Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 020507
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1107 PM MDT SAT AUG 1 2015

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 344 PM MDT SAT AUG 1 2015

CONVECTION HAS DEVELOPED THIS AFTERNOON OFF THE HIGHER TERRAIN...IN
ADDITION TO THE SURFACE TROUGH THAT IS SITUATED ROUGHLY NEAR
CHEYENNE TO CHADRON NEBRASKA. MODERATE INSTABILITY IS IN PLACE
EAST OF THIS AREA WITH DEW POINTS IN THE LOW 50S TO LOW 60S UNDER
FAIRLY STEEP LAPSE RATES. ONE STORM IN SOUTHERN SIOUX COUNTY
PULSED VIGOROUSLY AT TIMES EARLIER THIS AFTERNOON...AND WOULD
EXPECT THIS TO BE THE TREND THROUGH THE REST OF THE AFTERNOON WITH
CONVECTION EAST OF THIS BOUNDARY. DEEP LAYER SHEAR ANALYSIS SHOWS
ROUGHLY 30-40 KTS IN PLACE...SO SOME ORGANIZATION OF CONVECTION IS
POSSIBLE BUT THE MAJORITY OF STORMS WILL REMAIN STRONG IN NATURE
WITH SOME HAIL...GUSTY WINDS AND MODERATE RAINFALL POSSIBLE OUT OF
THE STRONGER ACTIVITY. A WEAK WAVE APPROACHING FROM THE NORTHWEST
COULD KEEP A FEW STORMS GOING THROUGH SUNSET ALONG AND EAST OF THE
LARAMIE RANGE...ESPECIALLY IN AREAS OF OUTFLOW BOUNDARY
INTERACTION SO KEPT ISOLATED POPS FOR THESE AREAS THRU 03Z.
OTHERWISE TONIGHT SHOULD REMAIN DRY AND MILD.

THE SFC BOUNDARY WILL PUSH EAST TONIGHT AS THE WAVE MOVES
OVERHEAD...BUT YET ANOTHER SFC FRONT WILL DROP SOUTH ACROSS THE
PLAINS SUNDAY AFTERNOON. AT THE SAME TIME...A STRONGER SHORTWAVE
APPROACHING FROM THE SOUTHWEST WILL INDUCE STRONGER EAST-
SOUTHEASTERLY WINDS AT THE SFC AND LOW LEVEL MOISTURE ADVECTION
THROUGH THE DAY. THUS...WE ARE ONCE AGAIN EXPECTING ISOLATED
SHOWERS AND THUNDERSTORMS IN THE AFTERNOON FOR THE MOUNTAINS AND
THE WYOMING PLAINS AS THE FRONT PUSHES THROUGH AND WAVE APPROACHES
FROM THE SOUTHWEST. THAT SHORTWAVE WILL MOVE OVERHEAD ON
MONDAY...BRINGING WITH IT A MARKED INCREASE IN MONSOONAL MOISTURE.
PERHAPS WILL SEE SHOWERS/STORMS INITIATE EARLIER IN THE DAY AND
WITH A BROADER COVERAGE OF ACTIVITY ACROSS THE CWA. LOOKING AT
MODERATE TO HEAVY RAINFALL RATES FROM THIS ACTIVITY. WITH THE VERY
DRY ANTECEDENT CONDITIONS WEST OF THE LARAMIE RANGE AND ACROSS
CONVERSE/NIOBRARA COUNTIES...NOT ANTICIPATING ANY SIGNIFICANT
FLOODING ISSUES HERE. AREAS FURTHER SOUTH AND EAST...WILL HAVE TO
WATCH FOR THE POSSIBILITY OF FLASH FLOODING IN AREAS THAT SEE
HEAVIER RAINFALL OVER THE NEXT COUPLE OF DAYS WHICH COULD SATURATE
SOILS.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 344 PM MDT SAT AUG 1 2015

