Severe Thunderstorm Warning 5, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
156 PM CDT FRI APR 20 2001

...CHALLENGE IS THUNDERSTORMS THIS EVENING...THEN TEMPS/PRECIP IN
LATER PERIODS...

MODELS INITIALIZED WITH TROUGH IN WEST...WEAK RIDGING OVER EASTERN
TWO THIRDS OF CONUS. AT THE SURFACE...LOW PRESSURE OVER MINNESOTA
ASSOCIATED WITH UPPER WAVE EJECTING NORTHEAST...TROUGH/COLD FRONT
EXTENDING INTO NORTH CENTRAL KANSAS...THEN BOUNDARY WESTWARD TO NEXT
SURFACE LOW OVER NORTHERN UTAH. MODELS SIMILAR IN SOLUTIONS BRINGING
NEXT WAVE OUT OF WESTERN TROUGH THIS EVENING WITH LEE SIDE
CYCLOGENESIS BY 00Z. AS UPPER WAVE LIFTS...SURFACE LOW TO FOLLOW INTO
NORTHEAST NEBRASKA...THEN OUT OF AREA BY 18Z SATURDAY. THEN MAIN
UPPER TROUGH BEGINS TO SHIFT EASTWARD...WITH NEXT ROUND OF WEATHER ON
SUNDAY.

THIS EVENING...CURRENT WARM FRONT POSITION EXTENDING OVER NORTHERN
KANSAS...CLOSE TO RUC40 PROGS. RUC BEGINS TO EJECT SURFACE LOW ONTO
PLAINS BY 00Z...WITH WARM FRONT LIFTING NORTHWARD. THIS TO BE FOCUS
FOR EVENING THUNDERSTORM ACTIVITY. AS LOW QUICKLY LIFTS NORTHEAST...
THUNDERSTORM THREAT ALSO SHIFTS NORTH AND EAST. DRY LINE AT 03Z IN
WESTERN CWA...AND WILL PUSH SLOWLY EAST. WITH CAPES APPROACHING 1000
J/KG IN SOUTHWEST...SHOULD SEE LATE AFTERNOON/EVENING DEVELOPMENT.
CORFIDI VECTORS WOULD INDICATE EAST NORTHEAST MOVEMENT...GENERALLY
ALONG THE WARM FRONT. ISENTROPIC LIFT ON 305K SURFACE EVIDENT IN
SOUTHERN/EASTERN CWA THROUGH 03Z...THEN PUSHING EAST. WILL GO
HIGHEST POPS EAST OF A LINE FROM VALENTINE TO NORTH PLATTE.

TONIGHT...AS UPPER LOW PUSHES NORTHEAST...WESTERLY WINDS TO INCREASE
OVER WESTERN CWA...BRINGING END TO THUNDERSTORM THREAT IN WEST AS
DOWNSLOPING/DRYING OCCUR. SKIES TO BECOME MOSTLY CLEAR WITH EXCEPTION
OF FAR NORTHWEST. IN NORTHEASTERN CWA...WARM FRONT TO CONTINUE
LIFTING NORTHEAST. WILL NOT CARRY POPS FOR TONIGHT...ONLY IN EVENING
PERIOD. COLD FRONT JUST NORTH OF CWA BY 12Z AS EVIDENCED BY BOUNDARY
LAYER RELATIVE HUMIDITY FIELDS/COLD AIR ADVECTION PATTERN. WILL WORD
NORTHERN TIER AS PARTLY CLOUDY...INCREASING CLOUDS LATE. LOW TEMPS TO
BE MODERATED BY WELL MIXED ATMOSPHERE/WESTERLY DOWNSLOPING WINDS...
GENERALLY IN THE 40 TO 45 RANGE.

