000
FXUS65 KCYS 060953
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
253 AM MST TUE JAN 6 2009
.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...
CYCLONIC NORTHWEST FLOW WILL TURN ANTICYCLONIC IN SHORT ORDER THIS
MORNING AS BROAD LOW AMPLITUDE RIDGING MOVES ONTO THE WEST COAST.
SEVERAL FORECAST CHALLENGES WITH THIS ISSUANCE INCLUDING HIGH WINDS
IN THE MOUNTAINS AND FOOTHILLS AND OROGRAPHIC SNOW ON THE WEST
SLOPES OF THE MED BOWS. AMAZINGLY WINDS CONTINUE TO GUST TO BETWEEN
55 AND 60 MPH AT BORDEAUX AT THIS HOUR EVEN WITH MEAGER GRADIENTS
AND H7 WINDS OF 30 TO 40 KTS THIS AM. EVEN THESE GRADIENTS WILL DROP
OFF TO 20 TO 30 KTS LATER THIS MORNING. SO TO PREVENT CONFUSION WITH
THE MUCH MORE SIGNIFICANT EVENT EXPECTED LATER TONIGHT...WILL HANDLE
THIS LOCALIZED EVENT WITH A SPS FOR NOW...BARRING ANY SIGNIFICANT
JUMP IN GUSTS. THE AFOREMENTIONED SIGNIFICANT WIND EVENT EXPECTED
TO BEGIN TONIGHT WILL BE A RESULT OF TIGHTENING GRADIENT COMBINING
WITH THE RFQ OF A 145KT JET MOVING OVERHEAD. CRAIG TO CASPER
GRADIENTS EXCEED THE 60 DM THRESHOLD BY AROUND MIDNIGHT...PEAKING
BETWEEN 80 AND 90 DM SOMETIME BETWEEN 12Z AND 18Z WEDNESDAY. AT THE
SAME TIME H7 ISOTACHS PEAK BETWEEN 60 AND 70 KTS ACROSS SE WY. NAM12
SOUNDINGS ON THE LEEWARD SLOPES SUGGEST A CRITICAL STABLE LAYER
DEVELOPING NEAR MOUNTAIN-TOP WEDNESDAY MORNING. FROUDE CALCULATIONS
DURING THIS TIME USING 30 M/S OF CROSS-BARRIER FLOW AND 6C/KM LAPSE
RATES YIELD AROUND .92. ALTHOUGH NOT EXACTLY AT THE FAVORABLE FROUDE
NUMBER OF 1...GIVEN THE PRESENCE OF THIS STABLE LAYER AND
SIGNIFICANT CROSS BARRIER FLOW...THE POSSIBILITY EXISTS FOR SOME
MOUNTAIN WAVE DEFLECTION TOWARDS THE SURFACE ALONG LEE
FOOTHILLS...ESPECIALLY ON WEDNESDAY MORNING. WILL POST A HIGH WIND
WATCH ACROSS ALL OF THE FAVORED WIND AREAS...INCLUDING THE CHEYENNE
FOOTHILLS FOR LATE TONIGHT THROUGH WEDNESDAY EVENING. WOUND NOT BE
SURPRISED TO SEE GUSTS EXCEED 70 OR 80 MPH IN AREAS.
THE OTHER CONCERN WITH THIS PACKAGE IS THE INCREASING OROGRAPHIC
MOISTURE ACROSS THE WINDWARD SLOPES OF THE MED BOWS FOR TONIGHT AND
WEDNESDAY. ALTHOUGH AN INCH OR TWO OF LIGHT SNOW WILL OCCUR ACROSS
THIS AREA TODAY...EXPECT SNOWFALL RATES TO PICK UP TONIGHT AND
DURING THE DAY ON WEDNESDAY. GENERALLY EXPECT 24 HOUR SNOWFALL
TOTALS OF 8 TO 14 INCHES ACROSS THE SIERRA MADRES...WITH 4 TO 8
INCHES IN THE SNOWIES. EVEN THOUGH SNOWFALL AMOUNTS MAY STRUGGLE TO
REACH WINTER STORM CRITERIA...THE COMBINATION OF WIND AND SNOW
WARRANTS A WATCH. SO WILL ISSUE A WINTER STORM WATCH FOR THIS AREA
FOR TONIGHT AND WEDNESDAY. INTERESTINGLY THE MAIN CONCERN IN THE
NORTHERN SECTIONS OF THE SNOWY RANGE...WILL BE THE STRONG WIND IN
THE ARLINGTON AREA.
