Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 271815
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1215 PM MDT SAT SEP 27 2014

.SHORT TERM...(TODAY AND SUNDAY)
ISSUED AT 340 AM MDT SAT SEP 27 2014

QUIET WEATHER WITH CLEAR SKIES AND RELATIVELY MILD TEMPERATURES
WERE OBSERVED EARLY THIS MORNING ACROSS SOUTHEAST WYOMING AND
WESTERN NEBRASKA AS A RIDGE AXIS ALOFT BEGINS TO DRIFT EAST INTO
THE GREAT PLAINS. CURRENT IR AND WATER VAPOR SATELLITE IMAGERY
SHOWS A DEEP UPPER LEVEL LOW PUSHING ACROSS CENTRAL
CALIFORNIA...WITH THUNDERSTORM ACTIVITY EXTENDING NORTHWARD INTO
SOUTHERN IDAHO AND NORTHERN UTAH. THIS STORM SYSTEM IS EXPECTED TO
PRODUCE WIDESPREAD RAINFALL AND POSSIBLY MOUNTAIN SNOWFALL ACROSS
THE FORECAST AREA THROUGH MONDAY NIGHT. FOR TODAY...ONE MORE WARM
DAY EXPECTED AS THE UPPER LEVEL LOW WILL TEMPORARILY STALL ACROSS
THE WESTERN GREAT BASIN REGION THROUGH TONIGHT. THIS WILL KEEP
MOST OF THE SHOWERS AND ISOLATED TSTORM ACTIVITY FURTHER TO THE
WEST...WHICH MAY CLIP CARBON COUNTY. KEPT POP BETWEEN 20 TO 30
PERCENT WEST OF THE SNOWY RANGE...AND ACTUALLY LOWERED POP ALONG
THE LARAMIE RANGE LATE TODAY AND TONIGHT. HIGHS WILL REMAIN ABOVE
NORMAL WITH AFTERNOON TEMPS IN THE UPPER 70S TO UPPER 80S.

MODELS SHOW THE UPPER LEVEL LOW MOVING VERY LITTLE ON
SUNDAY...BASICALLY REMAINING OVER THE WESTERN GREAT BASIN.
HOWEVER...THE FIRST SHORTWAVE DISTURBANCE IN ASSOCIATION WITH A
95KT JET MAX WILL LIFT NORTHEASTWARD AROUND THE BASE OF THE LOW BY
SUNDAY AFTERNOON. SCATTERED TO NUMEROUS SHOWERS ARE EXPECTED TO
DEVELOP AND PUSH NORTHEAST THROUGH THE DAY WITH ISOLATED
THUNDERSTORMS POSSIBLE. BELIEVE THIS ACTIVITY WILL HOLD OFF UNTIL
LATE SUNDAY EVENING ACROSS WESTERN NEBRASKA DUE TO DRY AIR ALOFT
AND SOME SUBSIDENCE ON THE WESTERN EDGE OF THE UPPER LEVEL RIDGE
ACROSS THE PLAINS. INCREASED POP BETWEEN 60 TO 80 PERCENT ACROSS
SOUTHEAST WYOMING INTO SUNDAY EVENING. SOME OF THE TSTORMS WILL
PRODUCE GUSTY WINDS AND VERY HEAVY RAINFALL. GENERALLY EXPECT
BETWEEN ONE TENTH TO THREE TENTHS OF AN INCH OF RAIN WITH THIS
INITIAL BAND...BUT SOME OF THE HEAVIER SHOWERS MAY PRODUCE OVER
THREE QUARTERS OF AN INCH OF RAIN LOCALLY.

FOR MONDAY...THE MAIN SYSTEM WILL MOVE ACROSS THE CENTRAL ROCKY
MOUNTAINS AND IMPACT THE FORECAST AREA THROUGH MONDAY NIGHT. WILL
HAVE TO CLOSELY MONITOR THIS SYSTEM FOR THE POTENTIAL OF FLASH
FLOODING AND STRONG THUNDERSTORMS...SINCE MODELS INDICATE THE
UPPER LEVEL LOW BECOMING AN OPEN WAVE NEGATIVELY TILTED TROUGH AS
IT MOVES EASTWARD. THE GFS...ECMWF AND NAM ARE IN PRETTY GOOD
AGREEMENT...SHOWING THE POTENTIAL FOR WIDESPREAD MODERATE TO HEAVY
RAINFALL ALONG WITH RAIN CHANGING TO SNOW IN THE MOUNTAINS. THE
GEM GENERALLY STILL SHOWS A CLOSED LOW MONDAY NIGHT...STALLING
ACROSS WYOMING. AFTER A BRIEF LULL MONDAY MORNING WITH MAINLY
DRIZZLE...LOW STRATUS AND PATCHY FOG...SHOWERS AND TSTORMS WILL
QUICKLY DEVELOP AND INCREASE IN COVERAGE DURING THE AFTERNOON.
INCREASED POP BETWEEN 60 TO 75 PERCENT ACROSS MOST OF THE
AREA. TEMPERATURES WILL BE CLOSER TO NORMAL ON MONDAY AND
GENERALLY IN THE 60S ACROSS SOUTHEAST WYOMING AND LOW TO MID 70S
ACROSS WESTERN NEBRASKA.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 330 AM MDT SAT SEP 27 2014

