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000
FXUS65 KCYS 151154
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
554 AM MDT SAT JUN 15 2013

.UPDATE...
ISSUED AT 554 AM MDT SAT JUN 15 2013

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 554 AM MDT SAT JUN 15 2013

MVFR CIGS ARE STEADILY EXPANDING IN COVERAGE ACROSS THE EASTERN
PLAINS AND WILL AFFECT KCYS...KBFF...AND KSNY THROUGH MIDMORNING.
EXPECTING KCYS CIGS TO ACTUALLY DROP TO IFR ONCE WINDS VEER TO THE
NORTHEAST AFTER 13Z. SHOWERS AND THUNDERSTORMS WILL INCREASE IN
COVERAGE LATE THIS AFTERNOON AS A WEATHER DISTURBANCE APPROACHES
OVERHEAD FROM THE SOUTHWEST. BEST POTENTIAL FOR CONVECTION WILL
REMAIN ALONG AND JUST EAST OF THE LARAMIE RANGE...IN ADDITION TO
LOCATIONS NEAR THE COLORADO BORDER. CONDITIONS SHOULD REMAIN DRY
OUT WEST...WITH BREEZY SOUTHWEST WINDS EXPECTED THIS AFTERNOON.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 500 AM MDT SAT JUN 15 2013

SHOWERS AND THUNDERSTORMS HAVE MOVED WELL TO THE EAST OF THE CWA AT
THIS HOUR WITH A MID LAYER STRATUS DECK DEVELOPING OVER CONVERSE AND
NIOBRARA COUNTIES AND BEGINNING TO EXPAND SOUTHWARD. A MORE
NORTHWEST FETCH OFF THE SOUTHERN LARAMIE RANGE COULD KEEP THE LOW
CLOUDS AND FOG FROM DEVELOPING HERE...BUT GUIDANCE CONTINUES TO SHOW
THE DEVELOPMENT OF AT LEAST LOW STRATUS CLOSER TO SUNRISE SO WILL
KEEP MENTION IN THE FORECAST THROUGH MID MORNING.

THE MAIN STORY FOR TODAY WILL BE THE POSSIBILITY FOR SEVERE WEATHER
THIS AFTERNOON. IF THE LOW STRATUS DECK MATERIALIZES...IT WILL
DIMINISH OVERALL POTENTIAL FOR THUNDERSTORMS AND SEVERE WEATHER DUE
TO REDUCED SURFACE HEATING. HOWEVER...A WEAK SHORTWAVE MOVING
OVERHEAD IN THE AFTERNOON WILL INDUCE STRONG CONVERGENCE ALONG THE
LARAMIE RANGE...SO THERE WILL LIKELY BE INITIATION HERE EARLY
AFTERNOON WITH STORMS MOVING EAST INTO THE EASTERN PLAINS. NAM AND
GFS INDICATE THE CHEYENNE RIDGE WILL SEE A WEAKER CAP OVER
THIS HIGHER TERRAIN FEATURE BY LATE AFTERNOON...SO ANY STORMS THAT
DO MOVE INTO THIS AREA WILL HAVE A BETTER CHANCE OF STRENGTHENING
WITH OVER 1000 J/KG OF CAPE AND 45 TO 55 KT OF DEEP SHEAR PROGGED
IN THIS AREA. FURTHER TO THE NORTH AND EAST...FORECAST SOUNDINGS
SHOW A STRONGER CAP IN PLACE SO ANY STORMS THAT MOVE INTO THIS
REGION WILL STRUGGLE TO MAINTAIN. THEREFORE WILL KEEP THE FOCUS FOR
SEVERE POTENTIAL ESSENTIALLY FROM THE SOUTHERN LARAMIE RANGE EAST
INTO THE SOUTHERN NEBRASKA PANHANDLE. LARGE HAIL AND DAMAGING WINDS
WILL BE THE MAIN THREAT...ALTHOUGH LOW LCLS PROGGED ALONG THE
CHEYENNE RIDGE WITH INCREASING LOW LEVEL SHEAR AFTER 00Z COULD
INCREASE CHANCES FOR AN ISOLATED TORNADO AS WELL. CONFIDENCE IS
LOW IN THIS HAPPENING...BUT CANNOT BE COMPLETELY RULED OUT.