WITH WINDS EXPECTED TO PICK UP TONIGHT...OVERNIGHT LOWS WILL BE
REACHING DURING THE EVENING HOURS WITH TEMPERATURES MODERATING
THROUGHOUT THE NIGHT. TODAY WILL STILL BE CHILLY ACROSS THE AREA
WITH MOST AREAS NEAR CLIMATOLOGICAL NORMALS. THIS WILL CHANGE
HOWEVER...FOR WEDNESDAY AS ADIABATIC DOWNSLOPE WARMING WILL AID 40
AND 50 DEGREE TEMPS FOR LOCALES EAST OF THE MOUNTAINS.
.LONG TERM...THURSDAY THROUGH MONDAY...
CONTINUED MILD AND BREEZY/WINDY THURSDAY AS UPPER RIDGE AXIS
SHIFTS EAST ACROSS THE AREA. NEXT UPPER TROF TO AFFECT THE REGION
WILL MOVE OVER THE PACIFIC NW THURSDAY NIGHT THEN DIVE SE INTO THE
UTAH/AZ AREA BY LATE FRIDAY. SFC COLD FRONT WILL DROP SE ACROSS
THE CWA FRIDAY MORNING WITH SOME POST FRONTAL LIGHT SNOWS OVER
MAINLY THE WRN CWA FRIDAY WHERE DYNAMICAL SUPPORT WILL BE A LITTLE
BETTER. BULK OF ENERGY WITH UPPER TROF MOVES OVER SRN COLORADO AND
NEW MEXICO FRIDAY NIGHT BEFORE SHEARING OUT OVER THE SRN PLAINS
SATURDAY THUS EXPECT PCPN TO END OVER THE CWA BY FRIDAY NIGHT WITH
SFC HIGH SETTLING INTO THE CENTRAL PLAINS. TEMPERATURES WARM
SOMEWHAT OVER THE WEEKEND AS DOWNSLOPE FLOW RETURNS UNDER NW FLOW
ALOFT. MODELS BECOME MORE IN DISAGREEMENT WITH EVOLUTION OF UPPER
FEATURES INTO EARLY NEXT WEEK BUT OVERALL SEEM TO BE TRENDING
TOWARD MORE AMPLIFICATION OF ERN PACIFIC UPPER RIDGE WHICH IN TURN
WILL OPEN THE DOOR FOR SIGNIFICANTLY COLDER AIR TO INVADE THE
REGION NEXT WEEK.
&&
.AVIATION...
VFR CONDITIONS WILL PREVAIL AT AREA TERMINALS TODAY. WEST WINDS WILL
STRENGTHEN ACROSS SOUTHEAST WYOMING TONIGHT AND CONTINUE THROUGH
WEDNESDAY. WIND GUSTS HAVE THE POTENTIAL TO EXCEED 50 OR 60
KTS...MOSTLY AT THE KCYS TERMINAL. ADDITIONALLY...MOUNTAIN WAVE
DEVELOPMENT WEDNESDAY MORNING WILL CREATE SIGNIFICANT TURBULENCE IN
AND AROUND THE HIGHER TERRAIN. LOCALIZED MVFR CIGS/VSBYS WILL SPREAD
OVER THE MEDICINE BOW MOUNTAINS FOR TONIGHT AND WEDNESDAY. SEVERAL
INCHES OF SNOW ACCUMULATIONS CAN BE EXPECTED IN THIS AREA.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WATCH FROM 6 PM TUESDAY TO 6 PM WEDNESDAY FOR
WYZ063.
HIGH WIND WATCH FROM MIDNIGHT WEDNESDAY TO MIDNIGHT THURSDAY FOR
WYZ062-WYZ064-WYZ066-WYZ067-WYZ069.
NE...NONE.
&&
$$
SHORT TERM/AVIATION...HAHN
LONG TERM...RE
