Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 171724
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1124 AM MDT WED SEP 17 2014

.UPDATE...
ISSUED AT 1056 AM MDT WED SEP 17 2014

A FEW LIGHT SHOWERS CONTINUE TO MOVE DOWNSTREAM OF THE NORTHERN
LARAMIE RANGE THIS MORNING...WHILE A CLUSTER OF SHOWERS WITH A
LIGHTNING STRIKE OR TWO MOVES ACROSS NORTHERN CARBON COUNTY
AHEAD OF A WEAK SHORTWAVE TRAVERSING ACROSS WYOMING. ADDED IN SOME
ISOLATED LOW POPS FOR LATE THIS MORNING AND AFTERNOON TO THESE
AREAS TO FOLLOW CURRENT RADAR TRENDS. ALSO ADDED LOW POPS TO THE
SOUTHERN LARAMIE RANGE AND FOOTHILLS TO ACCOUNT FOR THE PROJECTED
MOVEMENT OF THE SHORTWAVE AND AS WINDS BECOMING UPSLOPE THROUGH
THE AFTERNOON. OTHERWISE...STILL LOOKING AT A VERY WARM DAY WITH
DRY CONDITIONS EXPECTED ELSEWHERE.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY NIGHT)
ISSUED AT 331 AM MDT WED SEP 17 2014

PRETTY QUIET IN THE SHORT TERM WITH WARM TEMPS AND GENERALLY DRY
CONDITIONS. A MID LEVEL RIDGE CENTERED OVER UT/CO WILL DOMINATE THE
PATTERN THROUGH THURSDAY. 700MB TEMPS ARE UP TO 13C BY THIS AFTN
WHICH WILL TRANSLATE INTO HIGHS IN THE MID TO UPPER 80S TO THE
EAST OF THE LARAMIE RANGE. LI VALUES ARE 0C TO -1C DURING THE AFTN
SO EXPECT SCATTERED CUMULUS DEVELOPMENT...PERHAPS A BIT MORE THAN
YESTERDAY. MIN RH VALUES DROP INTO 15-20 PERCENT RANGE OVER
SOUTHEAST WY...HOWEVER WEAK PRESSURE GRADIENTS AND WINDS WILL KEEP
FIRE WEATHER CONCERNS TO A MINIMUM. SFC HIGH PRESSURE BUILDING
OVER THE NORTHERN PLAINS TONIGHT WILL CAUSE WINDS TO GO SOUTH TO
SOUTHEASTERLY OVER THE NEBRASKA PANHANDLE WITH MOISTURE BEING
ADVECTED INTO THE AREA. NAM SOUNDINGS SUGGEST FOG DEVELOPMENT OVER
THE PANHANDLE AND ESPECIALLY THE EASTERNMOST ZONES...SO PUT PATCHY
FOG INTO THE GRIDS.

NOT MUCH CHANGE IN THE SYNOPTIC PATTERN FOR THURSDAY. 700MB TEMPS
ARE A FEW DEGREES WARMER THAN TODAY AND THIS WILL BE THE WARMEST
DAY THROUGH THE PERIOD. SOME LOCATIONS IN THE NEBRASKA PANHANDLE
WILL BE IN THE LOW 90S. AFTN CUMULUS DEVELOPMENT WILL BE MORE
LIMITED THAN TODAY WITH THE RIDGE AXIS OVERHEAD. MODELS SHOW THE
MID LEVEL RIDGE CENTER SHIFTING EASTWARD INTO THE CENTRAL PLAINS
BY FRI. THIS CAUSES THE FLOW ALOFT TO GO MORE SOUTHWESTERLY WITH
A MODEST INCREASE IN 700-500MB MOISTURE. THE MAIN CHANGE WITH THE
MODEL SOLUTION FOR FRI IS THAT THE LATEST RUNS ARE WEAKER WITH THE
SHORTWAVE MOVING FROM MONTANA INTO THE DAKOTAS. THE COLD FRONT
THAT WAS PROGGED TO PUSH ACROSS THE AREA DURING THE DAY ON FRI IS
DELAYED UNTIL FRI EVENING/NIGHT. THUS...TEMPS WILL ONLY BE SLIGHTLY
COOLER THAN THURS. THE GFS AND ECMWF ARE BOTH INDICATING LESS QPF
DURING THE AFTN AND EVENING WITH THE WEAKER AND MORE NORTHERN
SOLUTION OF THE SHORTWAVE. STILL KEPT MAINLY SLIGHT CHANCE TO LOW
END CHANCE POPS ON FRI AFTN WITH THE INCREASE IN MOISTURE.

