Severe Thunderstorm Warning 119, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
210 PM CDT SUN JUL 7 2002

...18Z SYNOPSIS...
     THE MSL ANALYSIS SHOWED A BOUNDARY THROUGH SOUTH DAKOTA AND
NORTHWEST NEBRASKA ALONG ABOUT AN ABR-PIR-BFF-CYS LINE. THE 6.7U
IMAGERY AND 400MB WIND PROFILERS INDICATED A TROUGH OVER EASTERN
WYOMING AND NORTHEAST COLORADO AND INTO SOUTHERN NEW MEXICO. THERE
WAS STILL A MOISTURE PLUME INDICATED ACROSS TEXAS AND COLORADO. THE
GOES DERIVED PRECIPITABLE WATER SHOWED 30-35MM THROUGH CENTRAL AND
NORTHWEST NEBRASKA.
...MODELS...
     THE PREFERRED SOLUTION IS A BLEND OF THE CURRENT FORECAST, THE
ETA AND THE GLOBAL FROM THIS MORNINGS RUN FOR DAYS1-4 AND A BLEND OF
THIS MORNINGS GLOBAL AND THE 07/00Z GLOBAL FOR DAYS4-7.
     THIS MORNINGS GLOBAL AND ETA ARE SIMILAR TO 60 HOURS AND ARE
BOTH SHOWING GOOD CONTINUITY WITH PREVIOUS RUNS.
     THE 07/00Z GLOBAL ALSO SHOWS GOOD CONTINUITY WITH THE 06/00Z RUN
IN REBUILDING THE UPPER HIGH IN THE WEST, DESPITE THE 6010M HEIGHT
CENTER ON DAY3 WHICH SEEMS TOO HIGH. THE 07/00Z RUN IS ALSO ABOUT
7C COOLER WITH THE 850MB TEMPERATURES THAN THE 06/00Z RUN.
YESTERDAYS ECMWF SUPPORTS THE GLOBAL SOLUTION AS WELL.

...FORECAST THROUGH DAY3...
     WEAK LOW LEVEL CONVERGENCE AND LOW LEVEL WARM ADVECTION IN
NORTH CENTRAL AND NORTHWEST NEBRASKA ALONG THE SURFACE BOUNDARY THIS
EVENING SHOULD INITIATE SOME UPWARD MOTION. THERE IS ALSO 800MB BASED
ELEVATED INSTABILITY WITH LIS OF -2C TO -4C. SO, SOME CONVECTION IS
LIKELY.  HOWEVER, THE 800MB AND 850MB CONDENSATION PRESSURE DEFICITS
WILL BE 100-125MB SO RAIN AMOUNTS WILL PROBABLY NOT BE REAL HIGH. I
THINK ITS ENOUGH TO WARRANT 30 PERCENT PROBABILITIES NORTH AND WEST
OF VTN-OGA-IML.
     CONVERGENCE, ELEVATED 2D-FRONTOGENESIS WILL PRODUCE STRONG LIFT
AGAIN TUESDAY AFTERNOON THROUGH WEDNESDAY WITH 800MB LIS OF -2C TO
-4C OVER THE NORTHERN AND WESTERN PARTS THE FORECAST AREA. THE REST
OF THE FORECAST AREA SHOULD GET THE SAME WEDNESDAY NIGHT AND THURSDAY
AS THE NEXT FRONT MAKES ITS WAY THROUGH THE FORECAST AREA.
     THE ETA AND GLOBAL MODELS ARE BOTH SHOWING A WARMING TREND AT
850MB WITH INCREASES OF 1-2C EACH DAY FOR DAYS 1 AND 2. THEN THERE IS
A 1C DROP FROM DAY2 TO DAY3. ALSO, AS THE UPPER TROUGH MOVES OUT OF
THE FORECAST AREA AND THE UPPER HIGH DEVELOPS, LITTLE OR NO
PRECIPITATION IS EXPECTED. FOR HIGHS, THE ETA GRIDS SEEM REASONABLE,
BUT MAY BE A COUPLE OF DEGREES TOO HIGH FOR DAYS 1 AND 2, WHILE, THE
GLOBAL GRIDS ARE PROBABLY ABOUT 5F TOO LOW. ACTUALLY, THIS IS BORNE
OUT BY THE VERIFICATION STATISTICS FOR THE PAST TEN DAYS.
     A LOOK AT THE BOUNDARY LAYER LAPSE RATES AND THE HOMOGENEOUS
WIND TO 800MB HAS ME BELIEVING THAT WIND WILL NOT DECOUPLE
COMPLETELY IN THE CENTRAL PART OF THE FORECAST AREA. THE PANHANDLE
AND NORTH CENTRAL ZONES SHOW A FAIRLY STRONG RADIATION INVERSION
DEVELOPING AFTER MIDNIGHT AND LIGHT WIND IN THE PANHANDLE. LOOKING
AT THE EARLY AFTERNOON DEWPOINTS WHICH RANGE FROM 60 TO NEAR 70, I
WOULD EXPECT OVERNIGHT LOWS TO DROP TO 55 TO 60 IN THE PANHANDLE,
60 TO 65 IN THE SOUTHWEST, AND 65 TO 70 IN THE NORTHEAST PART OF
THE FORECAST AREA. THE GRIDS FOR THE LOW TEMPERATURES SEEM TO BE A
LITTLE HIGH FOR DAYS1-5.

...FORECAST DAYS4-7
     A FRONT/TROUGH MOVING THROUGH MID-WEEK SHOULD BRING SOME RELIEF
FROM THE HEAT AND HUMIDITY. IT SHOULD ALSO RESULT IN DRIER WEATHER
OVER THE NORTH PLATTE FORECAST AREA. AS THE UPPER HIGH BUILDS IN THE
SOUTHWEST STATES, A RETURN TO HOT DRY WEATHER IS LIKELY BY THE NEXT
WEEKEND. SO, FOR DAYS 4-7, I WILL POPULATE THE GRIDS WITH THE
GLOBAL OUTPUT AND MAKE A FEW ADJUSTMENTS. CONSIDERING THE LACK OF
CLOUDINESS, LOW BOUNDARY LAYER RH, AND THE SEASON, THE THE HIGH
TEMPERATURE VALUES APPEAR TO BE TOO LOW BY 5-10F THURSDAY AND FRIDAY,
AND BY 3-5F SATURDAY AND SUNDAY. OVERNIGHT LOWS SEEM TOO HIGH BY 2-5F
THURSDAY AND FRIDAY AND ABOUT 5F SATURDAY AND SUNDAY. THE
PRECIPITATION GRIDS ARE ON TARGET.

.LBF...NONE.

SPRINGER