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000
FXUS65 KCYS 231725
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1125 AM MDT THU MAY 23 2013

.UPDATE...
ISSUED AT 1015 AM MDT THU MAY 23 2013

DENSE FOG ADVISORY NOW IN EFFECT UNTIL NOON FOR THE SUMMIT AREA
BETWEEN LARAMIE AND CHEYENNE. WEBCAMS CONTINUE TO SHOW
VISIBILITIES LESS THAN 1/4 MILE. SOUTH TO SOUTHEAST MOIST LOW
LEVEL UPSLOPE FLOW WITH DRY SOUTHWEST FLOW ALOFT CONTINUES TO
REINFORCE THE LOW LEVEL INVERSION IN THIS AREA AND MUCH OF
SOUTHEAST WYOMING. STARTING TO SEE SOME LOW LEVEL HEATING SLOWLY
PUSH CLOUD BASES UPWARDS. THIS TRENDS SHOULD CONTINUE THROUGH THE
AFTERNOON. EXPECTING FOG TO LIFT ACROSS THE AREA BY THIS AFTERNOON
BUT WITH SOUTH TO SOUTHEAST FLOW IN PLACE THAT IS NOT A CERTAINTY.
KNOCKED HIGH TEMPERATURES DOWN A FEW DEGREES WHERE STRATUS IS
EXPECTED TO HOLD IN THE LONGEST...BUT GIVEN THE HIGH SUN ANGLE
THIS TIME OF YEAR IT ONLY TAKES A FEW HOURS FOR TEMPERATURES TO
JUMP BUT STRATUS WILL NEED TO BREAK. CLOUDS HAVE ALREADY CLEARED
OUT AROUND CHADRON AND ALLIANCE AS DRIER AIR WORKS INTO THAT AREA.
NOT SURE HOW MUCH FARTHER THAT CLEARING LINE WILL MAKE IT EAST BUT
THINKING A LINE FROM SCOTTSBLUFF TO SIDNEY SHOULD BE CLOSE.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 426 AM MDT THU MAY 23 2013

A WEAK UPPER WAVE WILL MOVE OVERHEAD TODAY WITHIN A RELATIVELY
DIFFLUENT FLOW PATTERN ALOFT.  DEEPENING SFC LOW PRESSURE OVER
NORTHWESTERN WYOMING UNDER THE DIFFLUENT FLOW WILL MAINTAIN
MODERATE SOUTHERLY WINDS ACROSS THE FORECAST AREA TODAY. SUSTAINED
WINDS WILL LIKELY BE IN THE 25 TO 35 MPH RANGE WITH LOCALLY HIGHER
VALUES IN THE FAR NORTHERN AND WESTERN PORTIONS OF THE FORECAST AREA
WHERE THE GRADIENT WILL BE STRONGEST CLOSER TO THE SFC LOW. FORECAST
SOUNDINGS ACROSS THE AREA SHOW A DRY AND DEEP MIXED LAYER ACROSS
WESTERN CARBON COUNTY...WITH A MUCH MORE SHALLOW BOUNDARY LAYER
ACROSS THE EASTERN PLAINS DUE TO A STRONG INVERSION DEVELOPING AS
RELATIVELY STRONG 700 MB WAA PATTERN SETS UP ALONG AND EAST OF THE
LARAMIE RANGE. LOW CLOUDS AND FOG ACROSS THE EASTERN PLAINS WILL
BE SLOW TO MIX THIS MORNING UNDER THIS INVERSION AND WITH THE
SOUTHEAST UPSLOPE FLOW IN PLACE...BUT WILL BURN OFF EVENTUALLY WITH
HEATING OF THE DAY AND STRONG LLVL MIXING. NOT EXPECTING MUCH IN THE
MEANS OF CONVECTION DUE TO THE DRY AND CAPPED ENVIRONMENT IN SPITE
OF STRONG CONVERGENCE ALONG THE LARAMIE RANGE. MOISTURE AS SEEN ON
WATER VAPOR IMAGERY STREAMING UP FROM THE SOUTHWEST LOOKS RATHER
MARGINAL...SO THERE COULD BE A COUPLE THUNDERSTORMS MAINLY ROOTED
IN THE HIGH TERRAIN AS THE WEAK WAVE AND MOISTURE MOVE OVERHEAD
BUT LIKELY WILL NOT SUSTAIN AS THEY MOVE OFF THE MOUNTAINS.

