Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 300929
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
229 AM MST FRI JAN 30 2015

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 229 AM MST FRI JAN 30 2015

TODAY...DESPITE BROKEN TO OVERCAST SKIES OVER CARBON COUNTY...WE
MAY SEE SOME AREAS OF FOG THERE WITH TEMPERATURE AND DEWPOINT
SPREADS AROUND 3 DEGREES. WILL SEE INCREASING MIDDLE AND HIGH
CLOUDS AHEAD OF THE SHORTWAVE TROUGH ALOFT APPROACHING FROM
SOUTHERN ARIZONA...WITH A FEW SNOW SHOWERS OVER OUR SNOWY AND
SIERRA MADRE RANGES...DRY ELSEWHERE.

TONIGHT...AREAS OF FOG WILL INCREASE IN COVERAGE AS THE LOW LEVELS
SATURATE...THOUGH THE FOG COVERAGE WILL BE LIMITED SOMEWHAT BY
THE AMOUNT OF MIDDLE AND HIGH LEVEL CLOUDS. WITH SOME WEAK
SHORTWAVE TROUGH ALOFT ENERGY...UPSLOPE AND SATURATED LOW
LEVELS...EXPECT A CHANCE OF SNOW SOUTH OF A RAWLINS TO CHEYENNE
LINE.

SATURDAY...NEXT FAST MOVING SHORTWAVE TROUGH ALOFT...AN ALBERTA
TYPE CLIPPER...WILL MOVE TO NORTHEAST WYOMING SENDING THE NEXT
ARCTIC COLD FRONT SOUTH ACROSS OUR NORTHERN COUNTIES. ENOUGH LOW
AND MID LEVEL MOISTURE...NORTHERLY UPSLOPE AND WEAK UPWARD
VERTICAL MOTION TO PRODUCE A CHANCE OF LIGHT SNOW SOUTH OF A
RAWLINS TO SCOTTSBLUFF LINE.

SATURDAY NIGHT...STRONG COLD AIR ADVECTION AND CYCLONIC FLOW ALOFT
WILL WRING OUT A CHANCE OF LIGHT SNOW BUT WITH MINIMAL ACCUMULATIONS
DUE TO LACK OF LOW AND MID LEVEL MOISTURE.

SUNDAY...BREEZY AND COLD DAY WITH FAST NORTH NORTHWEST FLOW ALOFT
AND DECENT COLD AIR ADVECTION CONTINUING. HIGH TEMPERATURES WILL
STRUGGLE TO REACH FREEZING AT MOST LOCATIONS DESPITE SOME
SUNSHINE.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 229 AM MST FRI JAN 30 2015

