Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 311728
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1028 AM MST SAT JAN 31 2015

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 530 AM MST SAT JAN 31 2015

MADE A FEW CHANGES TO THE FORECAST FOR TODAY AS CURRENT WATER
VAPOR IMAGERY TRENDS SUGGEST ENERGY ASSOCIATED WITH THE SOUTHERN
STORM SYSTEM LOOKS TO LINGER OVER THE FORECAST AREA SLIGHTLY
LONGER THAN PREVIOUS THINKING. THE MIDLEVEL BAROCLINIC BAND ON
THE NORTHERN FRINGE OF THE UPPER LOW OVER THE DESERT SOUTHWEST IS
PROGGED TO REMAIN OVERHEAD THROUGH MIDDAY TODAY...WITH A SURFACE
TROUGH POSITIONED JUST SOUTHEAST OF THE FORECAST AREA EXTENDING
FROM CENTRAL COLORADO UP THRU CENTRAL NEBRASKA. SFC CYCLOGENESIS
OCCURRING OVER COLORADO TODAY WITHIN THIS TROUGH WILL PULL THE
MAIN COLD FRONT CURRENTLY OVER THE NORTHERN PLAINS SOUTH THRU THE
FORECAST AREA. SOUTHEASTERLY FLOW AT 700 MB OVER THE PLAINS AHEAD
OF THE MIDLEVEL FRONT WILL ADVECT IN SOME MOISTURE THIS MORNING
WITH WEAK ISENTROPIC LIFT DEVELOPING THROUGH THE DAY OVER THE
PANHANDLE AS THE SFC FRONT STEADILY SHIFTS SOUTH. THE MAIN PRECIP
BAND LOOKS TO DEVELOP OVER THE SOUTHERN PANHANDLE THIS MORNING
WITHIN THE AREA OF ISENTROPIC LIFT...AND THEN SHIFTS NORTH A BIT
INTO THE CENTRAL PANHANDLE THIS AFTERNOON BEFORE THE NORTHERN
STREAM SHORTWAVE FINALLY NUDGES THE MIDLEVEL FRONT AND ASSOCIATED
PRECIP BAND EAST EARLY THIS EVENING. SO BUMPED UP POPS AND SNOW
TOTALS ESPECIALLY ACROSS BOX BUTTE AND MORRILL COUNTIES WITHIN
MAIN AREA OF MIDLEVEL CONVERGENCE AND LIFT WHERE AROUND AN INCH OF
SNOW IS LIKELY THIS AFTERNOON. MODELS ALSO SHOW SOME WEAK
INSTABILITY IN THIS AREA AS WELL WHICH WILL AID IN OVERALL SHOWER
CHANCES. DO THINK PRECIP TYPE WILL BE MAJORITY SNOW BASED ON
TIMING OF THE SFC FRONT THIS MORNING...AND FORECAST SOUNDINGS
DEPICTING THE MAJORITY OF THE COLUMN WILL BE BELOW FREEZING.
CANNOT RULE OUT A MIX OF RAIN-SNOW AT THE ONSET OF PRECIP THO.
STILL EXPECTING SNOW SHOWERS TO CONTINUE IN THE SNOWY AND SIERRA
MADRES THIS MORNING AHEAD OF A SHORTWAVE MOVING UP FROM UTAH INTO
WESTERN CO.

THE NORTHERN STREAM SHORTWAVE TROUGH WILL SLIDE SOUTHEAST OVER THE
FORECAST AREA THIS EVENING WITH SHOWERS REDEVELOPING OVER MUCH OF
THE CWA THROUGH THE EVENING AND OVERNIGHT PERIOD. EXPECTING A
QUICK BURST OF SNOW WITH ANY SHOWER THAT OCCURS WITH ACCUMULATIONS
LOOKING TO GENERALLY BE ONE HALF INCH OR LESS IN THE LOWER
ELEVATIONS...AND AN INCH OR TWO IN THE MOUNTAINS. THE WAVE WILL
DEPART THE AREA QUICKLY SUNDAY MORNING WITH DRY AND COOLER
CONDITIONS ANTICIPATED FOR THE REST OF SUNDAY. HIGH PRESSURE WILL
BUILD OVER THE ROCKIES SUNDAY NIGHT WITH A WEAK DISTURBANCE MOVING
ATOP THE RIDGE AND OVER THE ROCKIES THROUGH THIS TIME. THE LEESIDE
PRESSURE TROUGH WILL DEEPEN QUITE RAPIDLY AHEAD OF THIS WAVE WITH
THE LLVL PRESSURE GRADIENT STRENGTHENING AS A RESULT. BY 06Z
MONDAY...THE CAG-CPR GRADIENT WILL BE ROUGHLY 55-60 DAM WITH WINDS
IN THE 750 TO 700 MB LAYER PROGGED TO BE IN EXCESS OF 50 KTS
THROUGH 12Z. A CROSS-SECTION PLOT THROUGH THE WIND PRONE AREAS
SHOW THE INVERSION SETTING UP JUST AROUND MOUNTAIN TOP LEVEL AND
WITHIN THE BAND OF STRONGER WINDS. SO...LOOKING AT PERHAPS A
MARGINAL HIGH WIND EVENT LATE SUNDAY NIGHT THROUGH MONDAY MORNING.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 530 AM MST SAT JAN 31 2015

