Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 240413
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
913 PM MST MON FEB 23 2015

.UPDATE...
ISSUED AT 907 PM MST MON FEB 23 2015

CLEAR SKIES AND LIGHT WINDS ON TAP FOR THE REST OF TONIGHT. NO
BIG ADJUSTMENT TO THE OVERNIGHT FORECAST ONLY NORMAL MINOR
ADJUSTMENTS TO REFLECT CURRENT CONDITIONS. PATCHY FOG STILL NOT
OUT OF THE QUESTION OF THE LARAMIE RANGE TONIGHT BUT NOT LOOKING
FOR BIG IMPACTS.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 253 PM MST MON FEB 23 2015

CURRENT VISIBLE SATELLITE LOOP SHOWS CLEAR SKIES OVER THE AREA
TODAY AND IN BETWEEN WEATHER SYSTEMS FOR A FEW DAYS. THE STORM
SYSTEM...WHICH RESULTED IN SNOW OVER MOST OF SOUTHEAST WYOMING AND
PORTIONS OF THE SOUTHERN NEBRASKA PANHANDLE...IS CURRENTLY CLOSED
OFF FROM THE MEAN FLOW ALOFT ACROSS THE DESERT SOUTHWEST. A WEAK
RIDGE OF HIGH PRESSURE ALOFT WILL NUDGE INTO THE FORECAST AREA
TONIGHT AND TUESDAY WITH A SLIGHT WARMING TREND. THE ONLY FORECAST
CONCERN TONIGHT WILL BE THE POTENTIAL FOR FOG WEST OF THE LARAMIE
RANGE AND POSSIBLY OVER TOWARDS DOUGLAS. CURRENT OBSERVATIONS SHOW
VARIABLE WINDS AND A PRETTY MOIST BOUNDARY LAYER IN THE HIGH
VALLEYS. BELIEVE THESE CONDITIONS WILL CONTINUE INTO TONIGHT WITH
A STRONG INVERSION DEVELOPING. DECIDED TO ADD PATCHY FOG FOR THE
VALLEYS WEST OF THE LARAMIE RANGE AND ALONG THE NORTH PLATTE RIVER
VALLEY NEAR DOUGLAS...EVEN THOUGH CONFIDENCE IS MARGINAL AT THIS
TIME. OTHERWISE...HIGHS ARE EXPECTED TO INCREASE ON TUESDAY WITH
TEMPERATURES IN THE MID 30S TO MID 40S IN THE AFTERNOON. SNOW
COVER MAY HOLD A FEW LOCATIONS OVER SOUTHEAST WYOMING A FEW
DEGREES LOWER THAN EXPECTED HOWEVER. THE WARMEST TEMPERATURES WILL
BE EAST OF I25 ACROSS NEAR THE WY/NE BORDER.

FOR TUESDAY NIGHT...MODELS SHOW THE NEXT UPPER LEVEL SHORTWAVE
RAPIDLY PUSHING SOUTHWARD OUT OF WESTERN CANADA. MODELS ARE IN
BETTER AGREEMENT TODAY WITH THE TIMING...SHOWING MOST OF THE
SNOWFALL HOLDING OFF UNTIL AFTER MIDNIGHT UP NORTH...AND AROUND
SUNRISE ALONG I80. AHEAD OF THE FRONT...IT WILL BE RELATIVELY MILD
WITH LOW TEMPERATURES POTENTIALLY NEAR 30 DEGREES EAST OF THE
LARAMIE RANGE. HIGHS ON WEDNESDAY WILL LIKELY BE IN THE MORNING AS
THE LEADING EDGE OF THE COLD FRONT QUICKLY MOVES THROUGH THE AREA
BY SUNRISE WITH WINDS SHIFTING INTO THE NORTH.

PERIODS OF SNOWFALL...MUCH COLDER TEMPERATURES...AND PERHAPS SOME
BLOWING SNOW OVER THE HIGH PLAINS ARE POSSIBLE ON WEDNESDAY AND
INTO WEDNESDAY NIGHT. HIGH CONFIDENCE IN TEMPERATURES LOWERING
INTO THE TEENS AND 20S DURING THE DAY ON WEDNESDAY AS THE COLDER
AIR MOVES INTO THE REGION. QPF AND SNOWFALL AMOUNTS WILL BE A
LITTLE TRICKY...BUT AS OF RIGHT NOW...SIGNIFICANT SNOW
ACCUMULATIONS ARE NOT EXPECTED. THERE WILL STILL BE TRAVEL IMPACTS
HOWEVER...MAINLY ACROSS SOUTHEAST WYOMING AS PERIODS OF MODERATE
TO HEAVY SNOW ARE POSSIBLE DUE TO SOME LLVL INSTABILITY. DYNAMIC
FORCING IS NOT IMPRESSIVE WITH THIS SYSTEM WITH LITTLE IF ANY JET
SUPPORT. THE MAIN FORCING MECHANISM (OTHER THAN INSTABILITY)
WILL PRIMARILY BE UPSLOPE WINDS AND LLVL CONVERGENCE...MAINLY
ALONG AND WEST OF THE LARAMIE RANGE. FORCING AND LIFT ARE IN
SHORT DURATION...SO SNOW ACCUMULATIONS SHOULD GENERALLY BE 1 TO 2
INCHES ACROSS THE LOWER ELEVATIONS INCLUDING THE HIGH
VALLEYS...AND 3 TO 5 INCHES ACROSS THE MOUNTAINS THROUGH WEDNESDAY
NIGHT. INCREASED POP BETWEEN 60 TO 90 PERCENT ACROSS SOUTHEAST
WYOMING...WITH LOWER VALUES ACROSS WESTERN NEBRASKA WHICH MAY NOT
SEE MUCH SNOW AT ALL. WINTER WEATHER ADVISORIES ARE POSSIBLE FOR
PORTIONS OF SOUTHEAST WYOMING...BUT IMPACTS APPEAR LOW TO MODERATE
AT THIS TIME DEPENDING ON INTENSITY OF THE SNOWFALL AND
POTENTIALLY BLOWING SNOW.

