Hail and Damaging Wind in Nebraska, August 29 to 31, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
131 PM CDT THU AUG 29 2002

...FORECAST CONCERNS REVOLVES AROUND POPS AND +RA POTENTIAL...

SYNOPSIS...THE BROKEN RECORD CONTINUES.  UPPER LOW OVER
INTERMOUNTAIN WEST CONTINUES TO SIT AND SPIN...WITH UPPER HIGH OVER
RIO GRANDE VALLEY OF WEST TX.  A RATHER VIGOROUS SHORT WAVE IS
EJECTING NORTHEAST BETWEEN THESE TWO SYSTEMS RIDING THE SUBTROPICAL
JET INTO NW COLORADO.  NO SIGNIFICANT SFC FEATURES IN THE REGION
AS OF LATE MORNING...HOWEVER 2-3 MB 3 HR PRESSURE FALLS ARE
OCCURRING OVER THE PANHANDLE AND SE WY HELPING TO TURN THE WINDS
EAST TO SOUTHEAST AND DRAWING THE MOISTURE WESTWARD ONTO THE HIGH
PLAINS.

DISCUSSION...LOOKS LIKE TONIGHT WILL BE AN EVEN BETTER SET UP FOR
CONVECTION ACROSS THE CWA AS RATHER POTENT S/W OVER COLORADO
TRAVERSES THE AREA.  MOST OF THE CONVECTIVE PARAMETERS POINT TO AN
MCS TRAVERSING THE AREA TONIGHT.  PRECIP WATER VALUES ARE NOT
FORECAST TO GET EXTREME...BUT WITH VALUES APPROACHING 150% OF
NORMAL HEAVY RAINFALL CERTAINLY A THREAT.  FLOODING CONCERN WAS
ADDRESSED IN EARLY UPDATED AFD SO NO POINT IN REHASHING IT NOW.

AFTER THE NOCTURNAL CONVECTION EXITS THE AREA DURING MORNING EXPECT
TO SEE SKIES CLEAR OUT AND WE SHOULD GET A BREAK FOR MUCH OF THE
AFTERNOON.  ATMOSPHERE SHOULD HAVE AMPLE TIME TO RECOVER FROM
NOCTURNAL CONVECTION WITH AFTERNOON CAPE VALUES BETWEEN 2-3K OVER
MUCH OF THE CWA.  LEE TROUGH IS FORECAST TO LINGER ACROSS THE WESTERN
PORTIONS OF THE CWA AND SHOULD FOCUS SURFACE CONVERGENCE ALONG THIS
FEATURE TO POSSIBLY IGNITE ANOTHER ROUND OF CONVECTION ACROSS MOST
AREAS.  MID LEVEL FLOW IS RELATIVELY WEAK HOWEVER DIRECTIONAL SHEAR
IS RESPECTABLE AND WITH AMPLE INSTABILITY AND LINGERING OUTFLOW
BOUNDARIES I AM NOT AT ALL COMFORTABLE LEAVING POPS OUT OF THE
FORECAST FOR TOMORROW AFTERNOON.  SWODY2 HAS MUCH OF THE CWA COVERED
IN THE SLIGHT RISK AND THIS SEEMS REASONABLE GIVEN THE ABOVE
MENTIONED PARAMETERS.

COULD SEE SOME LINGERING CONVECTION INTO THE EARLY EVENING HOURS
HOWEVER BEST SUPPORT SHIFTS WELL TO THE NORTHEAST OF THE CWA
OVERNIGHT AS THE NOSE OF LLJ FOCUSES THE BEST LOW LEVEL FORCING
OVER NORTHERN MINNESOTA.

SATURDAY LOOKS TO BE A HOT DAY WITH DAKOTA LOW DEVELOPING NEAR THE
BLACK HILLS.  RIDGING AT H5 DOESNT LOOK TO BE ENOUGH TO SUPPRESS
CONVECTION WITH DRY LINE SETTING UP OVER THE CWA.  FORECAST
SOUNDINGS FROM THE AREA SHOW CAPE GETTING UP TO BETWEEN 2-3K AGAIN
WITH CINH BY LATE AFTERNOON LESS 25 J/KG.  FEEL THAT THE BEST
THREAT OF AFTERNOON CONVECTION WOULD BE IN THE WEST BUT THIS FAR OUT
NOT WISE TO TRY AND PINPOINT EXACT LOCATIONS SO WILL RE-INTRODUCE
POPS INTO WEST/SOUTHERN CWA AND LEAVE POPS ALONE NE AREAS.

