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000
FXUS65 KCYS 181829
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1229 PM MDT SAT MAY 18 2013

.UPDATE...

.AVIATION...(FOR THE 18Z TAF ISSUANCE)
ISSUED AT 1229 PM MDT SAT MAY 18 2013

AN UPPER LEVEL DISTURBANCE WILL MOVE OVER THE FORECAST AREA
TODAY AND WILL INITIATE A MORE WIDESPREAD THUNDERSTORM OUTBREAK FOR
THIS AFTERNOON. STORMS ALREADY OCCURRING OVER WESTERN CARBON
COUNTY WILL INCREASE IN COVERAGE TO THE EAST THROUGH THE
AFTERNOON...WITH SOME STORMS OVER THE WESTERN NEBRASKA EXPECTED
EXPECTED TO BECOME SEVERE WITH VERY STRONG DOWNDRAFT WINDS...LARGE
HAIL...AND HEAVY RAIN THE MAIN THREATS AFTER 22Z. STORMS OVER
SOUTHEAST WYOMING WILL ALSO PRODUCE STRONG DOWNDRAFT WINDS ALONG
WITH SMALLER HAIL. MVFR TO BRIEF IFR CONDITIONS WILL LIKELY OCCUR
IN THE STORMS...ESPECIALLY ACROSS THE NEBRASKA SITES. SHOWERS AND
THUNDERSTORMS WILL LINGER INTO TONIGHT ACROSS THE EASTERN HIGH
PLAINS...AND WILL STEADILY DISSIPATE THROUGH THE OVERNIGHT PERIOD.
GUSTY NORTHWEST WINDS WILL THEN OVERSPREAD THE FORECAST AREA EARLY
SUNDAY MORNING...WITH RAIN SHOWERS AND MVFR CIGS EXPECTED IN THE
NORTHERN PANHANDLE.

&&

.SHORT TERM...(TODAY AND SUNDAY NIGHT)
ISSUED AT 351 AM MDT SAT MAY 18 2013

THE LINE OF THUNDERSTORMS WHICH PRODUCED SOME ISOLATED SEVERE
WEATHER OVER THE WESTERN NEBRASKA PANHANDLE FRIDAY EVENING
SHIFTING NORTHEAST OVER THE DAKOTAS AND NORTH CENTRAL NEBRASKA
EARLY THIS MORNING. THE COLD FRONT RESPONSIBLE FOR THIS ACTIVITY
HAS JUST PUSHED ACROSS THE WYOMING/NEBRASKA BORDER...AND IS
EXPECTED TO CONTINUE PUSHING EAST. HOWEVER...MODELS SHOW THIS
FRONT STALLING OVER WEST CENTRAL NEBRASKA TODAY. THIS WILL SET THE
STAGE FOR ANOTHER ROUND OF POTENTIAL SEVERE THUNDERSTORMS THIS
AFTERNOON AND THIS EVENING EAST OF THE LARAMIE RANGE...WITH THE
BEST CHANCE ACROSS WESTERN NEBRASKA DUE TO AMPLE UPPER LEVEL
DYNAMICS...MOISTURE...AND PLENTY OF BL INSTABILITY. CURRENT MODEL
SOUNDINGS FROM SIDNEY TO CHADRON NEBRASKA SHOW LI/S AROUND -7C
WITH CAPE VALUES BETWEEN 1500 TO 2500 J/KG. FURTHER TO THE WEST
ACROSS SOUTHEAST WYOMING...CHANCES OF SEVERE WEATHER ARE LESS BUT
STRONG STORMS ARE POSSIBLE AS A NEGATIVELY TILTED SHORT WAVE
ALOFT LIFT NORTHEAST ACROSS THE AREA. LOCALLY HEAVY
RAINFALL...SMALL HAIL AND GUSTY WINDS ARE POSSIBLE WITH THESE
STORMS ACROSS MOST OF SOUTHEAST WYOMING...ALTHOUGH A FEW
THUNDERSTORMS MAY REACH SEVERE CRITERIA. HIGH TEMPERATURES TODAY
WILL BE 5 TO 10 DEGREES COOLER COMPARED TO FRIDAY...BUT STILL IN
THE 70S AND LOW 80S EAST OF THE LARAMIE RANGE.

FOR SUNDAY...MODELS INDICATE THE MAIN UPPER LEVEL TROUGH AXIS
PUSHING EASTWARD OVER WYOMING...BECOMING A CLOSED LOW AND
EVENTUALLY STALLING OVER THE GREAT PLAINS. WITH LOW TO MIDLEVEL
MOISTURE ADVECTION INTO SOUTHEAST WYOMING...BELIEVE SHOWER
ACTIVITY WILL BECOME WIDESPREAD BY LATE SUNDAY AS A SECONDARY
BOUNDARY PUSHES SOUTHEAST ACROSS THE AREA...WHICH WILL ALSO RESULT
IN TEMPERATURES RETURNING TO NEAR NORMAL OR SLIGHTLY BELOW NORMAL.
LLVL INSTABILITY WILL COMBINE WITH THE COOLER AIR ALOFT TO PRODUCE
ISOLATED TO SCATTERED THUNDERSTORMS. INCREASED TEMPERATURES A FEW
DEGREES ON SUNDAY...MAINLY SINCE THE PRIMARY AREA OF RAIN SHOWERS
WILL BE SLOW TO MOVE INTO THE FORECAST AREA FROM NORTHERN WYOMING.
EXPECT HIGH TEMPERATURES IN THE 50S TO UPPER 60S.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 351 AM MDT SAT MAY 18 2013

THE MAIN CONCERN DURING THIS TIMEFRAME IS HOW MUCH RAIN COVERAGE CAN
BE EXPECTED ON MONDAY AND TUESDAY AND HOW COOL TEMPERATURES WILL BE.

