Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 282114
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
314 PM MDT THU AUG 28 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 313 PM MDT THU AUG 28 2014

LIGHT TO MODERATE RAIN HAS BEEN ONGOING FOR MUCH OF THE DAY ACROSS
SOUTHEAST WY AND THE WESTERN NE PANHANDLE. THIS IS OCCURRING ON THE
BACK SIDE OF A VIGOROUS MIDLVL SHORTWAVE CURRENTLY EXITING THE AREA
TO THE EAST OVER NE. WIDESPREAD CLOUDS/PCPN HAS WREAKED HAVOC ON THE
FCST TODAY WITH TEMPS ONLY IN THE 50S AT LAR AND CYS. AFTN RADAR AND
SATELLITE IMAGERY SHOWS THIS ACTIVITY HAS DECREASED IN COVERAGE AS
OF 20Z...AND BELIEVE THIS TREND SHOULD CONTINUE THROUGH THE EARLY
EVE HOURS AS BETTER UPPER-LEVEL SUPPORT SHIFTS TO THE EAST AND IS
REPLACED BY SUBSIDENCE BENEATH A SHORTWAVE RIDGE AXIS. VISIBLE SAT
INDICATES SKIES ARE CLEARING OVER OUR WESTERN ZONES...SO EXPECT A
QUIET OVERNIGHT PERIOD FOR THE MOST PART WITH MORE CLOUDS OVER THE
PANHANDLE. RAIN SHOULD END COMPLETELY BY 03-06Z FRI. WENT A LITTLE
WARMER FOR LOWS TONIGHT FARTHER EAST WHERE RADIATIONAL COOLING WILL
BE LESS.

WARMING TREND ENSUES FOR FRI WITH BROAD UPPER-LEVEL RIDGING IN PLACE
OVER THE CWA. ECMWF H7 TEMPS INCREASE TO 10-12 DEG C ON FRI...SO IT
SHOULD BE QUITE A BIT WARMER WITH DRY/SUBSIDING CONDITIONS IN PLACE
ACROSS THE AREA AND NO MAJOR INHIBITING FACTORS FOR SOME DECENT SFC
HEATING. A QUICK SHOT OF MIDLVL MOISTURE WITH A WEAK WAVE TRAVERSING
THE FLOW SHOULD PRODUCE ISOLATED SHOWERS AND STORMS...GENERALLY IN
THE AFTN. GFS INSTABILITY PARAMETERS ARE UNIMPRESSIVE WITH LIS ONLY
AROUND -1 TO -2C AND LESS THAN 500 J/KG SBCAPE. CONVECTION ON FRI
SHOULD BE GARDEN VARIETY. SAT WILL BE THE WARMEST DAY OF THE PERIOD
AHEAD OF A MORE SIGNIFICANT SHORTWAVE MOVING ACROSS THE PAC NW. MID
LEVEL LAPSE RATES AROUND 8-9 DEG C/KM SUGGEST BETTER INSTABILITY ON
SAT...BETTER OVER THE PANHANDLE WHERE SURFACE CAPES MAY APPROACH
1000 J/KG. INCREASED POPS FOR SAT AFTN AND EVE WITH EXCELLENT MODEL
AGREEMENT BETWEEN THE GFS/NAM/ECMWF WITH INCREASING 700-500 MILLIBAR
QG ASCENT. GOOD CONVERGENCE ALONG THE COLD FRONT WILL HELP GENERATE
CONVECTION AS WELL. COLD FRONT BLASTS ACROSS THE CWA ON SAT AFTN AND
EARLY EVE...ENHANCING PCPN CHANCES AND SETTING THE STAGE FOR A COOL
START TO THE EXTENDED PERIOD. IT WILL BE BREEZY AS WELL WITH 35 KTS
OF FLOW AT H7...ESPECIALLY ALONG AND WEST OF THE LARAMIE RANGE ON
SAT AFTN.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 313 PM MDT THU AUG 28 2014

