Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 242300
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
400 PM MST TUE FEB 24 2015

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 358 PM MST TUE FEB 24 2015

TONIGHT...FAST MOVING SHORTWAVE TROUGH ALOFT SWEEPS SOUTHEASTWARD
ACROSS THE NORTHERN AND CENTRAL ROCKIES...SENDING THE INITIAL
SURGE OF COLDER AIR SOUTHWARD INTO OUR COUNTIES LATE TONIGHT...AND
WITH THE LOW AND MID LEVELS SATURATING UP...ALONG WITH UPWARD
VERTICAL MOTION FROM THE BAROCLINIC BAND AND OROGRAPHIC
PROCESSES...WE EXPECT WIDESPREAD SNOWS TO CRANK UP OVER OUR SNOWY
AND SIERRA MADRE RANGES AS WELL AS THE NORTHERN LARAMIE RANGE. WE
ALSO EXPECT SCATTERED LIGHT SNOWS IN THE FEW HOURS BEHIND COLD
FRONTAL PASSAGE.

WEDNESDAY...NEXT SURGE OF ARCTIC AIR SWEEPS SOUTH ACROSS OUR
COUNTIES NORTH TO SOUTH DURING THE DAY...WITH MODERATE TO STRONG
COLD AIR ADVECTION IN ITS WAKE...THUS HAVE TOUCHED UP THE GRIDDED
FORECASTS TO HAVE MAXIMUM TEMPERATURES AROUND MID MORNING WITH
STEADY OR SLOWLY FALLING AFTERNOON TEMPERATURES. DECENT UPWARD
VERTICAL MOTION SETS UP OVER A SATURATED AIRMASS ALONG AND WEST OF
INTERSTATE 25 IN THE AFTERNOON...WHICH CORRESPONDS WELL TO THE
700- 500 MB AND 500-300 MB LAYERS WITH RESPECT TO QUASIGEOSTROPHIC
FORCING...THUS WE HAVE BUMPED UP POPS NEAR 100 PERCENT ALONG AND
WEST OF I-25 WITH 40 TO 80 PERCENT AFTERNOON POPS POST ARCTIC COLD
FRONTAL.

WEDNESDAY NIGHT...UPWARD MOTION WANES ALONG WITH LESS MOISTURE IN
THE LOW AND MID LEVELS...THUS EXPECT A CORRESPONDING DECREASE IN
AREAL SNOW COVERAGE AND INTENSITIES.

THURSDAY...DECENT LOW AND MID LEVEL UPSLOPE DEVELOPS FROM THE
SOUTHERN LARAMIE RANGE AND CHEYENNE SOUTHWARD ALONG THE FRONT
RANGE OF COLORADO AS SEEN BY UPWARD VERTICAL MOTION FIELDS...AND
THUS WE EXPECT AN INCREASE IN AREAL SNOW COVERAGE THURSDAY
AFTERNOON WITH POPS FROM 30 TO 65 PERCENT FROM SOUTHERN ALBANY
COUNTY ACROSS LARAMIE COUNTY INCLUDING CHEYENNE. MINIMAL
ACCUMULATION LIKELY WITH LIMITED DYNAMICS THOUGH WITH POWDERY SNOW
EXPECTED...SOME LOCALES MAY SEE 1 TO 3 INCHES...ESPECIALLY OVER
THE SOUTHERN LARAMIE RANGE.

THURSDAY NIGHT...LOW LEVEL EAST AND SOUTHEAST UPSLOPE DEVELOPS
NICELY OVER THE LARAMIE VALLEY...SOUTHERN LARAMIE RANGE WEST OF
CHEYENNE AND OVER LARAMIE COUNTY WYOMING INCLUDING CHEYENNE...THUS
WE EXPECT WIDESPREAD FREEZING FOG TO DEVELOP...LIKELY DENSE AT
TIMES DUE TO THIS COMMON WINTER AND SPRING PATTERN. WILL LIKELY
ALSO SEE SOME LIGHT FLURRIES WITH MINIMAL ACCUMULATION...AND WILL
NEED TO WATCH FOR THE POSSIBILITY OF FREEZING PRECIPITATION FROM
LARAMIE TO CHEYENNE...IF THE COLD AIR DEPTH NEAR THE SURFACE IS
SUFFICIENTLY OVERRUN BY THE SOUTHWEST AND WARMER 700 MB
FLOW...THOUGH THIS POSSIBILITY SEEMS RELATIVELY REMOTE.

