Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 312113
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
313 PM MDT TUE MAR 31 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 313 PM MDT TUE MAR 31 2015

THE MAIN CONCERN WITH THIS FORECAST PACKAGE IS TEMPERATURES
TRENDS TOMORROW AFTER THE FRONTAL PASSAGE.

TONIGHT:
LATEST LOOK AT THE OBS ACROSS THE AREA WAS SHOWING RH VALUES WELL
BELOW RED FLAG CRITERIA. HOWEVER...WINDS HAVE BEEN HAVING A
DIFFICULT TIME MIXING OUT IN THE NEBRASKA PANHANDLE. THIS COULD
STILL CHANGE DURING THE NEXT HOUR OR TWO. AS A RESULT...WE ARE
PLANNING ON KEEPING THE RED FLAG WARNING GOING.

LATEST WATER VAPOR LOOP WAS SHOWING THE UPPER LEVEL TROF PUSHING
ONSHORE INTO THE PACIFIC NORTHWEST. MEANWHILE...THE SURFACE LOW
WAS DEVELOPING OVER NORTHERN MONTANA. THIS FEATURE WILL CONTINUE
TO SLIDE EAST INTO THE NORTHERN PLAINS TONIGHT INTO TOMORROW. AS A
RESULT...IT WILL CAUSE A FRONTAL BOUNDARY TO DRAG THROUGH NORTHERN
WYOMING TONIGHT AND START SPILLING INTO SOUTHEAST WYOMING AND THE
NEBRASKA PANHANDLE WEDNESDAY MORNING. AHEAD OF THIS
BOUNDARY...WESTERLY FLOW SHOULD PREVAIL OVERNIGHT WHICH WILL NOT
ALLOW FOR MUCH RECOVERY IN THE HUMIDITY VALUES THIS EVENING. WE
HAVE ALSO TWEAKED TEMPERATURES UP A COUPLE OF DEGREES FROM
SUPERBLEND.

WEDNESDAY:
THE WRFARW WAS SHOWING THE FRONTAL BOUNDARY SURGING THROUGH
SOUTHEAST WYOMING AND POSSIBLY REACHING THE I-80 CORRIDOR BY MID
MORNING. THIS SHOULD ALLOW FOR DEWPOINTS TO CLIMB SLIGHTLY BEHIND
THE BOUNDARY...BUT THE AIR MASS WILL STILL QUITE BE DRY BELOW 650
MB FOR ANY PRECIPITATION. TEMPERATURES...MAY ALSO PEAK OUT AROUND
MIDDAY BEFORE SLOWLY DROPPING BEHIND THE BOUNDARY WITH AN INCREASE
CLOUD COVER AND PRECIPITATION ESPECIALLY ALONG THE I-80 CORRIDOR.
THE I-80 CORRIDOR MAY ALSO SEE SOME SCATTERED RAIN SHOWERS DUE TO
DECENT INERTIAL INSTABILITY AND WEAK 700-600MB FRONTOGENISIS
DURING THE AFTERNOON. MAY ALSO SEE SOME SNOW SHOWERS IN THE
MOUNTAINS.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 313 PM MDT TUE MAR 31 2015

