Severe Thunderstorm Warning 242, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
242 PM CDT MON AUG 14 2000

...POPS WILL BE THE CHALLENGE THROUGHOUT THE FORECAST...

PERSISTENT UPPER PATTERN WITH A LARGE RIDGE OVER THE CENTRAL U.S....
A CLOSED LOW OVER THE EAST COAST AND A TROF IN THE PAC NW. AT THE
SURFACE...LOW PRESSURE IS CENTERED IN EXTREME SERN NORTH DAKOTA WITH
A COLD FRONT EXTENDING SWWD ACROSS ERN SOUTH DAKOTA...CENTRAL
NEBRASKA AND INTO NERN COLORADO.

MANY DIFFERENCES IN THE MODELS OVER THE NEXT TWO DAYS. ETA/AVN BOTH
RESOLVE A SHORTWAVE THROUGH NORTHERN NEBRASKA MONDAY...HARD TO FIND
ON NGM. ETA IS MOST AGGRESSIVE IN DEVELOPING PRECIP OVER SOUTHERN
NEBRASKA TUESDAY NIGHT. AVN ALSO RESOLVED SOME CONVECTION TUESDAY
NIGHT BUT LIMITS ACTIVITY TO FAR WESTERN AREAS OF CWA. ETA CONTINUES
PRODUCING PRECIP ALONG SOUTHERN AND EASTERN AREAS OF CWA WEDNESDAY AS
ANOTHER FRONT/WAVE APPROACH...AVN ALSO HINTS AT THIS POSSIBILITY BUT
IS LESS AGGRESSIVE. NGM CARRIES SURFACE BOUNDARY FARTHER SOUTH AND
EJECTS AFOREMENTIONED WAVE INTO KANSAS...THUS DEVELOPS BULK OF
PRECIP TUESDAY NIGHT/WEDNESDAY SOUTH AND EAST OF CWA. ETA/AVN HAVE
BEEN DOING WELL AT THE SURFACE RECENTLY AND THINK ETA MAY HAVE THE
RIGHT IDEA TUESDAY NIGHT WITH POSITION OF SURFACE BOUNDARY ALONG
KS/NE BORDER...POTENTIAL LLJ AND WEAK UPPER FORCING.

HIGH AND DRY CONDITIONS EXPECTED TONIGHT ACROSS THE CWA. SURFACE
FRONT CURRENTLY EXTENDS FROM JUST WEST OF ONL TO NEAR IML AND WILL
SLOWLY PASS SOUTH AND EAST OF THE CWA THIS EVENING. MUCH LOWER
DEWPOINTS WILL ADVECT INTO THE AREA TONIGHT ON NORTHERLY LOW LEVEL
WINDS. MUCH OF THE SOUTHERN HALF OF THE CWA IS LIKELY TO DECOUPLE
IN WEAKER GRADIENTS...NOT THE CASE FARTHER NORTH. GUIDANCE MINS SEEM
REASONABLE.

ETA/AVN BRING A WAVE OUT OF THE MONSOON FLOW INTO NORTHERN NEBRASKA
TUESDAY. WV PICS INDICATE A HEALTHY PLUME OF MID LEVEL MOISTURE
SPREADING INTO NEBRASKA FROM CO/WY. ONLY A SCATTERING OF
CLOUDS CURRENTLY EVIDENT ON VISIBLE IN SAME AREA. TIME SECTIONS
INDICATE BEST VV ARE EXPECTED AT MID LEVELS THUS RH FIELDS MAY BE
ACCURATE GIVEN THAT IT SHOULD EVOLVE ALONG THETA-E RIDGE AND AREA
WHERE LOWER LEVEL CONVERGENCE WILL BE INCREASING AS WINDS BACK TO
THE EAST/SOUTHEAST. AS WAVE TRAVELS EAST IT WILL LOSE SUPPORT AT
LOWER LEVELS AND ENCOUNTER AN INCREASINGLY STABLE ENVIRONMENT...THUS
POPS WILL NOT BE CARRIED EAST OF VTN DESPITE QPF OUTPUT FROM
MODELS. SOUTHERN PART OF CWA SHOULD BE RELATIVELY UNAFFECTED BY THIS
FEATURE DURING THE DAYTIME ON MONDAY. TEMPS WILL BE A CHALLENGE
BECAUSE OF THE POTENTIAL FOR CLOUD COVER WITH AFOREMENTIONED
FEATURE. DESPITE...HAVE OPTED TO GO SLIGHTLY ABOVE GUIDANCE TEMPS
TUESDAY. WITH RECENT STRETCH OF HOT/DRY WX...DRY GROUND AND EXPECTED
LOWER DEWPOINTS THERE IS A GOOD CHANCE TEMPS WILL RECOVER FURTHER
THAN FORECAST BY MOS.

