Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 102150
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
350 PM MDT THU APR 10 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY
ISSUED AT 350 PM MDT THU APR 10 2014

SURFACE OBSERVATIONS AND CURRENT ANALYSIS SHOW A STATIONARY
FRONT...WHICH PUSHED ACROSS THE AREA AS A COOL FRONT LAST
NIGHT...SLOWLY RETREATING EASTWARD THIS AFTERNOON. THE FRONT HAS
JUST WENT THROUGH CHEYENNE AT 3 PM...AND IS GENERALLY JUST EAST
OF THE LARAMIE RANGE EXTENDING NORTHWARD BETWEEN CASPER AND
DOUGLAS. HIGH CLOUDS HAS PREVENTED CONVECTION FROM DEVELOPING IN
ADDITION TO SLIGHTLY COOLER TEMPERATURES...SO HAD TO LOWER HIGH
TEMPERATURES TODAY A FEW DEGREES. THIS BAND OF HIGH CLOUDS IS
MOVING ACROSS SOUTHEAST WYOMING WITH CLEARING ACROSS CENTRAL
WYOMING AS AN UPPER LEVEL DISTURBANCE MOVES EASTWARD ACROSS THE
AREA THIS AFTERNOON. SOME CONVECTION HAS STARTED TO DEVELOP NORTH
OF DOUGLAS ALONG THE FRONT...SO EXPECT SOME ACTIVITY IN THE FORM
OF THUNDER SHOWERS TO DEVELOP AND PUSH EAST ACROSS THE HIGH PLAINS
THROUGH THIS EVENING. DID LOWER POP ALONG THE I80 CORRIDOR SINCE
THAT AREA WILL BE THE LAST TO GET OUT OF THE AREA OF HIGH
CLOUDINESS. ANY THUNDER SHOWERS MAY CONTAIN SOME SMALL
HAIL/GRAUPEL AND GUSTY WINDS.

QUIET WEATHER EXPECTED ON FRIDAY WITH NEARLY ZONAL FLOW AS UPPER
LEVEL FLOW WILL START TO SHIFT INTO THE WEST AHEAD OF THE NEXT
STORM SYSTEM FORMING OVER SOUTHERN CANADA...FORECAST TO MOVE INTO
THE AREA THIS WEEKEND. ANOTHER WARM DAY FRIDAY AFTERNOON WITH
TEMPERATURES INCREASING INTO THE MID 60S (WEST) TO MID 70 (EAST) IN
THE AFTERNOON.

FOR SATURDAY...STRONG UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT
WILL MOVE INTO WYOMING. DO NOT EXPECT ANY SNOWFALL UNTIL SATURDAY
NIGHT...BUT DAYTIME RAIN SHOWERS CAN NOT BE RULED OUT AHEAD OF THE
FRONT. KEPT POP BETWEEN 25 TO 35 PERCENT ALONG AND NORTH OF
I80...MAINLY FOR SCATTERED SHOWERS AND ISOLATED THUNDER. EXPECT
THE STRONG COLD FRONT TO BEGIN ENTERING THE NORTHERN PART OF THE
FORECAST AREA (LUSK AND DOUGLAS) BY EARLY AFTERNOON AS
TEMPERATURES QUICKLY FALL FROM NEAR 70 TO THE MID 40S WITH
NORTHERLY WINDS.

.LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 350 PM MDT THU APR 10 2014

