Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 122144
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
344 PM MDT SAT APR 12 2014

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 340 PM MDT SAT APR 12 2014

CONVECTION HAS BEEN STEADILY INITIATING SINCE NOON MAINLY ALONG AND
WEST OF I-25 WITH EVEN A FEW LIGHTNING STRIKES NOTED IN CARBON
COUNTY. CONVECTIVE ACTIVITY WILL CONTINUE TO BLOSSOM INTO THE
EVENING HOURS WITH LIFTED INDICES AROUND -1C AND PROGD SBCAPE VALUES
OF 200-500 J/KG ARE REALIZED. AT THE SFC...WINDS HAVE TURNED
NORTHEAST THIS AFTERNOON AS PRESSURES HAVE BEEN STEADILY FALLING
ACROSS COLORADO. AT 20Z...THE BEST PRESSURE RISES WERE FOUND ACROSS
MONTANA AND WRN NORTH DAKOTA. THESE PRESSURE RISES WILL SHIFT SOUTH
TONIGHT AS THE COLD AIR MASS SETTLES IN. SATELLITE PIX STILL SHOW
TWO SEPARATE SHORTWAVES...ONE DIVING SE THRU THE PACNW AND THE SRN
STREAM ACCELERATING ENE TOWARDS THE FOUR CORNERS. THE SRN STREAM
SHORTWAVE WILL EJECT ONTO THE CENTRAL PLAINS SUNDAY MORNING...WHILE
THE NRN STREAM ENERGY FOLLOWS...TAKING AIM ON THE CENTRAL ROCKIES.
ALTHO THE BULK OF THE SRN STREAM SHORTWAVE WILL REMAIN SOUTH OF THE
CWA...IT HAS BEEN EFFECTIVE IN ADVECTING PACIFIC MOISTURE AHEAD OF
THE TRAILING AND STRONGER NRN STREAM DISTURBANCE. AS THE COLD AIR
MASS SAGS SOUTH TONIGHT...PERSISTENT WEST/SOUTHWEST FLOW ABOVE IT
WILL SET-UP FAVORABLE OVERRUNNING/ISENTROPIC LIFT. ADDITIONALLY...
STRONG NORTHEAST WINDS WILL ENHANCE OROGRAPHICS...ESPECIALLY ALONG
THE LARAMIE AND SNOWY RANGES. H3 JET COUPLING OF RRQ/LFQ WILL
FURTHER ENHANCE MOIST ASCENT. PROGD BUFKIT SOUNDINGS ALSO SHOWS
SATURATION WITHIN THE BEST DENDRITIC GROWTH LAYER DURING THE DAY ON
SUNDAY. EVERYTHING STILL POINTS TO A WIDESPREAD MODERATE TO HEAVY
SNOW EVENT MAINLY IMPACTING SOUTHEAST WYOMING. HAVE KEPT SNOW
AMOUNTS FAIRLY SIMILAR TO THOSE INHERITED...POINTING TO 4 TO 8
INCHES BELOW 7500 FEET IN SE WY...WITH 8 TO 14 INCHES ABOVE. THE
EXCEPTION WILL BE ACROSS LOWER ELEVATIONS OF CARBON COUNTY AND MOST
OF THE WESTERN NEBRASKA PANHANDLE WHERE EITHER LESS FAVORABLE
CONDITIONS EXIST OR LOWER ELEVATIONS DELAYS TRANSITION TO SNOW. THE
OTHER CONCERN WILL BE BLOWING SNOW AS WINDS GUST UP TO 35 MPH. THE
ONE QUESTION THAT REMAINS IS WHAT IMPACT IF ANY THE STEEPER SUN
ANGLE HAS DURING THE DAYTIME...ESPECIALLY ON ROADWAYS. HOWEVER...
THINK SNOWFALL RATES WILL BE SUFFICIENT TO OVERCOME THIS. IN AN
EARLIER UPDATE...UPGRADED THE WINTER STORM WATCH TO A WARNING FOR
MUCH OF SOUTHEAST WYOMING. HAVE ALSO ISSUED ADVISORIES IN COUNTIES
CLOSEST TO THE NEBRASKA STATELINE AND NRN SIOUX COUNTY. DELAYED THE
BEGINNING TIME ACROSS EXTREME SOUTHEAST WYOMING TO 3 AM...AS THE
COLDER AIR WILL GET IN A BIT LATER THAN EARLIER ANTICIPATED.
OTHERWISE...SNOW WILL COME TO AN END SUNDAY EVENING...SO THE 00Z
MONDAY END TIME OF THE HAZARD STILL LOOKS ON TRACK. TEMPS ARE GOING
TO BE SIGNIFICANTLY COLDER SUNDAY WITH HIGHS STRUGGLING TO GET OUT
OF THE 20S MANY AREAS.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 340 PM MDT SAT APR 12 2014

MONDAY...MODERATELY STRONG NORTHWEST FLOW ALOFT WILL PRODUCE A
BREEZY TO WINDY DAY WITH ONLY SLIGHT MODIFICATION IN MAXIMUM
TEMPERATURES DUE TO HIGH ALBEDO FROM THE RECENT SNOWPACK...THOUGH
STILL EXPECT HIGH TEMPERATURES TO CLIMB ABOVE FREEZING AT LOWER
ELEVATIONS DUE TO RATHER HIGH MID APRIL SUN ANGLE AND DOWNSLOPE LOW
LEVEL WINDS.

