Severe Thunderstorm Warning 1, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
130 PM CDT SUN MAY 5 2002

...POTENTIAL FOR SEVERE TSTMS THIS EVENING WILL BE THE MAIN FORECAST
CONCERN...FOLLOWED BY MUCH COOLER TEMPS AND CHANCE OF RAIN MID WEEK.

MODELS IN EXCELLENT AGREEMENT IN MASS FIELDS OUT TO 60 HOURS AS EAST
CONUS RIDGE AMPLIFIES IN RESPONSE TO A WEST CONUS TROF DIGGING S THRU
THE CASCADES.  SW FLOW ALOFT WILL BE MAINTAINED OVER THE CWA THRU THE
FCST PERIOD...EXCEPT FOR A BRIEF PERIOD OF ZONAL FLOW ON THU.  MODELS
ALSO IN GOOD AGREEMENT IN SFC PRESS FIELDS AS LEE-SIDE MOUNTAIN TROF
REFORMS EACH AFTN OVR THE HIGH PLAINS THE NEXT COUPLE OF DAYS...THEN
RELOCATES ABOUT 250 MILES E OVER THE CENT PLAINS BY MORNING.

VIS SAT IMG AND AREA METARS THIS AM INDICATE STATUS DECK ARND 1K FT
EXTENDING FROM NW KS TO CENT NEBR WHERE BL MOIST FLUX CONVRG IS
ONGOING (H85 DP TEMP +12C).  12Z HIGH RES ETA SHOWS THIS STATUS DECK
DISSIPATING BY EARLY AFTN AS DAYTIME HEATING AND MIXING INCREASES.
SFC HEATING AND INCREASED CONVECT THIS AFTN WILL ALLOW BL MOIST TO
BECOME MIXED MORE EVENLY IN THE LOW AND MID LAYERS...BUT PW WILL
REMAIN NEAR 3/4 EAST OF HWY 83.  MID LVL ACCUS ALSO EVIDENT FROM NE
NEBR TO SE SD INVOF MODERATE H70 TEMP ADVCT ARND 10C/12HR.  MODERATE
LOW LVL JET (20 TO 30 KTS) ACRS KS INTO EAST NEBR THIS AFTN WILL
KEEP MOIST STREAMING NWRD WITH AXIS OF H85 THETA-E RIDGE SETTING UP
ACRS CENT KS INTO SE NEBR AHD OF DRY LINE.  +8 TO +10C DP VALUES
WILL REMAIN ACRS THE ERN 1/2 OF CWA UNTIL MIDNIGHT.

WEAK S/W WILL MOVE OVR THE W PORTION OF THE CWA LATE THIS AFTN AND
SHOULD PROVIDE ADEQUATE LIFT TO INITIATE CONVECT FROM KILM TO KVTN.
MARGINAL TO MODERATE INSTABILITY (CAPES 500-1500 J/KG AND SFC BASED
LIS DOWN TO -7C) WILL EXIST ABOUT 50 MILES EAST OF DRY LINE (NEAR
HWY 61) BY MID AFTN.  MODERATE CAP (50-100 J/KG) CURRENTLY IN PLACE
ACRS THE CWA WILL DEGRADE RAPIDLY AFTER 3 PM.  SOME OF THE TSTMS
WILL THEN HAVE THE POTNL TO BECOME SVR WITH LRG HAIL (0C LVL ARND
11KT FT / WET BULB NEAR 9.2KT FT) AND DAMAGING WINDS (INVERTED V
SOUNDING) EAST OF AN KILM/KVTN LINE.  SFC WNDS WILL BACK IN RESPONSE
TO SFC LOW ALNG THE KS/CO BORDER MOVING E INTO S CENT NEBR.  STRONG
H30 DIV SIGNATURE AND 3KM STM REL HLCY INCREASING TO 275 M2/S2 ACRS
THE NE PORTION OF OUR CWA (E OF HWY 183) WILL BE ADEQUATE FOR
ROTATING UPDRAFTS...THUS INCREASING THE RISK POTENTIAL FOR ISOLATED
WEAK (F0-F1) TORNADOS THIS EVENING.  IN ADDITION BRN VALUES >45
SUGGESTS THAT THE STORMS WILL EVOLVE AS MULTI-CELLS THIS AFTN...BUT
SUPER CELL STRUCTURE AND INTENSITY COULD INCREASE EARLY THIS EVEN IN
THE NE CWA AS BRN VALUES DECREASE TO 15 AND TT VALUES INCREASE TO
NEAR 63.