SATURDAY...COLD FRONT TO RAPIDLY MOVE THROUGH CWA BY 18Z. WITH
INITIAL PUSH...SOME MIXING TO OCCUR WITH HIGH TEMPERATURES IN
SOUTHERN CWA INTO THE MID 50S TO AROUND 60 EARLY...WITH FALLING TEMPS
THROUGH THE DAY. IN THE NORTH...CLOUDS AND COLD AIR ADVECTION TO KEEP
READINGS COOLER...IN THE 40S. LAYER RELATIVE HUMIDITY INDICATES
MOSTLY CLOUDY NORTH...PERHAPS SOME SUN EARLY IN FAR SOUTHERN CWA.
WITH THE WINDS BECOMING MORE EASTERLY...UPSLOPE FLOW TO CONTRIBUTE
ENOUGH LIFT TO DEVELOP STRATUS DECK OVER WESTERN CWA. AS A SHORTWAVE
EJECTS INTO PANHANDLE LATE IN THE DAY..THIS WILL BE ENOUGH TO TRIGGER
SHOWERS...PERHAPS MIXING WITH SOME SNOW IN NORTHERN AREAS. WILL CARRY
LOW POPS FOR LATE AFTERNOON SHOWERS WEST.

SATURDAY NIGHT...AS A SERIES OF SHORTWAVES CONTINUE TO MOVE OVER AREA
WITH PLENTY OF BOUNDARY LAYER MOISTURE AND UPSLOPE FLOW...WILL CARRY
POPS FOR ENTIRE CWA. WITH SIGNIFICANT MODEL DIFFERENCES IN AMOUNT OF
COLD AIR...RANGING FROM COLDER ETA WITH ALL H85 TEMPS BELOW 0C OVER
ENTIRE CWA...AND AVN WARMER WITH 0C ISOTHERM ONLY INTO FAR NORTHWEST
CWA. WILL BLEND...AND CONTINUE WORDING OF MIXED PRECIP IN SOUTHERN
CWA...ALL SNOW NORTHWEST. WITH STRONG COLD AIR ADVECTION...AND MODELS
TRENDING COOLER...WILL FAVOR COLDER FWC GUIDANCE NUMBERS...WITH LOWS
IN THE UPPER 20S TO LOWER 30S.

SUNDAY...AS UPPER LOW BEGINS TO EJECT...UPPER TROUGH BECOMES SOMEWHAT
NEGATIVELY TILTED. MODEL DIFFERENCES NOTED IN POSITION OF SURFACE LOW
AND AMOUNT OF COLD AIR OVER CWA. BOTH ETA/AVN INDICATING MODERATE
ISENTROPIC LIFT TO AID IN PRECIP EVENT. WITH THE QUESTION OF EXTENT
OF COLD AIR...WILL BLEND...AND GO WITH POPS FOR RAIN...POSSIBLY
MIXING WITH SNOW...ALL SNOW NORTHWEST. HIGH TEMPERATURES IN THE MID
30S TO MID 40S.

SUNDAY NIGHT...AVN INDICATING DECENT WRAP AROUND MOISTURE COMBINING
WITH COLD AIR. WILL GO WITH POPS FOR SNOW. AN SPS WARRANTED FOR SOME
ADVANCE NOTICE...WITH AVN SNOW ACCUMULATOR INDICATING 6 OR MORE
INCHES FAR NORTHWEST CWA. WITH THE CLOUDS AND COLD AIR ADVECTION...
LOWS INTO THE 20S LIKELY.

EXTENDED...WITH TRANSITION FROM TROUGHING TO RIDGING IN CENTRAL
PLAINS...FOLLOWING COLD AND CLOUDY MONDAY...THINGS TO DRY OUT AND
WARM UP. WILL CONTINUE- SLIGHT CHANCE OF SNOW MONDAY...THEN DRY
REMAINDER OF EXTENDED.

.LBF...NONE.

M. MUTCHLER

NEZ004>010-022>029-035>038-056>059-069>071-202045-

SEVERE WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1143 AM CDT FRI APR 20 2001

...STORM SPOTTER GROUPS MAY BE NEEDED IN WESTERN AND NORTH CENTRAL
NEBRASKA THIS AFTERNOON AND TONIGHT...

