Severe Thunderstorm Warning 270, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
228 PM CDT WED AUG 22 2001

...MAIN CHALLENGES CONTINUE TO BE TEMPS AND POPS...

SFC ANALYSIS INDICATE A NEARLY STATIONARY FRONT EXTENDING FROM
NORTHERN IA...THROUGH EASTERN NE...AND ACROSS WESTERN KS WITH A SFC
TROF FROM NORTH CENTRAL WY TO SOUTHWEST NE AT 17Z.  THERE HAVE BEEN
A FEW LIGHTNING STRIKES OVER NORTHWEST KS AND MORE ACROSS CENTRAL CO
ASSOCIATED WITH A STRONG SHORTWAVE.  AN UPPER LOW CURRENTLY OVER
SOUTHEAST UT WILL MOVE OUT INTO THE CENTRAL PLAINS ON THU.

THE AVN/ETA ARE IN GOOD AGREEMENT THROUGH THE FIRST 36 HRS BUT THEN
DIVERGE IN THEIR SOLUTION.  THE ETA WANTS TO LIFT THE UPPER LOW
NORTHEAST WHILE THE AVN KEEPS IT CLOSED OFF AND MOVES IT INTO
NORTHEAST KS.  BOTH SOLUTIONS HAVE MOVED THE UPPER LOW TRACK A
LITTLE FURTHER SOUTH OVER THE LAST FEW RUNS.  THE TRACK OF THE
UPPER LOW AFTER 36 HRS WILL NOT HAVE MUCH AFFECT FOR THIS FORECAST
SINCE IT WILL BE EAST OF THE CWA BY THAT TIME. THEREFORE WILL GO
WITH A ETA/AVN BLEND FOR THIS FORECAST PACKAGE.

CLOUDS WILL CONTINUE TO STREAM INTO THE SOUTHERN PORTION OF THE CWA
TONIGHT IN THE SOUTHWEST FLOW ALOFT.  ONE SHORTWAVE PUSHING INTO
WESTERN KS THIS EVENING MAY HAVE ENOUGH ENERGY SLIPPING INTO THE
SOUTHERN SECTIONS OF THE CWA TO INCLUDE 20 OR 30 POPS. WEAK WARM
AIR ADVECTION AND UPSLOPE FLOW ACROSS THE EASTERN PANHANDLE TONIGHT
IS ENOUGH TO WARRANT KEEPING THE 20 POPS IN THAT AREA.  LAPSE RATES
IN THIS AREA ARE ALSO ABOVE 7.5 C/KM.  CLOUDS AND EAST TO SOUTHEAST
WINDS WILL KEEP TEMPS NEAR NGM GUIDANCE NUMBERS OVERNIGHT.

BY EARLY THU MORNING...THE UPPER LOW PUSHES INTO CENTRAL CO WITH A
SHORTWAVE ROTATING AROUND IT INTO SOUTHWEST NE.  THIS WILL BE
ACCOMPANIED BY WARM AIR ADVECTION AND THE CONTINUED UPSLOPE FLOW
WHICH WILL ENHANCE PCPN CHANCES.  THE SHORTWAVE ENERGY WILL CONTINUE
TO TRACK NORTHEAST THROUGH THE DAY AS THE UPPER LOW PUSHES ALONG
THE KS/NE BORDER DURING THE AFTERNOON.  WITH THE SYSTEM CONTINUING
TO TRACK FURTHER TO THE SOUTH WITH EACH RUN...CONFIDENCE IS NOT REAL
HIGH ON GETTING WIDESPREAD RAIN EXCEPT MAYBE THE FAR SOUTH
TOMORROW. THEREFORE WILL GO WITH 60 POPS IN THE SOUTH AND THEN
TAPER THEM OFF TO 20 POPS ACROSS THE NORTH.  TEMPS WILL BE COOLEST
UNDER THE RAIN SHIELD OVER THE SOUTH...AROUND 80...AND THEN WARM TO
THE MID 80S IN THE NORTH.

