Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 301556
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
956 AM MDT THU APR 30 2015

.UPDATE...
ISSUED AT 955 AM MDT THU APR 30 2015

TODAYS FORECAST LOOKS TO BE RIGHT ON TRACK. SUNNY SKIES THIS
MORNING WILL GIVE WAY TO SHOWERS AND ISOLATED THUNDERSTORM
ACTIVITY THIS AFTERNOON AND EVENING...PARTICULARLY INTO SOUTHERN
PORTIONS OF THE FORECAST AREA. THE MAIN FOCUS FOR SHOWERS AND
THUNDERSTORMS WILL BE NEAR A MIDLEVEL FRONTAL BOUNDARY WHICH WILL
HANG UP NEAR THE INTERSTATE 80 CORRIDOR THIS AFTERNOON AND
EVENING. RELATIVELY COOL AND STABLE AIR WILL BE FOUND FARTHER
NORTH...MAKING CONVECTION LESS OF A CONCERN. WILL KEEP AN EYE ON
CAPE VALUES THIS AFTERNOON...BUT THERE ARE BIG DIFFERENCES AMONGST
MODELS WITH THE NAM SHOWING 1000-1500 J/KG CAPE. THIS APPEARS TO
BE A BIT TOO HIGH WHICH SEEMS TO BE COMMON IN THE NAM OUTPUT. THE
GFS AND RUC SEEM MORE REASONABLE AROUND 500 J/KG OR LESS THIS
AFTERNOON. REGARDLESS...NOT EXPECTING SEVERE THUNDERSTORMS WITH
ANY CHANCE FOR SEVERE THUNDERSTORMS VERY LOW. GENERALLY LOOKING
FOR GARDEN VARIETY THUNDERSTORMS WITH SMALL HAIL AND GUSTY WINDS
POSSIBLE WITH A FEW STRONGER THUNDERSTORMS.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 230 AM MDT THU APR 30 2015

UPPER RIDGE AXIS SHIFTING EAST OF THE CWA THIS MORNING WITH AN
UPPER SHORTWAVE MOVING EAST OVER THE NW PART OF THE COUNTRY. THIS
SYSTEM WILL PROGRESS RATHER QUICKLY EAST THROUGH THIS EVENING AND
PUSH A COLD FRONT ACROSS THE CWA BY LATE THIS AFTERNOON. UPSLOPE
FLOW AND SOME INSTABILITY WILL ALLOW FOR SCTD SHOWERS AND A FEW
TSTRMS TO DEVELOP OVER SE WY THIS AFTERNOON WITH ACTIVITY
PROGRESSING EAST ACROSS THE PANHANDLE THIS EVENING. A NARROW BAND
OF DECENT CAPE PROGGED THIS AFTERNOON OVER THE SRN PANHANDLE AND
FAR SE WY WITH VALUES FROM ABOUT 500-1000J/KG SO A STRONGER STORM
OR TWO NOT OUT OF THE QUESTION. ACTIVITY SHOULD END LATER THIS
EVENING AS A SFC HIGH SETTLES DOWN THE HIGH PLAINS AND INSTABILITY
FALLS OFF. ZONAL UPPER FLOW THEN SETS UP OVER THE CWA FRIDAY
THROUGH SATURDAY WITH SEVERAL RIPPLES IN THIS FLOW. SHOULD SEE
SOME CONVECTION FIRE MAINLY OVER THE SRN MTNS FRIDAY AFTERNOON
THEN GREATER COVERAGE OF ACTIVITY SATURDAY AFTERNOON. TEMPS MILD
THROUGH THE PERIOD.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 230 AM MDT THU APR 30 2015

UNSETTLED WEATHER LOOKS LIKELY IN THE LONG TERM AS A VERY SLOW
MOVING UPPER LOW MOVES THROUGH THE AREA.

AFTERNOON CONVECTION COULD STILL BE ONGOING SATURDAY EVENING ALONG
THE I-80 CORRIDOR FROM CHEYENNE TO RAWLINS. CONVECTION FORECAST TO
COME TO AN END THOUGH TOWARDS MIDNIGHT.

