Severe Thunderstorm Warning 86, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
357 AM CDT FRI JUN 29 2001

...POPS AND TEMPS WILL BE A CHALLENGE 2ND PERIOD AND BEYOND...

BLOCKED UPPER PATTERN WITH RIDGING FROM THE SOUTHWESTERN STATES INTO
THE CENTRAL/NORTHERN PLAINS WHILE A CLOSED UPPER LOW REMAINS OVER
MISSOURI. AT THE SURFACE...A WEAK FRONT EXISTS FROM THE DAKOTAS
INTO EASTERN WYOMING.

CONVECTION IN THE ETA CONTINUES TO BE OVERDONE AND ALSO EXHIBITS
ERRATIC STORM MOTIONS. AVN APPEARS TO BE MORE CONSERVATIVE WITH
REALISTIC STORM MOTIONS AND IS PREFERRED FOR MUCH OF THE FORECAST.

CONVECTION IN BOYD AND HOLT COUNTIES CONTINUES TO PROPAGATE
SLOWLY SOUTH/SOUTHWEST PER CORFIDI VECS. SIMILAR TO THE
LAST FEW NIGHTS...CONVECTION SHOULD GRADUALLY FADE AROUND SUNRISE
WHEN LLJ RELAXES. OTHERWISE...MORE OF THE SAME TODAY WITH THE UPPER
RIDGE AXIS TO REMAIN OVER THE AREA. SURFACE FRONT IN SOUTH DAKOTA
WILL LOSE DEFINITION AND BECOME AN INVERTED TROF OVER THE CWA TODAY
AS LEE TROFING/LOW PRESSURE DEEPEN IN COLORADO/WYOMING. MODELS HAVE
RESOLVED NO CHANGE IN LOW LEVEL TEMP PROFILES...YET GUIDANCE FOR
ABOUT THE 4TH CONSECUTIVE DAY IS ONLY FORECASTING HIGHS IN THE 80S.
WILL GO ABOVE GUIDANCE AGAIN TODAY.

ETA AND AVN DIFFER GREATLY THIS EVENING. ETA DEVELOPS CONVECTION
ALONG INVERTED TROF WHILE AVN IS DRY. SINCE ENVIRONMENT WILL
REMAIN RELATIVELY UNCHANGED AND THERE WILL BE AN ABSENCE OF WAVES
...DO NOT THINK INVERTED TROF WILL BE ENOUGH TO INITIATE CONVECTIVE
DEVELOPMENT. ETA AND AVN HAVE BOTH REMAINED CONSISTENT WITH THEIR
RESPECTIVE SOLUTIONS CONCERNING RIDGE RUNNER TO ENTER WESTERN SOUTH
DAKOTA AROUND 06Z. AVN TRACKS CONVECTION EAST ACROSS SOUTH DAKOTA
AND NORTHERN PORTION OF CWA. ETA PROPAGATES CONVECTION MORE TO THE
SOUTHEAST WITH HEAVIEST PRECIP INTO LBF CWA. THIS MOTION IS NOT
SUPPORTED BY STEERING WINDS OR CORFIDI VECS UNTIL CONVECTION PASSES
EAST OF THE AXIS SO THE AVN SOLUTION SEEMS MORE REALISTIC AND POPS
WILL REMAIN CONSERVATIVE.

CONVECTIVE CLOUD DEBRIS AND FAIR AMOUNT OF LL CAA IN MODELS OVER
NORTHEAST PORTION OF CWA SATURDAY. LINGERING CONVECTION IN THE
MORNING APPEARS LIKELY OVER THE NORTHEAST. EXACT POSITION OF SURFACE
FRONT WILL BE DIFFICULT TO DETERMINE AND WILL BE LARGELY INFLUENCED
BY CONVECTION FROM FRIDAY NIGHT. REGARDLESS OF THE CONVECTIVE
SCENARIO FRIDAY NIGHT...IT APPEARS LIKELY THE SURFACE FRONT WILL
REMAIN SOUTH OF NORTHERN ZONES MUCH OF SATURDAY THUS TEMPS WILL BE
TRIMMED. FAR SOUTHWEST MAY VERY WELL REMAIN SOUTH OF THE FRONT
WHICH IS ALSO SUPPORTED BY MODEL LL TEMP PROFILES.

FRONT IS FORECAST TO RELAX SOUTHWARD AGAIN SATURDAY NIGHT AS
CANADIAN HIGH SETTLES INTO THE NORTHERN PLAINS. IN THIS SCENARIO...
THE ETA CONVECTION ACTUALLY LOOKS MORE REALISTIC FOR THE FOLLOWING
REASONS. FRONTOGENESIS INCREASES AND A LLJ IS ONCE AGAIN EXPECTED.
PLENTY OF INSTABILITY AND MOISTURE WILL BE AVAILABLE SO CONVERGENCE
ALONG THIS FEATURE MAY BE ENOUGH TO SUSTAIN ANY CONVECTION. POPS
WILL ONCE AGAIN FAVOR EASTERN AREAS OF CWA. UPPER RIDGE WILL
CONTINUE TO DEFLECT WAVES/CONVECTION EAST OF SOUTHWEST COUNTIES.

IN THE EXTENDED...MEDIUM RANGE GUIDANCE FAIRLY CONSISTENT IN
GRADUALLY MOVING FRONT INTO KANSAS WHERE IT IS EXPECTED TO STALL.
NORTHWEST UPPER FLOW WILL EVOLVE AS CANADIAN TROF DEEPENS AND
WESTERN RIDGE AMPLIFIES. MRF CONTINUES TO RESOLVE A FAIR AMOUNT OF
LAYER Q-VEC CONVERGENCE/FRONTOGENESIS/DIVERGENCE IN VICINITY MON
THRU WED SO CHANCE MENTION WILL REMAIN IN FORECAST. DRY BY THURSDAY
AS SURFACE HIGH IS FINALLY EXPECTED TO SETTLE SOUTHWARD.

.LBF...NONE.

DJB