THE UPPER LOW WILL CONTINUE TO TRACK EAST ALONG THE KS/NE BORDER
THU NIGHT WITH MAJORITY OF THE WARM AIR ADVECTION PUSHING EAST OF THE
CWA.  AN INVERTED TROF SETS UP OVER OUR EASTERN ZONES WHICH WILL
PROVIDE MOISTURE CONVERGENCE.  A DEFORMATION ZONE OVER THE NORTHERN
PORTION MAY ALSO ENHANCE LIFT.  THEREFORE WILL KEEP LOW POPS
GOING ACROSS THE NORTHWEST AND MID POPS ACROSS THE SOUTH AND EAST.
WILL GO ABOVE GUIDANCE FOR LOW TEMPS...ESPECIALLY IN THE EAST WHERE
THERE WILL BE PLENTY OF CLOUDS.

MOST OF THE PCPN WILL BE EAST OF THE AREA BY FRIDAY MORNING...
EXCEPT POSSIBLY SOME LINGERING MORNING SHOWERS AROUND CUSTER COUNTY.
TEMPS SHOULD WARM INTO THE MID 80S ACROSS THE WEST WITH AROUND 80
IN THE EAST AS H8 TEMPS RANGE ROM 26C IN THE WEST TO ONLY 18C IN THE
EAST.  A SHORTWAVE PUSHING THROUGH THE NORTHWEST FLOW FRIDAY NIGHT
WILL BRING A SLIGHT CHANCE OF SHOWERS TO THE WEST.  THIS IS ALSO
WHERE THE BEST INSTABILITY IS WITH LAPSE RATES ABOVE 7.0 C/KM.

IN THE EXTENDED...NORTHWEST FLOW CONTINUES WITH WEAK SHORTWAVES
SWINGING THROUGH THE WESTERN SECTIONS.  IT IS DIFFICULT TO KNOW THE
TIMING OF THE SHORTWAVES. IF THE SHORTWAVES COME EARLY IN THE DAY...
THE CHC OF THUNDERSTORMS WILL BE MINIMAL BUT IF THEY COME THROUGH
DURING PEAK HEATING...THERE WILL BE A BETTER CHC FOR TSTMS.  WILL
TRY TO INDICATE THE BEST CHC OF PCPN BY INCLUDING A SLIGHT CHC IN
THE FORECAST.  TEMPS WILL GENERALLY BE IN THE 80S EXCEPT POSSIBLY 85
TO 95 IN THE WEST...ESPECIALLY BY NEXT WEEK WHEN THE RIDGE STARTS
PUSHING EASTWARD INTO THE AREA.

.LBF...NONE.

DDB

NEZ004>010-022>029-035>038-056>059-069>071-222045-

SEVERE WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1107 AM CDT WED AUG 22 2001

...STORM SPOTTER ACTIVATION IS NOT ANTICIPATED THIS AFTERNOON OR
TONIGHT OVER WESTERN AND NORTH CENTRAL NEBRASKA...

WIDELY SCATTERED THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON AND
TONIGHT ACROSS THE EASTERN NEBRASKA PANHANDLE AND SOUTHERN
PORTIONS OF SOUTHWEST NEBRASKA. HOWEVER THESE THUNDERSTORMS ARE NOT
EXPECTED TO REACH SEVERE LIMITS.

THUNDERSTORMS SHOULD FIRE ALONG THE FRONT RANGE OF THE ROCKIES THIS
AFTERNOON AND A FEW STORMS MAY DRIFT EASTWARD INTO WESTERN PORTIONS
OF THE OUTLOOK AREA THROUGH THE EVENING HOURS. NO SIGNIFICANT UPPER
LEVEL DISTURBANCE AND UNFAVORABLE UPPER LEVEL WINDS ARE EXPECTED TO
KEEP ANY STORMS WHICH MAY DEVELOP BELOW SEVERE LIMITS.

DP