THE MIXING HEIGHT ACROSS THE PANHANDLE AND SOUTHERN WYOMING
PLAINS LOOKS TO BE ROUGHLY BETWEEN 700 MB AND 750 MB TODAY WITH
WINDS AT THE TOP OF THE LAYER GENERALLY 30 TO 35 KTS. THEREFORE WILL
REFRAIN FROM ANY WIND HIGHLIGHTS ACROSS THE PANHANDLE ALTHOUGH
WIND SPEEDS WILL APPROACH ADVISORY CRITERIA IN THE LATE AFTERNOON.
GUSTS IN THE DEEPER MIXED LAYER FURTHER WEST LOOK TO GENERALLY BE
40 TO 45 KTS THIS AFTERNOON. THEREFORE...OVERALL WINDY DAY IN
STORE FOR THE FORECAST AREA.

CONTINUED SOUTH-SOUTHEASTERLY UPSLOPE FLOW TONIGHT WILL BRING A
RETURN OF LOW CLOUDS AND FOG TO THE EASTERN PLAINS...ALTHOUGH A
COLD FRONT WITH PRE-FRONTAL DRYLINE LOOKS TO MOVE EASTWARD ACROSS
SOUTHEAST WYOMING BETWEEN 07 AND 16Z AND WILL STALL ALONG THE
WY/NE BORDER. DRIER AIR BEHIND THE DRYLINE WILL STEADILY CLEAR
OUT THE LOW CLOUDS AND FOG THROUGH THE MORNING WITH WINDS SHIFTING
TO THE SOUTHWEST BEHIND THE FRONT. THIS WILL ALSO PROVIDE FOCUS
FOR THUNDERSTORM ACTIVITY ALONG THE BOUNDARY FRIDAY AFTERNOON FOR
THE WESTERN NEBRASKA PANHANDLE. WILL STILL BE DEALING WITH WARM
700 MB TEMPS ALOFT SO THE CAP WILL REMAIN RELATIVELY STRONG ACROSS
NEBRASKA...EXCEPT FOR RIGHT ALONG THE BOUNDARY WHERE SOMEWHAT
COOLER AIR ALOFT WILL HELP REDUCE THE CAP THROUGH LATE AFTERNOON.
BULK SHEAR VALUES WILL AVERAGE FROM 40 TO 45 KTS FRIDAY AFTERNOON
ACROSS THE PANHANDLE SO SOME STORMS THAT DO FORM OFF THE STALLED
BOUNDARY COULD BECOME STRONG TO SEVERE...BUT THIS WILL BE VERY
DEPENDENT ON THE STRENGTH OF THE CAP AND WHETHER ENOUGH MOISTURE
ADVECTS INTO THE MIDLEVELS TO DEVELOP STRONG THUNDERSTORMS.

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 426 AM MDT THU MAY 23 2013

THERE IS GENERAL CONSENSUS WITH THE 00Z MEDIUM RANGE MODELS
DEPICTING A MEAN SOUTHWESTERLY FLOW ALOFT OVER THE WESTERN HALF
OF THE CONUS THIS WEEKEND. CLOSED 500MB LOW OVER SOUTHWEST CANADA
AND ASSOCIATED TROUGH AXIS EXTENDING ALONG THE PACIFIC COAST
DRIFTS SLOWLY EAST THIS WEEKEND AND AMPLIFIES OVER THE GREAT BASIN
EARLY NEXT WEEK. THIS WILL BACK THE WINDS ALOFT TO SOUTHERLY FOR
TUESDAY AND WEDNESDAY. THE GFS...ECMWF AND THEIR ENSEMBLES
MAINTAIN A DRYLINE/SURFACE TROUGH OVER THE HIGH PLAINS THROUGH
MONDAY. GREATEST INSTABILITY FOR TSTORM DEVELOPMENT WILL LIE EAST
OF THE DRYLINE...MAINLY FROM THE EASTERN NEBRASKA PANHANDLE INTO
THE GREAT PLAINS. DAYTIME DEW POINTS WILL RISE INTO THE 50S WITH
SBCAPES OF 1500-2000 J/KG. TO THE WEST...MORE ISOLATED HIGH BASED
CONVECTION WILL BE POSSIBLE EACH AFTERNOON.

