000
FXUS63 KOAX 100850
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
345 AM CDT FRI OCT 10 2008
.DISCUSSION...
...MAIN FORECAST CONCERNS ARE POPS SAT THRU TUE...AND GUSTY WINDS
THRU SUN...
THE FORECAST WILL BE DOMINATED BY THE INFLUENCE OF THE LARGE
LONGWAVE TROF CURRENTLY OVER THE WESTERN US...AND ASSOCIATED SURFACE
FEATURES. WATERVAPOR LOOP SHOWED THE CIRCULATION HAS CUT OFF NEAR
BOISE...HOWEVER THIS IS ONLY THE LEADING SHORTWAVE AS MUCH OF THE
VORTICITY REMAINS BEHIND THAT SHORTWAVE. 300 MB ANALYSIS INDICATED
FASTEST JET WINDS AT 00Z WERE STILL ON THE BACK SIDE...WITH 125
KNOTS ON THE BRITISH COLUMBIA COAST AND 100 KNOTS OVER SALT LAKE.
BROAD AREA OF SIGNIFICANT HEIGHT FALLS NEAR AND AHEAD OF THE TROF
AXIS EVIDENT OF THE DEEPENING OF THE WAVE...WITH 180 METER FALLS AT
300 MB AT SALT LAKE.
SURFACE CYCLOGENESIS WAS OCCURRING OVER THE WESTERN HIGH PLAINS OF
COLORADO IN RESPONSE TO THE APPROACHING UPPER TROF AND FLOW
REGIME... WITH RELATIVELY GOOD MODEL AGREEMENT ON THE EVOLUTION OF
THE PATTERN. MODELS TAKE A WARM FRONT CURRENTLY ANALYZED NEAR THE
KANSAS-NEBRASKA BORDER AND MOVE IT NORTH...WITH FORECAST AREA DEEP
IN THE WARM SECTOR THROUGH MUCH OF THE WEEKEND. GIVEN THE MAGNITUDE
OF THE BAROCLINIC ZONE...THE FAST FLOW ALOFT...AND THE RESULTING
PRESSURE GRADIENT FROM THE DEEPENING SURFACE LOW...STRONG SOUTH
WINDS ARE EXPECTED TODAY THROUGH SUNDAY...INCLUDING A STRONG
NOCTURNAL LOW LEVEL JET.
THIS WARM SECTOR AIRMASS WILL BE WARM AND WINDY...THEREFORE HAVE
SLIGHTLY INCREASED THE TEMPERATURES AND THE WIND SPEEDS THROUGH
SUNDAY. THE GOING POPS SEEMED CONSISTENT WITH THE LATEST ANALYSIS
AND MODEL RUNS...THEREFORE DID NOT MAKE BIG CHANGES TO THE
POP FORECAST OTHER THAN TO START THE POPS A BIT LATER ON SATURDAY
AND ENDED A BIT EARLIER IN THE NORTHWEST ON SUNDAY.
THE TWO PRIMARY RAIN MAKERS WITH THIS SYSTEM WILL BE THE ISENTROPIC
LIFT IN THE WARM SECTOR SATURDAY EVENING THROUGH SUNDAY...THEN WITH
THE COLD FRONTAL FORCING SUNDAY NIGHT INTO EARLY MONDAY. NAM AND
GFS PROG A PEAK IN THE FORCING AT 06Z MONDAY...WHEN FRONTOGENESIS IS
VERY STRONG FROM THE SURFACE UP TO 700 MB AND UNDERNEATH STRONGLY
CONVERGING Q VECTORS FROM 700 MB UP TO THE TROP. AT THE SAME TIME
THE LOW LEVEL JET WILL FEEDING INTO THAT REGION...WITH MOISTURE
ADVECTION FROM THE SUB-TROPICS. PRECIPITABLE WATER VALUES ARE
PROGGED AS HIGH AS 1.90 INCHES OVER OMAHA. THEREFORE HAVE PLACED
THE HIGHEST POPS...80 PERCENT...SUNDAY NIGHT WITH THE HIGHEST QPF
VALUES.
TEMPERATURES MONDAY SHOULD BE SIGNIFICANTLY COLDER...HOWEVER THERE
IS WIDE SPREAD IN THE ENSEMBLE SOLUTIONS MAKING CONFIDENCE LOW IN
JUST HOW COOL TO GO. GOING HIGHS WERE NOT FAR FROM ENSEMBLE MEANS
AND HAVE TWEAKED DOWNWARD JUST A DEGREE OR TWO BASED ON TRENDS IN
THE 850 MB TEMPERATURE PROG.
&&
.AVIATION...
FOR TAF SITES KOMA/KLNK/KOFK FORECAST VALID THRU 11/06Z.
SLY WINDS GUSTING AROUND 30KT EXPECTED ALL SITES THIS AFTN AS SFC
PRES GRADIENT TIGHTENS IN RESPONSE TO DEEPENING LOW PRES IN NE CO.
SFC WINDS WILL THEN SUBSIDE AOB 12KT AROUND 00Z. OTHERWISE...OTLK IS
VFR THRU THE PD.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
NIETFELD/DEE
