Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 011225 CCA
AFDCYS

AREA FORECAST DISCUSSION...AMENDED AVIATION SECTION.
NATIONAL WEATHER SERVICE CHEYENNE WY
524 AM MST SUN MAR 1 2015

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 400 AM MST SUN MAR 1 2015

LATEST GOES WATER VAPOR IMAGERY SHOWED THE SPLIT CLOSED UPPER LOW
SLOWLY SINKING SOUTHEAST ALONG THE CENTRAL CA COAST. THE BASE OF
THE NORTHERN STREAM TROUGH WAS MOVING EAST ACROSS THE DAKOTAS. A
DEFORMATION ZONE STRETCHED NORTHEAST TO SOUTHWEST FROM WESTERN NE
ACROSS NORTHERN CO. NARROW BAND OF UPPER LIFT COMBINED WITH MOISTURE
AND WEAK UPSLOPE RESULTED IN AN AREA OF LIGHT SNOW OVER PORTIONS
OF SOUTHEAST WY AND WESTERN NE. HRRR MODEL PROGS THIS AREA TO WEAKEN
AS IT MOVES FURTHER EAST THROUGH DAYBREAK. TEMPERATURES WERE IN THE
SINGLE DIGITS AND TEENS WITH LIGHT WINDS.

FORECAST CONCERNS DURING THE SHORT TERM WILL FOCUS ON THE DEVELOPING
WINTER STORM AND ITS IMPACTS ON OUR AREA...PARTICULARLY FROM LATE
TONIGHT THROUGH TUESDAY. CLOSED UPPER LOW NEAR SOUTHERN CA COAST
GRADUALLY OPENS UP AND EJECTS NORTHEAST AS ANOTHER SHORTWAVE DROPS
SOUTH ALONG THE CA COAST DURING THE NEXT 24 TO 48 HOURS. THE MODEL
CONSENSUS PROGS A LOW PRESSURE SYSTEM TO FORM NEAR THE FOUR CORNERS
REGION AND TRACK NORTHEAST ACROSS COLORADO. LIGHT SNOW REDEVELOPS
LATER TODAY OVER THE SOUTHERN MOUNTAINS AND BECOMES MORE WIDESPREAD
AND HEAVIER LATE TONIGHT INTO MONDAY. THE GFS IS SLIGHTLY DEEPER
AND FASTER THAN THE ECMWF WITH REGARDS TO THE SURFACE LOW AND ITS
MOTION. THEY ARE SIMILAR WITH THE EASTWARD TRACK OF THE LOW INTO
THE CENTRAL PLAINS EARLY TUESDAY MORNING. THEY ALSO AGREE WITH THE
ARCTIC COLD FRONTAL PASSAGE DURING THIS TIME PERIOD. WINDS SHIFT
TO NORTHERLY AND BECOME GUSTY TUESDAY. SNOW WILL BE WIDESPREAD
OVER THE CWA MONDAY NIGHT AND TUESDAY. THE COMBINATION OF FALLING
AND BLOWING SNOW WILL RESULT IN HAZARDOUS TRAVEL WEST OF THE
LARAMIE RANGE...ESPECIALLY MONDAY THROUGH TUESDAY. LATEST WPC
GUIDANCE PROGS 1-2 FT OF SNOW FOR THE SNOWY/SIERRA MADRE RANGES
WITH UP TO A FOOT FOR THE NEARBY VALLEYS. ISSUED A WINTER STORM
WATCH FOR WY ZONES 111-114 LATE TONIGHT THROUGH LATE TUESDAY NIGHT
FOR THE POTENTIAL OF HEAVY SNOW. FURTHER NORTH AND EAST...WE`RE
LOOKING AT ADVISORY ACCUMULATIONS...GENERALLY 4-8 INCHES. THE
SOUTHERN LARAMIE RANGE COULD GET CLOSE TO A FOOT AS WELL. THE NEXT
SHIFT MAY UPGRADE AND/OR EXTEND THE WINTER HEADLINES AFTER LOOKING
AT THE 12Z/18Z MODEL GUIDANCE.

HIGHS TODAY WILL BE SIMILAR TO SATURDAY WITH MOSTLY UPPER TEENS TO
UPPER 20S. LOWS TONIGHT AND MONDAY NIGHT WILL AVERAGE IN THE TEENS.
MONDAY WILL BE MILDER WITH SOUTHWESTERLY WINDS. EXPECT HIGHS IN THE
30S TO AROUND 40. TEMPERATURES TUESDAY WILL NOT RISE MUCH FROM THE
EARLY MORNING LOWS...AND WILL BE FALLING THROUGH THE DAY IN THE
WAKE OF THE COLD FRONTAL PASSAGE.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 AM MST SUN MAR 1 2015