BY DAWN ON FRIDAY...WE ARE ANTICIPATING TOTAL SNOWFALL AMOUNTS OF
1 TO 4 INCHES AT LOWER ELEVATIONS...MAINLY WEST OF INTERSTATE
25...WITH SNOWFALL AMOUNTS OF 5 TO 10 INCHES OVER THE
MOUNTAINS...THUS LATER FORECAST SHIFT TEAMS MAY NEED TO ISSUE
WINTER WEATHER ADVISORIES IN SOME LOCATIONS...ESPECIALLY OVER THE
SNOWY AND SIERRA MADRE RANGES...AND OVER THE VALLEY LOCATIONS IN
AND AROUND SARATOGA WHICH WILL HAVE FAVORABLE MOIST UPSLOPE TO THE
NORTHERN SLOPES OF THE SNOWY AND SIERRA MADRE RANGES...THUS
SNOWFALL EXPECTED TO BE LOCALLY HIGHER IN THESE LOCALES.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 358 PM MST TUE FEB 24 2015

PROGRESSIVE NORTHWEST FLOW LATE THIS WEEK WILL SPLIT OVER THE
WEEKEND AS SHORTWAVE ENERGY BECOMES CUT OFF FROM THE NRN STREAM
OVR THE GREAT BASIN. THIS FTR EVENTUALLY PHASES BACK INTO THE NRN
STREAM EARLY NEXT WEEK. BEFORE THEN...LIKELY A FOGGY START TO THE
DAY ON FRIDAY IN THE IMMEDIATE LEE OF THE LARAMIE RANGE AS LLVL
FLOW TURNS SOUTHEASTERLY UPSLOPE. THERE MAY BE SOME FLURRIES AS
WELL DURING THE MORNING HOURS AS WELL...THOUGH CONFIDENCE IS
HIGHEST IN THE FOG/LOW STRATUS SCENARIO. FRIDAY WILL BE DRY FOR
AREAS OUTSIDE OF THE MOUNTAINS...BUT STILL COLD WITH HIGHS ONLY
REACHING THE TEENS/LOW 20S. FLOW BACKS TO THE SOUTHWEST ON
SATURDAY AS THE AFOREMENTIONED SHORTWAVE ENERGY CUTS OFF OVR THE
GREAT BASIN. SOUTHWEST FLOW AROUND THE POSITIVELY TILTED TROF
WILL PRODUCE FAVORABLE ISENTROPIC LIFT SET-UP...THE BULK OF WHICH
IS PROGD TO STAY SOUTH OVR COLORADO. MAY SEE ANOTHER COUPLE OF
INCHES HOWEVER...MOST OF WHICH WILL BE CONFINED TO AREAS ALONG
THE COLORADO/WYOMING STATELINE. THIS SYSTEM PHASES WITH THE NRN
STREAM ON SUNDAY...KICKING IT OUT INTO THE PLAINS. ANOTHER COLD
DAY AHEAD FOR SUNDAY WITH JUST SOME LINGERING SNOW SHOWERS
POSSIBLE AS THE SHORTWAVE ENERGY EJECTS INTO THE PLAINS. MONDAY
LOOKS DRY WITH TEMPERATURES PERHAPS RETURNING BACK TO FREEZING.
ALTHOUGH MEDIUM RANGE GUIDANCE STRUGGLES IN TIMING AND STRENGTH
DURING ACTIVE PATTERNS...THERE MAY BE ANOTHER LIGHT SNOW EVENT
AGAIN FOR NEXT TUESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1042 AM MST TUE FEB 24 2015

MAIN IMPACTS TO AVIATION WILL BE FOUND AFTER 09-12Z OF THIS TAF
CYCLE. 17Z SATELLITE IMAGES SHOW A DIMINISHING POCKET OF SCT-
BKN050 CIGS DROPPING SOUTH KDGW-KCDR. ALTHO IT WILL LIKELY LAST
DURING THE FIRST FEW HOURS OF THE TAF...EXPECT DISSIPATION TO
CONTINUE. OTHERWISE...WINDS WILL GENERALLY BE WEST AT AROUND 10
KNOTS THIS AFTERNOON. CONDITIONS WILL DETERIORATE TONIGHT AS A
COLD FRONT SLIDES THROUGH TAF SITES 09-12Z. ALONG WITH A WIND
SHIFT TO NORTHWEST AND EVENTUALLY NORTH...WILL SEE A PERIOD OF
LIGHT SNOW OR SNOW SHOWERS DEVELOP AT TAF SITES. KRWL/KCDR WILL
SEE SNOW EARLIEST AROUND 09Z AND ALL OTHER SITES 12-18Z. FOR NOW
HAVE TRENDED TAFS INTO THE MVFR CATEGORY...THOUGH WILL LIKELY SEE
LOCATIONS DROPPING INTO IFR FOR A TIME ON TUESDAY. ALTHOUGH WILL
AWAIT HIGHER CONFIDENCE IN TIMING/LOCATION TO ADD IFR INTO TAFS.

&&

.FIRE WEATHER...
ISSUED AT 358 PM MST TUE FEB 24 2015

NO ISSUES EXPECTED BASED ON PROGGED HUMIDITIES AND WINDS AND
EXPECTED SNOWFALL.

&&

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

&&

$$

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


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