Tornadoes and Hail in Nebraska, June 20, 2003

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
340 PM CDT FRI JUN 20 2003

...THUNDERSTORM CHANCES THIS WEEKEND WILL BE MAIN FORECAST
CHALLENGE...

PATTERN OF WEAK SHEAR ENVIRONMENT HAS ENDED. MID LEVEL WINDS NOW SW
AT 30 TO 35 KTS. PW VALUES WILL REMAIN ABOVE AN INCH THE NEXT 24
HOURS THEN GRADUALLY FALL. GFS AND ETA IN GOOD AGREEMENT WITH THE H5
PATTERN UNTIL 60 HOURS BEYOND. THE GFS THEN IS MORE PROGRESSIVE WITH
THE SHORTWAVE TROUGH IN THE PAC NW. IN FACT AT 84 HRS THE ETA HAS A
CLOSED LOW INTO NWRN OR WHILE THE GFS HAS AN OPEN WAVES TROUGH AXIS
ALONG THE NEVADA/UTAH BORDER. PREFER THE SLOWER ETA SOLUTION WHICH
TRANSLATES INTO THE MEDIUM RANGE OF THIS FORECAST.

AT 18Z...WV IMAGERY INDICATES A STRONG DISTURBANCE MOVING THROUGH
THE MOUNTAINS OF CENTRAL NM AND CO. THIS WILL TRANSLATE
NORTHEASTWARD INTO MOISTURE RICH CENTRAL PLAINS. WEAKLY CAPPED
ENVIRONMENT AT 00Z SAT FROM THE TX PNHDLE NORTHWARD INTO WR SD.
SBCAPES 1500-2000 J/KG WEST OF MERRIMAN TO OGA. THIS AREA IN 30-40KT
SHEAR ENVIRONMENT TO SUPPORT ISOLATED RIGHT MOVING SUPERCELLS THIS
EVENING IN THE WEST PER CORFIDI VECTOR. STORMS MAY CONGEAL INTO MCS
FROM SWRN INTO CENTRAL NEBRASKA OVERNIGHT.

SATURDAY...A WELL DEVELOPED SFC TROUGH AND ASSOC DRYLINE SETUP JUST
WEST OF VTN AND LBF. DWPTS IN EAST IN THE MID TO UPPER 60S. STRONG
HEATING FROM UPPER 80S TO LOWER 90S. SB CAPES IN EAST COULD EXCEED
3000 J/KG. WILL RUN 20 POPS SWRN TIER...30 POPS WEST TO EAST IN THE
AFTN.

CONVECTION WILL MOVE NORTHEAST SATURDAY EVENING. HIGHEST POPS TO
FAR THE NORTHEAST. SFC FRONT PUSHING INTO SRN SD WILL KEEP CHCS
GOING ALL NIGHT ACROSS THE NORTH.

SUNDAY...FRONT SAGGING SLOWLY SOUTHEAST DURING THE DAY WILL KEEP
NEED FOR 30 POPS NORTH AND 20 POPS SOUTH INTO SUNDAY EVENING. CHC
REMAIN SUNDAY AFTERNOON AND SUNDAY NIGHT AS FRONT LOOKS TO STALL OUT
NWRN KS TO SERN NEBR. HIGHS UPPER 80S SOUTHEAST TO LOWER 80S
NORTHWEST.

MONDAY...FRONT SHOULD LIFT BACK NORTH AS A WARM FRONT AS TEMPS RISE
TO NEAR 90 SOUTHEAST AND LOWER 80S FAR NW. DISTURBANCES RIDING ALONG
THE SWRLY FLOW COULD AGAIN FIRE SOME AFTERNOON AND NIGHTTIME
STORMS...ESPECIALLY ACROSS NORTH CENTRAL NEBRASKA.

