Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 031807
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1108 AM MST TUE MAR 3 2015

.UPDATE...
ISSUED AT 1052 AM MST TUE MAR 3 2015

UPDATED WINTER WEATHER HEADLINES TO CONVERT THE WINTER STORM
WARNING TO AN ADVISORY. SOME POCKETS OF BLOWING SNOW CONTINUE
ALONG WITH SOME LIGHT SNOW SHOWER ACTIVITY THIS MORNING. THE
NORTHERN STREAM DISTURBANCE WHICH IS CURRENTLY OVER WESTERN
WYOMING WILL MOVE EASTWARD TODAY AND TONIGHT BRINING ANOTHER SHOT
OF LIGHT SNOW TO THE FORECAST AREA THIS AFTERNOON AND EVENING.
MOST SNOW ACCUMLUATIONS WILL BE ALONG THE SOUTHERN TIER OF THE
FORECAST AREA WITH 1 TO 2 INCHES OF ACCUMLUATION OUTSIDE OF THE
MOUNTAINS. MOST OF THE FORECAST AREA WILL PICK UP LESS THAN ONE
INCH. WINDS WILL REMAIN ON THE BREEZY SIDE AND WILL PRODUCE SOME
BLOWING AND DRIFTING THIS AFTERNOON AND EVENING.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 520 AM MST TUE MAR 3 2015

HIGH-IMPACT WINTER STORM CONTINUES THIS MORNING FOR A LARGE PART
OF THE CWA. AS EXPECTED...MODERATE TO HEAVY SNOW HAS BECOME QUITE
WIDESPREAD THIS MORNING WITH AN ARCTIC COLD FRONT BLASTING SOUTH
INTO NORTHERN CO. STRONG NORTHERLY WINDS ARE OCCURRING POST FROPA
WITH EXCELLENT MIXING VIA INTENSE COLD ADVECTION ALOFT. PEAK WIND
AT KCYS WAS 42 KTS JUST BEFORE 10Z...AND REMAINS STEADY AT 20 TO
30 MPH AT THIS HOUR WITH VERY LOW VISIBILITY OCCURRING IN FALLING
AND BLOWING SNOW. DO NOT EXPECT MUCH FOR AMOUNTS AS LLVL FORCING
WILL DISAPPEAR QUICKLY...BUT WILL NEED TO MONITOR FOR A POSSIBLE
SHORT FUSED ADVISORY IF HEAVY BANDING PERSISTS INTO THE MORNING
COMMUTE. A WARM DAY YESTERDAY AHEAD OF THE ARCTIC FRONT SET US UP
FOR A FLASH FREEZE...SO ROADWAYS ARE ALREADY QUITE SLICK IN TOWN
HERE THIS MORNING. SUSPECT THIS IS THE CASE AREAWIDE BASED ON THE
ROAD CLOSURES WE HAVE SEEN ALREADY WITH LARGE SECTIONS OF I25 AND
I80 AFFECTED WEST OF LARAMIE AND NORTH OF CHEYENNE.

