Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 120338
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
938 PM MDT THU SEP 11 2014

.UPDATE...
ISSUED AT 909 PM MDT THU SEP 11 2014

LATEST WYDOT WEBCAMS WERE SHOWING SOME ACCUMULATION ON GRASSY
AREAS AROUND DOUGLAS THIS EVENING. WE MADE A FEW PHONE CALLS
ACROSS CONVERSE COUNTY THIS EVENING AND THERE WAS ONE REPORT SOUTH
OF DOUGLAS WITH 3 INCHES. ELSEWHERE...IT APPEARS LIKE AMOUNTS WERE
GENERALLY ONE INCH OR LESS. LATEST IR LOOP WAS SHOWING THE CLOUDS
STARTING TO CLEAR OUT ACROSS NORTHERN WYOMING. LATEST RADAR LOOP
WAS SHOWING FAIRLY NARROW BANDS OF LIFT WITH GOOD INSTABILITY AND
WEAK FRONTOGENISIS IN AREAS EAST OF THE LARAMIE RANGE.
MEANWHILE...IT APPEARS LIKE THE STRONGEST LIFT ASSOCIATED WITH THE
RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET IS STARTING TO EXIT
THE AREA ACCORDING TO THE AIRCRAFT DATA. THIS AREA OF LIFT SHOULD
EXIT SOUTHEAST WYOMING BY MIDNIGHT AND THE NEBRASKA PANHANDLE BY
08Z OR SO. AS A RESULT...WE SHOULD NOT SEE ANYTHING MORE THAN AN
ONE INCH OF ACCUMULATION THIS EVENING DUE TO THE BULK OF THE SNOW
FALLING IN LOWER ELEVATIONS.

THE MODELS ARE HAVING A DIFFICULT TIME WITH CURRENT TEMPERATURE
TRENDS DUE TO SUCH A STRONG DENSE AIR MASS. LOCAL ARW SEEMS TO
HAVE THE BEST HANDLE ON THE CURRENT TRENDS AND CONTINUES TO FILTER
COLDER TEMPS ALONG AND JUST EAST OF THE LARAMIE RANGE.
THEREFORE...WE HAVE DROPPED TEMPERATURES OVERNIGHT A COUPLE OF
DEGREES. WITH THAT IN MIND WE WENT AHEAD AND ISSUED A FREEZE
WARNING FOR THE WESTERN TWO THIRDS OF LARAMIE COUNTY AND VEDAUWOO.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 355 PM MDT THU SEP 11 2014

FROST ADVISORIES AND FREEZE WARNINGS IN EFFECT FOR ALL OF
SOUTHEAST WYOMING AND THE NEBRASKA PANHANDLE. NO HEADLINES FOR THE
MOUNTAINS AS FREEZING TEMPERATURES CAN AND DO OCCUR YEAR ROUND.

AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA TONIGHT
PRODUCING A PERIOD OF SNOW AND DRAGGING UNSEASONABLY COLD AIR
SOUTHWARD. CURRENTLY MAINLY DRIZZLE AND RAIN ACROSS MUCH OF THE AREA
BUT STARTING TO SEE SNOW SPREAD INTO THE NORTHERN CWA. THE COLD
AIR ALOFT WILL QUICKLY SPREAD SOUTHWARD OVER THE NEXT FEW
HOURS...WITH RAIN CHANGING TO SNOW OVER THE SUMMIT AND SNOW
EXPECTED INTO CHEYENNE BY EARLY THIS EVENING. SNOW ACCUMULATIONS
WILL BE MINIMAL FOR MOST OF THE AREA. EXPECTING A FEW INCHES IN
THE NORTHERN LARAMIE RANGE WITH AN INCH OR SNOW OF ACCUMULATION IN
THE SOUTHERN LARAMIE RANGE AND ALONG THE PINE RIDGE. ELSEWHERE
SNOW WILL GENERALLY ONLY STICK ON GRASSY AND ELEVATED SURFACES.
THERE IS THE POTENTIAL FOR A HEAVIER BAND OF FRONTOGENETIC SNOW
LATER THIS EVENING OVER THE SOUTHERN NEBRASKA PANHANDLE AND FAR
SOUTHEAST WYOMING...BUT REALLY MISSING DEEPER INSTABILITY NEEDED
FOR VERY HIGH SNOW RATES. THAT SAID IT IS POSSIBLE FOR A FEW
INCHES OF ACCUMULATION UNDER ANY NARROWER BANDS BUT OVERALL
WEATHER IMPACTS SHOULD STILL BE MINIMAL GIVEN WARM GROUND
TEMPERATURES.