.LONG TERM...(SATURDAY THROUGH TUESDAY)
ISSUED AT 415 AM MDT WED SEP 17 2014

00Z MEDIUM RANGE MODEL SOLUTIONS ARE FAIRLY SIMILAR WITH THE CWA
WEDGED BETWEEN A UPPER TROUGH TO THE NORTHEAST...SHORTWAVE RIDGE
TO THE SOUTH AND CLOSED LOW OVER CENTRAL/SOUTHERN CA EARLY IN THE
WEEKEND. THE GFS IS TRENDING A BIT SLOWER WITH THE NORTHEASTWARD
PROGRESS OF THE CLOSED LOW INTO THE GREAT BASIN SUNDAY...WITH A
MORE AMPLIFIED DOWNSTREAM RIDGE OVER THE ROCKY MOUNTAINS.

A SURFACE RIDGE WILL EXTEND SOUTH FROM MT INTO NM THIS WEEKEND...
THEN SLIDE EAST INTO THE GREAT PLAINS EARLY NEXT WEEK. A PLUME OF
SUBTROPICAL MOISTURE FROM THE SOUTHWEST WILL SPREAD NORTHEAST INTO
CO AND WY. ISOLATED DIURNAL CONVECTION WILL INITIALLY DEVELOP OVER
THE SOUTHERN MOUNTAINS SATURDAY...BECOMING MORE SCATTERED ACROSS
SOUTHEAST WY SUNDAY. MORE WIDESPREAD CONVECTION WILL DEVELOP SUNDAY
NIGHT AND LINGER THROUGH MONDAY NIGHT AS THE LOW TRACKS ACROSS WY
AND NORTHERN CO. PRECIPITABLE WATER VALUES RISE TO AROUND AN INCH
WITH QPFS BETWEEN 0.25 AND 0.75 INCH. LOW OPENS INTO A SHORTWAVE
TROUGH TUESDAY AS IT ENTERS THE CENTRAL HIGH PLAINS. CONVECTIVE
COVERAGE TAPERS OFF TO MORE ISOLATED TUESDAY AS THE LIFT AND
MOISTURE MOVE SOUTHEAST OF THE CWA.

TEMPERATURES WILL AVERAGE NEAR SEASONAL NORMALS THROUGH THE
EXTENDED...WITH A SLOW COOLING TREND EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 1122 AM MDT WED SEP 17 2014

VFR CONDITIONS ARE EXPECTED TODAY. SHOWERS AND ISOLATED TSTMS ARE A
POSSIBILITY ALONG AND WEST OF THE LARAMIE RANGE AFTER 18Z WED. ADDED
VCTS TO TERMINALS AS FAR EAST AS KCYS. GUSTY AND ERRATIC SFC WINDS
ARE THE PRIMARY HAZARD FROM THIS ACTIVITY GIVEN THE DRY AIR IN THE
LOW LEVELS. SOUTH-TO-SOUTHEAST WINDS WILL BRING AMPLE MOISTURE INTO
THE WESTERN NE PANHANDLE LATE TONIGHT AND EARLY THU. PATCHY FOG AND
LOW CIGS MAY DEVELOP AFTER 09Z AND PERSIST THROUGH 15Z. MOST LIKELY
SITES FOR IFR CIGS OR VSBYS ARE KSNY AND KAIA. KBFF COULD ALSO SEE
SOME LOWER CLOUDS OR MINOR VSBY REDUCTIONS WITH LIGHT UPVALLEY FLOW
AROUND SUNRISE.

&&

.FIRE WEATHER...
ISSUED AT 331 AM MDT WED SEP 17 2014

WARM AND DRY CONDITIONS WILL CONTINUE OVER THE NEXT FEW DAYS.
MINIMUM AFTERNOON HUMIDITY VALUES WILL DROP TO 15 TO 25 PERCENT
OVER MUCH OF THE LOWER ELEVATIONS TODAY AND THURSDAY. WINDS WILL
NOT BE PARTICULARLY STRONG WITH GUSTS GENERALLY LESS THAN 20 MPH
SO NO ELEVATED OR CRITICAL FIRE WEATHER CONDITIONS ARE EXPECTED.
TEMPERATURES WILL BEGIN TO COOL ON FRIDAY BUT MORE SO OVER THE
WEEKEND.

&&

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

$$

UPDATE...RJM
SHORT TERM...FINCH
LONG TERM...JAMSKI
AVIATION...HAMMER
FIRE WEATHER...FINCH





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