THE COLD FRONT THAT SLIDES SOUTH ACROSS OUR AREA CONTINUES ITS
SOUTHWARD PUSH LATE WEDNESDAY WITH A COOL AIRMASS FIRMLY ENTRENCHED
ACROSS OUR AREA GOING THROUGH FRIDAY BEFORE WE SEE SOME MODIFICATION
OF TEMPERATURES GOING INTO THE WEEKEND. A WETTER TREND IS STILL
EXPECTED LATE WEDNESDAY THROUGH THURSDAY...BUT THE BULK OF THE
HEAVIER PRECIPITATION WILL MORE LIKELY FALL TO OUR SOUTH SEEING THE
GFS AND THE ECMWF HAVE THE CORE OF THE UPPER JET DYNAMICS SETTING UP
THURSDAY JUST TO OUR SOUTH.  HIGHEST POPS WILL BE ALONG THE COLORADO
BORDER AND JUST NORTH WHERE WE ARE ADVERTISING LIKELY POPS FOR
RAIN/SNOW DURING THE DAY ON THURSDAY. WHILE WE WILL HAVE TO WATCH
THE EVENTUAL PLACEMENT OF THE JET DYNAMICS FOR WHERE THE HEAVIER
SNOWFALL WILL OCCUR...RIGHT NOW SNOWFALL AMOUNTS DON`T APPEAR TO BE
OVERLY SIGNIFICANT WITH MOST OF IT MELTING AS IT FALLS FOR THE FIRST
FEW HOURS IN THE LOWER ELEVATIONS WITH HIGHER ELEVATIONS PICKING UP
A FEW INCHES.  THE RECENT EXTENDED WARM PERIOD WILL LIKELY HELP WITH
ROAD CONDITIONS...WITH MOST SNOWFALL HAVING LITTLE IN THE WAY OF
TRAVEL IMPACTS FOR MOST AREAS EXCEPT FOR MAYBE SOME LOCALIZED BRIEF
IMPACTS FOR THE HIGHER ELEVATIONS ACROSS THE WESTERN ZONES.

OTHERWISE...WE START CLEARING OUT BY FRIDAY MORNING WITH LINGERING
CHANCE POPS FOR LIGHT SNOW IN THE MOUNTAINS. THE WEEKEND OUTLOOK
FEATURES DRY CONDITIONS AND A RETURN OF TEMPERATURES IN THE 60S IN
THE HIGH PLAINS TO THE EAST AND 40S TO MID 50S IN THE HIGH VALLEYS
AND MOUNTAIN RANGES ACROSS THE WESTERN ZONES WITH SOUTHWESTERLY
DOWNSLOPE WINDS.  THE GFS AND THE ECMWF DEPICT A SERIES OF POORLY
TIMED SHORTWAVE MOVING ACROSS THE CENTRAL ROCKIES BY SUNDAY WITH A
SURFACE LOW REFLECTION DEVELOPING ACROSS NORTHERN COLORADO. THE MAIN
UPPER TROUGH MOVES INTO THE CENTRAL ROCKIES EARLY NEXT WEEK BRINGING
A SLIGHT CHANCE OF PRECIPITATION AND COOLER TEMPERATURES TO THE
REGION MONDAY INTO TUESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1127 AM MDT TUE MAR 31 2015

THE MAIN CONCERN WITH THIS FORECAST PACKAGE IS THE TIMING OF THE
BOUNDARY MOVING THROUGH WEDNESDAY MORNING.

LATEST SATELLITE LOOP WAS SHOWING MAINLY CLEAR SKIES WITH FAIRLY
LIGHT WIND SPEEDS. THE WIND SPEEDS SHOULD GRADUALLY INCREASE THIS
AFTERNOON AS THE BOUNDARY LAYER BEGINS TO MIX. OTHERWISE...A SURFACE
FRONT WILL PUSH THROUGH THE NORTHERN PORTION OF THE FORECAST AREA
AFTER 12Z. THIS WILL PRIMARILY IMPACT THE CDR TAF SITE THE
EARLIEST WITH SNY BEING THE LATEST AROUND 16Z OR SO. NO PRECIPATION
IS EXPECTED AS THIS BOUNDARY PASSES THROUGH.

&&

.FIRE WEATHER...
ISSUED AT 313 PM MDT TUE MAR 31 2015

GUSTY WEST WINDS WILL CONTINUE THIS EVENING AHEAD OF THE FRONTAL
BOUNDARY. THIS WILL LIMIT ANY RECOVERY IN THE HUMIDITY VALUES THIS
EVENING. THE NEXT CHANCE FOR RED FLAG CONDITIONS WILL BE THIS
WEEKEND AS THE UPPER LEVEL RIDGE BUILDS INTO THE AREA AND A
STRONG UPPER LEVEL TROF MOVES INTO THE INTERMOUNTAIN WEST EARLY
NEXT WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING FOR WYZ301-302-306-
     310.

NE...RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING FOR NEZ311>313.

&&

$$

SHORT TERM...REC
LONG TERM...JG
AVIATION...REC
FIRE WEATHER...REC



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