MAIN IMPACT OF THE PERIOD WILL COME IN THE FIRST 24 HOURS AS A
STRONG SHORTWAVE DIVES SOUTHEAST THROUGH THE ROCKIES...BRINGING A
BRIEF BUT POTENTIALLY SIGNIFICANT RETURN TO WINTER SATURDAY NIGHT
AND SUNDAY. MEDIUM RANGE GUIDANCE HAVE TRENDED A BIT FURTHER WEST
WITH THE BASE OF THE SHORTWAVE...TRACKING IT FROM IDAHO SATURDAY
NIGHT INTO UTAH DURING THE DAY ON SUNDAY. STRENGTHENING SFC LOW OVR
THE SOUTHERN PLAINS WILL DEEPEN THE COLD AIR MASS...EVENTUALLY UP TO
AROUND 15 KFT MSL ON SUNDAY. SNOW-LEVELS BETWEEN 10-11 KFT EARLY
SATURDAY EVENING WILL DESCEND TO AROUND 5 KFT BY SUNRISE SUNDAY. AS
A RESULT...EXPECT RAIN SATURDAY EVENING TO TRANSITION TO SNOW
OVERNIGHT SATURDAY. THE EXCEPTION WILL BE ACROSS LOWER ELEVATIONS OF
THE WESTERN NEBRASKA PANHANDLE...WHERE RAIN WILL BE SLOWEST TO
TURN-OVER. SO...WITH A DEEPENING COLD NE UPSLOPE FLOW IN THE
BOUNDARY LAYER AND MOIST WEST/SOUTHWEST FLOW ABOVE...EXPECT A VERY
FAVORABLE OVERRUNNING SET-UP ATOP AN ALREADY FAVORABLE NORTHEASTERLY
UPSLOPE PATTERN IN THE BL. ADDITIONALLY...LFQ/RRQ H3 JET COUPLETING
WILL FURTHER ENHANCE LIFT OVER THE CWFA. SNOWFALL RATES WILL
STRENGTHEN SATURDAY NIGHT AND ON SUNDAY MORNING...WITH WIDESPREAD
MODERATE TO HEAVY SNOWFALL LOOKING INCREASINGLY POSSIBLE. AS FOR
SNOWFALL ACCUMULATIONS...HAVE TRENDED THE FORECAST TO 6+ INCHES
ABOVE 8 KFT MSL...WITH 4+ INCHES POSSIBLE BETWEEN 5 AND 8 KFT MSL.
WARMER TEMPERATURES WILL PROLONG TRANSITION TO SNOW AT LOWER
ELEVATIONS...LIMITING SNOWFALL ACCUMULATION POTENTIAL BELOW 3
INCHES. ALTHOUGH THE 12Z GFS IS SLOWER IN MOVING THE SYSTEM
THRU...IT IS ITS FIRST RUN IN DOING SO...SO WILL CONTINUE WITH THE
TREND OF DECREASING PRECIPITATION CHANCES FROM NORTH TO SOUTH SUNDAY
AFTERNOON/EVENING. SNOW MAY EVEN MIX BACK WITH RAIN FOR A TIME ON
SUNDAY...ESPECIALLY IN LOWER ELEVATIONS. THE OTHER CONCERN WITH THIS
SYSTEM WILL BE NORTHEAST WINDS THAT WILL GUST 30 TO 40 MPH LATE
SATURDAY NIGHT AND SUNDAY MORNING AND THE RESULTANT BLOWING/DRIFTING
SNOW. HAVE ADDED THIS TO THE FORECAST AND CONTINUED THE TREND OF
INCREASING PRECIPITATION CHANCES. FOR NOW...AM LEANING TOWARDS
ADVISORY SNOW AMOUNTS...BUT THIS MAY NEED TO BE ADJUSTED AS DETAILS
BECOME MORE CLEAR OVER THE COMING DAYS. TEMPERATURES WILL BE SHARPLY
COLDER SUNDAY...AS TEMPERATURES WILL HOLD STEADY IN THE 30S ALL DAY.

SNOW ENDS BY LATE SUNDAY...GIVING WAY TO TRANSITORY RIDGING EARLY
NEXT WEEK THIS WILL YIELD DRY CONDITIONS AND MODERATING
TEMPERATURES. IN FACT...HIGHS WILL BOUNCE BACK INTO THE 40S FOR
MONDAY AND INTO THE 50S TO NR 60F BY TUESDAY.

MEDIUM RANGE MODEL SOLUTION DIVERGE SIGNIFICANTLY WED-THU TIMEFRAME
WITH THE GFS TRACKING AN UPPER-LOW IN THE FOUR CORNERS...WHILE THE
ECMWF KEEPS THE FLOW NEARLY ZONAL. AT THIS POINT...SEE NO REASON TO
FAVOR ONE SOLUTION OVER THE OTHER UNTIL A TREND IS ESTABLISHED.
SO...WILL KEEP TEMPERATURES NR CLIMATOLOGY AND SHOWER CHANCES IN
BOTH DAYS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY MORNING)
ISSUED AT 1143 AM MDT THU APR 10 2014

GUSTY WEST/SOUTHWEST WINDS WILL AGAIN BE THE MAIN IMPACT AT SE WY
TERMINALS TODAY WITH GUSTS OF 25 TO 35 KNOTS COMMON. THERE MAY BE
A FEW LATE DAY SHOWERS IN THE VICINITY OF KCYS SO HAVE INCLUDED
VCSH THERE. WINDS WILL BE MUCH LIGHTER OVER THE PANHANDLE
TODAY...GENERALLY LESS THAN 10 KNOTS. MAY BE A STRAY SHOWER OR TWO
AT THESE SITES LATE THIS AFTERNOON/EARLY THIS EVENING AS WELL.
KSNY LOOKS TO BE IN THE BEST LOCATION FOR THUNDER CHANCES SO
STEERED TOWARDS VCTS. PRECIP CHANCES DRY UP AFTER 03Z.

&&

.FIRE WEATHER...
ISSUED AT 350 PM MDT THU APR 10 2014

MODERATE FIRE WEATHER CONCERNS ON FRIDAY WITH DAYTIME MINIMUM
HUMIDITIES BETWEEN 15 TO 20 PERCENT AND BREEZY CONDITIONS AT
TIMES. NOT CONFIDENT ENOUGH FOR A FIRE WEATHER WATCH SINCE
WIDESPREAD CRITICAL CONDITIONS ARE NOT EXPECTED TO BE OBSERVED
EAST OF THE LARAMIE RANGE. HUMIDITIES WILL THEN TREND HIGHER THIS
WEEKEND AS A STRONG STORM SYSTEM PUSHES ACROSS THE AREA. THERE IS
A GOOD CHANCE OF SIGNIFICANT SNOW ACCUMULATIONS ACROSS PORTIONS OF
SOUTHEAST WYOMING SATURDAY NIGHT AND SUNDAY AS A STRONG COLD FRONT
MOVES SOUTHWARD OUT OF CANADA.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...HAHN
AVIATION...TJT/HAHN
FIRE WEATHER...TJT








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