FXUS65 KCYS 070451
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
951 PM MST SUN DEC 6 2009
.UPDATE...
IN AN EARLIER UPDATE INCREASED SNOW CHANCES JUST A BIT FOR THIS
EVENING AND THROUGH THE OVERNIGHT. LITTLE OR NO ADDITIONAL
ACCUMULATION IS EXPECTED OVERNIGHT. TEMPERATURES HAVE BEEN SLOWLY
FALLING THROUGH THE EVENING AND AM STILL ANTICIPATING DOUBLE
DIGITS BELOW ZERO IN LARAMIE...WITH NEGATIVE SINGLE DIGITS
ELSEWHERE. A BAND OF UPSTREAM MID/HIGH CLOUD MAY HELP HOLD
TEMPERATURES UP A BIT OVERNIGHT...THOUGH MOSTLY LIKELY NOT
SIGNIFICANTLY. OFF AND ON FLURRIES/LIGHT SNOW WILL CONTINUE INTO
MONDAY...THOUGH AGAIN ACCUMULATIONS WILL NOT BE MUCH AT ALL. HAHN
&&
.PREV DISCUSSION... /ISSUED 243 PM MST SUN DEC 6 2009/
SHORT TERM...TONIGHT THROUGH TUESDAY...
SNOWFALL ACROSS THE CWA WINDING DOWN EARLY THIS AFTERNOON AS UPPER
TROF NOW MOVING EAST OUT OF THE REGION. WILL CANCEL WINTER WX ADVY
AS LITTLE ADDITIONAL SNOWFALL EXPECTED TONIGHT. VERY COLD
TEMPERATURES WILL PERSIST THROUGH MONDAY AS COLD SFC HIGH SETTLES
INTO THE NORTHERN AND CENTRAL PLAINS WITH SOME LIGHT SNOW/FLURRIES
AROUND. ATTENTION THEN TURNS TO NEXT UPPER TROF/LOW THAT WILL DIG
SSE ALONG THE WEST COAST MONDAY BEFORE TURNING EAST AND ACCELERATING
MONDAY NIGHT THROUGH TUESDAY... REACHING THE CENTRAL PLAINS BY
TUESDAY EVENING. THIS WILL BRING ANOTHER ROUND OF SNOW TO THE CWA
WITH SNOW EXPECTED TO BEGIN INCREASING FROM THE WEST LATER MONDAY
AFTERNOON AND MONDAY NIGHT AS SFC UPSLOPE FLOW ENHANCES AS PRESSURES
FALL OVER THE CENTRAL ROCKYS. CURRENT TRACK FAVORING THE HEAVIEST
SNOW FOR THE CWA BEING OVER THE SE PART PRIMARILY TUESDAY MORNING.
OBVIOUSLY TRACK WILL BE CRITICAL BUT IT APPEARS ANOTHER 3-6 INCHES A
DECENT BET. SPEED OF SYSTEM WILL LIMIT SNOWFALL AMOUNTS WITH
SNOWFALL LIKELY TAPERING OFF FROM NW-SE TUESDAY AFTERNOON AS
INVERTED SFC TROF MOVES EAST AND UPSLOPE WANES. TEMPERATURES
REMAINING QUITE COLD AND WILL CONTINUE TO FAVOR COLD SIDE OF
GUIDANCE AND EVEN A LITTLE BELOW THOSE NUMBERS IN TYPICALLY COLD
AREAS.
LONG TERM...TUESDAY NIGHT THROUGH SUNDAY. HIGH CONFIDENCE IN GFS
AND ECMWF MODEL SOLUTIONS THROUGH SATURDAY AS THEIR 500 MB SYNOPTIC
PATTERNS ARE QUITE SIMILAR. GFS HAS HIGHER AMPLITUDE RIDGE ALOFT
OVER THE ROCKIES ON SUNDAY VERSUS THE ECMWF WITH 500 MB HEIGHTS 120
METERS HIGHER THAN THE ECMWF HAS OVER WYOMING.