FOR SUNDAY...ANOTHER SHORTWAVE MOVING UP FROM THE SOUTHWEST WILL
COMBINE WITH A WAVE MOVING DOWN FROM CANADA TO BRING MORE WIDESPREAD
CHANCES FOR SHOWERS AND THUNDERSTORMS TO THE FORECAST AREA. A FRONT
ASSOCIATED WITH THE NORTHERN WAVE WILL MOVE SOUTH ACROSS THE EASTERN
PLAINS THROUGH THE AFTERNOON PROVIDING FOCUS FOR CONVECTIVE
INITIATION. SFC TEMPERATURES WILL ALSO BE WARMER AS THE THERMAL
RIDGE AXIS MOVES OVERHEAD WHICH WILL INCREASE INSTABILITY ACROSS THE
FORECAST AREA AND DIMINISH THE CAP. DEEP LAYER SHEAR WILL REMAIN
AROUND 40 TO 50 KT...SO THE THREAT FOR SEVERE WEATHER WILL
ENCOMPASS A LARGER PORTION OF THE EASTERN PLAINS BUT THE MAIN FOCUS
LOOKS TO BE IN THE NEBRASKA PANHANDLE WHERE UPWARDS OF 2000 J/KG OF
CAPE IS FORECAST HERE IN THE AFTERNOON. SOUNDINGS SHOW LCL HEIGHTS
AROUND 10KFT...SO EXPECTING LARGE HAIL AND DAMAGING WINDS TO ONCE
AGAIN BE THE MAIN THREATS.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 430 AM MDT SAT JUN 15 2013

THERE IS NOT MUCH DIFFERENCE BETWEEN THE 14/18Z AND 15/00Z MODELS...SO
CONFIDENCE IS MODERATE TO HIGH WITH THEIR SOLUTIONS. A UPPER RIDGE AXIS
NEAR THE CONTINENTAL DIVIDE MONDAY AMPLIFIES AS IT MOVES ALONG AND EAST
OF THE FRONT RANGE TUESDAY AND WEDNESDAY IN RESPONSE TO A DIGGING UPPER
TROUGH ALONG THE PACIFIC COAST. THIS TROUGH WILL MOVE EASTWARD THROUGH
THE GREAT BASIN FOR THE LATTER HALF OF THE WEEK.

WITH REGARDS TO SENSIBLE WEATHER...LEE SURFACE TROUGH OR DRY LINE WILL
BE THE PRIMARY FOCUSING MECHANISM FOR DIURNAL CONVECTION DURING THE
HALF OF THE WEEK. MOIST UPSLOPE SOUTHEASTERLY FLOW WITH DEW POINTS
IN THE 50S WILL EXTEND ALONG AND EAST OF THE LARAMIE RANGE. SHORTWAVE
ENERGY ALOFT WILL ROUND THE RIDGE ACROSS WYOMING AND COLORADO MONDAY
AFTERNOON AND EVENING. A LOW LEVEL THETA-E RIDGE WILL EXTEND FROM THE
NORTHEAST COLORADO PLAINS INTO EAST CENTRAL WYOMING...WITH SBCAPES
OF 1500-2000 J/KG. SCATTERED TSTORMS WILL FORM OVER THE LARAMIE RANGE
EARLY MONDAY AFTERNOON AND INTENSIFY AS THEY MOVE INTO THE MORE
UNSTABLE ENVIRONMENT ON THE PLAINS BY LATE MONDAY AFTERNOON. THE SPC
DAY3 OUTLOOK DEPICTS A SLIGHT RISK OF SEVERE TSTORMS FROM THE CENTRAL
AND SOUTHERN LARAMIE RANGE EAST ACROSS THE SOUTHEAST WYOMING PLAINS
AND SOUTHWEST NEBRASKA PANHANDLE. THE PRIMARY THREATS WOULD BE DAMAGING
WIND GUSTS AND LARGE HAIL. THE TSTORMS WILL DECREASE IN COVERAGE AND
INTENSITY LATE MONDAY EVENING.

