Severe Thunderstorm Warning 138, NWS North Platte, NE

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
238 PM CDT WED JUL 4 2001

...MCS POTENTIAL TONIGHT IS THE CHALLENGE...

STAGNANT UPPER PATTERN WITH RIDGING OVER WESTERN NOAM AND TROFING
EAST. AT THE SURFACE...A STATIONARY BOUNDARY EXTENDS ACROSS KANSAS
WITH LEE TROFING FROM EASTERN MT TO EASTERN CO.

WAVE CURRENTLY CRESTING THE RIDGE AXIS THROUGH NRN WY/SRN MT EXPECTED
TO MOVE SOUTHEAST INTO ERN WY/WRN SD/NE PANHANDLE BETWEEN 00Z AND
06Z. HARD TO SEE THE WAVE IN WV PICS BUT THERE IS SOME EVIDENCE IN
VIS/IR PICS WITH JET LEVEL CIRRUS. THIS FEATURE IS EXPECTED TO HELP
INITIATE CONVECTION IN SAME VICINITY WHERE BEST POOLING OF CAPE AND
MOISTURE WILL AND IS OCCURRING. IN FACT IF CURRENT CAPE VALUES OF
4000 TO 5500 J/KG FROM NERN CO/EXTREME SWRN NE/SOUTHERN PANHANDLE
PERSIST...MODEL SFC BASED CAPE FORECASTS WILL BE WELL UNDERDONE AND
OBVIOUSLY MORE ENERGY WILL BE AVAILABLE THAN FORECAST. CORFIDI VEC
PROPAGATION INDICATES ANY CONVECTION WILL TRAVEL DIRECTLY ALONG THE
AXIS OF BEST MOISTURE/CAPE THROUGH THE SOUTHERN PANHANDLE AND
SOUTHWEST. 0-6 KM SHEAR WILL BE LESS THAN 10 KNOTS SO GREATEST
THREAT WILL LIKELY BE HAIL. ALSO EXPECTING A 25 TO 30 KNOT LLJ TO
DEVELOP BY 06Z WHICH SHOULD SUSTAIN MCS SOUTHWARD. BOTH ETA/AVN
AGREE ON MCS SCENARIO SO POPS WILL BE INCREASED FOR WESTERN ZONES.

LARGE SCALE SUBSIDENCE EXPECTED THURSDAY IN WAKE OF MCS PER LAYER Q-
VECS. MODEL MID LEVEL LAPSE RATES ARE ALSO STABLE OVER MUCH OF THE
CWA THURSDAY MORNING WHICH INDICATE ENVIRONMENT MAY BE WORKED OVER
...LAPSE RATES DO NOT RECOVER UNTIL LATE AFTERNOON IN THE WEST. ALSO
AN ABSENCE OF WAVES AND SURFACE BOUNDARY IN THE CWA...REMNANT
BOUNDARIES FROM MCS SHOULD BE IN KANSAS. THUS WILL KEEP FORECAST FOR
THURSDAY DRY. MODELS ARE NOT QUITE AS AGGRESSIVE WITH COOLING
THURSDAY RELATED TO SURFACE HIGH CENTER MOVING INTO THE GREAT LAKES.
HOWEVER...RAIN COOLED ENVIRONMENT IN WAKE OF MCS WILL LIKELY INHIBIT
WARMING. LARGE DISCREPANCY IN GUIDANCE WITH THE IN BETWEEN FAN
PREFERRED.

RIDGE AXIS EXPECTED TO SHIFT INTO THE PLAINS THURSDAY NIGHT WITH
THE HIGH CENTERED IN EASTERN COLORADO. THIS WOULD LIKELY BEGIN TO
DEFLECT SHORTWAVES WELL NORTH OF THE CWA WHICH IS THE CASE IN BOTH
THE ETA/AVN. AT THE LOWER LEVELS...BOTH INDICATE THAT A SURFACE
TROF/FRONT WILL MOVE THROUGH THE CWA FORCED ALONG BY A SIGNIFICANT
WAVE MOVING FROM ND INTO MN. NO REAL EFFECTS EXPECTED OTHER THAN A
WIND SHIFT.

SURFACE FRONT AND AMOUNT OF CAA SEEM A BIT STRONG IN THE ETA ON
FRIDAY WHEN COMPARED TO THE AVN CONSIDERING THE STRENGTH OF THE UPPER
RIDGE OVER THE AREA. AVN SURFACE SOLUTION LOOKS BETTER IN WASHING
OUT BOUNDARY VERSUS THE ETA WHICH MAINTAINS EAST/NORTHEAST WINDS AND
HANGS FRONT ALONG THE KS/NE BORDER. WITH UPPER HIGH CENTER NEAR THE
AREA SHEAR WILL REMAIN VERY WEAK AND SHORTWAVES WILL CONTINUE TO BE
WELL NORTH OF THE CWA. DRY FORECAST WILL CONTINUE. LOW LEVEL TEMP
PROFILES SUPPORT AN INCREASE OF 3 TO 6 DEGREES IN MAX TEMPS.

MORE OF THE SAME FRIDAY NIGHT AS OVERALL ENVIRONMENT WILL BE
RELATIVELY UNCHANGED. AVN DOES RESOLVE A PAIR OF WAVES THROUGH SOUTH
DAKOTA AND NEBRASKA...THE SOUTH DAKOTA WAVE BEING THE DOMINANT
FEATURE. SHEAR/INSTABILITY/DYNAMICS WOULD DEFINITELY SUPPORT THE
NORTHERN WAVE AND THIS IS REFLECTED IN AVN QPF WHICH INITIALLY
DEVELOPS AN AREA OF LIGHT QPF WITH NEBRASKA WAVE THAT FADES AWAY AND
NORTHERN FEATURE QPF INCREASES SIGNIFICANTLY.

IN THE EXTENDED...MEDIUM RANGE GUIDANCE INDICATES VERY LITTLE CHANGE
TO THE OVERALL PATTERN INTO THE MIDDLE OF NEXT WEEK. WAVES WILL
CONTINUE TO MOVE THROUGH THE DAKOTAS THIS WEEKEND WITH SOME CHANCE
THAT SOUTHERN END OF COMPLEXES MAY REACH NORTHERN COUNTIES. COMPLEX
THAT MRF/AVN DEVELOP MONDAY VERY QUESTIONABLE GIVEN PROXIMITY TO
CENTER OF UPPER RIDGE...HARD TO ENVISION ENOUGH SHEAR IN THIS
REGION TO SUPPORT MCS. THUS THIS HAS BEEN DISCOUNTED AND DRY
FORECAST CONTINUED. RIDGE EXPECTED TO AMPLIFY TUE/WED. MRF SURFACE
SOLUTION SEEMS SUSPECT WITH STRONG HIGH CENTER OVER COLORADO BUT
GENERAL PATTERN SUGGEST UPPER FLOW MAY INDUCE FROPA AND CAA OVER
THE PLAINS RESULTING IN MORE STABLE AND DRY CONDITIONS.

.LBF...NONE.

DJB