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
TONIGHT EAST OF A LINE FORM VALENTINE TO OGALLALA TO IMPERIAL.
OTHER THUNDERSTORMS...WHICH ARE NOT EXPECTED TO REACH SEVERE
LIMITS...ARE POSSIBLE ACROSS THE REMAINDER OF THE OUTLOOK AREA.

A STRONG SPRING STORM SYSTEM WILL MOVE OUT ONTO THE PLAINS BY THIS
AFTERNOON INTO THIS EVENING. AS THE SURFACE LOW DEEPENS...SOUTHERLY
WINDS WILL BRING IN ADDITIONAL MOISTURE INTO THE SOUTHERN AND
EASTERN PORTIONS OF THE OUTLOOK AREA. THIS WILL COMBINE WITH
INSTABILITY ALOFT AND A WARM FRONT LIFTING NORTH...TO GENERATE
SCATTERED THUNDERSTORMS ACROSS THE OUTLOOK AREA THIS AFTERNOON INTO
THIS EVENING. AS COLD AIR ALOFT WORKS INTO THE SYSTEM ACROSS THE
WESTERN PORTION INITIALLY...THE STORMS WILL BE CAPABLE OF PRODUCING
LARGE HAIL AND DAMAGING WINDS INTO THE EVENING HOURS. BY LATE
AFTERNOON...WINDS IN THE ATMOSPHERE WILL BECOME FAVORABLE FOR
ROTATING THUNDERSTORMS...SO AN ISOLATED TORNADO MAY BE POSSIBLE
NEAR THE WARM FRONT...MAINLY EAST OF A LINE FROM BROKEN BOW TO NORTH
PLATTE TO HAYES CENTER.

THE THUNDERSTORMS ARE EXPECTED TO DECREASE IN COVERAGE AND INTENgSITY
BY MIDNIGHT.

JWS

NEZ004>010-022>029-035>038-056>059-069>071-210915-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NORTH PLATTE NE
340 PM CDT FRI APR 20 2001

...A SPRING SNOW STORM TAKES AIM FOR THE CENTRAL PLAINS...

A STRONG STORM SYSTEM WILL MOVE ONTO THE CENTRAL PLAINS SUNDAY...
PUSHING THROUGH THE REGION BY MIDDAY MONDAY. WITH THE SURFACE LOW
PRESSURE SYSTEM EXPECTED TO TRACK OVER PORTIONS OF KANSAS...COLD
CANADIAN AIR WILL BE DRAWN INTO MUCH OF WESTERN AND NORTH CENTRAL
NEBRASKA THROUGH THE PERIOD. WITH MUCH COLDER TEMPERATURES...
COMBINING WITH MOISTURE STREAMING NORTHWARD AHEAD OF THE STORM
SYSTEM...CONDITIONS WILL BE SET FOR A WINTRY MIX OF PRECIPITATION...
INCLUDING THE POSSIBILITY OF FREEZING RAIN AND ACCUMULATING SNOW.

AT THIS TIME...WITH THE MAIN STORM SYSTEM OFF THE WEST COAST...THE
EXACT TIMING AND TRACK OF THIS SYSTEM REMAINS UNCERTAIN. A SLIGHTLY
MORE NORTHERLY TRACK WOULD RESULT IN WARMER TEMPERATURES...AND A
DIMINISHED POSSIBILITY FOR ACCUMULATING SNOW. A MORE SOUTHERLY TRACK
WOULD RESULT IN LESS MOISTURE AVAILABLE FOR ANY PRECIPITATION THAT
MAY FALL.

PERSONS PLANNING TRAVEL...OR ANY OUTDOOR ACTIVITIES...IN WESTERN AND
NORTH CENTRAL NEBRASKA LATE THIS WEEKEND...SHOULD CONTINUE TO MONITOR
NOAA WEATHER RADIO AND LOCAL MEDIA OUTLETS FOR FURTHER UPDATES
CONCERNING THIS POTENTIAL SPRING SNOW STORM.

M. MUTCHLER