Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 280404
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
904 PM MST SAT DEC 27 2014

.UPDATE...
ISSUED AT 855 PM MST SAT DEC 27 2014

JUST A FEW TWEAKS TO TEMPERATURES AND WINDS ARE BEING MADE FOR
THE MID-EVENING UPDATE...OTHERWISE EXPECT LOWS IN THE SINGLE
DIGITS AT MOST LOWER ELEVATION LOCATIONS WITH SUBZERO READINGS IN
THE HIGHER VALLEYS AND MOUNTAINS OF SOUTHCENTRAL AND SOUTHEAST
WYOMING. MOST AREAS SEEING SOME SLICK ROAD CONDITIONS CONTINUE
WITH MODEST MELTING EARLIER TODAY AND THE RE-FREEZE
TONIGHT...WITH THE USUAL PATCHES OF POST-STORM BLACK ICE NOTED IN
HIGHER ELEVATIONS WHERE HIGHER WINDS ARE BLOWING PRE-EXISTING
SNOWCOVER OVER THE ROADWAY. WE CONTINUE HIGH WIND WARNINGS FOR THE
HIGHER ELEVATIONS WEST OF CHEYENNE ALONG INTERSTATE 80 AND NORTH
OF CHEYENNE ALONG INTERSTATE 25 AND THE BORDEAUX AREA NEAR
CHUGWATER WY.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 413 PM MST SAT DEC 27 2014

MAIN CHALLENGES AGAIN WILL BE WINDS AND MINIMUM
TEMPERATURES. WINDS HAVE PEAKED BRIEFLY NEAR ARLINGTON AND ELK
MOUNTAIN JUST ABOVE OUR HIGH WIND CRITERIA...AND HAVE SINCE SUBSIDED
SOMEWHAT...THOUGH WITH PROGGED LOW AND MID LEVEL GRADIENTS AND
PROGGED INCREASE IN 850 MB AND 700 MB CRAIG TO CASPER GRADIENTS
TONIGHT...EXPECT WINDS TO ONCE AGAIN INCREASE...ESPECIALLY IN THE
WAKE OF A PASSING SHORTWAVE TROUGH ALOFT. WILL CONTINUE WITH OUR
HIGH WIND WARNING FOR BORDEAUX AND THE INTERSTATE 80
SUMMIT...STARTING AT 5 PM...THOUGH WINDS MAY PEAK THERE A BIT LATER
BASED ON THE PROJECTED AFOREMENTIONED CRAIG TO CASPER HEIGHT
DIFFERENCES...AND WOULD PREFER TO ERR ON THE SIDE OF PUBLIC
SAFETY...KEEPING OUR 5 PM START TIME THE SAME.

AS ALWAYS...QUITE CHALLENGING FORECASTING MINIMUM TEMPERATURES WITH
SNOWFIELD AND WITH WINDS DIMINISHING THIS EVENING SLIGHTLY BEFORE
PICKING UP AGAIN AFTER MIDNIGHT. TOOK THE BEST EDUCATED GUESS BASED
ON METEOROLOGICAL PARAMETERS AND CURRENT TRENDS.

SUNDAY...ONE FINAL RELATIVELY SEMI-MILD DAY BEFORE THE ARCTIC
INTRUSION SUNDAY NIGHT. POSITIVELY TILTED SHORTWAVE TROUGH ALOFT
APPROACHES WESTERN WYOMING...SPREADING INCREASING CHANCES FOR SNOW
ACROSS OUR WESTERN AND NORTHERN COUNTIES IN THE AFTERNOON...WITH
WIDESPREAD SNOW ACROSS OUR SNOWY AND SIERRA MADRE RANGES.

SUNDAY NIGHT...THE SHORTWAVE TROUGH ALOFT MOVES TO EASTERN WYOMING
BY DAWN MONDAY...WITH THE ARCTIC COLD FRONT ADVANCING SOUTHWARD TO
NEAR THE COLORADO STATE LINE BY LATE NIGHT. MOST LOCALES WILL SEE
LIGHT TO MODERATE SNOW WITH THE AIRMASS SATURATING...AND LIFT
PROVIDED BY DYNAMICS...OROGRAPHICS AND UPSLOPE.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 413 PM MST SAT DEC 27 2014

MONDAY THROUGH SATURDAY...
AN ABRUPT CHANGE TO AN ARCTIC AIR MASS ALONG WITH WHAT LOOKS TO BE A
LIGHT SNOW EVENT WILL BE THE MAIN FORECAST CONCERN EARLY NEXT WEEK.
ARCTIC FRONT WILL BE SOUTH OF THE AREA TO BEGIN THE PERIOD WITH LLVL
NORTH/NORTHEAST FLOW IN PLACE. LIGHT SNOW WILL LIKELY BE ONGOING
MONDAY AND MONDAY NIGHT AS CHUNKS OF SHORTWAVE ENERGY AND EMBEDDED
PACIFIC MOISTURE OVERRUN THE LLVL UPSLOPE AND ARCTIC AIR MASS. 12Z
MODELS HAVE TRENDED DOWNWARD WITH PRECIPITATION AMOUNTS ACROSS THE
AREA WHICH YIELDS MORE CONFIDENCE IN A HIGH POP BUT LOW QPF EVENT.
MODELS LINGER THE LIGHT SNOW EVEN INTO TUESDAY. IT LOOKS LIKE
GENERALLY 1-3 INCHES CAN BE EXPECTED ACROSS LOWER ELEVATIONS...WITH
PERHAPS 6-12 INCHES OVER THE HIER TERRAIN. THE OTHER STORY WITH THIS
EVENT WILL BE THE FRIGID TEMPERATURES. H7 TEMPERATURES OF -22 TO -
24C WILL YIELD HIGH TEMPERATURES THAT WILL ONLY REACH THE SINGLE
DIGITS MONDAY AND WILL LIKELY TOP AT AROUND 0C FOR TUESDAY. UPPER
LOW BECOMES DETACHED FROM THE NRN STREAM ON TUESDAY CLOSING OFF OVR
SRN CALIFORNIA. THIS WILL EFFECTIVELY DEFLECT NRN STREAM ENERGY TO
THE NORTH WED-FRI. TEMPERATURES WILL SLOWLY MODERATE BACK TO NEAR
FREEZING FRIDAY/SATURDAY...WITH WINDS BECOMING BREEZY ACROSS WIND
PRONE AREAS OF SOUTHEAST WYOMING AS WELL. DID INTRODUCE SOME LIGHT
SNOW CHANCES AS THE NRN STREAM JET INCHES CLOSER ON SATURDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 413 PM MST SAT DEC 27 2014

WYOMING TAFS...WINDS DECREASING. LOCALIZED IFR IN FOG AND LOW CLOUDS
AT LARAMIE THIS EVENING...WITH MVFR AND MOUNTAIN OBSCUREMENT NEAR
RAWLINS AFTER 15Z SUNDAY. WINDS GUSTING OVER 30 KNOTS AT RAWLINS AND
LARAMIE LATE TONIGHT AND SUNDAY MORNING...AND AT CHEYENNE AFTER 15Z
SUNDAY.


&&

.FIRE WEATHER...
ISSUED AT 413 PM MST SAT DEC 27 2014

NO ISSUES BASED ON EXPECTED WINDS AND HUMIDITIES.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL 11 AM MST SUNDAY FOR WYZ106-110-116-117.

NE...NONE.
&&

$$

UPDATE...JG
SHORT TERM...RUBIN
LONG TERM...CAH
AVIATION...RUBIN
FIRE WEATHER...RUBIN


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