AN UPPER LEVEL RIDGE WILL BUILD OVER THE ROCKIES SUNDAY NIGHT INTO
MONDAY WITH STRONG WAA OCCURRING OVER THE CWA THROUGH THIS TIME.
LOOKING AT TEMPS SPIKING INTO THE 40S AND 50S FOR MONDAY. SHORTWAVE
ENERGY ON THE NOSE OF A 100 KT JET WILL MOVE QUICKLY ATOP THE
RIDGE AND OVER THE ROCKIES AS WELL AND THE LEESIDE PRESSURE TROUGH
WILL RAPIDLY DEEPEN IN ADVANCE OF THIS WAVE. MODELS SHOW WINDS IN
THE 800-700 MB LAYER OVER SOUTHEAST WYOMING INCREASING TO 50+ KTS
LATE SUNDAY NIGHT AS THE LLVL PRESSURE GRADIENT STRENGTHENS. WITH
WAA IN PLACE...LIKELY TO SEE STRONG WINDS BECOME TRAPPED NEAR THE
SURFACE IN THE WIND PRONE AREAS OF SOUTHEAST WYOMING. UPSLOPE FLOW
ALONG THE WESTERN SLOPES WILL STRENGTHEN AS THESE WINDS DEVELOP
AND WILL COMBINE WITH INCREASED PACIFIC MOISTURE TO BRING A GOOD
CHANCE FOR OROGRAPHIC SNOW DURING THIS TIME AS WELL. THE LLVL
PRESSURE GRADIENT WILL RELAX SLIGHTLY ON MONDAY EVENING AS THE
INITIAL WAVE SHIFTS EAST...BUT ANOTHER AND SOMEWHAT STRONGER VORT
MAX WILL MOVE INTO THE NORTHERN ROCKIES MONDAY NIGHT AND WILL
REINTENSIFY THE GRADIENT. STILL THINKING THE WIND PRONE AREAS WILL
SEE A SECOND ROUND OF HIGH WINDS WHILE OROGRAPHIC SNOW INTENSIFIES
OVER THE MOUNTAINS MONDAY NIGHT THROUGH TUESDAY MORNING. HIGH
WINDS COULD EXPAND FURTHER EAST ONTO THE PLAINS LATE TUESDAY
MORNING WITH NEARLY 60 KTS PROGGED AT 750 MB AND ONLY PATCHY
CIRRUS OVERHEAD TO POTENTIALLY INHIBIT MIXING. CANT RULE OUT A FEW
SHOWERS MAINLY OVER THE NORTHERN ZONES FROM CONVERSE TO BOX BUTTE
COUNTIES TUESDAY MORNING AS THE VORT MOVES ACROSS THE NORTHERN
ROCKIES AND AN ASSOCIATED COLD FRONT STALLS OVER THIS AREA.

BEYOND TUESDAY...CONFIDENCE IS LOW WHETHER HIGH WINDS WILL BE
REALIZED IN THE WIND PRONE AREAS ONCE AGAIN WEDNESDAY
MORNING...OR IF THE COLD FRONT WILL MOVE SOUTH THRU THE PLAINS
EARLY ENOUGH TO SHUT OFF THE HIGH WINDS AND BRING RAIN/SNOW TO
THE CWA INSTEAD. THE 00Z GFS...EC AND GEM ALL SHOW VARIED
SOLUTIONS WITH THE SOUTHWARD SURGE OF THE FRONT...WITH THE GEM
NEARLY 12HRS FASTER THAN THE GFS...AND THE EC 6HRS SLOWER THAN THE
GFS. WITH THIS LEVEL OF VARIABILITY ON TIMING...WILL TREND TOWARD
A MIDDLE GROUND SOLUTION FOR NOW WHICH MEANS WINDY CONDITIONS WILL
PREVAIL THROUGH WEDNESDAY MORNING BUT WILL NOT QUITE REACH HIGH
WIND LEVELS. WILL KEEP MAINLY SLIGHT CHANCE POPS TUESDAY NIGHT
INTO WEDNESDAY MORNING FOR MUCH OF THE CWA EXCEPT IN THE
MOUNTAINS WHERE CHANCE POPS ARE REASONABLE. MOSTLY DRY CONDITIONS
AND LESS WIND WILL PREVAIL FOR THURSDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1002 PM MST THU JAN 29 2015

VFR FOR MOST TAF SITES THROUGH THE TAF FORECAST PERIOD. ONLY
CONCERN IS NEAR KRWL WHERE MVFR TO IFR CIGS ARE POSSIBLE AFTER 12Z
FRIDAY AND WILL REMAIN SO INTO FRIDAY NIGHT. LIGHT WINDS ACROSS
THE AREA THROUGH FRIDAY NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 229 AM MST FRI JAN 30 2015

MINIMAL CONCERNS. A STRONG ARCTIC COLD FRONT WILL
SWEEP QUICKLY NORTH TO SOUTH ACROSS THE DISTRICT ON
SATURDAY...USHERING IN COLDER TEMPERATURES FOR SUNDAY. WARMING
TEMPERATURES FOR MONDAY AND TUESDAY BEFORE ANOTHER COLD FRONT BRINGS
COOLER TEMPERATURES FOR WEDNESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

SHORT TERM...RUBIN
LONG TERM...RJM
AVIATION...SML
FIRE WEATHER...RUBIN


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