Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 152353
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
553 PM MDT TUE APR 15 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 214 PM MDT TUE APR 15 2014

TONIGHT...POSITIVELY TILTED LOW AMPLITUDE SHORTWAVE TROUGH ALOFT
OVER CENTRAL MONTANA AND IDAHO THIS AFTERNOON...WILL MOVE TO EASTERN
WYOMING BY MIDNIGHT...THEN TO CENTRAL NEBRASKA BY DAWN. ITS
ASSOCIATED COLD FRONT WILL ENTER OUR WESTERN COUNTIES THIS
EVENING...EXTENDING FROM SURFACE LOW PRESSURE OVER SOUTH CENTRAL
SOUTH DAKOTA...AND THE PACIFIC ORIGIN COLD FRONT WILL CLEAR OUR
COUNTIES BY DAWN. DEEPER MOISTURE AND DYNAMICS WILL AFFECT OUR
NORTHERN COUNTIES CLOSER TO WHERE THE DEEPER SHORTWAVE TROUGH
MOISTURE AND DYNAMICS COEXIST...ALONG WITH SCATTERED OROGRAPHIC
SHOWERS OVER THE SNOWY AND SIERRA MADRE RANGES.

WINDS COULD BE A CHALLENGE AFTER MIDNIGHT...IN THE SUBSIDENCE SECTOR
OF THE SHORTWAVE TROUGH ALOFT...AS THE 500-300 MB AND 700-500 MB
LAYERS SHOW DOWNWARD VERTICAL MOTION ON THE QUASIGEOSTROPHIC
FORCING...SO OUR EVENING AND MIDNIGHT SHIFT TEAMS WILL NEED TO
CLOSELY MONITOR THE POSSIBILITY FOR LOCALIZED WINDS APPROACHING 50
TO 60 MPH AFTER MIDNIGHT IN OUR TYPICALLY WIND PRONE LOCATIONS OF
ARLINGTON...BORDEAUX AND VEDAUWOO.

WEDNESDAY...COLDER AIR WILL CONTINUE TO FILTER IN DURING THE DAY IN
THE WAKE OF THE SHORTWAVE TROUGH ALOFT PASSAGE...AND WITH THE
DEEPEST MOISTURE AND DYNAMIC LIFT OVER OUR NORTHERN COUNTIES...HAVE
PAINTED 30 TO 50 PERCENT AFTERNOON POPS...LESSER TO THE SOUTH.

WEDNESDAY NIGHT...IN CONTRAST TO YESTERDAYS MODEL RUNS...LIFT AND
MOISTURE WILL BE CONSIDERABLY LESS THAN PREVIOUSLY EXPECTED...THUS
ONLY SOME LOW TOKEN POPS NEAR DEEPER MOISTURE AND LIFT OVER OUR
SNOWY AND SIERRA MADRE RANGES NEAR THE COLORADO AND WYOMING STATE
LINES. AREAS OF FOG ON TAP LATE NIGHT FROM LUSK TO CHADRON AND
ALLIANCE...AND FROM LARAMIE TO CHEYENNE...WHERE BOUNDARY LAYER PROGS
SHOW HUMIDITIES ABOVE 80 PERCENT.

THURSDAY...NORTHWEST FLOW PREVAILS OVER OUR COUNTIES DOWNWIND OF THE
GREAT BASIN UPPER RIDGE AXIS. WITH MINIMAL LOW AND MID LEVEL
MOISTURE...AND LIMITED LIFT...NO PRECIPITATION EXPECTED.

THURSDAY NIGHT...RIDGING ALOFT TRANSITIONS OVER THE ROCKIES AND OVER
WYOMING...INDUCING RETURN SOUTH FLOW OVER OUR COUNTIES...WITH LOW
LEVEL MOISTURE LIKELY ADVECTING NORTHWARD TOWARDS OUR COUNTIES FROM
TEXAS AND WESTERN KANSAS. LOW LEVEL BOUNDARY WILL LIE FROM LUSK TO
CHADRON AND WE MAY SEE LOW CLOUD AND FOG DEVELOPMENT NORTH OF THIS
BOUNDARY AS SUGGESTED BY THE NAM BOUNDARY LAYER PROGS.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 315 PM MDT TUE APR 15 2014

