Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 300838
AFDCYS

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

.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 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1057 PM MDT WED APR 29 2015

MOSTLY CLEAR SKIES AND LIGHT WINDS WILL CONTINUE THROUGH THE
OVERNIGHT PERIOD. A COLD FRONT WILL DROP SOUTH ACROSS THE PLAINS
BEGINNING AFTER SUNRISE THURSDAY WITH WINDS SHIFTING TO THE
NORTH-NORTHWEST AND BECOMING GUSTY AT TIMES WITH THE FRONT. THESE
WINDS WILL THEN SHIFT TO THE NORTHEAST THROUGH THE AFTERNOON AS
THE FRONT SLIDES WESTWARD INTO THE MOUNTAINS...WITH SHOWERS AND
THUNDERSTORMS DEVELOPING OFF THE MOUNTAINS AND MOVING TO THE
NORTHEAST THROUGH THE AFTERNOON AND EVENING. STILL EXPECT THIS
ACTIVITY TO AFFECT WYOMING TERMINALS AFTER 19Z...AND NEBRASKA
LOCATIONS AFTER 00Z FRIDAY.

&&

.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.
&&

$$

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


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