Severe Thunderstorm Warning 108, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
209 AM CDT SUN JUL 1 2001

...MAIN CHALLENGE TO BE THUNDERSTORM POTENTIAL AND TEMPS...

TRICKY PATTERN CONTINUES TO PLAGUE AREA WITH NORTHWEST FLOW ALOFT.
UPPER LEVEL RIDGE VERY STABLE OVER FOUR CORNERS REGION...WITH
TROUGH NORTH OF LAKE SUPERIOR TO ROTATE EASTWARD JUST NORTH OF GREAT
LAKES TODAY. TIMING OF VORT MAXES PROBLEMATIC FOR MODELS...HENCE
TIMING OF POSSIBLE PRECIPITATION. BOTH AVN AND ETA INDICATED THERE
SHOULD HAVE BEEN AN MCS OVER OUR CWA BY 03Z SUNDAY...PERSISTING
THROUGH 06Z...AND NO SUCH ANIMAL DEVELOPED.  ONE OR TWO STORMS HAVE
DEVELOPED IN VICINITY...SO PERHAPS MODELS ARE SIMPLY TOO FAST.  COLD
FRONT CURRENTLY BISECTS CWA FROM WEST TO EAST. GOOD CONVERGENCE ALONG
FRONT WOULD SUGGEST CONVECTION A GOOD BET AS FAIR AMOUNT OF H7 OMEGA
PRESENT...ALONG WITH STEEP LAPSE RATES OVER SOUTHERN CWA...BUT SO FAR
CONVECTION ONLY SPOTTY AT BEST. H5 VORT MAXES VERY WEAK...YET PRESENT
OVER MUCH OF CWA. BAD PHX SOUNDING IN ETA AND NGM FORCES ME TO LEAN
TOWARD AVN FOR FORECAST.

MODELS TOO QUICK BRINGING IN LOW CLOUDS FROM SOUTH DAKOTA TO
COVER CWA. EXPECT THE LOW CLOUDS WILL GET HERE BEFORE DAWN.
MODELS PUTTING OUT TEMPS 5 DEGREES LOWER THAN PREVIOUS 00Z
FORECAST DUE TO CLOUD COVER. THIS TIME OF YEAR...IF CLOUDS BURN
OFF...THERE IS USUALLY NO PROBLEM GETTING TEMPS TO REBOUND...AND
THINK TEMPS FORECAST BY WARMER FWC MAY BE SLIGHTLY UNDERDONE FOR
SUNDAY IN AREAS THAT WILL BURN OFF CLOUDS BY NOON. CURRENT TEMPS
ALL SLIGHTLY TOO COOL THAN 06Z ANALYSIS.  AVN SLOWER TO BURN CLOUDS
OFF...AND IN FACT ALLOWS THEM TO PERSIST OVER VTN TO BURWELL LINE
THROUGH 00Z. THINK MOST CLOUDS SHOULD BURN OFF AS APPEARS THERE
WILL BE ADEQUATE MECHANICAL MIXING. ANY CONVECTION FORECAST IS MAINLY
INSTABILITY-DRIVEN...AND THEREFORE DIFFICULT TO TIME AND PLACE
CORRECTLY. H7 WAA AND OMEGA APPEARS TO BE SOMEWHAT BETTER INDICATOR
OF WHERE CONVECTION SHOULD BE.

SUNDAY NIGHT INTO MONDAY...AVN APPEARS TO BE OVER-DEVELOPING UPPER
LEVEL LOW CROSSING NORTHERN CO. 06Z MONDAY THERE ARE A FEW COMMON
FEATURES BETWEEN MODELS...MAINLY CONCERNING WEAK UPSLOPE ALONG FRONT
RANGE OF CO ROCKIES TRIGGERING CONVECTION...AND VORT MAX DEVELOPING
MCS OVER BLACK HILLS JUST NORTH OF FRONT. A BIT UNUSUAL IN THAT
MODELS SHIFT PCPN TO SECONDARY LOCATION EAST OF BLACK HILLS OVER
SD...RATHER THAN FOLLOWING UPPER LEVEL STEERING FLOW AND BRINGING IT
SOUTHEAST INTO OUR CWA EARLY MONDAY...AS FRONT SAGS TO POSITION FROM
SOUTHERN PANHANDLE TO SOUTH CENTRAL SD. BEST INSTABILITY ALONG
FRONT...AND SUSPECT THERE WILL BE SOMETHING DEVELOPING THERE BY
MONDAY LATE AFTERNOON DESPITE DRY MODELS.  WILL LEAVE LOW POPS IN FOR
MONDAY ALONG FRONT. MODELS ALSO PUTTING QUITE WARM TEMPS IN WESTERN
CWA...ESPY SOUTHWEST CWA WHERE THEY ARE KEEPING IT DRY MONDAY. WITH
POSSIBILITY OF CONVECTION BEING PRESENT AND CUTTING OFF SOME
INSOLATION...THINK IT BEST TO SPLIT THE DIFFERENCE BETWEEN 850
TEMPS AND GUIDANCE FOR HIGHS.

MONDAY NIGHT...THINK ALL BUT NORTHWEST ZONES (NORTH OF FRONT) HAVE
SOME CHANCE OF PRECIP. WILL INCLUDE A FEW MORE CLOUDS THAN ETA
INDICATES.

NO CHANGES TO EXTENDED0 AT THIS TIME.

.LBF...NONE.

S. MUTCHLER