UPPER TROUGH SWINGS EAST SATURDAY NIGHT INTO SUNDAY AND SHOULD
ALLOW THE SURFACE TROUGH TO MOVE THROUGH THE CWA.  WITH STRONG LLJ
IN PLACE CONVECTION MAY BE ABLE TO SURVIVE INTO A GOOD PORTION OF
SATURDAY NIGHT AS THE FRONT MOVES THROUGH THE CWA.  WITH THAT IN
MIND WILL KEEP POPS IN THE AREA SATURDAY NIGHT.

THIS MORNINGS ETA RUN HAS SPED UP THE PROGRESSION OF THIS WAVE
AND HAS THE FRONT THROUGH MOST OF THE CWA BY SUNDAY.  SO REALLY AM
NOT AS CONFIDENT AS DAYS PAST WITH THE CHANCE FOR SUNDAY. CONSIDERING
THAT THE MODELS HAVENT BEEN ALL THAT CONSISTENT WITH THE TIMING
THE PAST COUPLE OF RUNS...NOT INCLINED TO YANK POPS OUT JUST YET.
AVN SHOWS THE FRONT HANGING UP MORE ON SUNDAY SO FOR NOW POPS LOOK OK
BUT IF LATER RUNS KEEP TRENDING FASTER THEN SUNDAY MAY BE DRY AFTER
ALL.  BUT NO NEED TO YANK AT THIS POINT.  FOR NOW A POP-LESS SUNDAY
NIGHT SHOULD SUFFICE.

EXTENDED...29/00Z OF THE GLOBAL FEATURES SOME RATHER DRAMATIC
CHANGES AS COMPARED WITH THE 28/00Z RUN...MOST NOTABLY ON THE
STRENGTH OF THE TROUGH AND ASSOCIATED COOL DOWN AROUND THE TUE/WED
TIME FRAME NEXT WEEK.  THE LATEST RUN IS ADVERTISING A SIGNIFICANT
INTRUSION OF CHILLY AIR LATE MONDAY INTO TUES.  THE OPERATIONAL RUN
IS STRONGER WITH THIS TROUGH THAN MOST OF THE ENSEMBLE MEMBERS.  THE
28/12Z RUN OF THE ECMWF IS MUCH WEAKER WITH THE MID WEEK COOL
DOWN.  CONSIDERING THIS IS THE FIRST RUN THAT DROPS H8 THAT LOW I
WILL NOT BITE JUST YET.

BOTH THE ECMWF AND GLOBAL WOULD TEND TO SUPPORT THE NOTION OF
INTRODUCING PRECIP INTO MONDAYS FORECAST.  WILL AWAIT THE 12Z AVN
AND IF IT OFFERS THE SAME AMOUNT OF SUPPORT FOR THIS WILL GO AHEAD
AND INTRODUCE CHANCE POPS INTO MONDAY.

BEYOND TUESDAY BOTH THE ECMWF AND THE 29/00Z RUN OF THE GLOBAL
TRANSISTIONING TO MORE OF TROUGH WEST AND RIDGE EAST WHICH WOULD
SPELL A RETURN TO A MORE ACTIVE WEATHER PATTERN TOWARD THE MIDDLE
OR END OF NEXT WEEK.  THIS IS SIX TO SEVEN DAYS OUT AND WE HAVE
PLENTY OF TIME TO LET THE MODELS FLIP FLOP AROUND BEFORE WE NEED TO
INTRODUCE POPS INTO THAT TIME FRAME.  BUT IF THE EXTENDED MODELS
ARE ONTO SOMETHING THEN WE MAY SEE YET ANOTHER WET AND ACTIVE WEEK.

.LBF...FLOOD WATCH TILL 3 AM MDT FOR GARDEN...DEUEL...AND KEITH
COUNTIES.

IZZI/44