Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 050917
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
317 AM MDT WED AUG 5 2015

.SHORT TERM...(TODAY THROUGH THURSDAY NIGHT)
ISSUED AT 300 AM MDT WED AUG 5 2015

THE MAIN CONCERN WITH THIS PORTION OF THE FORECAST IS THE
CONVECTION POTENTIAL THIS AFTERNOON/EVENING AND CRITICAL FIRE
CONDITIONS ON THURSDAY.

TODAY-TONIGHT:
LATEST WATER VAPOR LOOP WAS SHOWING TWO DISTINCT SHORTWAVES
MOVING THROUGH THE WEST. ONE OF THE WAVES WAS MOVING THROUGH
SOUTHWEST MONTANA WHILE THE OTHER ONE WAS MOVING THROUGH NEVADA.
LATEST RADAR LOOP WAS SHOWING A FEW LIGHT SHOWERS IN NORTHWEST
WYOMING IN RESPONSE TO THE SHORTWAVE IN SOUTHWEST MONTANA. NOT
EXPECTING THE SHOWER ACTIVITY FROM THE WAVE IN MONTANA TO AFFECT
OUR CWFA TODAY. HOWEVER...WE ARE EXPECTING MORE OF A RESPONSE TO
THE SECONDARY WAVE MOVING OUT OF NEVADA. THIS FEATURE WILL INDUCE
GOOD UPPER LEVEL DIFFLUENCE OVER THE AREA TODAY. AS A RESULT...WE
COULD START SEEING A FEW SHOWERS AND THUNDERSTORMS DEVELOP IN
CARBON COUNTY BY LATE MORNING.

THERE IS ALSO A GOOD SIGNAL FOR OROGRAPHIC THUNDERSTORMS IN THE
SIERRA...SNOWY AND LARAMIE RANGES BY MIDDAY. THE INITIAL
CONVECTION DEVELOPMENT OVER THE MOUNTAINS DOES NOT APPEAR TO VERY
STRONG. HOWEVER...AS THIS CONVECTION STEERS EAST WOULD NOT BE
SURPRISED TO SEE THIS CONVECTION STRENGTHEN AS THEY ENCOUNTER
BETTER SHEAR AND INSTABILITY ESPECIALLY IN THE NEBRASKA PANHANDLE.
IN ADDITION...CANNOT RULE A FEW STRONG TO SEVERE STORMS IN
CONVERSE AND NIOBRARA COUNTIES WHERE THE UPPER LEVEL WAVE WILL BE
PRESENT. THE BULK OF THE CONVECTION SHOULD MOVE OUT OF THE REGION
BY LATE THIS EVENING AS THIS UPPER LEVEL WAVE MOVES INTO THE
NORTHERN PLAINS.

THURSDAY-THURSDAY NIGHT:
DECENT SUBSIDENCE IS PROGGED TO MOVE INTO THE AREA ON THURSDAY
WHICH WILL YIELD IN DOWNSLOPE FLOW AND MUCH DRIER CONDITIONS.
BASED ON THESE FACTORS WE RAISED TEMPERATURES TWO TO THREE DEGREES
FROM THE BLENDS. GOOD MIXING WILL ALSO PRODUCE GUSTY WEST WINDS
WHICH MAY CERTAINLY IMPACT ANY ONGOING FIRES.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 300 AM MDT WED AUG 5 2015

THE 00Z MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT WITH THEIR MASS
FIELDS. THE CENTER OF THE UPPER RIDGE THAT WAS SITUATED OVER THE
SOUTHERN ROCKY MOUNTAINS WILL SHIFT EAST AND BECOME STATIONARY
OVER THE SOUTHERN GREAT PLAINS. MEANWHILE...A CLOSED PACIFIC LOW
MOVING ASHORE INTO NORTHERN CA EARLY FRIDAY WILL TRANSITION TO A
TROUGH AS IT TRACKS NORTHEAST ACROSS THE GREAT BASIN AND NORTHERN
ROCKY MOUNTAINS AND GREAT PLAINS THIS WEEKEND. AS THE TROUGH
PASSES NORTHWEST OF THE CWA...THE PLUME OF SUBTROPICAL MOISTURE
WILL BRING INCREASING CHANCES OF SHOWERS/TSTORMS FRIDAY NIGHT AND
SATURDAY. TSTORMS MAY LINGER OVER WESTERN NE SATURDAY NIGHT WITH
DRIER CONDITIONS FORECAST ACROSS SOUTHEAST WY. SUNDAY INTO THE
EARLY PART OF THE WORK WEEK WILL MAINLY BE DRY AND WARM AS THE
UPPER RIDGE REBUILDS OVER THE ROCKY MOUNTAINS. THE MODELS DO
HINT AT SOME SUBTROPICAL MOISTURE TRAPPED UNDER THE RIDGE FOR
ISOLATED AFTERNOON/EARLY EVENING CONVECTION...ESPECIALLY OVER THE
SOUTHEAST WY MOUNTAINS. CANNOT RULE OUT POSSIBILITY OF A FEW
TSTORMS DRIFTING EAST ONTO THE ADJACENT PLAINS. TEMPERATURES FOR
THE MOST PART WILL AVERAGE SLIGHTLY ABOVE SEASONAL NORMALS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 300 AM MDT WED AUG 5 2015

PATCHY FOG AND LOW CIGS PRODUCING MVFR TO IFR RESTRICTIONS WILL
CONTINUE THROUGH 15Z ACROSS PORTIONS OF EAST CENTRAL WY INTO THE
WESTERN NE PANHANDLE...WITH VFR CONDITIONS RESUMING THEREAFTER.
EXPECT ISOLATED TSTORMS TO DEVELOP WEST OF THE LARAMIE RANGE BY
18Z THEN GRADUALLY INCREASE IN COVERAGE AS THEY MOVE EASTWARD ONTO
THE PLAINS THIS AFTERNOON AND EARLY EVENING. THE MAIN HAZARDS WILL
BE GUSTY/ERRATIC WINDS...SMALL HAIL AND BRIEF PERIODS OF MVFR
VSBY.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MDT WED AUG 5 2015

DRIER AIR WILL START INFILTRATING CARBON COUNTY LATE THIS AFTERNOON.
THIS WILL HELP INCREASE THE MIXING POTENTIAL WHICH MAY YIELD TO
GUSTY SOUTHWEST WINDS AT 30 TO 35 MPH. MINIMUM RELATIVE HUMIDITIES
MAY DROP BELOW 20 PERCENT LATE IN THE DAY. THE BIGGER CONCERN FOR
CRITICAL FIRE WEATHER CONDITIONS IS ON THURSDAY AS DEEP LEVEL
MIXING COMMENCES. WE DID CONSIDER A FIRE WEATHER WATCH...BUT THERE
IS STILL SOME CONCERN ON HOW LOW THE RELATIVE HUMIDITIES COULD DROP.
FOR NOW...WE WILL SEE HOW THE CURRENT WILDFIRES EVOLVE THROUGH THE
DAY AND WATCH THE WESTERN HALF OF THE AREA TO SEE HOW MUCH DRYING
TAKES PLACE THIS AFTERNOON.

&&

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

$$

SHORT TERM...REC
LONG TERM...MAJ
AVIATION...MAJ
FIRE WEATHER...REC


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