LATEST WATER VAPOR LOOP SHOWS LARGE SCALE TROUGHING ENCOMPASSING
MUCH OF THE WESTERN CONUS WITH THE LEAD SHORTWAVE NOW EXITING
INTO THE CENTRAL PLAINS. WITH THAT...WE SHOULD CONTINUE TO LOSE
DYNAMIC SUPPORT ASSOCIATED WITH THE 150+ KT H25 JET OVER CENTRAL
NEBRASKA AND WILL HAVE TO RELY ENTIRELY ON LLVL CONVERGENCE AND
FRONTOGENESIS FOR ENHANCED SNOWFALL RATES. SFC COLD FRONT ALREADY
ANALYZED ALONG THE CO/WY BORDER WILL CONTINUE TO MOVE SOUTH ALONG
THE FRONT RANGE...SO EXPECT SNOW TO LIGHTEN UP BEFORE LONG. EVEN
SO...WE SAW SOME HEFTY SNOW RATES OVER PLATTE/NIOBRARA COUNTIES
OVERNIGHT WITH THE INITIAL FRONTAL SURGE. INITIAL CALLS TO AREA
DISPATCHERS INDICATE GENERALLY 3 TO 5 INCHES WITH WINDS CREATING
PROBLEMS. NUMEROUS POWER OUTAGES WERE REPORTED IN NIOBRARA COUNTY
AND INTERSTATE 25 WAS CLOSED IN PLATTE. ADDITIONAL LIGHT ACCUMS
ARE POSSIBLE THROUGH THE MORNING. NAM/GFS SUGGEST WINDS BECOMING
NORTHEASTERLY ALONG THE CENTRAL LARAMIE RANGE BY MID AFTN AS SFC
PRESSURE RISES SPREAD INTO SOUTH CENTRAL NE. DEFINITELY CONCERNED
WITH POTENTIAL UPSLOPE ENHANCEMENT CAUSING SNOW TO REDEVELOP IN
THE AFTN/EVE WITH THE ARRIVAL OF A SECONDARY SHORTWAVE. HRRR IS
HITTING THIS AREA HARD BEYOND 21Z. EVEN THOUGH WINDS WILL MOST
LIKELY BE A NON FACTOR LATER ON...OPTED TO UPGRADE TO A WINTER
STORM WARNING GIVEN OBSERVED IMPACTS AND POTENTIAL FOR AT LEAST
ANOTHER COUPLE INCHES OF SNOW THROUGH TONIGHT.

ALL AREAS SHOULD SEE THE WORST CONDITIONS RIGHT AWAY IN THE AM
WITH THE STRONGEST WINDS OCCURRING THEN. THE MODELS SHOW FLOW
ALOFT WEAKENING CONSIDERABLY AFTER 15Z...SO BLOWING SNOW SHOULD
BECOME LESS OF A PROBLEM WITH TIME. PRECIPITATION COVERAGE WILL
TRANSITION TO SNOW SHOWERS FOR A TIME...BUT ANOTHER SHOT OF PCPN
IS EXPECTED LATE THIS AFTN AND EVE WITH A SECONDARY SHORTWAVE AND
ASSOCIATED MID LEVEL MOISTURE PLUME UPSTREAM OVER EASTERN IDAHO AS
OF 12Z PER MORNING SATELLITE IMAGERY. MIDLVL DRY SLOT HAS PROVEN
TO BE A MAJOR INHIBITOR FOR SNOW SO FAR ALONG THE I80 CORRIDOR
BETWEEN CHEYENNE AND SIDNEY...SO EXPECT THE BEST CHANCES FOR SNOW
LOCALLY TO COME TONIGHT. AMOUNTS WILL PROBABLY BE ON THE LOW SIDE
SO DECIDED AGAINST AN ADVISORY FOR NOW...BUT THE DAY SHIFT WILL
NEED TO REVISIT. KEPT ALL OTHER HEADLINES THE SAME...EXCEPT FOR
EXTENDING THEM THROUGH 07Z WED AS THE NEXT DISTURBANCE WILL KEEP
SNOW POTENTIAL GOING A LITTLE LONGER THAN EARLIER EXPECTED. AS
SNOW ENDS LATE TONIGHT...WINTER HAZARDS WILL TRANSITION TO WIND
CHILLS WITH WIDESPREAD -20F TO -30F READINGS LIKELY. FULLY EXPECT
SOME SORT OF WIND CHILL HEADLINES WILL BE NECESSARY ON THE HEELS
OF THE CURRENT WINTER PRECIPITATION PRODUCTS.

