Severe Thunderstorm Warning 217, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
142 PM CDT WED JUL 26 2000

...CHALLENGE TO BE TSTMS TONIGHT...AND AGAIN ON THURSDAY...

MODELS INITIALIZED SIMILAR WITH RIDGING IN WEST...STRONG UPPER LOW
TRANSITIONING NORTHERN PLAINS INTO NORTHERN GREAT LAKES REGION...
WITH WEAKER TROUGH ENTERING SOUTHWEST CANADA REGION. AT THE
SURFACE...LOW PRESSURE CENTERED OVER NORTHERN WISCONSIN WITH
TRAILING COLD FRONT INTO IOWA/EASTERN NEBRASKA. 18Z SURFACE
ANALYSIS INDICATED WEAK FRONTAL BOUNDARY FROM NORTHEAST
COLORADO...NORTH OF AKRON...TO OGALLALA TO BROKEN BOW TO NORFOLK.

PER CONSISTENCE AND HANDLING OF WEAKER VORT LOBES ENTERING SOUTHWEST
WYOMING THIS MORNING...ALONG WITH SPATIAL RESOLUTION...WILL FAVOR
THE ETA SOLUTION.

TONIGHT...MAIN FOCUS WILL BE ON TIMING OF WEAK SHORTWAVES AFFECTING
CWA. BY 21Z...ETA PLACES WEAK DIFFERENTIAL POSITIVE VORTICITY
ADVECTION OVER MUCH OF CWA...MAINLY SOUTH AND EAST OF A LINE FROM
VALENTINE TO ALLIANCE. AS UPPER LEVEL JET ROUNDS TOP OF RIDGE AND
PLUNGES SOUTH...STRONG AREA OF DIVERGENCE ASSOCIATED WITH LEFT EXIT
REGION OVER NORTHEAST COLORADO BY 03Z. THIS COUPLES WELL WITH
PLACEMENT OF MODERATE SHORTWAVE AND MID-LEVEL OMEGA FIELDS. ALL OF
THIS HINTING AT AN OVERNIGHT MCS...MOVING VERY SLOWLY EAST
SOUTHEAST. WILL HIT POPS HIGHEST...BUT ONLY 30 PERCENT...IN FAR
SOUTHWEST. WITH WEAKER FORCING NORTH AND EAST...WILL KEEP POPS AT
20 PERCENT MOST AREAS...WITH NO MENTION OF PRECIP FAR NORTHWEST.
OVERNIGHT LOWS NEAR GUIDANCE NUMBERS...INTO THE 60 TO 65 RANGE.

THURSDAY...RELATIVE HUMIDITY FIELDS INDICATE MOSTLY SUNNY SKIES...
WITH PLENTY OF WARMING. WITH LEE SIDE TROUGHING...A FRONTAL BOUNDARY
DROPPING INTO NORTHERN KANSAS...FLOW WILL BE EAST TO SOUTHEAST WITH
PLENTY OF BOUNDARY LAYER MOISTURE. DEWPOINTS PROGGED TO BE INTO THE
MID TO UPPER 60S BY 18Z...PROVIDING ONE INGREDIENT FOR AFTERNOON
THUNDERSTORMS. WITH CAPES APPROACHING 3000 J/KG...700-500 MB LAPSE
RATES GREATER THAN 8 C/KM...AND LIFTED INDICES BELOW -6...PLENTY OF
INSTABILITY. ALL WE NEED NOW IS A LIFTING MECHANISM. WE HAVE THAT
IN THE FORM OF MODERATE UPSLOPE FLOW...VORTICITY MAX ENTERING FROM
WEST...AND WARM AIR ADVECTION. QUESTION REMAINS WHEN AND WHERE WILL
INITIATION OCCUR. WILL HIT AFTERNOON POPS HIGHEST IN WESTERN INTO
CENTRAL CWA. WITH STRONG INSOLATION AND WARM AIR ADVECTION...
AFTERNOON TEMPS TO BE NEAR GUIDANCE NUMBERS...TO AROUND 90.

THURSDAY NIGHT...STRONG VORTICITY MAX TO PUSH EAST...STILL
AFFECTING NORTHEAST CWA LATE EVENING. ANOTHER SHORTWAVE PUSHES
THROUGH WESTERN CWA AFTER 06Z. WILL HAVE TO KEEP POPS IN FOR ENTIRE
CWA...WITH LOWEST FAR NORTHWEST. LAYER RELATIVE HUMIDITY FIELDS
INDICATE PARTLY CLOUDY SKIES WEST...WITH MOSTLY CLOUDY EAST. CLOUDS
AND PRECIP WILL KEEP TEMPS UP A BIT...WITH LOWS GENERALLY IN THE
LOWER TO MID 60S.

FRIDAY...AS UPPER RIDGE CONTINUES TO BUILD NORTH NORTHEAST...WILL
SEE A GRADUAL DRYING TREND. BOUNDARY LAYER MOISTURE INDICATES
STRATUS IN THE MORNING...ENHANCED BY EASTERLY UPSLOPE FLOW. WILL
WORD BECOMING MOSTLY SUNNY IN WEST...PARTLY SUNNY EAST. COLD AIR
ADVECTION NOTED AT 850 MB WITH COOL EASTERLY FLOW. FEEL FAN NUMBERS
MORE IN LINE WITH CLOUDS AND WINDS...AND WILL KEEP HIGHS IN THE LOWER
TO MID 80S EAST...TO AROUND 90 FAR WEST.

EXTENDED...WITH MODERATE SHORTWAVE TRANSITIONING UPPER RIDGE INTO
CENTRAL PLAINS FRIDAY NIGHT INTO SATURDAY...WILL CONTINUE SLIGHT
CHANCE OF THUNDERSTORMS FOR THESE PERIODS. BEYOND THAT...RIDGE
CONTINUES TO BUILD EASTWARD TO GREAT LAKES REGION...SHUNTING MOST OF
THE MID LEVEL FORCING WELL EAST OF AREA. WILL KEEP SUNDAY AND MONDAY
DRY. MORNING LOWS TO BE IN THE MID 50S TOC MID 60S...HIGHS IN THE MID
80S TO MID 90S.

.LBF...NONE

M. MUTCHLER