Severe Thunderstorm Warning 232, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
245 PM CDT FRI AUG 14 1998

FORECAST CHALLENGE WITH THIS AFTERNOONS CYCLE...EFFECTS OF THE NEXT
SHORT WAVE TROUGH

MODEL PERFORMANCE DISCUSSION...
    LAST NIGHTS ETA, NGM, AND AVN DID WELL WITH MOST OF THE HEIGHT
FEATURES AT 500MB. THE ETA AND AVN DID THE BEST WITH THE LOCATION OF
THE IDAHO/MONTANA VORT MAX. LOOKING AT SATELLITE, THOUGH, THE ETA
APPEARS TO HAVE OVERDONE THE STRENGTH OF THE VORTICITY IN THAT AREA. IT
DOES HAVE THE VORT MAX WEAKENING AS IT MOVES INTO THE ANTICYCLONIC
DIFFLUENCE IN CENTRAL NEBRASKA. THE ETAS SPEED OF THE MOVEMENT SEEMS
MORE REASONABLE THAN THE SLOWER AVN BECAUSE THE HEIGHT GRADIENT IS
TIGHT AND THE VORTEX SHOULD MOVE ALONG AT A PRETTY GOOD CLIP UNTIL IT
REACHES THE DIFFLUENT 500MB HEIGHT FIELD IN CENTRAL NEBRASKA AT ABOUT 36
HOURS. THE AVN AND ETA COME TOGETHER AT THAT TIME. SO, HAVE CHOSEN THE
ETA FOR THE FIRST TWO PERIODS AND COMBINED THE ETA AND THE AVN/MRF FOR
THE LAST TWO.

FIRST PERIOD DISCUSSION...
    THE HIGHER VORTICITY LOBE COMING OUT OF SOUTH DAKOTA TONIGHT WILL
PRODUCE SOME CYCLONIC VORTICITY ADVECTION IN CENTRAL NEBRASKA BY 00Z
WITH THE CVA MOVING INTO SOUTH CENTRAL NEBRASKA BY 06Z. HOWEVER, QG
FORCING IS WEAK. NEVERTHELESS, WITH THE THETA-E RIDGE AT 850MB AND
ASSOCIATED INSTABILITY LINING UP ALONG THE SOUTH DAKOTA BORDER, SOME
THUNDERSTORM DEVELOPMENT IS TO BE EXPECTED. THE STRONGER CVA AND
850-500MB QG-FORCING APPEARS IN THE PANHANDLE AT 06Z AND SPREADING INTO
CENTRAL AND NORTH CENTRAL NEBRASKA BY 12Z. SO WOULD GO WITH 20-30
PERCENT POP IN NORTH CENTRAL ZONES AND THE EASTERN PANHANDLE, I.E.,
NORTH AND WEST OF AN ONL-MHN-IML LINE.
    TEMPERATURES TONIGHT SHOULD BE A LITTLE WARMER THAN THEY WERE LAST
NIGHT AS THE WIND BECOMES MORE SOUTHERLY. LOOKS LIKE M50S IN THE EASTERN
PANHANDLE TO L60S N. CENTRAL ARE A REASONABLE BET.

SECOND PERIOD AND BEYOND...
    CVA WITH THE SHORT WAVE TROUGH MOVES OUT OF THE WESTERN THIRD OF
THE STATE BY SATURDAY EVENING AND CONTINUES IN THE CENTRAL PARTS UNTIL
06Z SUNDAY MORNING. LOW LEVEL (MEAN 900-800MB) MIXING RATIO THERE OF
9-11 G/KG IS PROBABLY ENOUGH MOISTURE TO PRODUCE SIGNIFICANT
PRECIPITATION. WITH LIS OF -4 TO -6 AND CAPE OF AROUND 2000, EXPECT
SCATTERED THUNDERSTORMS SOUTH AND EAST OF A VTN-OGA LINE SATURDAY AND
SATURDAY NIGHT. THUNDERSTORMS SHOULD END BY 06Z SUNDAY IN ALL BUT
EASTERN NEBRASKA.
    THE 850MB TEMPERATURES ARE EXPECTED TO INCREASE ABOUT 2C FROM TODAY
TO SATURDAY EVENING AND LITTLE OR NO CHANGE BY SUNDAY. THICKNESS
INCREASES OF ABOUT 20-30M EACH DAY. WITH AT LEAST SCATTERED MID AND LOW
CLOUDS SATURDAY IN ALL BUT THE PANHANDLE...WARM ADVECTION SHOULD BE
TEMPERED. I EXPECT TEMPERATURES SATURDAY ABOUT THE SAME AS TODAYS OR A
COUPLE OF DEGREES F COOLER. SUNDAYS TEMPS ARE LIKELY TO BE A LITTLE
WARMER THAN TODAYS, SINCE SUBSIDENCE WITH NVA IS LIKELY TO KEEP CLOUDS
OUT.

SUGGESTED CCF

PRELIMINARY GUIDANCE FOR COORDINATION ONLY. OFFICIAL FORECAST IS
CONTAINED WITHIN THE PRODUCT OMAZFPLBF.

LBF BU 058/087 060/091 060 49023
VTN BU 060/087 061/087 061 49232

OGA BU 058/088 060/091 060 49023
IML BU 060/088 062/091 062 49023
BBW BU 060/086 063/086 064 49023
ANW BU 062/085 063/087 064 49223
ONL BU 063/085 065/087 065 49223

EASTERN PANHANDLE
    UU 055/090 057/093 058 49220

SPRINGER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE  NORTH PLATTE NE
416 PM CDT FRI AUG 14 1998

TIME(CDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0408 PM    18 NNE ATKINSON           NE   1.75 INCH HAIL
08/14/98   HOLT

M. MUTCHLER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE  NORTH PLATTE NE
416 PM CDT FRI AUG 14 1998

TIME(CDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0408 PM    18 NNE ATKINSON           NE   1.75 INCH HAIL
08/14/98   HOLT

M. MUTCHLER