Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 281002
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
402 AM MDT TUE JUL 28 2015

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 402 AM MDT TUE JUL 28 2015

AN UNSEASONABLY STRONG COLD FRONT CONTINUES TO ADVANCE EAST ACROSS
THE WESTERN NE PANHANDLE EARLY THIS AM. POST-FROPA WINDS HAVE
BEEN RATHER GUSTY WITH EXCELLENT LLVL COLD ADVECTION AND FAVORABLE
SFC PRESSURE RISES (8MB/6HR) SPREADING ACROSS CENTRAL/EASTERN
WYOMING OVER THE LAST SEVERAL HOURS. WIND GUSTS BETWEEN 40 AND 50
MPH WERE COMMON BETWEEN 04Z AND 08Z...BUT WINDS ARE STARTING TO
RELAX A BIT AS MSLP GRADIENTS WEAKEN FROM W-E. THE DEEPEST COLD
AIR STILL LAGS WELL TO THE NORTHWEST OF THE SURFACE FRONT. IN
FACT...THE 07Z LAKE YELLOWSTONE OBSERVATION SHOWED A TEMPERATURE
OF 34 DEGREES. HIGHER ELEVATIONS AT JACKSON HOLE EVEN RECEIVED
ACCUMULATING SNOW WHICH IS NO SURPRISE GIVEN H7 TEMPS WELL BELOW 0
DEG C. FORTUNATELY (OR UN- FORTUNATELY IF YOU ARE HOPING FOR
WINTER)...DO NOT EXPECT THIS TO HAVE AN IMPACT ON OUR CWA AS THE
COLDEST AIR SHOULD SLIDE EASTWARD ALONG THE WY-MT BORDER BEHIND
THE CLOSED LOW AND ATTENDANT NEG TILT MID LVL SHORTWAVE.
HOWEVER...COLD ADVECTION ALOFT WILL CONTINUE FOR MUCH OF THE AREA
THROUGH MID AFTN. H7 TEMPS WILL BE AROUND 10 DEG C COOLER THAN
YESTERDAY...BUT PLENTY OF SUNSHINE AND SUBSIDENCE UNDER CONFLUENT
FLOW ALOFT WILL LIMIT THE OVERALL EFFECT. STILL EXPECT TO SEE
HIGHS AROUND 10-15 DEGREES F COOLER THAN MONDAY.

VERY FEW FORECAST CONCERNS THROUGH THE PERIOD ASIDE FROM CHALLENGES
IN THE FIRE WEATHER REALM FOR TODAY. WE ARE SEEING EXTREMELY POOR RH
RECOVERIES TONIGHT IN FWZ 310 WHERE WINDS HAVE STAYED UP LONGER AND
PROMOTED LLVL MIXING. KCYS HAD AN RH OF 30 PCT AT 08Z...SO THINK WE
WILL BE GETTING CLOSE TO THAT CRITERIA BY EARLY AFTN AS A MUCH DRIER
AIR MASS BECOMES ESTABLISHED POST-FROPA. ALTHOUGH FORECAST SOUNDINGS
FROM ALL MODELS SHOW WINDS ALOFT GRADUALLY WEAKENING...BOTH THE GFS
AND NAM AGREE WITH DEEP MIXING TO AROUND 10K FEET...SO WE WILL MOST
LIKELY SEE AT LEAST OCCASIONAL GUSTS AROUND 25 MPH OR SO. THIS WILL
BE TRICKY THOUGH AS A MODEST MSLP GRADIENT SUGGESTS A VERY MARGINAL
EVENT WITH WEAKER SUSTAINED WINDS. DECIDED AGAINST RED FLAG WARNING
ISSUANCE FOR NOW...BUT WE WILL CONTINUE TO MONITOR. NO OTHER ISSUES
TO SPEAK OF. DO NOT EXPECT ANY CHANCES FOR PCPN OVER THE NEXT 24 TO
48 HOURS WITH H7-H3 RH VALUES LESS THAN 20 PERCENT AND LARGE SCALE
SINKING MOTION. CANNOT RULE OUT SOME CONVECTION OVER THE FAR EASTERN
PLAINS ON THU AFTN ALONG THE SFC TROUGH...BUT ALL SIGNS STILL POINT
TO IT BEING EXTREMELY DRY ALOFT. WILL MAINTAIN SCHC POPS THOUGH AS
THE GFS AND ECMWF BOTH SHOW CAPES AROUND 1500 J/KG ALONG WITH SOME
LIGHT QPF.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 402 AM MDT TUE JUL 28 2015

THURSDAY NIGHT/FRIDAY...RELATIVELY DRY NORTHWEST FLOW ALOFT
CONTINUES. WITH MEAGER LOW AND MID LEVEL MOISTURE...WILL KEEP THE
FORECAST DRY...WHICH MESHES UP WELL WITH OUR SURROUNDING OFFICES.

SATURDAY...MOSTLY DRY WEATHER LOOKS LIKE THE BEST BET AS FLOW ALOFT
STAYS NORTHWEST WITH MINIMAL LOW AND MID LEVEL MOISTURE AND
RELATIVELY WARM MID LEVEL TEMPERATURES...LIKELY ACTING AS A LIMITING
FACTOR FOR THUNDERSTORM INITIATION.

SUNDAY...GREAT BASIN RIDGE ALOFT CONTINUES TO DOMINATE. AGAIN...WITH
MINIMAL LOW AND MID LEVEL MOISTURE...THUNDERSTORM CHANCES APPEAR
QUITE MEAGER.

MONDAY...GFS PROGS SLIGHT INCREASE IN LOW AND MID LEVEL MOISTURE
WHICH MAY HELP TO SPARK ISOLATED THUNDERSTORMS IN THE
AFTERNOON/EVENING HOURS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 402 AM MDT TUE JUL 28 2015

VFR. GUSTY WINDS AFTER DAYBREAK...DECREASING AFTER SUNSET
TONIGHT.

&&

.FIRE WEATHER...
ISSUED AT 402 AM MDT TUE JUL 28 2015

GUSTY WEST TO NORTHWEST WINDS WILL CONTINUE THROUGH THE LATE MORNING
ACROSS MUCH OF THE DISTRICT AND WILL SLOWLY SUBSIDE THROUGH THE DAY.
WINDS MAY DECREASE ENOUGH DURING THE AFTERNOON AT TIME OF LOWEST
AFTERNOON HUMIDITIES TO KEEP FIRE WEATHER CONCERNS MARGINAL...BUT
WILL CLOSELY MONITOR TRENDS DURING THE LATE MORNING ESPECIALLY
ACROSS FIRE WEATHER ZONE 310 WHERE HUMIDITY RECOVERIES OVERNIGHT
HAVE BEEN POOR. HUMIDITIES WILL IMPROVE ACROSS THE PLAINS ON WEDNESDAY
WITH MUCH LESS WIND ACROSS THE DISTRICT.

&&

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

$$

SHORT TERM...CLH
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...RJM



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