WARMEST TEMPERATURES FOR TODAY OCCURRED OVERNIGHT WITH VERY STRONG
H7 COLD AIR ADVECTION EXPECTED TO DRIVE TEMPERATURES DOWNWARD INTO
THE AFTERNOON. TEMPERATURES WILL FALL BELOW ZERO ACROSS MUCH OF
THE AREA TONIGHT DESPITE WIDESPREAD ABUNDANT MOISTURE ALOFT
LEADING TO THICK CLOUDS AND SNOW GIVEN UNSEASONABLY COLD THERMAL
PROFILES IN THE LLVLS. HIGHS WEDNESDAY SHOULD BE WELL BELOW ANY
CONSENSUS GUIDANCE WITH FRESH SNOWPACK AND 700 MILLIBAR TEMPS
REMAINING VERY COLD / -20C PER THE NAM. SHOULD FINALLY SEE SOME
IMPROVEMENT ON THURSDAY AS WESTERLY DOWNSLOPE WINDS RETURN FOR
AREAS EAST OF THE LARAMIE RANGE...ALLOWING HIGHS TO CLIMB BACK
ABOVE FREEZING.

.LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 520 AM MST TUE MAR 3 2015

PROGRESSIVE NORTHWEST FLOW THRU THE WEEKEND WILL GIVE WAY TO A
BUILDING RIDGE OF HIGH PRESSURE AND A RETURN TO ABOVE AVERAGE
TEMPERATURES FOR EARLY NEXT WEEK. BOTH THE 00Z GFS AND ECMWF
ADVERTISE TWO CLIPPER SHORTWAVES EMBEDDED WITHIN THE FLOW WILL
TRAVERSE SOMEWHERE THRU THE NRN ROCKIES FRIDAY AND SATURDAY. AS IS
TYPICAL IN PROGRESSIVE NORTHWEST FLOW...TIMING AND STRENGTH
DIFFERENCES EXIST IN JUST HOW THESE DISTURBANCES PUSH THRU. EITHER
SCENARIO CARRIES LITTLE IF ANY IMPACTS FROM THESE SYSTEM.
ALTHOUGH...THE DID HAD SOME MOUNTAIN SNOW SHOWER CHANCES ON SUNDAY
WITH THE GFS STEERING ONE OF THE CLIPPERS DIRECTLY OVR THE REGION.
THE NORTHWEST FLOW WILL CONTINUE SUNDAY AND MONDAY...WITH THE RIDGE
AXIS ARRIVING ON TUESDAY. TEMPERATURES WILL HOLD CLOSE TO SEASONAL
LEVELS FRIDAY THROUGH SUNDAY WITH HIGHS GENERALLY REACHING THE 30S
WEST AND 40S OVR THE ERN PLAINS. THE APPROACHING UPPER-RIDGE AND
ASSOCIATED WAA WILL LIFT HIGH TEMPERATURES ABOVE AVERAGE FOR THE
FIRST TIME SINCE THE THIRD WEEK OF FEBRUARY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY MORNING)
ISSUED AT 1108 AM MST TUE MAR 3 2015

FAIRLY WIDESPREAD MVFR CONDITIONS WILL PERSIST OVER THE TERMINALS
THROUGH THIS EVENING WITH SCTD IFR CIGS AND VSBYS IN SNOW.
CONDITIONS SHOULD IMPROVE LATER THIS EVENING AND OVERNIGHT.

&&

.FIRE WEATHER...
ISSUED AT 520 AM MST TUE MAR 3 2015

A WINTER STORM WILL CONTINUE TO IMPACT MUCH OF SOUTHEAST WYOMING
AND THE WESTERN NEBRASKA PANHANDLE THROUGH TONIGHT. SIGNIFICANT
SNOWFALL ACCUMULATIONS ARE LIKELY ALONG WITH STRONG NORTHERLY
WINDS RESULTING IN EXTREMELY DANGEROUS TRAVEL CONDITIONS. VERY
COLD TEMPERATURES ARE EXPECTED TODAY AND TONIGHT WITH WIDESPREAD
DANGEROUS WIND CHILLS POSSIBLE ON EARLY WEDNESDAY MORNING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR
     WYZ101>111-113-115>117.

     WINTER STORM WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ112-114.

NE...WINTER WEATHER ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR NEZ002-
     003-095-096.

&&

$$

UPDATE...SML
SHORT TERM...HAMMER
LONG TERM...HAHN
AVIATION...RE
FIRE WEATHER...HAMMER



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