WILL KEEP 30 POPS FOR MOST ERN COUNTIES FOR TONIGHT...WITH ONLY CHC
FOR ISO ELEV TSTMS ACRS PORTIONS OF CENT AND W NEBR THIS EVEN AS THE
DRY LINE SURGES E AND H85-H50 LAPSE RATES INCREASE TO 9C/KG.  LOW
LVL MOIST MUCH DEPRIVED IN THE W AS H85 DPS PLUNGE TO ARND -3C BY
MIDNIGHT.

WAA AND WEAK DOWNSLOPE WND COMPONENT ON MON IN THE SW CWA WILL ALLOW
AFTN HIGHS TO REACH INTO THE MID 80S...70S ELSEWHERE WITH VARIABLE
WNDS.  WILL KEEP 20 POPS GOING FOR THE NE MON NIGHT BASED OF AVN
CONSISTENCY AND H85 FRONTOGENESIS FOR COOLER AIR POISED TO MOVE IN
AFTER MIDNIGHT.

THE BROAD UPPER TROF OVER THE WEST CONUS WILL AMPLIFY THRU MID WEEK
AS THE RIDGE TO OUR EAST LIFTS IN RESPONSE.  A STRONG SFC COLD FRONT
WILL SURGE S THRU THE CWA ON TUE W/ MUCH COOLER TEMPS REMAINING ACRS
THE FA THRU WED.  -SHRA CHANCES WILL INCREASE ACRS THE CWA TUE AND
AND REMAIN INTO WED AS H7 FRONTOGENESIS PERSISTS.  H85 TEMPS ARND
-3C ACRS THE NRN CWA PER THE AVN SUGGEST SOME SNOW MIX POSSIBLE...
BUT WILL LEAVE OUT FOR NOW PENDING MORE RELIABLE MODEL DATA.  DRIER
WX AND A GRAD WARMUP WILL RETURN LATE IN THE WEEK AS WEAK RIDGING
BUILDS OVER THE CENT PLAINS.

THANKS HASTINGS...GOODLAND AND OMAHA FOR COORDINATION.

.LBF...NONE.

44

NEZ004>010-022>029-035>038-056>059-069>071-094-052045-

HAZARDOUS WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1144 AM CDT SUN MAY 5 2002

...STORM SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON ACROSS
WESTERN AND NORTH CENTRAL NEBRASKA...

THUNDERSTORM DEVELOPMENT WILL BE POSSIBLE MAINLY EAST OF AN IMPERIAL
TO THEDFORD TO VALENTINE LINE THIS AFTERNOON AND EVENING. THE AREA OF
GREATEST CONCERN WILL BE ALONG AND EAST OF HIGHWAY 183 OVER NORTH
CENTRAL NEBRASKA. SOME STORMS COULD BECOME SEVERE WITH LARGE HAIL AND
DAMAGING WINDS. STRONG WIND FIELDS SUGGEST THERE IS A POTENTIAL FOR
ISOLATED TORNADOES WITH THE STRONGEST STORMS.

THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A DRYLINE ACROSS
SOUTHWEST NEBRASKA THIS AFTERNOON AND MOVE SLOWLY EAST OR NORTHEAST.
OTHER STORMS WILL DEVELOP NORTHWARD THROUGHOUT THE AFTERNOON AND
EARLY EVENING.

STORM DEVELOPMENT WILL BE HIGHLY DEPENDENT ON MOISTURE.  DEW POINTS
EAST OF HIGHWAY 83 ARE FORECAST TO RISE INTO THE MID 50S THIS
AFTERNOON BUT REMAIN IN THE 30S AND 40S ARE TO THE WEST BEHIND THE
DRYLINE.

THE LOCATION OF THE DRYLINE COULD VARY WEST OR EAST THIS AFTERNOON
SO AREAS NEAR HIGHWAY 83 SHOULD REMAIN ALERT TO RAPIDLY CHANGING
WEATHER CONDITIONS.