Tornado Warning 27, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
115 PM CDT SUN JUN 27 1999

...FCST CHALLENGE CONCERNS AMNT AND EXTENT OF PCPN ASSOCIATED WITH
DVLPMNT OF MCS TNGT...

ANOTHER ROUND OF WDSPRD CONVECT ACTIVITY EXPECTED TNGT AS ATMOS QUICKLY
RECOVERS FM LAST NGTS CONVECTION.  1800 UTC SFC ANALYSIS INDICATED WK
SFC LOW PRES OVR ERN WY WITH 2ND LOW OVR CNTRL KS.  WNDS AT SFC-H7
CONTG TO SLOLY VEER BACK INTO THE SE PER LTST SFC OBS AND MCK
PROFILER...WHICH WL ADVECT VRY HIGH THETA-E VALUES BACK INTO WRN HI
PLNS FOR REST OF AFTN INTO ERY TNGT.

APPROACH OF H5 SHRT WV MOVG EWD THRU NRN RCKYS WL INCRS DYNAMIC FORCING
AND MID LVL COOLING OVR LBF CWA...WITH LOW LVL JET AT H8 PROVIDING
ADTNL DESTAB OF LWR ATMOS AS WRM AND MOIST LOW LVL AIR FM GULF ADVECTED
OVR SFC BOUNDARY IN CNTRL KS.  CAPES OF 2000-3500 J/KG...H7-H5 DELTA T
OF 24C...AND H7-H5 LAPSE RATES OF ARND 8.5C/KM UNDERSCORE THE CONVECT
POTNL TNGT.  GOOD DIRECTIONAL AND SPEED SHEAR SHD SUPPORT SUPERCELL
DVLPMNT THIS EVNG...WITH WDSPRD HVY RAIN BCMG THE PRIMARY THREAT BY
MIDNIGHT AS CONVECTION BCMS ORGANIZED INTO AN MCS N OF THE FRONTAL
BOUNDARY.

WDLY SCT-SCTD CONVECT ACTVTY SHD MOV EWD OFF HIGH PLNS OF WY AND CO LTE
THIS AFTN...ORGANIZING INTO AN MCS OVR SWRN NE...NERN CO...AND NWRN KS
ERY TNGT ON NOSE OF H8 LLJ...WITH SYSTM TURNING MORE SEWD INTO
INSTABILITY AXIS WITH TIME.  MCS H2 DIVERGENCE SIGNATURE VRY NOTICABLE
BY H+18HRS (0600 UTC) PROGS ON BOTH ETA AND NGM...HOWEVER SRN PLACEMENT
OF ETA PREFERRED OVR NGM WHICH HAS CONSISTENTLY PLACED HVST RAFL N OF
ACTUAL AREA PST SVRL DAYS.

WITH PRECIPITABLE WATER VALUES OF 100-150% OF NRML OVR AREA...AND MCS
LKLY TO MOV OVR AREAS WHICH RCVD 1-4 LAST NGT...FLASH FLOOD WATCH WL
CONT TO BE NEEDED FOR MUCH OF SWRN NEB...AND NO CHG TO AREAL COVERAGE
FM PREV FCST SEEMS NEEDED ATTM.

MID LVL FORCING TGT WL BE GREATEST OVR NRN PTNS OF LBF CWA WHICH WL BE
CLOSER TO H5 SHRT WV MOVG EWD THRU NRN PLAINS...BUT LOW LVL SUPPORT FOR
MCS AND HVY RAFL POTNL BEST IN SW.  RESULT WL BE THAT ENTR LBF CWA WL
LKLY EXPERIENCE RN TNGT...BUT WITH EXCESSIVE RN NOT LKLY TO FALL IN
N CNTRL ZNS DESPITE RELATIVELY LOW FLASH FLOOD VALUES IN THIS AREA.

MCS SHD BE S AND E OF MOST OF LBF CWA BY DAYBREAK MON WITH WRN AND N
CNTRL NEB TO INITIALLY FALL UNDER WK CAA AND INCRG SUBSIDENCE ON
BACKSIDE OF SYS.  MOST OF AREA SHD RMN DRY THRU MUCH OF DAY...BUT WITH
THE THREAT OF SCT CONVECTION AGN INCRG IN FAR W AS TSTMS DVLP OVR FRONT
RANGE AND PROGRESS EWD.  MID LVL LAPSE RTES RMN STEEP OVR AREA THRU AT
LEAST TUE...AND WITH SFC WNDS VEERING BACK INTO THE SE OVR ALL OF WRN
AND N CNTRL NEB MON NGT...THE THREAT OF ANOTHER ROUND OF CONVECT WL
INCRS THRUT THE 3RD INTO THE 4TH PD OF THIS FCST...AND LKLY PERSIST
INTO THE EXTENDED FCST.

93-95P EXTENDED GRAPHICS LOOK REASONABLE AND WL NOT SIG MODIFY.

.LBF...FLASH FLOOD WATCH TONIGHT ZONES 036>038-056>059-069>071

WERT