Severe Thunderstorm Warning 348, NWS Omaha, NE

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
935 PM CDT TUE SEP 17 2002

CURRENT WATER VAPOR IMAGERY AND THIS EVENINGS UPPER-AIR ANALYSIS
SHOW A FAIRLY VIGOROUS SHORTWAVE EJECTING NEWD ACROSS WRN NEB INTO
SD, DOWNSTREAM FROM THE PRIMARY MID-LEVEL TROUGH THAT WAS LOCATED
OVER THE GREAT BASIN.  00Z SOUNDINGS FROM KS AND NEB STILL INDICATED
A PAUCITY OF LOW-LEVEL MOISTURE, WITH SOME IMPROVEMENT NOTED AT
DDC.  LATEST REGIONAL VWP AND PROFILER DATA INDICATES AN INCREASING
WARM ADVECTION REGIME BECOMING ESTABLISHED ACROSS THE CNTRL PLAINS
WITH THE NELIGH, NEB SITE CLEARING INDICATING THE DESTABILIZATION
PROCESS IS UNDERWAY (I.E. STRONG VEERING WINDS BENEATH BACKING WINDS
ALOFT).

ALTHOUGH THE NEW ETA ONLY GENERATES MINOR AMOUNTS OF QPF ACROSS OUR
CWFA OVERNIGHT, OBSERVATIONAL DATA INDICATES GOOD REASON TO INCREASE
THE POPS.  THUS, WE WILL DO SO IN ALL ZONES.

OTHERWISE, ONLY MINOR ADJUSTMENTS WILL BE MADE TO THE TEMPERATURES
AND SKY COVERAGE.

THE UPDATED SET OF ZONES WILL BE OUT SHORTLY.

MEAD

--325 PM CDT DISCUSSION--
FORECAST CHALLENGES ARE PCPN TIMING/CHCS TNGT INTO THU AND TEMPS WED
AND THU.  12Z AVN HAS TRENDED TWD A LTL STGR/MORE CLOSED
SOLUTION WITH 500 MB TROF ON THU...A LTL DIFFERENT THAN PREV
RUN...SO GENERALLY WENT WITH ETA...WHICH WAS ALSO A LTL WARMER AND
LOOKED OVERALL A LTL BETTER.

SHORT TERM...COMPLEX UPR PATTERN PREVAILING ACRS THE PLAINS WITH
TROF OVR MO SPREADING BANDS OF SHWRS/ISOLD TSTMS TWD SERN ZONES.
ANOTHER TROF EJECTING TWD NEBR PNHDL AHD OF A DEEPENING LARGER UPR
TROF OVR NWRN U.S.  MAY HAVE TO MAKE LAST MINUTE ADJ FOR ONGOING
PCPN FAR SERN ZONES IF ACTIVITY CONTS TO WORK TWD THAT AREA.  OTRW
VSBL STLT SHOWD CU FIELD EXPANDING ON NRN EDGE OF RETURNING
MSTR/INSTABILITY AXIS TWD NRN KS.  ETA INDICATED BEST 850 MB THETA E
ADVCTN OVR CWA IN 00Z-06Z TIME FRAME SO A CASE COULD BE MADE FOR
ACTIVITY PSBLY STARTING BFR LATE TNGT IN OUR FCST AREA.   HOWEVER...
SUBSIDENCE BHND SYS DEPARTING MO COULD HINDER/DELAY DVLPMNT.
DECIDED TO WORD CHCS AFTER MID EVENING SWRN ZONES AND LEFT LATE NGT
NERN ZONES. THIS IS OUTSIDE ANY EARLIER ACTIVITY THAT MAY CREEP TWD
SERN ZONES BECAUSE OF MO SYS. ALSO ADDED SMALL POPS NWRN ZONES WITH
THE LOW LVL THETA E ADVCTN EXPECTED.  LTL CHANGES TO LOWS.

WED...MADE LTL CHANGES TO FCST.  ETA FCST INCREASING 850 MB THETA E
ADVCTN AGAIN IN THE AFTN...MAINLY NERN ZONES...AS WNDS BACK AHEAD OF
ORGANIZING UPR TROF.  SO THAT AREA MAY HAVE A SLIGHTLY HIGHER PCPN
CHC...SPCLY SINCE WRM FNT MAY SET UP ACRS SRN NEBR.  ATTM DID NOT
BASE FCST ON CLDS/PCPN HOLDING TEMPS BACK TOO MUCH...ARND 80 NORTH
TO MID/UPR 80S S.

WED NGT/THUR...HIGHEST POPS APPEARED TO BE WED NGT AS THE UPR TROF
AND FRONT APPROACH AREA.  ALTHO BRIEF LOOK AT 18Z META SUGGESTS SYS
MAY BE SPLITTING INTO 2 MAIN AREAS WHICH MAY LIMIT PCPN CHCS.  WITH
FROPA LATE WED NGT/EARLY THU...PREV COOLER TEMPS LOOK GOOD...BUT NOT
AS COOL AT AVN.  OTHER THAN MORNING POPS SERN ZONES WL KEEP FCST DRY
THU AFTN AS ETA WAS FCSTG MODERATELY STG DIVERGING Q VECTORS IN
700-500 MB LAYER.  ALSO 500 MB TEMPS/HGTS WERE NOT THAT COOL/LOW YET
WITH THIS SYS.

WARMUP ON FRI ON TRACK AHEAD OF NEXT UPR SYS...WHICH WL BE STGR
WITH MUCH COOLER UPR TEMPS WHICH SHOULD ALSO TRANSLATE INTO COOLER
SFC TEMPS.  ONLY QUESTION IS HOW FAR S WL THE ENERGY AND COOLER
TEMPS DIG.  12Z AVN IS LESS AGGRESSIVE WITH COOLING/PCPN CHCS SAT
THAN 00Z AVN...SO ALTHO DID LOWER HIGHS SAT A LTL FM 00Z BASED
FCST...DID ADJUST UP FROM PRELIMINARY THINKING EARLIER THIS
MORNING.  ALSO CHANGED PCPN TYPE TO MORE R/RW INSTEAD OF T/RW POST
FRONTAL WITH SYSTEMS SAT INTO NEXT TUE AND DID NOT STRAY TOO FAR FM
NATIONAL GUID FOR TEMPS.

CHERMOK
.OMA...NONE
MEAD