Severe Thunderstorm Warning 181, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
210 PM CDT TUE AUG 20 2002

SYNOPSIS...LATE MORNING SFC ANALYSIS HAS LOW PRESSURE CENTER OVER
NORTHEAST WY WITH WARM FRONT STRETCHING SOUTHEAST BISECTING THE CWA.
MOISTURE CONTINUES TO POOL NEAR THE WARM FRONT WITH TDS IN THE 60S
OVER THE AREA.  H5 RIDGE OVER MISSOURI WITH EMBEDDED S/WS ROTATING
AROUND THE PERIFERY OF THE RIDGE.  AT 18Z WATER VAPOR SHOWS THE MOST
SIGNIFICANT OF THE S/WS CURRENTLY MOVING THRU WESTERN COLORADO.

DISCUSSION...AFOREMENTIONED STRONG S/W OVER COLORADO WILL TRAVERSE
THE AREA LATE THIS AFTERNOON INTO TONIGHT.  WITH ATMOSPHERE
FORECAST TO BECOME QUITE UNSTABLE WOULD EXPECT A FAIR AMOUNT OF
CONVECTION TO FIRE UP THIS PM.  QUESTION THEN REVOLVES AROUND HOW
MUCH THIS CONVECTION CAN SURVIVE THE NIGHT.  THINK THAT THIS
EVENING WILL SEE SOME DECENT COVERAGE...BUT CHANCES WILL LIKELY
DWINDLE OVERNIGHT AS THE BEST FORCING SHIFTS INTO SOUTH DAKOTA ON
THE NOSE OF THE LLJ AND CLOSER TO THE WARM FRONT.  WILL MONITOR
RADAR AND MAKE LAST MINUTE DECISION ON POPS TONIGHT.

TOMORROW BECOMES A REAL CHALLENGE WITH POPS AND TEMPS FOR THAT
MATTER.  MODELS OBVIOUSLY ARE NOT GOING TO HAVE ANY CLUE WHAT
TONIGHTS CONVECTION WILL DO TO BOUNDARIES.  EXPECTATION IS THAT
THERE WILL BE LEFT OVER BOUNDARIES SOMEWHERE IN THE CWA AND WITH LEE
TROUGH/DRY LINE SETTING UP LOOKS LIKE A FAIRLY DECENT SHOT AT
CONVECTION TOMORROW.  CAPES OF 3K+ WITH LITTLE IF ANY CINH BY
AFTERNOON TOMORROW SO CONVECTION COULD FIRE UP JUST ABOUT
ANYWHERE.  WILL GENERALLY CARRY 30 POPS ACROSS THE BOARD TOMORROW.

AGAIN WEDNESDAY NIGHT WILL BE HIGHLY DEPENDENT ON HOW THINGS PLAY
OUT THE NEXT 24 HOURS.  ETA/AVN BOTH DEVELOPING FAIRLY DECENT
CONVECTIVE BULLSEYE IN/NEAR THE CWA.  CONSIDERING WE ARE PROGGED TO
BE ON THE NOSE OF 50KT LLJ WITH WARM FRONT NEAR KS/NE BOARDER THINK
THAT SLIGHTLY HIGHER POPS ARE JUSTIFIABLY...WILL PROBABLY BREAK OUT
THE 40 POP FOR 3RD PERIOD

FRONT SHOULD MAKE SOME PROGRESS SOUTH INTO KANSAS THURS/THURS
NIGHT.  ETA FURTHER SOUTH WITH THE FRONT AND ASSOCIATED CONVECTION
THINK THIS SEEMS FAIRLY REASONABLE.  ALREADY HAVE A DRY FORECAST
THURS AFTERNOON...WITH SFC BOUNDARY NEAR KS/NE BOARDER WILL GO
AHEAD AND INTRODUCE LOW POPS SOUTH THURS AFTERNOON.  THURSDAY NIGHT
WITH POSSIBLE ELEVATED DEVELOPMENT WITH LLJ WILL GO AHEAD AND KEEP
POPS AREA WIDE SINCE THEY ARE ALREADY THERE.

WITH SFC HIGH FORECAST TO BUILD INTO THE AREA FRIDAY.  WILL GO AHEAD
AND PULL POPS OUT OF FRIDAY AND FRIDAY NIGHT.  LOOKS LIKE THE
CONVECTION WILL PROBABLY STAY NEAR THE FOOTHILLS AND DONT THINK
THAT IT WILL MAKE IT INTO THE PANHANDLE COUNTIES.  WITH NO REAL
SUPPORT FROM A LLJ LEE SIDE CONVECTION SHOULDNT MAKE IT ONTO
THE HIGH PLAINS FRIDAY NIGHT.