GUIDANCE STILL SHOWS A BOUNDARY LAYING ALONG THE LARAMIE RANGE
SUNDAY AND THIS WILL BE THE FOCUSING MECHANISM FOR MORE WIDESPREAD
SHOWERS AND THUNDERSTORMS SUNDAY AFTERNOON. SOME DIFFERENCES
BETWEEN THE GFS AND ECMWF ON LOCATION OF THE CONVECTION. GFS
FOCUSING ON AREAS EAST OF THE LARAMIE RANGE WHILE ECMWF
CONCENTRATING ON AREAS WEST. TENDING TOWARDS THE ECMWF SOLUTION
AND CONCENTRATED HIGHER POPS WEST.

WEAK UPPER TROUGH MOVES THROUGH SUNDAY NIGHT INTO MONDAY MORNING SHOULD
MOVE CONVECTION EAST INTO THE PANHANDLE OVERNIGHT. BUT CONVECTION
BLOSSOMS AGAIN OVER SOUTHEAST WYOMING MONDAY AFTERNOON AS ANOTHER
PIECE OF ENERGY SPINS OFF A LOW OVER THE DESERT SOUTHWEST. SURFACE
HIGH PRESSURE OVER THE DAKOTAS WILL GIVE US A FAVORABLE SOUTHEAST
UPSLOPE FLOW THAT WILL ENHANCE SHOWERS EAST OF THE LARAMIE RANGE.
BOTH THE GFS AND ECMWF SHOW POSSIBILITY OF HEAVY RAIN OVER THE
SOUTHERN PANHANDLE INTO THE CHEYENNE AREA MONDAY EVENING.

BY TUESDAY...UPPER LOW FORECAST TO BE MOVING INTO SOUTHWESTERN
COLORADO. A 60KT JET FINGER IN A FAVORABLE LOCATION FOR SOUTHEAST
WYOMING AND NEBRASKA PANHANDLE TO SEE THE POSSIBILITY OF SOME
SEVER THUNDERSTORMS TUESDAY. SOMETHING THAT WILL BECOME CLEARER AS
WE CLOSER TO THE EVENT.

LOW FORECAST TO MOVE INTO EASTERN COLORADO WEDNESDAY. SHOULD SEE
WIDESPREAD SHOWERS/THUNDERSTORMS DURING THE DAY WEDNESDAY. GOOD
NEWS IS THAT BOTH GFS AND ECMWF ARE KEEPING WARM TEMPERATURES AT
700MBS...AROUND +6C...SO PRECIP WILL FALL AS LIQUID AND NOT AS
SNOW.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 528 AM MDT THU APR 30 2015

FIRST OFF...DO BELIEVE WE ARE HAVING ISSUES WITH THE KCYS
VISIBILITY SENSOR THIS MORNING. WILL HAVE TECHNICIANS CHECK IT OUT
WHEN THEY COME IN. VISIBILITY HERE AT KCYS IS IN GOOD SHAPE.

VFR CONDITIONS MOST OF THE DAY TODAY FOR ALL SOUTHEAST WYOMING
AND NEBRASKA PANHANDLE AIRPORTS. COLD FRONT STILL ON TRACK TO MOVE
INTO THE AREA FROM WEST TO EAST THIS AFTERNOON...SO COULD BE
LOOKING AT SHOWERS AND THUNDERSTORMS BEGINNING AT KRWL SHORTLY
AFTER 19Z. SREF GUIDANCE SHOWING LOWERING CONDITIONS HERE AT KCYS
AFTER 06Z WITH NORTHEAST UPSLOPE WINDS BEHIND THE FRONT. STARTED
TRENDING KCYS DOWN TO ACCOUNT FOR THIS.


&&

.FIRE WEATHER...
ISSUED AT 230 AM MDT THU APR 30 2015

A COOL FRONT WILL PASS ACROSS THE DISTRICTS TODAY BRINGING A
NORTHERLY WIND SWITCH AND SCATTERED SHOWERS AND A FEW TSTRMS THIS
AFTERNOON INTO THIS EVENING. CONCERNS LOW OVERALL THROUGH THE
UPCOMING WEEKEND WITH NON-CRITICAL WEATHER CONDITIONS AND GREENING
FUELS.

&&

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

&&

$$

UPDATE...SML
SHORT TERM...RE
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...RE



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