TUESDAY`S SETUP FOR DIURNAL CONVECTION WILL BE SIMILAR TO MONDAY...
WITH MORE SCATTERED COVERAGE SHIFTING EAST INTO THE WESTERN NEBRASKA
PANHANDLE. INSTABILITY PARAMETERS APPEAR FAVORABLE FOR STRONG TO
SEVERE TSTORMS FROM MID AFTERNOON THROUGH LATE EVENING. WEDNESDAY...
A PACIFIC COLD FRONT WILL EXTEND FROM LOW PRESSURE IN WESTERN MONTANA
TO ANOTHER LOW IN EASTERN IDAHO THROUGH WESTERN UTAH AND SOUTHERN
NEVADA. THE SURFACE DRY LINE/TROUGH WILL SHIFT EAST OF THE NEBRASKA
PANHANDLE WEDNESDAY AFTERNOON. DRIER SOUTHWESTERLY FLOW AT THE SURFACE
AND ALOFT WILL RESULT IN WARMER TEMPERATURES.

THE FRONT WILL MOVE EAST ACROSS SOUTHEAST WYOMING AND WESTERN NEBRASKA
THURSDAY AFTERNOON AND EVENING. MOST OF THE CWFA WILL REMAIN CAPPED
FOR TSTORM DEVELOPMENT...EXCEPT AREA NORTH OF A LINE FROM LUSK TO
ALLIANCE. THIS SAME AREA MAY EXPERIENCE A FEW AFTERNOON AND EVENING
TSTORMS FRIDAY AS A WEAK UPPER LEVEL SHORTWAVE MOVES SOUTHEAST ACROSS
THE WESTERN DAKOTAS AND NORTHEAST WYOMING.

TEMPERATURES MONDAY AND TUESDAY WILL BE NEAR SEASONAL NORMALS...THEN
WARM TO ABOVE SEASONAL NORMALS FOR THE LATTER HALF OF THE WEEK. EXPECT
BREEZY WEST TO SOUTHWEST WINDS FROM LATE MORNING THROUGH EARLY EVENING
EACH DAY ALONG AND WEST OF THE LARAMIE RANGE.

&&

.FIRE WEATHER...
ISSUED AT 500 AM MDT SAT JUN 15 2013

A WEAK WEATHER DISTURBANCE WILL MOVE ACROSS THE DISTRICT LATE THIS
AFTERNOON AND EVENING AND WILL SPARK OFF ISOLATED TO SCATTERED SHOWERS
AND THUNDERSTORMS THROUGH THIS TIME. THE BEST CHANCE FOR THUNDERSTORMS
WILL BE ALONG AND EAST OF THE LARAMIE RANGE...WHILE MOSTLY DRY AND
BREEZY CONDITIONS WILL OCCUR OUT WEST IN THE MOUNTAINS. HUMIDITIES
LOOK TO DROP TO BETWEEN 8 AND 18 PERCENT ACROSS CARBON AND ALBANY
COUNTIES THIS AFTERNOON...WITH WEST WINDS GUSTING 20 TO 25 MPH. A FEW
STORMS WILL BECOME SEVERE FROM THE SOUTHERN LARAMIE RANGE IN WYOMING
EAST INTO THE SOUTHERN NEBRASKA PANHANDLE...WITH STRONG DOWNDRAFT
WINDS...LARGE HAIL...AND BRIEF HEAVY RAINFALL EXPECTED. MORE WIDESPREAD
SHOWERS AND THUNDERSTORMS WILL OCCUR ON SUNDAY.

&&

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

$$

UPDATE...RJM
SHORT TERM...RJM
LONG TERM...JAMSKI
AVIATION...RJM
FIRE WEATHER...RJM