National Weather Service Forecast Discussion

000
FXUS65 KBOU 061130
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
420 AM MST MON JAN 6 2009

.SHORT TERM...CORE OF STRONG 140 KNOT PLUS JET WILL WORK INTO
COLORADO TODAY...AND THEN PASS EAST OF THE FRONT RANGE THIS
EVENING.  THIS WILL BRING INCREASING WINDS AND SOME SNOW TO THE
MOUNTAINS.

FIRST THE WINDS...PASSAGE OF UPPER JET CORE AND INCREASING PRESSURE
GRADIENT WILL BRING FAVORABLE CONDITIONS FOR STRONG WINDS LATER
TONIGHT/WEDNESDAY.  THIS WILL BRING INCREASING LARGE SCALE
SUBSIDENCE...COINCIDING WITH A LOWERING OF THE STABLE LAYER TO NEAR
MOUNTAIN TOP...AND AN INCREASE IN CROSS BARRIER FLOW TO AROUND 40
KNOTS.  MEANWHILE...SANGSTER WIND PROGRAM SHOWS DP/DN VALUES
INCREASING INTO THE 235-255 RANGE...A BIT WEAKER THAN RUNS 24 HOURS
AGO BUT STILL STRONG.  CONFIDENCE IS NOT QUITE HIGH ENOUGH TO FIRE
OFF A WARNING AT THIS TIME...SO WILL KEEP THE WATCH IN EFFECT
STARTING AT MIDNIGHT TONIGHT WITH THE PASSAGE OF UPPER JET CORE.

IN THE MEANTIME...EXPECT GENERALLY BREEZY CONDITIONS TODAY WITH
MODERATE FLOW ALOFT...GOOD MIXING...AND MAIN SURFACE TROUGH PUSHING
THROUGH THE CENTRAL PLAINS.  THEN WINDS EAST OF I-25 WILL RELAX THIS
EVENING WITH LOSS OF DAYTIME HEATING.  STRONGER WINDS LATER TONIGHT
WILL THEN BE CONFINED TO IN/NEAR THE FRONT RANGE IN TYPICAL CHINOOK
FASHION.

WITH REGARD TO SNOW...STABILITY HAS BEEN A REAL LIMITING FACTOR WITH
MOST LOCATIONS ONLY SEEING A TRACE TO PERHAPS AS MUCH AS 3 INCHES IN
ZONE 31 SO FAR.  A MID LEVEL CLOUD BAND IS MOVING SLOWLY EASTWARD
ACROSS THE MOUNTAINS EARLY THIS MORNING...WITH DRYING NOTED BEHIND
THIS SO THE LIGHT SNOW THIS MORNING SHOULD DIMINISH TO SCATTERED
SHOWERS/FLURRIES BEHIND THIS FEATURE.  NEXT INCREASE IN MID LEVEL
MOISTURE IS STILL SLATED TO MOVE IN TOWARD 00Z.  HOWEVER...STABILITY
IS VERY LIMITED AGAIN...WARM ADVECTION REGIME STARTS LATER
TONIGHT...AND WE HAVE LARGE SCALE SUBSIDENCE AFTER PASSAGE OF UPPER
LEVEL JET...SO NOT VERY EXCITED AT ALL ABOUT SNOW AMOUNTS.
OROGRAPHIC SNOW MODEL SHOWS 1-3 INCHES MOST AREAS WITH 2-6 POSSIBLE
IN ZONE 31.  WIND WILL PROBABLY BE THE BIGGEST THING SO DOWNGRADED
WINTER STORM WATCH TO WINTER WEATHER ADVISORY FOR SNOW/BLOWING SNOW.

.LONG TERM...STRONG NORTHWESTERLY FLOW IS GOING TO BE ONGOING OVER
THE STATE WEDNESDAY MORNING...CONTINUING THE POSSIBILITY OF MOUNTAIN
SNOWS AND GUSTY WINDS.  HOWEVER...ONGOING WARM ADVECTION IN THE
MOUNTAINS WILL CREATE STABILITY IN THE LOW AND MID LAYERS WHICH WILL
LIMIT THE OROGRAPHIC SNOWFALL AND VERTICAL SHEAR PROFILES MAY BE TOO
STRONG FOR STRONG WINDS TO EXTEND VERY FAR FROM THE HIGHER MOUNTAIN
TERRAIN.  CROSS SECTIONS ACROSS THE STATE DO NOT SHOW ANY
EXTRAORDINARY WIND SPEEDS BELOW 700 MB.  HOWEVER...THE 140 KNOT JET
ALOFT WILL BE COMING NEARLY STRAIGHT OUT OF THE NORTH.  IF THE JET
TIPS A LITTLE TO THE NNE...THEN A FLOW REVERSAL WILL BE IN PLACE AND
AN AMPLIFIED WAVE WOULD RESULT.  SINCE THE MODELS DO NOT OFTEN SHOW
THE WINDS GOING FAR ENOUGH TO THE NORTH...WILL HOLD ONTO THE HIGH
WIND WATCH IN THE MOUNTAINS AND FOOTHILLS AS THE THREAT IS CERTAINLY
STILL THERE.  THE NORTHWESTERLY FLOW PATTERN WILL ONLY SLOWLY CHANGE
THROUGH THURSDAY WHEN IT BECOMES MORE WESTERLY AS AN UPPER RIDGE
AXIS MOVES OVER.  SINCE THE RIDGE WILL BE RELATIVELY FLAT...GUSTY
WINDS ARE LIKELY TO CONTINUE.  DID NOT SEE TOO MANY THINGS IN THE
FORECAST PACKAGE THAT NEEDED CHANGING THIS TIME AROUND.  THE
PERSISTENT DOWNSLOPE FLOW AND APPROACH OF THE UPPER RIDGE WILL BRING
WARMING AND CONTINUED DRY CONDITIONS TO THE PLAINS.

&&

.AVIATION...VFR CONDITIONS WILL PREVAIL THROUGH TONIGHT.  DAYTIME
HEATING AND MIXING SHOULD ALLOW WEAKER WEST/SOUTHWEST SURFACE WINDS
TO SHIFT TO WEST/NORTHWEST AND INCREASE AROUND 17-18Z. THEN GUSTS IN
THE 20-25 KNOT RANGE POSSIBLE THROUGH THIS AFTERNOON.  WINDS WILL
DECREASE AGAIN BY 00Z-02Z AND TURN MORE SOUTHWESTERLY.  STRONGER
WINDS LATE TONIGHT SHOULD REMAIN CONFINED TO LOCATIONS CLOSER TO THE
FOOTHILLS AND KBJC.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...HIGH WIND WATCH MIDNIGHT TONIGHT
   THROUGH WEDNESDAY EVENING FOR THE FRONT RANGE MOUNTAINS/FOOTHILLS/
   ADJACENT PLAINS...ZONES 33..34>36..38..39.
 WINTER WEATHER ADVISORY TONIGHT AND WEDNESDAY PORTIONS NORTH CENTRAL
   MOUNTAINS...ZONE 31.

$$

BARJENBRUCH/KDRBY

NWS BOU Office Area Forecast Discussion