MONDAY AND TUESDAY:
THE MODELS APPEAR TO BE IN GOOD AGREEMENT IN SHOWING THE UPPER LEVEL
LOW CONTINUING TO GET CUTOFF OVER THE NORTHERN PLAINS. THE MODELS
ARE SHOWING PIECES OF ENERGY PIVOTING AROUND THIS LOW OVER PORTIONS
OF SOUTHEAST WYOMING AND THE NEBRASKA PANHANDLE. AS THIS OCCURS...WE
WILL MOST LIKELY SEE PERIODS OF SHOWERS AND ISOLATED THUNDERSTORMS
DEVELOP ACROSS MUCH OF THE AREA...AND MOVE FROM NORTH TO SOUTH. WE
DID TWEAK POPS UP A BIT MONDAY THROUGH TUESDAY MAINLY ACROSS THE
EASTERN THIRD OF FORECAST AREA. THE EXTENSIVE CLOUD COVER SHOULD
ALSO KEEP TEMPERATURES WELL BELOW NORMAL WITH HIGHS MAINLY IN THE
50S WITH SOME LOWER 60S IN THE PANHANDLE. WE DID DROP HIGHS A BIT
FROM THE PREVIOUS SHIFT...AND IT IS POSSIBLE THAT WE MAY HAVE TO
DROP HIGHS EVEN MORE IF WE DO NOT RECEIVE ANY SUNSHINE.

WEDNESDAY:
THERE IS SOME UNCERTAINTY DURING THIS TIME ON FAST THIS SYSTEM WILL
FILL IN AND BEGIN TO SHIFT EAST. THE ENSEMBLES ARE SHOWING SOME
SIGNS OF THE UPPER LEVEL TROF MOVING ON-SHORE ACROSS THE WEST COAST
ON WEDNESDAY. THIS SHOULD ALLOW FOR THE UPPER LEVEL RIDGE TO BUILD
ACROSS THE ROCKIES AND BRING SOME WARMER TEMPERATURES TO THE AREA.
WE PLAYED THINGS CONSERVATIVE FOR NOW AND TWEAKED TEMPERATURES DOWN
A COUPLE OF DEGREES FROM THE PREVIOUS FORECAST SINCE THERE IS STILL
SOME POSSIBILITY THAT SOME SHOWERS MAY LINGER ACROSS THE PANHANDLE.
OTHERWISE...WE MAY SEE A FEW MOUNTAIN SHOWERS...BUT THE STEERING
FLOW APPEARS TO BE FAIRLY WEAK WHICH SHOULD KEEP MOST OF THE
CONVECTION IN THE MOUNTAINS.

THURSDAY-FRIDAY:
THE UPPER LEVEL TROF CONTINUES TO PUSH TOWARDS THE NORTHERN ROCKIES
WHICH SHOULD ALLOW FOR THE GULF MOISTURE TO RETURN TO AREAS EAST OF
THE LARAMIE RANGE. IN FACT...WE COULD SEE DEWPOINTS CLIMB BACK TO
THE 50S BY THE END OF THE NEXT WEEK. THIS COULD SET THE STAGE FOR
AFTERNOON THUNDERSTORMS ACROSS THE MOUNTAINS DURING THE AFTERNOON
WITH SOME OF THESE STORMS POSSIBLE BECOMING STRONG TO SEVERE AS THEY
MOVE OVER THE EASTERN PLAINS. WE WILL CONTINUE TO MONITOR THIS
TROF...BUT IF IT TRACKS A LITTLE FURTHER EAST THAN NORTHWARD...THIS
COULD INCREASE THE SHEAR POTENTIAL.

&&

.FIRE WEATHER...
ISSUED AT 351 AM MDT SAT MAY 18 2013

SURFACE COLD FRONT IS CURRENTLY PUSHING ACROSS THE AREA AND INTO
WESTERN NEBRASKA EARLY THIS MORNING. THIS WILL RESULT IN COOLER
TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK ALONG
WITH HIGHER HUMIDITIES AND A GOOD CHANCE FOR WIDESPREAD WETTING
RAINS EAST OF THE LARAMIE RANGE THIS WEEKEND...WITH THE
POSSIBILITY OF WETTING RAINS WEST OF THE LARAMIE RANGE BY EARLY
NEXT WEEK. FIRE WEATHER CONCERNS ARE MINIMAL THROUGH NEXT
WEDNESDAY DUE TO HIGHER HUMIDITIES AND GREEN FUELS.

&&

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

$$

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