TUESDAY...DECENT WARMING TREND EXPECTED AS THE FLOW ALOFT BACKS TO
WEST NORTHWEST IN ADVANCE OF THE NEXT APPROACHING SHORTWAVE TROUGH
ALOFT FROM MONTANA AND IDAHO...BOOSTING MAXIMUM TEMPERATURES WELL
INTO THE 50S AND SOME LOWER 60S DUE TO DEVELOPING SURFACE LEE
TROUGHING AND 700 MB TEMPERATURES CLIMBING TO 0 CELSIUS.

WEDNESDAY...NEXT SHORTWAVE TROUGH ALOFT PASSAGE ALONG WITH ITS
ASSOCIATED COLD FRONTAL PASSAGE WILL BRING COOLER TEMPERATURES AND
SCATTERED SHOWERS DUE TO LIFT FROM CYCLONIC FLOW ALOFT AND ADEQUATE
LOW AND MID LEVEL MOISTURE.

THURSDAY...AFOREMENTIONED SHORTWAVE TROUGH ALOFT MOVES INTO THE
CENTRAL PLAINS STATES...WITH LEFTOVER SCATTERED SHOWERS ONGOING INTO
THE AFTERNOON HOURS ALONG AND EAST OF INTERSTATE 25. RESIDUAL CLOUD
COVER AND PROJECTED THICKNESSES AND 700 MB TEMPERATURES WILL YIELD
HIGH TEMPERATURES IN THE UPPER 30S AND 40S AT LOWER ELEVATIONS.

FRIDAY...TYPICAL MID APRIL SYNOPTIC PATTERN EXPECTED WITH
PROGRESSIVE SHORTWAVE TROUGHS ALOFT...AND OUR COUNTIES WILL BE IN
THE WARM SECTOR MUCH OF THE DAY IN ADVANCE OF THE NEXT SHORTWAVE
TROUGH ALOFT MOVES ACROSS MONTANA AND WYOMING...THUS YIELDING
MAXIMUM TEMPERATURES IN THE 50S AND LOWER 60S. ISOLATED SHOWERS
EXPECTED OVER THE HIGHER TERRAIN DUE TO DIFFERENTIAL HEATING...
INCLUDING THE NORTHERN LARAMIE...SNOWY AND SIERRA MADRE RANGES AND
OVER THE PINE RIDGE FROM LUSK TO NEAR CHADRON.

SATURDAY...DRYING OUT PERIOD IN THE WAKE OF THE SHORTWAVE TROUGH
PASSAGE. SLOW WARMING TREND ON TAP BASED ON PROJECTED 1000-500 MB
THICKNESSES AND 700 MB TEMPERATURES...NEAR 5610 METERS AND 2
CELSIUS...RESPECTIVELY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY MORNING)
ISSUED AT 1241 PM MDT SAT APR 12 2014

STRONG CANADIAN ORIGIN COLD FRONT PROGRESSES SOUTHWARD TO A RAWLINS
TO KIMBALL LINE BY EARLY THIS EVENING...WITH SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS DEVELOPING...PRODUCING LOCALIZED MVFR
IN SHOWERS AND ERRATIC WINDS AND WIND GUSTS TO 40 MPH IN AND NEAR
THUNDERSTORMS.

WIDESPREAD LIFR AND IFR DEVELOPING TONIGHT FROM NORTH TO SOUTH
IN EVENING RAIN...MIXING WITH AND CHANGING OVER TO SNOW LATE
THIS EVENING AND AFTER MIDNIGHT. ISOLATED THUNDERSTORMS OVERNIGHT...
MAINLY THIS EVENING. NORTH WIND INCREASING WITH GUSTS TO 25 TO 35
MPH. MOUNTAINS OBSCURED.

AFTER DAYBREAK SUNDAY...WIDESPREAD LIFR AND IFR IN SNOW AND BLOWING
SNOW WITH MOUNTAINS COMPLETELY OBSCURED. BLUSTERY NORTH WINDS.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MDT SAT APR 12 2014

NO FIRE WEATHER CONCERNS THROUGH EARLY NEXT WEEK AS A SIGNIFICANT
SPRING SNOWSTORM BRINGS SIGNIFICANT SNOW ACCUMULATIONS TO MUCH OF
THE AREA.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM MDT
     SUNDAY FOR WYZ102.

     WINTER STORM WARNING FROM 9 PM THIS EVENING TO 6 PM MDT SUNDAY
     FOR WYZ101-103>105-110-114.

     WINTER STORM WARNING FROM 3 AM TO 6 PM MDT SUNDAY FOR WYZ106-107-
     115>118.

     WINTER WEATHER ADVISORY FROM 3 AM TO 6 PM MDT SUNDAY FOR WYZ108-
     112-119.

NE...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM MDT
     SUNDAY FOR NEZ095.

&&

$$

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






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