Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 231754
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1154 AM MDT MON MAR 23 2015

.UPDATE...
ISSUED AT 906 AM MDT MON MAR 23 2015

LATEST RADAR LOOP WAS SHOWING SOME BANDS OF SHOWERS DEVELOPING IN
DAWES AND NORTHERN SIOUX COUNTIES. THESE BANDS SHOULD CONTINUE TO
LIFT NORTHEAST DURING THE COURSE OF THE MORNING. AS A RESULT...WE
WENT AHEAD AND BUMPED UP THE PRECIPITATION CHANCES IN THAT AREA
THIS MORNING. WE WILL ALSO MOST LIKELY UPGRADE OUR HIGH WIND WATCH
TO A HIGH WIND WARNING DUE TO THE GRADIENTS INCREASING DURING THE
COURSE OF THE EVENING AS THE UPPER LEVEL TROF PASSES THROUGH THE
AREA. STILL INVESTIGATING THE TIMING OF WHEN WIND SPEEDS MAY
EXCEED WARNING CRITERIA.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 410 AM MDT MON MAR 23 2015

OVERNIGHT WATER VAPOR IMAGERY LOOP SHOWED A UPPER RIDGE AXIS OVER
THE HIGH PLAINS WITH A SHORTWAVE TROUGH APPROACHING SOUTHWEST WY
FROM UT. A MORE VIGOROUS UPPER TROUGH WAS MOVING THROUGH THE
PACIFIC NORTHWEST AND GREAT BASIN...PRODUCING SOME CG LIGHTNING
ACTIVITY. THE REGIONAL SURFACE ANALYSIS DEPICTED A WEAK PRESSURE
PATTERN WITH FRONTS TO THE NORTH...SOUTH AND WEST. CLOUDS WERE
INCREASING FROM WEST TO EAST IN ADVANCE OF THE APPROACHING TROUGH.
WINDS WERE LIGHT AND TEMPERATURES RANGED FROM THE MID 20S TO UPPER
30S.

PRIMARY FORECAST CHALLENGES DURING THE SHORT TERM WILL DEAL WITH
THUNDERSTORMS...STRONG WINDS AND ACCUMULATING SNOWFALL. 00Z MODEL
GUIDANCE SUITE IS IN GOOD AGREEMENT PROGGING THE SHORTWAVE TROUGH
TO TRACK EAST ACROSS THE CWA TODAY...FOLLOWED BY THE MORE POTENT
TROUGH TUESDAY. SHOWERS DEVELOP THIS MORNING MAINLY ALONG AND WEST
OF LARAMIE RANGE...SPREADING EAST ONTO THE PLAINS THIS AFTERNOON.
INSTABILITY WILL BE MARGINAL /LI`S TO -1 AND SBCAPES 400-800 J/KG/
FOR ISOLATED THUNDER...AND SPC HAS HIGHLIGHTED THE ENTIRE CWA WITH
GENERAL TSTORM RISK FOR TODAY. TODAY WILL BE ANOTHER MILD DAY WITH
HIGHS IN THE LOW-MID 60S ALONG AND EAST OF I-25...WITH 40S AND 50S
TO THE WEST.

SHOWERS WILL CONTINUE TONIGHT...WITH SNOW LEVELS DROPPING TO 6500
FT AND 700MB TEMPERATURES FALLING INTO THE SINGLE DIGITS BELOW
ZERO CELSIUS. LIGHT TO MODERATE SNOWFALL WILL ACCOMPANY THE
SHOWERS. WESTERLY WINDS WILL RAMP UP LATER TONIGHT FOR THE WIND
PRONE AREAS OF SOUTHEAST WY WHERE A HIGH WIND WATCH HAS BEEN
ISSUED. THE CRAIG-CASPER 700-850MB GRADIENT INCREASES TO AOA 60
METERS BEGINNING AFTER 06Z TUE...WITH PREFRONTAL GAP WIND EVENT
DEVELOPING. THE 850MB GRADIENT WEAKENS BELOW 50 METERS AFTER 12Z
TUE...HOWEVER THE 700MB GRADIENT REMAINS BETWEEN 55 AND 60 METERS
THROUGH TUE EVENING. ALSO...700MB WINDS ARE PROGGED FROM 50 TO 60
KT DURING THIS TIME PERIOD. PATTERN TRANSITIONS FROM GAP TO BORA
WIND TUESDAY AFTER FROPA...WITH STRONG WINDS POTENTIALLY SPREADING
OUT ONTO THE HIGH PLAINS. DRYING DOWNSLOPE WINDS WILL PRECLUDE
SHOWER ACTIVITY FOR MOST AREAS EAST OF I-25. IT WILL BE 5-7
DEGREES COOLER TUESDAY.

AS THE SECONDARY TROUGH AND COLD FRONT MOVE ACROSS THE CWA TUESDAY
NIGHT AND WEDNESDAY...SHOWERS WILL BECOME WIDESPREAD...WITH
ACCUMULATING SNOW FOR THE MOUNTAINS. SNOW LEVELS WILL DROP TO 5500
FT TUESDAY NIGHT AND WEDNESDAY MORNING WITH RAIN-SNOW MIX ALONG
AND EAST OF I-25. TEMPERATURES WEDNESDAY WILL BE ABOUT 10 DEGREES
COOLER THAN TUESDAY...WITH HIGHS IN THE 40S TO NEAR 50 EAST AND
20S AND 30S WEST. GUSTY NORTHWEST WINDS WILL MAKE IT FEEL 5-10
DEGREES COOLER.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 350 AM MDT MON MAR 23 2015