BY THE MIDDLE OF NEXT WEEK...A CLOSED LOW EMERGES OVER ARIZONA WITH
A GREATER FETCH OF PACIFIC MOISTURE INTO THE REGION. SHORTWAVE
ENERGY MOVING NORTHWARD INTO COLORADO AND WYOMING WILL ENHANCE THE
SHOWER/TSTORM COVERAGE TUESDAY THROUGH WEDNESDAY.

TEMPERATURES WILL AVERAGE ABOUT 5 TO 10 DEGREES ABOVE SEASONAL
NORMAL SATURDAY THROUGH MONDAY...THEN GRADUALLY COOL TO NORMAL
VALUES TUESDAY AND WEDNESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY MORNING)

AREA OF MVFR TO IFR CIGS WILL LIKELY PERSIST THROUGH EARLY FRIDAY
JUST EAST OF THE LARAMIE RANGE...BREAKING FOR A TIME THIS AFTERNOON
OVER THE PANHANDLE BEFORE RETURNING TONIGHT.  FOG...DENSE AT
TIMES...WILL ALSO PERSIST IN THE KCYS VCTY DUE TO MOIST SOUTH WINDS
RIDING UP THE CHEYENNE RIDGE.  A FEW SHOWERS POSSIBLE OVER THE MTNS
THIS AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 426 AM MDT THU MAY 23 2013

MOIST SOUTHEASTERLY UPSLOPE FLOW WILL MAINTAIN LOW CLOUDS...AREAS
OF FOG AND PATCHY DRIZZLE ALONG AND EAST OF THE LARAMIE RANGE THIS
MORNING WITH THE FOG STEADILY BURNING OFF AFTER SUNRISE. MODERATE
SOUTHERLY WINDS WILL OCCUR TODAY ACROSS MUCH OF THE DISTRICT WITH
GUSTS OF 35 TO 45 MPH COMMON ACROSS THE AREA. SOMEWHAT STRONGER
WINDS GUSTING UP TO 50 MPH WILL OCCUR ACROSS ZONE 301...303 AND
304 THIS AFTERNOON. HUMIDITIES WILL REMAIN ABOVE 40 PERCENT ALONG
AND EAST OF THE LARAMIE RANGE TODAY BUT WILL DROP TO THE MID TEENS
TO UPPER 20S OUT WEST. A THUNDERSTORM OR TWO IS POSSIBLE OVER THE
HIGHER MOUNTAINS OF SOUTHEAST WYOMING LATE THIS AFTERNOON AS
WELL. LOW CLOUDS AND FOG WILL RETURN TO THE EASTERN PLAINS OF
WYOMING AND THE WESTERN NEBRASKA PANHANDLE TONIGHT WITH
SOUTHERLY WINDS EASING AND SHIFTING TO THE SOUTHWEST THROUGH
FRIDAY MORNING. MUCH DRIER AND WARMER CONDITIONS WILL OVERSPREAD
SOUTHEAST WYOMING ON FRIDAY...WITH A CHANCE FOR THUNDERSTORMS OVER
THE NEBRASKA PANHANDLE IN THE LATE AFTERNOON.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...DENSE FOG ADVISORY UNTIL NOON MDT TODAY FOR WYZ116-117.

NE...NONE.
&&

$$

UPDATE...LIEBL
SHORT TERM...RJM
LONG TERM...JAMSKI
AVIATION...RE
FIRE WEATHER...RJM