MODELS ARE IN GOOD AGREEMENT GOING INTO THE WEEKEND...BUT POOR RUN
TO RUN CONSISTENCY RESULTING IN LIMITED CONFIDENCE WITH THE LONG
RANGE FORECAST AND ESPECIALLY THE EXTENDED. MODELS ARE TRENDING
FURTHER NORTH AND MORE PROGRESSIVE WITH THE COLD FRONT ON SATURDAY
AS THE SOUTHERN JET IS PLACED FURTHER NORTH. THEREFORE...WINDY
CONDITIONS ARE LESS LIKELY ON FRIDAY AS THE FRONT BRUSHES THE
AREA. AS AN UPPER LEVEL TROUGH ASSOCIATED WITH THE SOUTHERN JET
EJECTS NORTHEAST ACROSS THE SOUTHWEST UNITED STATES AND SOUTHERN
ROCKY MOUNTAINS FRIDAY...SHOWERS AND TSTORMS ARE POSSIBLE SATURDAY
AFTERNOON AND EVENING. PRETTY GOOD AGREEMENT WITH THIS
SOLUTION...SO INCREASED POP ALONG I80 INTO SATURDAY EVENING FOR
SCATTERED SHOWERS AND ISOLATED THUNDER. TEMPERATURES WILL REMAIN
NEAR OR SLIGHTLY ABOVE NORMAL...GENERALLY IN THE 50S AND 60S.

GFS CONTINUES TO SHOW A STRONG RIDGE ALOFT DEVELOPING ACROSS THE
WEST INTO EARLY NEXT WEEK...BUT THIS TIME ALONG THE SPINE OF THE
ROCKY MOUNTAINS AND INTO THE GREAT PLAINS. WHILE THE ECMWF SHOWS
NEARLY ZONAL FLOW AS ANOTHER PACIFIC STORM SYSTEM PUSHES ONSHORE
ACROSS THE PACIFIC NORTHWEST COASTLINE. THE GFS IS MORE AMPLIFIED
AS WELL...WITH THIS SAME STORM CONSIDERABLY FURTHER SOUTH ALONG
THE SOUTHERN CALIF COASTLINE. PRETTY CONFIDENT THAT THE FORECAST
AREA WILL SEE A SIGNIFICANT WARM UP...SO INCREASED TEMPERATURES
WELL ABOVE NORMAL. KEPT POP BELOW 15 PERCENT FOR NOW ON MONDAY AND
TUESDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY AFTERNOON)
ISSUED AT 535 PM MDT TUE APR 15 2014

THE MAIN CONCERN WITH THIS TAF ISSUANCE IS THE POTENTIAL FOR A
BORA TYPE WIND EVENT POSSIBLY DEVELOPING OVER SOME OF OUR TAF
SITES OVERNIGHT INTO WEDNESDAY MORNING.

LATEST WATER VAPOR LOOP WAS SHOWING A VORT LOBE OF ENERGY
APPROACHING NORTHWEST WYOMING. WE WILL HAVE TO KEEP AN EYE ON THE
WIND FIELDS ACROSS WESTERN WYOMING THIS EVENING AS THIS FEATURE
PASSES THROUGH. THE DRIER AIR ALOFT IN COMBINATION WITH STRONG
SUBSIDENCE WILL FAVOR FOR THOSE HIGHER WIND SPEEDS ALOFT TO REACH
THE SURFACE MAINLY AFTER MIDNIGHT. NOT SURE EXACTLY WHICH TAF
SITES WILL BE IMPACTED THE MOST AT THIS TIME...BUT BASED ON
CURRENT SATELLITE TRENDS IT MAY APPROACH THE LARAMIE AND CHEYENNE
TAF SITES BETWEEN 09Z AND 12Z. FOR NOW...WE WILL PLAY THINGS
CONSERVATIVE ON THE WIND SPEED BEFORE 12Z...BUT AFTER DAYBREAK
THINGS WINDS SHOULD PICKUP FAIRLY QUICKLY FOR A 2 TO 4 HOUR
TIMEFRAME WITH WEST-NORTHWEST WINDS INCREASING TO SPEEDS UP TO
40KTS.

THE PRECIPITATION CHANCES ARE NOT LOOKING THAT GREAT AT THIS TIME
ACROSS CDR AND AIA TAF SITES...BUT THEY COULD EXPERIENCE A PERIOD
OR TWO OF LIGHT RAIN/SNOW MIX ALONG WITH MVFR CONDITIONS AFTER 06Z.



&&

.FIRE WEATHER...
NO FIRE WEATHER CONCERNS THROUGH THURSDAY WITH A
COLD FRONTAL PASSAGE TONIGHT...BRINGING COOLER TEMPERATURES AND
HIGHER AFTERNOON HUMIDITIES. HUMIDITIES WILL BEGIN TO LOWER FRIDAY
INTO THE 20 TO 30 PERCENT IN THE AFTERNOON AS SURFACE LEE TROUGHING
DEVELOPS...WITH SOME RECOVERY ON SATURDAY...AND 20 TO 30 PERCENT
AFTERNOON HUMIDITIES ON EASTER SUNDAY AS RIDGING ALOFT KEEPS OUR
WEATHER DRY WITH RELATIVELY LIGHT WINDS SUNDAY THROUGH TUESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

SHORT TERM...RUBIN
LONG TERM...TJT
AVIATION...REC
FIRE WEATHER...RUBIN






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