NORTHWEST FLOW WILL BE OVERHEAD WEDNESDAY NIGHT WITH WINDS ALOFT
INCREASING THROUGH THURSDAY. THIS JET ENERGY COMBINED WITH
STRENGTHENING MID LEVEL ENERGY AND A COLD FRONT PROGGED TO MOVE
SOUTH THROUGH THE AREA MIDDAY THURSDAY WILL BRING A CHANCE FOR
SHOWERS TO MUCH OF THE CWA. PRECIP TYPE WILL LIKELY BE LIGHT SNOW
THURSDAY MORNING BUT SHOULD CHANGE TO RAIN OR A MIX OF RAIN/SNOW
THRU THE DAY BELOW 9000 FT WITH THE HEATING OF THE DAY. IN
ADDITION...WNW SFC WINDS WILL BE BREEZY AHEAD OF THE FRONT ALONG
AND WEST OF THE LARAMIE...AND WILL SWITCH TO THE NNW AND EXPAND IN
COVERAGE TO THE EAST BEHIND THE FRONT AND AS THE JET MOVES
OVERHEAD. LOOKING AT A BROAD COVERAGE OF GUSTS 25 TO 35 MPH. THINK
THAT SHOWERS WILL LINGER ON THURSDAY NIGHT INTO FRIDAY MORNING
DOWNSTREAM OF THE BIG HORNS AND LARAMIE RANGE FROM THE COMBINATION
OF JET FORCING AND OROGRAPHICS UNTIL THE JET STEADILY SHIFTS EAST
ON FRIDAY.

A HIGH AMPLITUDE RIDGE WILL BUILD OVER THE WESTERN CONUS ON FRIDAY
AND OVER THE ROCKIES ON SATURDAY. CONDITIONS WILL DRY AND WARM AS
THE RIDGE BUILDS FROM THE WEST WITHIN INCREASINGLY SUBSIDENT
ANTICYCLONIC FLOW. THE RIDGE WILL FLATTEN LATE SATURDAY AND SUNDAY
AS A POTENT VORT MAX DIGS SOUTHEAST ACROSS CANADA INTO THE UPPER
MIDWEST...WITH OTHER WEAKER PIECES OF ENERGY MOVING ACROSS THE
ROCKIES AS WELL. THE LEESIDE SFC PRESSURE TROUGH WILL DEEPEN AHEAD
OF THIS SYSTEM BEGINNING EARLY SATURDAY MORNING WITH H7 WINDS
INCREASING TO AROUND 40 KTS BY EARLY SUNDAY MORNING. THUS LOOKING AT
BREEZY-WINDY CONDITIONS DEVELOPING ACROSS THE WIND PRONE AREAS THRU
THIS TIME. THE MAIN COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL DIVE
SOUTH ACROSS THE FORECAST AREA MIDDAY SUNDAY AND WILL LIKELY SPARK
OFF A FEW RAIN SHOWERS...DEPENDING ON AVAILABLE DEEP LAYER MOISTURE.
WINDS WILL TURN MOIST SOUTHEASTERLY UPSLOPE SUNDAY NIGHT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1148 AM MDT MON MAR 23 2015

VFR CONDITIONS THROUGH THE TAF PERIOD. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND PERSIST
THROUGH THE EVENING. NOT EXPECTING MUCH REDUCED VIS OR LOWERING OF
CIGS...HOWEVER COULD BE A FEW HIGHER WIND GUSTS. SOUTH-TO-
SOUTHWEST WINDS WILL GUST TO 25-30 KTS THROUGH THE AFTERNOON. A
FRONT WILL PASS OVER THE SITES BY LATE TONIGHT WITH WINDS BECOMING
WESTERLY. BY TUES MORNING...GUSTS TO 35-40 KTS WILL BE POSSIBLE AT
THE WY SITES. WINDY CONDITIONS WILL PERSIST THROUGH MUCH OF TUES.

&&

.FIRE WEATHER...
ISSUED AT 315 AM MDT MON MAR 23 2015

A UPPER LEVEL DISTURBANCE AND SURFACE TROUGH WILL INTERACT WITH
PACIFIC MOISTURE TO PRODUCE SCATTERED SHOWERS AND A FEW AFTERNOON
THUNDERSTORMS TODAY. WINDS WILL INCREASE TONIGHT ACROSS SOUTHEAST
WYOMING AHEAD OF AN APPROACHING COLD FRONT. STRONG WINDS WILL BE
POSSIBLE FOR THE NORMALLY WIND PRONE AREAS OF SOUTHEAST WYOMING
LATE TONIGHT AND TUESDAY. SCATTERED RAIN AND SNOW SHOWERS WILL
CONTINUE TUESDAY MAINLY ALONG AND WEST OF THE LARAMIE RANGE. LIGHT
TO MODERATE SNOW ACCUMULATIONS CAN BE EXPECTED OVER THE MOUNTAINS.
GUSTY DOWNSLOPE WINDS WILL RESULT IN DRIER CONDITIONS FOR THE
PLAINS WITH MINIMUM RELATIVE HUMIDITIES BETWEEN 15 AND 20 PERCENT
TUESDAY AFTERNOON.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO 8 PM MDT TUESDAY FOR
     WYZ106-110-116-117.

     HIGH WIND WATCH TUESDAY EVENING FOR WYZ106-110-116-117.

     HIGH WIND WATCH FROM TUESDAY MORNING THROUGH TUESDAY EVENING FOR
     WYZ115-118.

NE...NONE.
&&

$$

UPDATE...REC
SHORT TERM...MAJ
LONG TERM...RJM
AVIATION...ZF
FIRE WEATHER...MAJ


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