A RELATIVELY COOL AND UNSETTLED END OF THE WEEKEND EXPECTED AS AN
UPPER TROUGH AND ASSOCIATED SFC FRONT MOVES THRU. THE ECMWF IS
6-12 HOURS QUICKER WITH FROPA MOVING IT THRU AT THE END OF THE
PREVIOUS PERIOD. COMPARATIVELY...THE GFS HOLDS IT BACK UNTIL LATER
SUNDAY. IN EITHER CASE...EXPECT AT LEAST SOME CONVECTIVE
DEVELOPMENT SUNDAY...WITH BEST COVERAGE DURING THE LATE AFTERNOON
AND OVR THE NRN NEBRASKA PANHANDLE. TROUGH AXIS WILL CLEAR THE
AREA SUNDAY NIGHT AND WHEN COMBINED WITH NIGHTTIME STABILIZATION
WILL BRING AN END TO SHOWER/THUNDERSTORM CHANCES BY NIGHTFALL.
ANOTHER FAST MOVING SHORTWAVE WILL TRACK ACROSS THE AREA AGAIN ON
MONDAY. THERE MAY BE JUST ENOUGH MOISTURE/INSTABILITY TO INITIATE
AN ISOLATED SHOWER/STORM LATE MONDAY AFTERNOON OR EARLY MONDAY
EVENING EAST OF A CHADRON TO ALLIANCE LINE. A MUCH DRIER AIR MASS
WILL ADVECT IN TUE-THU ALLOWING A LLVL THERMAL RIDGE TO AMPLIFY.
THE RESULT WILL BE FOR DRY AND WARMER CONDITIONS. SUNDAY WILL BE
THE COOLEST DAY OF THE PERIOD IN THE COOL POST-FRONTAL AIR MASS.
PROGD H7 TEMPS ONLY REACH AROUND 8C...WHICH WILL KEEP AFTERNOON
TEMPS IN THE 60S AND 70S. H7 TEMPS WILL RETURN TO 12-16C FOR MON-
THU...BRINGING HIGH TEMPS BACK WELL INTO THE 70S WEST AND 80S TO
NR 90S EAST BY WED-THU.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY MORNING)
ISSUED AT 1228 PM MDT THU AUG 28 2014

MAIN AVIATION CONCERNS TODAY WILL BE THE TIMING AND STRENGTH AS
BAND OF WRAP-AROUND RAIN SHOWERS AND EMBEDDED THUNDERSTORMS IMPACT
AREA TERMINALS. AT NOON...THIS BAND EXTENDED FROM NR KCDR/KAIA
SOUTHWEST TO KLAR. MVFR/IFR CIGS AND VSBS HAVE BEEN COMMON BENEATH
THIS AREA OF RAIN. IT WILL SLIDE EAST ACROSS THE KCYS...KBFF AND
KSNY THROUGH THE REST OF THE AFTERNOON. ALTHOUGH THE AREA HAS BEEN
FAIRLY COOL BENEATH THICK CLOUD-COVER...MAY SEE A FEW WEAK
EMBEDDED THUNDERSTORMS THIS AFTERNOON AS WELL. THIS BAND OF PRECIP
WILL SHIFT EAST OF ALL SITES BY 00Z...LEAVING CLEARING SKIES AND
VFR CONDITIONS THRU THE REMAINDER OF THE PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 313 PM MDT THU AUG 28 2014

NO MAJOR FIRE WEATHER CONCERNS OVER THE NEXT FEW DAYS. THE WEATHER
SYSTEM RESPONSIBLE FOR THE RECENT RAINFALL WILL MOVE TO THE EAST OF
THE AREA TONIGHT...GIVING WAY TO A GRADUAL WARMING TREND ON FRI AND
SAT. MINIMUM RELATIVE HUMIDITY VALUES WILL BE IN THE UPPER TEENS OR
LOW 20S FOR WESTERN ZONES. AFTERNOON SHOWERS AND THUNDERSTORMS MAY
PRODUCE GUSTY AND ERRATIC WINDS THROUGH THE REST OF THE WEEK...BUT
IN GENERAL STRONG STORMS ARE NOT EXPECTED. A STRONG COLD FRONT WILL
MOVE FROM WEST TO EAST ACROSS THE AREA ON SAT AFTN...GIVING WAY TO
BREEZY CONDITIONS WITH WIND GUSTS UP TO 40 MPH OVER PARTS OF CARBON
COUNTY. COOLER TEMPERATURES WILL FOLLOW FOR SUN.

&&

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

&&

$$

SHORT TERM...HAMMER
LONG TERM...HAHN
AVIATION...HAHN
FIRE WEATHER...HAMMER





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