Hail and Damaging Winds in Nebraska, July 29, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
243 PM CDT SUN JUL 29 2001

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

UPPER PATTERN CONTINUES TO FEATURE A LARGE UPPER RIDGE SPANNING THE
CENTRAL AND SOUTHERN PORTIONS OF THE PLAINS AND ROCKIES. FARTHER
NORTH A FAST WESTERLY FLOW EXISTS OVER THE NORTHERN ROCKIES AND
PLAINS EMBEDDED BETWEEN THE AFOREMENTIONED UPPER RIDGE AND BROAD
TROFING OVER NORTHWESTERN CANADA. AT THE SURFACE...LOW PRESSURE IS
CENTERED IN EASTERN SOUTH DAKOTA WITH A COLD FRONT TRAILING BACK
INTO THE NEBRASKA PANHANDLE AND NORTHEASTERN COLORADO. MUCH DRIER
AIR WEST OF THIS FEATURE WITH DEWPOINTS IN THE 50S VERSUS 70S EAST
OF THE FRONT.

BOTH ETA/AVN 12Z RUNS DEVELOPED AN AREA OF CONVECTION IN THE
PANHANDLE AROUND 00Z WHICH MODELS EXPECT TO ENTER WESTERN PORTIONS
OF THE CWA. CONVECTION EXPECTED TO INITIATE IMMEDIATELY DOWNSTREAM
OF A SUB-SYNOPTIC FEATURE TO EJECT FROM WYOMING TONIGHT. ALREADY
EVIDENCE OF BUILDUPS ALONG THE FRONT RANGE INTO THE SOUTHWESTERN
PANHANDLE. AN ABUNDANCE OF INSTABILITY AND MOISTURE EXIST EAST OF AN
IML/OGA/VTN LINE WHERE CAPES OF 5000 TO 7000 J/KG AND DEWPOINTS IN
THE 70S. AFOREMENTIONED SURFACE BOUNDARY IS VISIBLE ON KLNX 88D FROM
NEAR VTN INTO THE SOUTHERN PANHANDLE. LATEST LAPS ANALYSIS SHOWS BEST
MOISTURE/THETA E CONVERGENCE ALONG THIS FEATURE. IF CONVECTION DOES
INITIATE THERE IS PLENTY OF SUPPORT FOR THE CONVECTION TO PERSIST.
SOME CONCERN OVER THE POTENTIAL FOR CONVECTION TO PERSIST LONGER THAN
THE MODELS FORECAST. MID LEVEL LAPSE RATES ARE FORECAST TO BE GREATER
THAN 8.5 C/KM ALONG WITH A LLJ OF 40 TO 45 KNOTS. IF CONVECTION IN
PANHANDLE BECOMES STRONG BEFORE ZONE ISSUANCE POPS WILL BE CARRIED
FARTHER EAST THAN IN CURRENT OZFLBF. GUIDANCE MINS APPEAR ON THE
MONEY GIVEN HIGH DEWPOINTS IN MIXING THROUGH THE NIGHT.

UPPER RIDGE EXPECTED TO AMPLIFY MONDAY WITH SURFACE BOUNDARY LOSING
DEFINITION AND LIFTING NORTH OF THE CWA. TEMP PROFILES INDICATE A
FEW DEGREES OF WAA...WHICH SHOULD RESULT IN TEMPS IN THE 90S ALL
LOCALES WITH SOUTHWESTERN ZONES AROUND 100. FULL SUNSHINE AND
BREEZY CONDITIONS AS PRESSURE GRADIENTS REMAIN MODERATELY STRONG.
AMPLIFICATION OF RIDGE SHOULD DIVERT ANY WAVES NORTH OF THE CWA.
MODELS DO NOT RESOLVE ANY SIGNIFICANT FEATURES NEAR THE AREA.
SURFACE BASED AND MID LEVEL INSTABILITY TO REMAIN HIGH. CINS WILL
BE HIGH AS WELL SO ZERO POPS WILL REMAIN IN THE FORECAST.

MODELS HAVE RESOLVED SLIGHTLY DIFFERENT SOLUTIONS MONDAY NIGHT
RELATED TO THE STRENGTH OF A WAVE EXPECTED TO TRAVERSE THE PANHANDLE.
THE AVN IS SLIGHTLY MORE BULLISH AND AS A RESULT HAS GREATER COVERAGE
OF QPF IN ADDITION TO BEING FARTHER EAST. STRENGTH OF UPPER RIDGE
WOULD TEND TO SUPPORT WEAKER ETA SOLUTION AND A COMPROMISE OF THE
TWO SEEMS PRUDENT FOR SEVERAL REASONS. H7-H5 LAPSE RATES TO EXCEED 8
C/KM OVER THE ENTIRE AREA...40 TO 50 KNOT LLJ FORECAST...LOW LEVEL
BOUNDARY WILL LIE JUST NORTH AND WEST OF THE AREA. SHOULD BE THE
WARMEST NIGHT OF THE WEEK WITH DEWPOINTS AROUND 70...SUSTAINED
MIXING AND SOME CLOUDS IN THE WEST.

MINOR MODEL DIFFERENCES MONDAY NIGHT ALSO CARRY INTO TUESDAY BUT THE
OVERALL SOLUTIONS REMAIN CLOSE. PREFER THE ETA SOLUTION...WHICH
CARRIES SURFACE BOUNDARY INTO THE CWA AND ESSENTIALLY BISECTS THE
AREA BY 00Z WED. ETA MID LEVEL LAPSE RATES AND SURFACE BASED
INSTABILITY SEEM LOW. ETA IS LIKELY WARMING MID LEVEL TEMPS DESPITE
LOWERING HEIGHTS. LOWER SFC BASED INSTABILITY APPEARS QUESTIONABLE
IN THE ABSENCE OF A SCOURING WESTERLY WIND COMPONENT. IN SPITE OF
THIS...THE ETA IS STILL DEVELOPING A HEALTHY LINE OF CONVECTION
THROUGH THE AREA BY 00Z WED ALONG THE SURFACE BOUNDARY IN
ASSOCIATION WITH WAVE TRAVERSING THE AREA. TEMPS WILL BE THE
GREATEST CHALLENGE OWING TO THE UNCERTAINTY OVER THE AMOUNT OF SKY
COVER. OPTED TO GO WELL ABOVE GUIDANCE EAST ASSUMING ENVIRONMENT
EAST OF SURFACE BOUNDARY WILL BE RELATIVELY UNCHANGED AND SUNSHINE
WILL BE ABUNDANT. NEAR GUIDANCE FAR WEST DUE TO CLOUDS AND PRECIP.

UPPER FEATURE AND SURFACE BOUNDARY TO SHIFT SLOWLY EAST TUESDAY
NIGHT. WILL CARRY BEST POPS IN SAME DIRECTION. SHOWERS AND WEAK
CAA SUPPORT COOLER GUIDANCE MINS.

IN THE EXTENDED...AVN/MRF SUGGEST EASTWARD PROGRESS OF SURFACE
BOUNDARY WILL SLOW SIGNIFICANTLY AS ADDITIONAL WAVES EJECT FROM
MONSOONAL FLOW. WILL CONTINUE CHANCE OF POPS OVER EASTERN PORTION
OF CWA WED...THEN SOUTHERN CWA THURSDAY. SURFACE FEATURE TO FADE BY
FRIDAY PER MRF WITH UPPER RIDGE EXPECTED TO RE-AMPLIFY AND MAINTAIN
POSITION THROUGH THE WEEKEND.

.LBF...NONE.

DJB