Severe Thunderstorm Warning 232, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
254 PM CDT FRI SEP 3 1999

FORECAST CHALLENGE TO BE AREAL RAINFALL TONIGHT THEN TEMPS BEYOND...

AT 17Z SFC HAND ANALYSIS SHOWED SEMI-STNRY FRONT EXTENDING FROM WEST
OF ONL TO E OF IML. KLNX 88D INDICATED SCT SHOWERS OVER WRN NEB
WITH FEW TSTMS ATTM. CLOUD COVERAGE HAS LIMITED HEATING THIS
AFTERNOON WITH CAP TO LIMIT CONVECTION TILL EVENING. WV IMAGERY
LOOP SHOWS ONE S/W MOVING E ACROSS WRN NEB AND THE NEXT WAVE NOW
MOVING ACROSS ERN CO.

ETA AND AVN MODELS MOST SIMILAR IN MOVING FRONT SLOWLY EAST THROUGH
36 HOURS WHILE NGM THE WARMEST AND HAS MOST NRN AND SLOWER TRACK OF
SYSTEM. PREFER A BLEND OF ETA/AVN MODELS. THE FRONT REMAINS PARALLEL
TO UPPER FLOW THROUGH TONIGHT WITH LITTLE FURTHER EWD MOVMT THROUGH
MIDNIGHT.

THE FRONTAL POSITION WILL RESULT IN THE POTENTIAL FOR FLOODING TO
OCCUR OVER PARTS OF PERKINS...HAYES AND CHASE COUNTIES OVERNIGHT
WHERE FFG REMAINS LOW. 8H LOW WHICH CONTINUES TO FORM OVER ERN CO
OVERNIGHT WILL RESULT IN INCREASED INFLOW AND WARMER AIR OVERRUNNING
FRONTAL BOUNDARY IN THE SW. INCREASED OMEGA DEPICTED WITH SHOWERS AND
THUNDERSTORMS TO MOVE NE ALONG FRONTAL BOUNDARY. JET DYNAMICS WILL
DIMINISH TONIGHT AS 5H TROUGH AXIS MOVES E AND FILLS. HOWEVER THE
INTERACTION OF THE UPPER AND LOWER JET AXIS BY MIDNIGHT WOULD EXPECT
SHOWERS AND THUNDERSTORMS TO BECOME NUMEROUS ALONG AND NORTH OF
BOUNDARY THEN ACTIVITY TAPERING OFF TOWARDS MORNING AS SFC AND 8H
FRONTS MOVES E OF FA. WILL ISSUE FLASH FLOOD WATCH FOR TONIGHT FOR
THESE THREE COUNTIES.

AVN/MRF BASED TEMPERATURE GUIDANCES USED WITH COOLDOWN TO OCCUR AS
FRONT MOVES E ON SATURDAY. UPSLOPE FLOW DIMINISHES ON SAT IN THE W
WITH SHOWERS/LIGHT RAIN ENDING IN THE MORNING WITH SOME BREAKS IN
THE CLOUDS IN THE SW IN THE AFTN. LITTLE WARMING TO OCCUR AS CLOUDS
LIMIT HEATING.

SAT NIGHT THE SFC HIGH WILL RIDGE SSE ACROSS THE FA WITH MUCH COOLER
AIR TO FILTER IN. 5H TROUGH MOVES E WITH ASSOCIATED COLD POOL WITH
PROVIDE SUFFICIENT INSTABILITY FOR MENTION OF SHOWERS ACROSS THE N.
FURTHER S DOWNGLIDE WINDS AND INCREASING SUBSIDENCE TO PROVIDE FOR
SOME CLEARING AND COOL TEMPERATURES.

SUNDAY THE UPPER RIDGE AND SFC HIGH BUILD EAST WITH INCREASING
SUBSIDENCE WITH DRY YET COOL TEMPERATURES.

IN THE EXTENDED MAINLY DRY CONDITIONS EXPECTED WITH A WARMING TREND
TO OCCUR AS MORE ZONAL FLOW DEVELOPS ALOFT.

.LBF...FLASH FLOOD WATCH NEZ058-069-070

KECK