YET ANOTHER WAVE FORECAST TO EJECT OUT OF CO/WY TUESDAY NIGHT ALONG
AND NORTH OF THE BOUNDARY THAT IS EXPECTED TO BE ALONG THE NE/KS
BORDER. INSTABILITY LOOKS MARGINAL AT BEST...BUT LOW LEVEL
CONVERGENCE OF THE WIND FIELDS AND ASSOCIATED MOISTURE SOUTH OF THE
BOUNDARY IS MORE FAVORABLE. ETA MAY HAVE LOWERED MOISTURE VALUES
NORTH OF FRONT TOO MUCH...IF SO CAPES ALONG AND NORTH OF FRONT MAY
BE HIGHER THAN CURRENTLY FORECAST. ALL MODELS HINT AT THIS TYPE OF
SCENARIO BUT DIFFER IN LOCATION AND COVERAGE OF PRECIP AS DISCUSSED
ABOVE AND WILL GO WITH THE ETA. NORTHERN AND WESTERN PORTIONS OF THE
CWA WILL BE FAR ENOUGH REMOVED FROM SURFACE BOUNDARY TO REMAIN DRY.
CLOUDS AND MIXING SUPPORT TEMPS AT OR SLIGHTLY ABOVE GUIDANCE.

WEDNESDAY IS EVEN MORE DIFFICULT TO FIGURE OUT WITH FRONT WASHING
OUT AND ANOTHER EXPECTED TO MOVE INTO THE CWA BY 00Z THURSDAY.
OVERALL FEATURES ON ETA/AVN BY 00Z THURSDAY ARE REMARKABLY SIMILAR.
BOTH INDICATE SURFACE LOW DEVELOPMENT ALONG FRONT IN VICINITY OF SERN
SD AND NERN CO WITH ENHANCED LOWER LEVEL CONVERGENCE...INSTABILITY
AND MOISTURE IN THESE AREAS. ETA CONTINUES THREAT OF PRECIP ALL
ALONG THE FRONT...HOWEVER BOTH MODELS FAVOR BEST CONVECTIVE
PRECIP THREAT NORTH AND EAST OF THE CWA NEAR SURFACE LOW AND
PASSING UPPER WAVE. GIVEN THAT FRONT IS FORECAST TO PASS THROUGH CWA
AT PEAK HEATING/WEAKEST CAP...WIDELY SCATTERED CONVECTION CANNOT BE
RULED OUT FOR SOME AREAS. TEMPS ARE A CHALLENGE AGAIN WEDNESDAY
GIVEN POTENTIAL FOR CLOUD COVER BUT WILL GO WITH WARMER FAN NUMBERS
EXPECTING MORE SUN THAN CLOUDS.

IN THE EXTENDED...THURSDAY AND FRIDAY LOOK DRY WITH FRONT DROPPING
INTO KANSAS. ANOTHER CHANCE OF STORMS BY SATURDAY AS THE NEXT WAVE
AND FRONT MOVE ACROSS THE STATE. COOLING MAY BE A BIT OVERDONE BY
THURSDAY/FRIDAY FROM AVN/MRF BUT WILL GO WITH 80S FOR NOW. 90S
AGAIN BY SATURDAY AS RIDGE AMPLIFIES AGAIN.

.LBF...NONE

DJB