THE EARLY PART OF NEXT WEEK WILL FEATURE WINDY CONDITIONS ACROSS
SOUTHEAST WYOMING AND INTERMITTENT SNOWS...MAINLY ACROSS THE MTNS.
THE LLVL CAG-CPR GRADIENT WILL BECOME HIGH ENOUGH (AROUND 60 METERS)
BY MON MORNING TO SUGGEST A MARGINAL HIGH WIND EVENT ACROSS THE WIND
PRONE AREAS.  HOWEVER...THE BETTER CHANCE OF HIGH WINDS WILL BE LATE
MON NIGHT INTO TUES AS THE LLVL GRADIENT INCREASES FURTHER TO 75-80
METERS AND FLOW ALOFT IS STRONGER.  THERE IS EVEN THE POTENTIAL FOR
HIGH WINDS TO SPREAD ONTO THE ADJACENT PLAINS OF SOUTHEAST WYOMING.
THE GRADIENT BEGINS TO DECREASE BY LATE TUES AS HIGHER PRESSURES AND
A COLD FRONT BACK INTO THE REGION.  TEMPS ON MON AND TUES WILL BE
ABOVE NORMAL WITH DOWNSLOPING WESTERLY WINDS PREVAILING.

THE OTHER STORY EARLY NEXT WEEK WILL BE THE OROGRAPHIC SNOWFALL
ACROSS THE SIERRA MADRE AND SNOWY RANGES.  MOIST NORTHWESTERLY FLOW
WILL TRANSPORT A GOOD AMOUNT OF PACIFIC MOISTURE INTO WYOMING.  BOTH
THE GFS AND ECMWF INDICATE A GOOD CHANCE OF SNOW THROUGH MIDDAY MON
AND THEN A BRIEF BREAK BEFORE MORE SNOW ARRIVES ON TUES AFTN.  SNOW
AMOUNTS (COMBINED WITH THE WINDY CONDITIONS) COULD WARRANT SOME SORT
OF WINTER WEATHER HEADLINE AT THAT TIME.  BY WED MORNING SNOW COULD
SPREAD ONTO THE PLAINS IN THE LLVL UPSLOPE BEHIND THE FRONT COMBINED
WITH SOME UPPER LEVEL SUPPORT. GENERALLY HAVE SLIGHT CHANCE POPS FOR
NOW ALONG WITH COOLER TEMPS.  IT IS A RATHER PROGRESSIVE PATTERN SO
INCREASING HEIGHTS AND TEMPS WILL OCCUR BY THURS AND FRI.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY MORNING)
ISSUED AT 1028 AM MST SAT JAN 31 2015

MAINLY VFR THIS AFTERNOON OVER KRWL AND KLAR TERMINALS BUT SHOULD
LOWER TO MVFR AND PATCHY IFR THIS EVENING.  OVER THE SE WY PLAINS
AND THE NEB PANHANDLE WIDESPREAD IFR AND SOME LIFR CIGS EXPECTED TO
PERSIST THROUGH TONIGHT WITH AREAS OF LIGHT SNOW IN WEAK UPSLOPE
FLOW.

&&

.FIRE WEATHER...
ISSUED AT 530 AM MST SAT JAN 31 2015

SNOW SHOWERS WILL PERSIST OVER THE SNOWY AND SIERRA MADRE
MOUNTAINS THROUGH MUCH OF TODAY...WHILE RAIN AND SNOW SHOWERS WILL
DEVELOP OVER THE PLAINS AND HIGH VALLEYS THIS AFTERNOON AND EVENING.
SNOW ACCUMULATIONS WILL REMAIN GENERALLY LIGHT. SUNDAY WILL
REMAIN COOL AND MOSTLY DRY WITH WINDY CONDITIONS RETURNING TO THE
WIND PRONE AREAS OF SOUTHEAST WYOMING LATE SUNDAY NIGHT. WARM AND
WINDY CONDITIONS WILL CONTINUE FOR THE DISTRICT THROUGH MIDWEEK.

&&

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

$$

SHORT TERM...RJM
LONG TERM...ZF
AVIATION...RE
FIRE WEATHER...RJM


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