MODELS ARE IN A LITTLE BETTER AGREEMENT TODAY IN THE LONG
TERM...BUT STILL STRUGGLING WITH THE TIMING OF SHORT WAVE ENERGY
EMBEDDED IN THE WEST TO NORTHWEST FLOW ALOFT. ALL MODELS NOW
INDICATE A FLATTER RIDGE COMPARED TO THE LAST FEW DAYS...WITH
WEAK SHORTWAVE DISTURBANCES MOVING ACROSS THE AREA. TUESDAY
APPEARS TO BE FAVORABLE FOR SCATTERED COVERAGE OF SHOWERS AND
TSTORMS THROUGH THE AFTERNOON OVER THE HIGH PLAINS...SO KEPT POP
ON THE HIGH SIDE ALONG AND EAST OF I25. THE GFS AND ECMWF SHOW A
PAIR OF STRONGER DISTURBANCES ON WEDNESDAY AND THURSDAY...AS A
COOL FRONT ACCELERATES SOUTHWARD ACROSS THE HIGH PLAINS BRINGING
COOLER TEMPERATURES TO THE REGION. KEPT POP LOW DURING THE
WEDNESDAY- THURSDAY TIME PERIOD BECAUSE OF THE TIMING OF THE FRONT
AND ASSOCIATED DISTURBANCE ALOFT...WHICH ALL MODELS SHOW MOVING
EAST OF THE FORECAST AREA BY THE AFTERNOON. THIS WOULD PUT MOST OF
SOUTHEAST WYOMING UNDER THE MID LEVEL SUBSIDENCE REGION BEHIND
THE TROUGH AXIS...WHICH IS NOT FAVORABLE FOR WIDESPREAD
CONVECTION. HOWEVER...THIS MAY CHANGE IN THE NEAR FUTURE IF MODEL
SOLUTIONS TREND A BIT MORE PROGRESSIVE. THE GFS AND ECMWF
SOLUTIONS ARE SIMILAR DURING THE MIDDLE OF THE WEEK...BUT THE
ECMWF IS FAR MORE WET...SHOWING LARGE AMOUNTS OF QPF EAST OF I25.

FOR LATE IN THE WEEK AND EARLY NEXT WEEKEND...MODELS ARE IN
REASONABLE AGREEMENT SHOWING AN UPPER LEVEL RIDGE AXIS MOVING
ACROSS THE FRONT RANGE...EXTENDING FROM COLORADO NORTHWARD INTO
SOUTHERN CANADA. ONCE THIS RIDGE AXIS PUSHES A BIT FURTHER
EAST...EXPECT A GREATER COVERAGE OF THUNDERSTORMS BY NEXT WEEKEND
AS SOME MONSOON MOISTURE BEGINS TO ADVECT NORTHWARD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1105 PM MDT SAT AUG 1 2015

BEST CHANCES FOR CONVECTION SHIFTS WEST INTO SOUTHEAST WYOMING
SUNDAY AFTERNOON AS AN UPPER DISTURBANCE APPROACHES FROM THE
WEST. LOOKS LIKE KLAR AND KCYS STAND THE BEST CHANCES FOR TSTMS
DURING THE AFTERNOON HOURS.

&&

.FIRE WEATHER...
ISSUED AT 344 PM MDT SAT AUG 1 2015

HUMIDITIES HAVE DROPPED INTO THE LOW TO MID TEENS THIS AFTERNOON
WEST OF A LINE FROM CHEYENNE- CHADRON. A FEW GUSTS AROUND 20 MPH
ARE OCCURRING ACROSS THIS AREA AS WELL...WITH THE STRONGEST WINDS
IN THE NORTH SNOWY RANGE FOOTHILLS. ISOLATED SHOWERS AND
THUNDERSTORMS DEVELOPED OVER THE HIGH COUNTRY AND ALONG THIS
BOUNDARY...WITH LIGHT RAINFALL LIKELY IN THE MOUNTAINS AND MORE
MODERATE RAINFALL RATES ACROSS THE PLAINS. MONSOONAL MOISTURE WILL
MOVE IN FOR MONDAY AND TUESDAY WITH HIGHER HUMIDITIES AND
INCREASED CHANCES FOR AFTERNOON AND EVENING THUNDERSTORMS. WARMER
AND DRIER WEATHER WILL PREVAIL FOR WEDNESDAY THROUGH FRIDAY.

&&

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

$$

SHORT TERM...RJM
LONG TERM...TJT
AVIATION...GCC
FIRE WEATHER...RJM


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