORE HAVE
SIDED MORE TWD THE MAV GUIDANCE...THOUGH NOT ALL THE WAY. THU INTO
FRIDAY SHOULD BE MAINLY DRY AS FRONT FINALLY GETS SHOVED INTO KS
AFTER WED CONVECTION. SHOULD BE A MODERATE RETURN OF WARM AIR FOR
FRIDAY AS INFLUENCE FROM ERN STATES UPPER LONG WAVE TROF WANES AND
SHARP RIDGE BUILDS IN THE ROCKIES.

12Z RUN OF ECMWF CONTINUES ITS MORE AGRESSIVE TREND OF MOVING THE
ERN PAC LOW INLAND INTO WRN CANADA...PROGRESSING IT ACOSS THE NRN
PLAINS. SINCE THIS IS ITS SECOND RUN...IT WILL BE INTERESTING TO SEE
IF THE GFS EVENTUALLY GOES THAT WAY. GFS HAS A SIMILAR IDE
INITIALLY...BUT SHOWS IT WILL BE HARDER TO BUCK THE STRONG RIDGE IN
PLACE OVER THE CENTRAL ROCKIES INTO THE FIRST OF NEXT WEEK. WOULD
TEND TO FAVOR THAT IDEA AND BEING MOST LIKELY AND HAVE NOT COOLED
TEMPS TOO MUCH YET.

&&

.AVIATION...
TONIGHT VFR CONDITIONS WILL BE ENCOUNTERED THROUGH MIDNIGHT CDT
EXCEPT IN AREAS OF CONVECTION THIS EVENING. CONVECTION WILL IMPACT
ALL ROUTES THROUGH 04Z. THE HIGH BASED THUNDERSTORMS WITH CEILING
BASES NEAR 10 KFT ATTM WILL LOWER BEYOND 22Z TO CAUSE LOCALLY MVFR
CEILING INTO THE EVENING. THEN CEILING DROPPING FURTHER WITH MVFR
CONDITIONS BECOMING MORE WIDESPREAD ALONG TWEB ROUTES 098...264 AND
274 FOR AREAS EAST OF HIGHWAY 97...FROM VALENTINE TO NORTH PLATTE
AFTER 09Z. THE LOW CEILING WILL LIFT BEYOND 15Z THROUGHOUT TO VFR
CONDITIONS.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...NONE.
&&

JWS/19

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
237 PM CDT TUE AUG 14 2007

NEZ004>010-022>029-035>038-056>059-069>071-094-150545-
SHERIDAN-EASTERN CHERRY-KEYA PAHA-BOYD-BROWN-ROCK-HOLT-GARDEN-
GRANT-HOOKER-THOMAS-BLAINE-LOUP-GARFIELD-WHEELER-ARTHUR-MCPHERSON-
LOGAN-CUSTER-DEUEL-KEITH-PERKINS-LINCOLN-CHASE-HAYES-FRONTIER-
WESTERN CHERRY-
237 PM CDT TUE AUG 14 2007 /137 PM MDT TUE AUG 14 2007/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WESTERN AND
NORTH CENTRAL NEBRASKA.

.DAY ONE...LATE AFTERNOON AND TONIGHT.

THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORM DEVELOPMENT
GENERALLY NORTH OF INTERSTATE 80 THROUGH THIS EVENING. HIGH BASED
THUNDERSTORMS WILL CONTINUE TO DEVELOP WITH THE STORMS TAPPING
INTO HIGHER BOUNDARY LAYER MOISTURE INTO THE EVENING FOR STORMS
TO INTENSIFY. THE MAIN THREAT WILL BE DAMAGING WINDS AND LARGE
HAIL...ALTHOUGH AN ISOLATED TORNADO WILL ALSO BE POSSIBLE WITH ANY
ROTATING STORMS THIS EVENING.

STORM MOTION IS EXPECTED TO BE AROUND 15 KNOTS AS STORMS INTENSIFY
INTO THE EVENING WITH LOCALLY HEAVY RAINFALL POSSIBLE DUE TO A SLOW
EASTWARD STORM MOTION.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

THE WEATHER WILL CONTINUE UNSETTLED INTO WEDNESDAY ACROSS THE SOUTHWEST AS
THE FRONT SLIPS SOUTH INTO NORTHERN KANSAS. THERE REMAINS A SLIGHT
RISK FOR SEVERE THUNDERSTORM ACROSS SOUTHWEST NEBRASKA INTO THE
NORTH CENTRAL WEDNESDAY AS ENERGY MOVES OUT OF THE ROCKIES WITH
CONVECTION DEVELOPING NORTH OF THE SURFACE BOUNDARY. STORMS WILL
AGAIN BE POSSIBLE INTO THE WEEKEND AS MOISTURE IS DRAWN NORTH ON
THE HIGH PLAINS AND THE FRONT ACROSS KANSAS RETURNS NORTH AS A
WARM FRONT THROUGH SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED FOR AREAS NORTH OF
INTERSTATE 80.

&&

THIS PRODUCT IS NOW AVAILABLE...ALONG WITH OTHER WEATHER...
HYDROLOGICAL AND CLIMATOLOGICAL INFORMATION...AT
HTTP://WWW.WEATHER.GOV/NORTHPLATTE

KECK