THE MAIN CHALLENGE IN THE EXTENDED WILL BE TEMPERATURE TRENDS AS WE
STILL ANTICIPATE A BAND OF NEW SNOWPACK SOMEWHERE IN THE CWA. GFS/EC
BOTH SHOW A SECONDARY SHORTWAVE DIVING ACROSS WY BETWEEN 00Z AND 12Z
WED. MODEST PVA SHOULD BE ENOUGH FOR SNOW SHOWERS TO LINGER INTO WED
MORNING OR PERHAPS EARLY AFTERNOON. MEDIUM RANGE 700-300 MILLIBAR RH
PROGS SUGGEST A DRYING COLUMN BY THIS TIME...SO EXPECT LESS THAN AN
INCH OF ADDITIONAL ACCUMULATION OVER THE LOWER ELEVATIONS AFTER 00Z
WED. TEMPERATURES WILL BE TRICKY ON TUE NIGHT AS CLOUDS WILL PREVENT
SIGNIFICANT RADIATIONAL COOLING. HOWEVER...MODELS AGREE WITH STRONG
LOW LEVEL COLD ADVECTION PUSHING H7 TEMPS AS LOW AS -20 DEG C BY 12Z
WED PER THE EURO. GIVEN AN AIR MASS THIS COLD...CONFIDENCE IS FAIRLY
HIGH THAT MANY AREAS WILL BE BELOW ZERO FOR LOWS. DID NOT STRAY TOO
FAR AWAY FROM GUIDANCE THOUGH. COOLEST TEMPERATURES ON WED SHOULD BE
FOUND OVER THE MOST SUBSTANTIAL SNOWPACK. GUIDANCE SUGGESTS THE BEST
CHANCE FOR LOW-ELEVATION SIGNIFICANT SNOWFALL EARLY IN THE WEEK WILL
BE WEST OF THE LARAMIE RANGE...SO UNDERCUT MOS BY SEVERAL DEGREES IN
THOSE AREAS. KEPT HIGHS BELOW GUIDANCE ACROSS THE BOARD WITH MUCH OF
THE AREA LIKELY TO RECEIVE ACCUMULATING SNOW IN THE SHORT TERM.

IMPROVING TEMPERATURES LATER IN THE WEEK AS UPPER-LEVEL RIDGING AND
LOW LEVEL DOWNSLOPE RETURN TO THE REGION. A BACK DOOR COLD FRONT IS
PROGGED TO SINK SOUTHWARD ON FRI AFTERNOON...POSSIBLY HAVING A SMALL
IMPACT ON HIGHS WITH COLD ADVECTION ALOFT. CANNOT RULE OUT ISOLATED
RAIN OR SNOW SHOWERS ON FRI NIGHT OR SAT MORNING WITH THE ARRIVAL OF
BETTER MID LEVEL SUPPORT. HOWEVER...KEPT THE FORECAST DRY FOR NOW AS
THIS SYSTEM LOOKS TO BE A BIT MOISTURE STARVED. STILL EXPECT A WINDY
PERIOD FROM WED NIGHT THROUGH FRI OVER THE WIND PRONE AREAS. THE GFS
HAS BEEN CONSISTENT WITH A STRONG H85 CAG-CPR GRADIENT IN EXCESS OF
60 METERS AND 45 TO 50 KT FLOW OVER ARL AND BRX AT H75 THROUGH MUCH
OF THAT TIME PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 515 AM MST SUN MAR 1 2015

SNOW SHOWERS WILL CONTINUE TO DIMINISH THIS MORNING WITH GENERALLY
VFR CONDITIONS PREVAILING. SPORADIC MVFR CIGS ARE POSSIBLE THROUGH
THE MORNING BENEATH A STRATUS DECK AROUND 5K FEET AGL. A COLD FRONT
WILL SWEEP ACROSS THE AREA TONIGHT...BRINGING ANOTHER ROUND OF SNOW
TO AREAS ALONG AND SOUTH OF I80. MVFR TO IFR CIGS/VSBYS ARE LIKELY
AFTER 06Z MON. WINDS WILL GENERALLY BE LIGHT THROUGH THE TAF PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 321 AM MST SUN MAR 1 2015

A WEAK UPPER LEVEL DISTURBANCE WILL PRODUCE LIGHT SNOW EARLY THIS
MORNING OVER FAR SOUTHEAST WYOMING AND SOUTHERN NEBRASKA PANHANDLE.
A LOW PRESSURE SYSTEM AND ASSOCIATED UPPER LEVEL TROUGH WILL APPROACH
FROM THE SOUTHWEST TONIGHT AND MONDAY...AND MOVE ACROSS THE CENTRAL
ROCKIES MONDAY NIGHT AND TUESDAY. SNOW WILL DEVELOP TONIGHT ACROSS
SOUTH CENTRAL WYOMING AND BECOME MORE WIDESPREAD MONDAY AND MONDAY
NIGHT. THE SNOW WILL BE HEAVY AT TIMES...ESPECIALLY OVER THE HIGHER
TERRAIN. THE SNOW WILL TAPER OFF TUESDAY NIGHT. A ARCTIC COLD FRONT
WILL PLUNGE SOUTH THROUGH THE DISTRICT MONDAY NIGHT. BITTERLY COLD
TEMPERATURES AND WIND CHILLS WILL PREVAIL TUESDAY THROUGH WEDNESDAY
BEFORE GRADUALLY MODERATING TEMPERATURES LATE IN THE WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE TUESDAY NIGHT
     FOR WYZ111>114.

NE...NONE.
&&

$$

SHORT TERM...MAJ
LONG TERM...CLH
AVIATION...CLH
FIRE WEATHER...MAJ


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