Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 282137
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
237 PM MST SUN DEC 28 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 236 PM MST SUN DEC 28 2014

TONIGHT...PRIMARY CHALLENGES WILL BE TIMING OF ARCTIC AIR AND AREAL
COVERAGE OF SNOW. ARCTIC COLD FRONT WILL SLOWLY SLIDE SOUTH ACROSS
OUR COUNTIES...USHERING IN THE BITTERLY COLD AIRMASS NOW OVER THE
NORTHERN DAKOTAS...WITH WIDESPREAD LIGHT SNOW DEVELOPING SOME 1 TO 3
HOURS AFTER COLD FRONTAL PASSAGE. INHERITED WINTER WEATHER
ADVISORIES FROM THE MIDNIGHT SHIFT TEAM ARE ON TRACK FOR THE
NORTHERN LARAMIE...SNOWY AND SIERRA MADRE RANGES. FOR THE EASTERN
PLAINS...WILL HAVE POPS NEARING 90 TO 100 PERCENT WITH SATURATED
AIRMASS LIFTED BY UPSLOPE AND DYNAMICS.

MONDAY...STRENGTH OF COLD AIR ADVECTION SUGGESTS THAT TEMPERATURES
WILL BE SLOWLY FALLING DURING THE DAYLIGHT HOURS. WITH THE NAM...GFS
AND ECMWF SHOWING THE BULK OF THE DYNAMICAL LIFT ASSOCIATED WITH THE
SHORTWAVE TROUGH OVER COLORADO...AND ALSO NEAR THE JET
ALOFT...EXPECT WE WILL SEE WIDESPREAD LIGHT POWDERY SNOW...WITH A 30
OR 40 TO 1 SNOW TO LIQUID RATIO...AND THEREFORE ONLY LIGHT SNOWFALL
ACCUMULATIONS. SINCE THE PRIMARY FOCUS OF THIS WINTER WEATHER EVENT
WILL BE MUCH COLDER TEMPERATURES AND WIND CHILLS BEHIND THE ARCTIC
COLD FRONT...WE HAVE OPTED TO ISSUE A SPECIAL WEATHER STATEMENT FOR
OUR CUSTOMERS...AND TO MAINTAIN THE INHERITED MOUNTAIN WINTER
WEATHER ADVISORY WHICH IS ON TRACK.

MONDAY NIGHT...WEAK UPWARD VERTICAL MOTION WILL CONTINUE ALONG WITH
UPSLOPE OF THE SATURATED LOW AND MID LEVELS...KEEPING LIGHT SNOW
FAIRLY WIDESPREAD IN THE EVENING...WITH LESS COVERAGE AFTER
MIDNIGHT. BITTERLY COLD WIND CHILLS FROM 20 BELOW TO 40 BELOW WILL
REQUIRE WIND CHILL ADVISORIES OR WIND CHILL WARNINGS. BY DAWN
TUESDAY...EXPECTING SNOWFALL TOTALS OVER THE NORTHERN
LARAMIE...SNOWY AND SIERRA MADRE RANGES OF 6 TO 12 INCHES...WITH 1
TO 4 INCHES OVER LOWER ELEVATIONS.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 236 PM MST SUN DEC 28 2014

THE AREA WILL BE IN THE MIDST OF AN ARCTIC OUTBREAK TO BEGIN THE
PERIOD...FOLLOWED BY TEMPERATURES GRADUALLY MODERATING BACK INTO THE
UPPER 20S FOR THE END OF THE WEEK AND NEXT WEEKEND. H3 155 KNOT
ZONAL JET STREAK WILL DRIFT BACK NORTH TOWARDS THE CWA...LIKELY
PROLONGING THE VERY LIGHT SNOW/FLURRIES ACROSS THE AREA AT LEAST
INTO THE MORNING HOURS. TEMPERATURES ARE GOING TO BE THE BIGGER
STORY...AND WITH A 1050MB HIGH PRESSURE SETTLING ACROSS THE AREA ON
TUESDAY AND THE EXISTING SNOW PACK...EXPECT MOST AREAS TO REMAIN
BELOW 0F. LARAMIE WILL LIKELY BE THE COLD SPOT ON TUESDAY...WHERE
HIGH TEMPERATURES MAY NOT SEE ABOVE DOUBLE DIGITS BELOW ZERO.
TUESDAY NIGHT WILL SEE THE COLDEST TEMPERATURES OF THE WEEK...WITH
20 TO 30 DEGREES BELOW ZERO WIDELY EXPECTED. WILL LIKELY NEED A WIND
CHILL HIGHLIGHT IN TIME FOR THIS PERIOD AND INTO WEDNESDAY NIGHT AS -
30 TO -40F LOOKS TO BE A GOOD BET.

THE GOOD NEWS OF THE WEEK IS THAT THE ARCTIC BLAST WILL BE SHORT
LIVED AND EVEN BY WEDNESDAY SHOULD BE SEEING AT LEAST SOME PROGRESS
WITH HIGH TEMPERATURES WARMING INTO THE SINGLE DIGITS WEST OF THE
LARAMIE RANGE AND TEENS OUT ON THE ERN PLAINS. OTHERWISE...EXPECT
DRY CONDITIONS TO PERSIST THRU THE END OF THE WEEK AS DRY SPLIT FLOW
KEEPS DISTURBANCES AT BAY.

MODEL SOLUTIONS ARE A LITTLE DIFFERENT FOR THE WEEKEND...WITH THE
GFS TRYING TO DRAG ANOTHER COLD FRONT SOUTH...WHILE THE ECMWF KEEPS
FLOW RATHER DRY SOUTHWESTERLY. CONFIDENCE IS NOT ALL THAT HIGH WITH
WHICH SCENARIO WILL BE THE VICTOR...BUT FOR NOW HAVE GENERALLY
FOLLOWED CONSENSUS STEERING IT TOWARDS THE WETTER/COOLER GFS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 236 PM MST SUN DEC 28 2014

WYOMING TAFS...MOUNTAINS BECOMING TOTALLY OBSCURED
TONIGHT. ARCTIC COLD FRONTAL PASSAGE FROM NORTHEAST TO SOUTHWEST
TONIGHT WILL CAUSE IFR TO BECOME WIDESPREAD IN LOWERING CEILINGS AND
VISIBILITIES WITH LOW CLOUDS...FOG AND SNOW. WINDS WILL TURN NORTH
AFTER FRONTAL PASSAGE WITH GUSTY WINDS FOR 1 TO 3 HOURS AFTER
FRONTAL PASSAGE.

NEBRASKA TAFS...ARCTIC COLD FRONTAL PASSAGE THIS EVENING WILL
PRODUCE WIDESPREAD IFR IN LOW CLOUDS...FOG AND SNOW...CONTINUING
THROUGH MONDAY AFTERNOON. WINDS TURNING NORTH AFTER COLD FRONT
PASSAGE AND GUSTY FOR 1 TO 3 HOURS.

&&

.FIRE WEATHER...
ISSUED AT 236 PM MST SUN DEC 28 2014

NO CONCERNS DUE TO PROJECTED TEMPERATURES...WINDS AND HUMIDITIES.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL 5 PM MST MONDAY FOR WYZ103-112-114.

NE...NONE.

&&

$$

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



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