EXTENDED DISCUSSION...THE LATEST MEDIUM RANGE MODELS INDICATE A LESS
MERIDIONAL FLOW PATTERN ACROSS THE WESTERN HALF OF THE U.S. THAN THE
PREVIOUS RUNS. AT 12Z WEDNESDAY...BOTH THE 00Z 20TH GFS AND THE 12Z
19TH ECMWF AGREE ON A NORTHERN BRANCH TROUGH FROM NORTH DAKOTA INTO
MANITOBA WITH A STRONGLY POSITIVELY TILTED TROUGH BACK INTO NRN
CALIFORNIA. THIS DIFFERS FROM PREVIOUS RUNS WHICH INDICATED A CLOSED
LOW IN SERN OR AND NRN UTAH RESPECTIVELY. THE 00Z 20TH CANADIAN
MODEL IS ALSO IN AGREEMENT WITH THE LATEST RUNS. WILL MAKE
ADJUSTMENTS TO THE EXTENDED WITH THE SURFACE BOUNDARY NOW EXPECTED
TO STALL OUT NEAR THE KS/NEBR BORDER AT 00Z WED...THEN SAG SLOWLY
SOUTH THROUGH THURSDAY. DISTURBANCES RIDING IN WSWRLY FLOW ALOFT
WITH OUR CWFA IN A MORE FAVORED NORTHERN SIDE OF THE SFC BOUNDARY
WILL PROVIDE CHCS FOR SHOWERS AND THUNDERSTORMS TUESDAY THROUGH
THURSDAY. WILL GO DRY FRIDAY WITH ZONAL FLOW AND DRIER AIR RETURNING
TO THE REGION. 12Z GFS TREND SUPPORTS THIS.

.LBF...NONE.

KAR

NEZ004>010-022>029-035>038-056>059-069>071-094-201630-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NORTH PLATTE NE
324 PM CDT FRI JUN 20 2003

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

.DAY ONE...TONIGHT
SEVERE THUNDERSTORMS CAPABLE OF LARGE HAIL AND DAMAGING WINDS ARE
EXPECTED TO DEVELOP TONIGHT ACROSS WESTERN NEBRASKA.  THE AREA OF
CONCERN COVERS LOCATIONS WEST OF LINE FROM MERRIMAN...IN CHERRY
COUNTY...TO PAXTON...IN KEITH COUNTY...WITH THE THREAT OF SEVERE
WEATHER INCREASING WESTWARD.

AS AN UPPER LEVEL DISTURBANCE APPROACHES THE AREA TONIGHT...WINDS
ALOFT WILL STRENGTHEN AND COMBINED WITH AN UNSTABLE AIRMASS AND
ABUNDANT SURFACE MOISTURE...THIS WILL MAKE A FAVORABLE ENVIRONMENT
FOR SUPERCELL THUNDERSTORMS.  THE ACTIVITY WILL MOVE EAST LATER
TONIGHT AND WEAKEN AS IT MOVES EAST. THE MAIN THREAT WILL BE LARGE
HAIL AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY
AN ACTIVE SEVERE WEATHER DAY IS EXPECTED SATURDAY.  THE AREA OF
GREATEST CONCERN COVERS LOCATIONS NEAR AND EAST OF HIGHWAY 83 BUT
SEVERE WEATHER COULD DEVELOP SOMEWHAT FARTHER WEST NEAR
OGALLALA...GRANT AND MERRIMAN.  THE ATMOSPHERE WILL BECOME VERY
UNSTABLE EAST OF HIGHWAY 83 SATURDAY AFTERNOON.  WINDS ALOFT WILL
REMAIN STRONG AND ISOLATED TORNADOES ARE POSSIBLE WITH STRONGEST
STORMS.  THE EXTREME INSTABILITY AND WINDS ALOFT ARE EXPECTED TO
PRODUCE A FEW LONG LIVED SUPER CELLS WHICH COULD PRODUCE ONE OR MORE
TORNADOES DURING THEIR LIFE CYCLE.

SUNDAY...AREAS EAST OF HIGHWAY 83 WILL REMAIN AT RISK FOR SEVERE
WEATHER SUNDAY AFTERNOON AND EVENING AS ANOTHER DISTURBANCE MOVES
THROUGH THE REGION.

MONDAY THROUGH THURSDAY...WINDS ALOFT WILL REMAIN STRONG AND A
STATIONARY FRONT WILL BE LOCATED NEAR OR ACROSS WESTERN AND NORTH
CENTRAL NEBRASKA.  THUS THE NECESSARY INGREDIENTS FOR SEVERE WEATHER
WILL BE IN PLACE.  A SERIES OF UPPER LEVEL DISTURBANCE WILL MOVE
THROUGH OR NEAR THE OUTLOOK AREA.  WINDS ALOFT...ABUNDANT MOISTURE
AND UPPER LEVEL DISTURBANCES COULD PRODUCE A VERY ACTIVE SEVERE
WEATHER PATTERN ACROSS WESTERN AND NORTH CENTRAL NEBRASKA.

.SPOTTER INFORMATION STATEMENT...
STORM SPOTTER ACTIVATION IS POSSIBLE TONIGHT AND AFTER 3 PM CDT ON
SATURDAY.  STORM MOTION WILL BE EAST AND NORTHEAST AT 20 TO 25 MPH
BOTH DAYS.

POWER