BY LATE TONIGHT THE SYSTEM WILL BE SLIPPING EAST INTO THE PLAINS
WITH SUBSIDENCE SETTING IN ALONG WITH DRYING ALOFT. WITH THE
MODELS TRENDING FASTER WITH THIS SYSTEM...NORTHERN AND WESTERN
PORTIONS OF THE FORECAST ARE EXPECTED TO CLEAR OUT...WHICH WITH
LIGHT WINDS COULD ALLOW TEMPERATURES TO DROP BELOW THE CURRENT
FORECAST...POSSIBLY INTO THE TEENS...IT JUST DEPENDS HOW FAST
THEY CLEAR OUT. FARTHER SOUTH AND EAST CLOUDS SHOULD HOLD IN
THROUGH THE NIGHT SUCH THAT TEMPERATURES WILL GENERALLY REMAIN
NEAR TO ABOVE FREEZING...THUS A FROST ADVISORY AND NOT A FREEZE
WARNING. CLEARING OUT ACROSS THE REMAINDER OF THE AREA THROUGH
FRIDAY MORNING WITH CLEAR TO PARTLY CLOUDY SKIES FOR FRIDAY
AFTERNOON.

.LONG TERM...SATURDAY THROUGH THURSDAY...
PERSISTENT NORTHWEST FLOW WILL PREVAIL THRU THE FIRST HALF OF NEXT
WEEK AS MID/UPPER-LEVEL RIDGE AMPLIFIES ACROSS WRN NOAM. ANY
AVAILABLE MOISTURE WILL BE SHUNTED SOUTH ACROSS THE DESERT
SOUTHWEST...AND ERN PAC SHOWS NO SIGNS OF MUCH AVAILABLE MOISTURE
FROM THAT DIRECTION...AT LEAST UNTIL THE END OF NEXT WEEK. IN THE
MEANTIME...A MUCH MORE TYPICAL DRY AUTUMNAL PATTERN TAKES HOLD THIS
WEEKEND AND EARLY NEXT WEEK. H7 TEMPERATURE PROGS WILL HOVER BETWEEN
10-12C AS WELL...WHICH WILL RESULT IN AFTERNOON HIGH TEMPERATURES
RETURNING TO NR 70 SAT-MON AND PERHAPS CLOSE TO 80 IN SPOTS TUE-THU.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY AFTERNOON)
ISSUED AT 552 PM MDT THU SEP 11 2014

THE MAIN CONCERN THIS EVENING WILL BE HOW THE LONG THE IFR
CONDITIONS WILL LINGER TONIGHT AND HOW MUCH THE SNOW WILL REDUCE
THE VISIBILITY THIS EVENING. LATEST WATER VAPOR IS SHOWING AN
INTENSE UPPER LEVEL WAVE MOVING THROUGH NORTHERN WYOMING AND
SLIDING SOUTHEAST. THIS FEATURE WILL CONTINUE TO SLIDE SOUTHEAST
THIS EVENING AND BRING GOOD LIFT FOR ABOUT 3 TO 4 HOURS THIS
EVENING ACROSS THE CYS...BFF...AIA AND SNY TAF SITES. THE SNOW
WILL TAKE PLACE MAINLY IN THE HIGHER ELEVATIONS ABOVE 5000FT.
BELOW 5000FT IT WILL BE MAINLY A MIX OF RAIN AND SNOW. THIS AREA
OF LIFT SHOULD MOVE OUT OF THE REGION AROUND MIDNIGHT OR SO...BUT
THE IFR CEILINGS SHOULD STICK AROUND OVERNIGHT DUE TO LIMITED
SUBSIDENCE IN THE BOUNDARY LAYER ALONG WITH SOME UPSLOPE
COMPONENT. WE SHOULD BEGIN TO SEE THINGS BEGIN TO CLEAR OUT
TOMORROW MORNING AS BROADER SCALE SUBSIDENCE MOVES INTO THE AREA.


&&

.FIRE WEATHER...
ISSUED AT 355 PM MDT THU SEP 11 2014

QUICK MOVING WINTER LIKE WEATHER SYSTEM WILL MOVE ACROSS THE FORECAST
AREA TONIGHT. SOME LIGHT SNOW ACCUMULATIONS ARE POSSIBLE ALONG THE
PINE RIDGE AND OVER THE LARAMIE RANGE...OTHERWISE MOST SNOW WHICH
OCCURS IN SOUTHEAST WYOMING AND NEBRASKA PANHANDLE WILL MOSTLY MELT
AFTER REACHING THE GROUND. WARMING TREND WILL BEING FRIDAY WITH DRY
WEATHER EXPECTED ACROSS THE FORECAST AREA THROUGH LATE NEXT WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...FREEZE WARNING UNTIL 9 AM MDT FRIDAY FOR WYZ101-102-104>111-113-
     115-116.

     FROST ADVISORY UNTIL 9 AM MDT FRIDAY FOR WYZ117>119.

NE...FREEZE WARNING UNTIL 9 AM MDT FRIDAY FOR NEZ002-095-096.

     FROST ADVISORY UNTIL 9 AM MDT FRIDAY FOR NEZ003-019>021-054-055.

&&

$$

UPDATE...REC
SHORT TERM...SML
LONG TERM...HAHN
AVIATION...REC
FIRE WEATHER...SML





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