EXTENDED...SIGNIFICANT MODEL DIFFERENCES AND VERY LITTLE IN THE WAY
OF ANY HELP FROM THE ENSEMBLES SO NOT INCLINED TO MAKE MANY CHANGES
MADE TO THE EXTENDED. THE SCENARIO FROM THE GLOBAL HAS UPPER TROUGH
OVER THE INTERMOUNTAIN WEST...WHICH WOULD LEAD ME TO BELIEVE THAT
THERE WILL BE SOME LEE TROUGHING SETTING UP NEXT WEEK. WITH
SOUTHEASTERLY LOW LEVEL FLOW SHOULD SEE SOME MOISTURE RETURN TO THE
HIGH PLAINS.  WOULD EXPECT THERE TO BE SOME CONVECTION DURING THE
AFTERNOON....HOWEVER NO CLUE ON WHICH DAY WILL PRESENT THE BEST
CHANCE.  TO AVOID PAINTING ENTIRE EXTENDED WITH SLIGHT CHANCE POPS
WILL GO AHEAD AND SIT ON THE DRY FORECAST FOR NOW. HOWEVER FULLY
EXCEPT THAT SOME LOW POPS WILL BE NEEDED EVENTUALLY IN THAT TIME
FRAME...JUST NOT READY TO ADD THEM YET

SOUTHEASTERLY LOW LEVEL FLOW WITH SOME HINT OF UPPER RIDGING NEARBY
LEADS ME TO THINK THAT AT LEAST CLIMO WOULD BE THE WAY TO GO WITH
TEMPS.  SO HAVE GENTLY NUDGED TEMPS UPWARD A CATEGORY ACROSS THE
BOARD.  WILL CONTINUE WITH DRY FORECAST AND KEEP TEMPS NEAR TO
SLIGHTLY ABOVE CLIMO.

.LBF...NONE.

IZZI/DP

NEZ004>010-022>029-035>038-056>059-069>071-094-202045-

HAZARDOUS WEATHER OUTLOOK FOR WESTERN AND NORTH CENTRAL NEBRASKA
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1056 AM CDT TUE AUG 20 2002

...STORM SPOTTER ACTIVATION MAY BE NEEDED LATE THIS AFTERNOON AND
TONIGHT ACROSS PORTIONS OF WESTERN AND NORTH CENTRAL NEBRASKA...

THERE IS THE THREAT OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO
EARLY TONIGHT ACROSS PORTIONS OF WESTERN AND NORTH CENTRAL
NEBRASKA.  THE GREATEST THREAT OF SEVERE WEATHER WILL OCCUR FROM
LATE THIS AFTERNOON THROUGH THIS EVENING NORTH OF A LINE
EXTENDING FROM BROKEN BOW IN CUSTER COUNTY...TO OSHKOSH IN
SHERIDAN COUNTY. OTHER THUNDERSTORMS WHICH ARE NOT EXPECTED TO
REACH SEVERE LEVELS ARE POSSIBLE OVER THE REST OF THE OUTLOOK AREA.

AN AREA OF LOW PRESSURE WILL PUSH OUT OF MONTANA AND INTO WESTERN
SOUTH DAKOTA BY EARLY EVENING. IN RESPONSE TO THIS SYSTEM A WARM
FRONT ACROSS KANSAS LAST NIGHT WILL LIFT RAPIDLY NORTH THROUGH
NEBRASKA TODAY. SOUTHEAST WINDS JUST NORTH OF THIS WARM FRONT WILL
ALLOW AMPLE MOISTURE TO MOVE INTO THE AREA. THIS MOISTURE ALONG WITH
SUNSHINE DURING THE AFTERNOON WILL ALLOW THE ATMOSPHERE TO BECOME
UNSTABLE BY AFTERNOON.  THESE FEATURES ALONG WITH AN UPPER
DISTURBANCE MOVING OUT OF THE CENTRAL ROCKIES WILL BRING SCATTERED
THUNDERSTORMS TO THE AREA THIS AFTERNOON AND EVENING.  WINDS ALOFT
WILL BE STRONG ENOUGH TO ALLOW SOME OF THESE STORMS TO BECOME SEVERE
WITH LARGE HAIL THE PRIMARY THREAT.