A CHANGE IN THE WEATHER PATTERN WILL MAKE FOR COOLER TEMPERATURES
AND CHANCES FOR PRECIPITATION THROUGH MUCH OF NEXT WEEK. THE UPPER
LEVEL RIDGE WHICH HAS BEEN IN PLACE OVER THE ROCKIES THE LAST
SEVERAL DAYS WILL BE REPLACED BY AN UPPER LEVEL TROUGH. THE MAIN
PIECE OF UPPER LEVEL ENERGY IS FORECAST TO MOVE OVER SOUTHEAST
WYOMING MONDAY NIGHT AND EARLY TUESDAY. SHOWERS AND A FEW
THUNDERSTORMS WILL BE POSSIBLE AS THE WAVE MOVES ACROSS THE AREA.
TEMPERATURES ALOFT WILL GENERALLY BE WARM ENOUGH THAT SNOW WILL NOT
BE MUCH OF A FACTOR...ALTHOUGH THE MOUNTAINS COULD SEE SOME LIGHT
SNOW ACCUMULATIONS WITH A FEW INCHES POSSIBLE BASED ON CURRENT MODEL
RUNS.

SHORTWAVE ENERGY WILL LIFT INTO THE NORTHERN PLAINS LATE TUESDAY AS
A KICKER DROPS OUT OF THE PACIFIC NORTHWEST AND AFTER THAT THE
DETAILS IN THE FORECAST BECOME CONVOLUTED. EXTENDED MODELS ALL HAVE
DIFFERENT IDEAS WITH REGARDS TO TIMING...PLACEMENT AND STRENGTH OF
SHORTWAVE ENERGY TUESDAY THROUGH THURSDAY. SUFFICE IT TO SAY HIGH
TEMPERATURES WILL BE BELOW NORMAL NEXT WEEK WITH THE MEAN UPPER
TROUGH IN PLACE AND NORTHWEST FLOW ALOFT. ISOLATED TO SCATTERED
AFTERNOON RAIN SHOWERS WILL BE POSSIBLE OVER THE PLAINS NEARLY
EVERYDAY AND THERE WILL BE CHANCES FOR LIGHT SNOW ACCUMULATIONS IN
THE MOUNTAINS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY MORNING)
ISSUED AT 1215 PM MDT SAT SEP 27 2014

VFR CONDITIONS TO PREVAIL AT MOST SITES THROUGH THIS UPCOMING
PERIOD. THE EXCEPTION WILL BE AT KRWL...WHERE ISOLATED CONVECTION
WILL PUSH NORTH OFF OF THE SIERRA MADRE RANGE BETWEEN 21-04Z.
SHOULD ALSO SEE SOME LOWER MVFR CIGS PUSH INTO KRWL AFTER 12Z
SUNDAY AS WELL...AS THE LOW PRESSURE AREA APPROACHES. A BETTER
CHANCE FOR SHOWERS AND THUNDERSTORMS WILL ARRIVE JUST BEYOND THIS
PERIOD...SUNDAY AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 227 AM MDT SAT SEP 27 2014

ONE MORE RELATIVELY DRY DAY EXPECTED ON SATURDAY AHEAD OF A STRONG
UPPER LEVEL LOW MOVING ACROSS CALIFORNIA AND NEVADA. SCATTERED
SHOWERS AND ISOLATED THUNDER WILL DEVELOP OVER CARBON THIS
AFTERNOON...BUT IS NOT EXPECTED TO PUSH EAST OF THE SNOWY RANGE
UNTIL SUNDAY AS THE UPPER LEVEL LOW STALLS OVER THE GREAT BASIN
REGION. MINIMAL FIRE WEATHER CONCERNS THROUGH THIS WEEKEND AND
INTO EARLY NEXT WEEK AS COOLER AIR...WIDESPREAD RAIN...AND
MOUNTAIN SNOWFALL IS EXPECTED SUNDAY THROUGH MONDAY NIGHT.
HUMIDITIES WILL TREND HIGHER EACH DAY...WITH DAYTIME MIN HUMIDITIES
BETWEEN 45 TO 60 PERCENT POSSIBLE ON MONDAY.

&&

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

$$

SHORT TERM...TJT
LONG TERM...SML
AVIATION...HAHN
FIRE WEATHER...TJT






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