Severe Thunderstorm Warning 2, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
200 PM CDT SUN MAY 2 1999

FCST CHALLENGE CONCERNS ENDING OF PCPN TNGT AND THREAT OF PCPN IN LATER
PERIODS WITH NEXT UPSTREAM SYSTEM.

1800 UTC SFC ANALYSIS INDICATED WK LOW PRES CNTRD OVR N CNTRL WY WITH
TROF EXTDG SEWD TO 2ND SFC LOW IN XTRM SWRN NEB.  2ND TROF EXTENDED FM
2ND LOW SWD THRU WRN THIRD OF KS INTO XTRM WRN OK.  UPR LOW IN VCNTY OF
OGA MOVG SLOLY NWD.

WDSPRD -SHRA IN ADVANCE OF CLOSED SYS OVR MUCH OF LBF CWA...WITH LN
CONVECT ACTVTY ALONG TROF FM E CNTRL NEB PNHDL TO NR MCK. INCRG
ISOLATION BHND SFC TROF AND COOLER TEMPS ALFT WL HELP TO DESTABILIZE
ATMOS FURTHER THIS AFTN...WITH PRIMARY WX THREAT BEING BRIEF HVY RN AND
SML HAIL.  TROF FCST BY ALL MODELS TO LIFT NEWD EXITING N CNTRL ZNS
BY/ARND MID AS AREA ENCOUNTERS INCRG SUBSIDENCE ON BACKSIDE OF SYS.
WITH THIS IN MIND...WL END THREAT OF PCPN IN SWRN ZNS THIS EVNG...WITH
PCPN THREAT ENDING IN N CNTRL NEB SHRTLY AFT MID.

ALL OF WRN AND N CNTRL NEB IN AREA OF SUBSIDENCE FOR MUCH OF MON AS UPR
SYS CONTS TO LIFT N INTO NRN PLAINS.  BRK IN WX TO BE SHORT-LIVED
HOWEVER...AS NEXT H5 KICKER MOVS RPDLY SE OUT OF NWRN PTN OF NATION
TOWARD CNTRL PLAINS.

ETA APPEARS FAR TOO AGRESSIVE IN DIGGING H5 WV TO TX PNHDL BY H+48
CONSIDERING THAT BULK OF ENERGY INITIALLY IS FOUND OVR NRN RCKYS.
THEREFORE...ETA PLACEMENT OF SFC LOW IN N CTRL KS ALSO APPEARS TO BE
QUESTIONABLE.  PREFER NGM/AVN SFC AND UPR PLACEMENT WHICH KEEPS UPR FLO
FLATTER...WITH SFC LOW LKLY TO BE FOUND FURTHER N OVR S CNTRL SD.
SLOWER MOVEMENT OF AVN PREFERRED OVR NGM THROUGH...WHICH IS ABT 6 HRS
LESS PROGRESSIVE THAN NGM...TO ACCOUNT FOR TYPICAL MODEL BIAS IN MOVG
DVLPG UPR SYSTMS TOO AGRESSIVELY PRIOR TO AND AFT CLOSURE.

DESPITE SUBSIDENCE OVR LBF CWA IN 2ND PD...APPROACH OF NXT H5 SYS AND
ATTENDANT CDFNT MAY BE CLOSE ENF TO NWRN ZNS TO WARRANT THREAT OF LTE
AFTN -SHRA/-TSRA...SPCLY SINCE LAPSE RTES OVR ENTR LBF CWA BTWN 7-8C/KM
WITH H7-H5 DELTA-T OF ARND 20C.  WL KEEP RMNDR OF ZNS DRY ON MON
DESPITE MID LVL INSTABILITY SINCE LTL IN WAY OF FOCUSING MECHANISM WL
BE PRESENT.  DRYING SWLY DOWNSLOPE WNDS SHD ALLOW TEMPS TO CLIMB WELL UP
INTO THE 70S ON MON...AND GUID REASONABLE AND CONSISTENT.

WITH MID LVL INSTABILITY RMNG OVR LBF CWA AND OMEGA FIELDS INCRG IN
VCNTY OF SFC FNT...WL INTRODUCE THREAT OF PCPN ALL SECTNS ON MON
NGT...CONTG INTO TUE BEF PCPN ENDS FM W.  HIST POPS WL BE IN NRN SECTNS
WHERE OMEGA FIELDS AND MN RH TO BE HIST.  ALTHO THREAT OF PCPN LKLY TO
END IN W BY TUE AFTN...WL CONT THREAT FOR ENTR DAY TO CVR FOR SLOWER
AVN SOLN...AND WL REFINE TEMPORALLY WHEN TIMING OF BACK EDGE OF PCPN
SHIELD BCMS BTR DEFINED.

.LBF...NONE.

WERT