.LONG TERM...(THURSDAY THROUGH NEXT MONDAY)

NORTHWEST FLOW ALOFT PREVAILS. CHANCES FOR SNOW WILL INCREASE
DURING THE DAYLIGHT HOURS...AS EVIDENCED BY THE NAM UPWARD
VERTICAL MOTION FIELDS ALONG THE INTERSTATE 25 CORRIDOR...AS A
WEAK SHORTWAVE TROUGH ALOFT MOVES ACROSS OUR COUNTIES...BUT MORESO
BY DECENT LOW AND MID LEVEL UPSLOPE ALONG THE SPINE OF THE LARAMIE
RANGE...THUS HAVE INCREASED POPS INTO THE 40 TO 60 PERCENT RANGE
IN THE AFTERNOON ACROSS THE UPSLOPE FAVORED TERRAIN FROM LARAMIE
TO CHEYENNE.

FRIDAY...SNOW CHANCES WILL DIMINISH AS LIFT WANES AND THE
ATMOSPHERIC COLUMN DRIES OUT SOMEWHAT. CONTINUED COLD PER 700 MB
TEMPERATURES NEAR -12 CELSIUS AND PROGGED THICKNESSES THOUGH NOT
THAT UNUSUAL FOR LATE FEBRUARY.

SATURDAY...IF YOU LOVE COLD OUTDOOR WINTER ACTIVITIES...YOU WILL
LOVE THIS DAY AS ARCTIC HIGH PRESSURE DOMINATES WYOMING AND NEBRASKA
AND THE NORTHERN ROCKIES AND NORTHERN PLAINS STATES KEEPING THE
ARCTIC COLD ENTRENCHED OVER OUR COUNTIES...WHILE A RELATIVELY MOIST
ATMOSPHERIC COLUMN OVER US...IS LIFTED BY PERIODIC WEAK SHORTWAVE
TROUGHS ALOFT RIDING OVER SOUTHEAST WYOMING AND WESTERN NEBRASKA ON
SOUTHWEST FLOW ALOFT...AND ALSO WITH LIFT PROVIDED BY DECENT LOW AND
MID LEVEL UPSLOPE. BOTH THE GFS AND ECMWF KEEP THE BULK OF THE
HEAVIER SNOW OVER WESTERN COLORADO AND OVER OUR WESTERN
COUNTIES...WHICH SEEMS REASONABLE AND PLAUSIBLE CONSIDERING THEIR
MESOSCALE AND SYNOPTIC PATTERNS.

SUNDAY...MARCH WILL COME IN LIKE A LAMB SNOWFALL WISE...ALBEIT STILL
COLD. FLOW ALOFT BECOMES MORE WEST TO EAST...AND WITH LESS LIFT FROM
UPSLOPE AND SYNOPTIC LIFTING...AND A DRYING ATMOSPHERIC COLUMN
MEANING LESS LOW AND MID LEVEL MOISTURE...WILL SEE ONLY ISOLATED TO
SCATTERED SNOW SHOWERS OVER OUR SNOWY...SIERRA MADRE AND NORTHERN
LARAMIE RANGES...AND DRY ELSEWHERE.

MONDAY...OUR EARLY MARCH PSEUDO THAW WILL COMMENCE AS OUR FLOW
BECOMES ZONAL AND THE ARCTIC AIRMASS RETREATS AND MODERATES...AIDING
IN HIGH TEMPERATURES NEARING OR EXCEEDING FREEZING AT LOWER
ELEVATIONS WITH THE PROMISE OF WARMER TEMPERATURES THROUGH
MIDWEEK. DRY WITH LACK OF LOW AND MID LEVEL MOISTURE AND LIFT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1045 AM MST MON FEB 23 2015

VFR. CLEAR THROUGH SUNSET...THEN INCREASING CLOUDS AT OR ABOVE
10000 FEET ABOVE GROUND LEVEL...AGL...WITH SCATTERED TO BROKEN
CEILINGS. AT ALL TAF SITES...WINDS GUSTING TO 25 KNOTS AT TIMES
THROUGH SUNSET TONIGHT...AND AGAIN AFTER SUNRISE TUESDAY...WITH
WIND GUSTS TO 25 KNOTS AT TIMES AT CHEYENNE AFTER 05Z...
11 PM...TONIGHT.


&&

.FIRE WEATHER...
ISSUED AT 153 PM MST MON FEB 23 2015

NO FIRE WEATHER CONCERNS THIS WEEK DUE TO PERIODS OF SNOWFALL AND
GENERALLY COLD TEMPERATURES WILL BE OVER SOUTHEAST WYOMING AND
WESTERN NEBRASKA. SLIGHTLY WARMER TEMPERATURES ARE EXPECTED ON
TUESDAY BEFORE ANOTHER ARCTIC SYSTEM INVADES THE AREA ON
WEDNESDAY. VERY COLD TEMPERATURES AND A GOOD CHANCE FOR LIGHT TO
MODERATE SNOW WILL OCCUR WEDNESDAY INTO THURSDAY WITH BELOW NORMAL
TEMPERATURES EXPECTED TO PERSIST THROUGH THE WEEKEND.

&&

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

&&

$$

UPDATE...SML
SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...TJT


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