TUESDAY NIGHT...CYCLONIC FLOW ALOFT CONTINUES. WITH DECREASING LOW
AND MID LEVEL MOISTURE...WILL SEE A CORRESPONDING DECREASE IN AREAL
SNOW COVERAGE WITH OROGRAPHIC SNOWS CONTINUING AFTER MIDNIGHT ACROSS
THE SNOWY RANGE.
WEDNESDAY...SCATTERED OROGRAPHIC SNOW SHOWERS CONTINUE ACROSS THE
SNOWY RANGE IN MOIST NORTHWEST CYCLONIC FLOW ALOFT. DRY ELSEWHERE.
HIGH TEMPERATURES IN THE SINGLE DIGITS AND TEENS WITH 700 MB
TEMPERATURES NEAR -20 CELSIUS AND 1000-500 MB THICKNESSES NEAR 5160
METERS.
THURSDAY...SLOW MODERATION IN TEMPERATURES AS FLOW ALOFT BACKS TO
WEST NORTHWEST. HIGH TEMPERATURES IN THE TEENS TO MID 20S WITH
1000-500 MB THICKNESSES NEAR 5250 METERS. DECREASE IN AREAL COVERAGE
OF OROGRAPHIC SNOW SHOWERS ACROSS THE SNOWY RANGE WITH DECREASE IN
LOW AND MID LEVEL MOISTURE.
FRIDAY...MOIST NORTHWEST FLOW ALOFT...THUS SCATTERED OROGRAPHIC SNOW
SHOWERS ACROSS THE NORTHERN LARAMIE RANGE...SNOWY RANGE AND LOCALES
JUST DOWNWIND OF THESE RANGES. DRY ELSEWHERE. LITTLE WARMER WITH
HIGH TEMPERATURES IN THE 20S TO LOWER 30S WITH 1000-500 MB
THICKNESSES NEAR 5310 METERS.
SATURDAY...TEMPERATURE MODERATION CONTINUES WITH HIGHS IN THE UPPER
20S TO UPPER 30S WITH 1000-500 MB THICKNESSES NEAR 5400 METERS.
INCREASE IN AREAL OROGRAPHIC SNOW SHOWER COVERAGE ACROSS THE SNOWY
RANGE...HENCE THE APPROS POS NAME...AND NORTHERN LARAMIE RANGE WITH
MOIST WEST NORTHWEST FLOW ALOFT.
SUNDAY...WILL SEE HIGH TEMPERATURES IN THE UPPER 20S TO NEAR 40
DEGREES WITH 1000-500 MB THICKNESSES NEAR 5370 METERS AND LIMITED
CLOUD COVER DOWNWIND OF A RELATIVELY CLOUD FREE RIDGE ALOFT ACROSS
THE GREAT BASIN STATES. FEW OROGRAPHIC SNOW SHOWERS ACROSS THE SNOWY
RANGE.
AVIATION...CEILINGS AND VISIBILITIES LOWERING OVERNIGHT TO IFR AND
MVFR IN SNOW SHOWERS...FOG AND LOW CLOUDS WITH LOCALIZED MVFR OVER
THE MOUNTAINS AND IN FAVORABLE UPSLOPE LOCALES. SNOW SPREADING FROM
WEST TO EAST ON MONDAY WITH IFR AND MVFR WEST OF INTERSTATE 25 AND
VFR AND MVFR EAST OF INTERSTATE 25. MOUNTAINS OBSCURED. WIDESPREAD
IFR AND LIFR MONDAY NIGHT IN SNOW...FOG AND LOW CLOUDS WITH THE
MOUNTAINS OBSCURED.
FIRE WEATHER...NO CONCERNS THROUGH TUESDAY WITH VERY COLD
TEMPERATURES AND SNOWFALL.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM/AVIATION...RE
LONG TERM...RUBIN
