Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 010956
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
356 AM MDT TUE SEP 1 2015

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 233 AM MDT TUE SEP 1 2015

TODAY...SHORTWAVE RIDGING ALOFT MOVES OVERHEAD THIS AFTERNOON.
MODELS AGREE ON ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS THIS
AFTERNOON OVER SOUTHERN CARBON AND ALBANY COUNTIES OF WYOMING IN LOW
AND MID LEVEL THETA-E RIDGE AXIS...SO ONLY MINOR TWEAKS MADE TO
INHERITED GRIDS. ANOTHER WARM DAY PER PROGGED THICKNESSES.

TONIGHT...ISOLATED STORMS WILL END IN THE EVENING WITH LOSS OF
DAYTIME HEATING.

WEDNESDAY...DRY SOUTHWEST FLOW ALOFT WILL PREVAIL AS THE BEST
MONSOONAL MOISTURE REMAINS OVER COLORADO. STILL THOUGH...850/700 MB
THETA-E RIDGE AXIS AND DIFFERENTIAL HEATING SUGGESTS ISOLATED
AFTERNOON SHOWERS AND THUNDERSTORMS OVER THE SOUTHERN LARAMIE RANGE
BETWEEN LARAMIE AND CHEYENNE...DRY ELSEWHERE.

WEDNESDAY NIGHT/THURSDAY...CONTINUED SOUTHWEST FLOW ALOFT. SURFACE
DRYLINE AND TROUGH DEVELOPS ALONG INTERSTATE 25. DECENT ENOUGH
850/700 MB THETA-E RIDGE AXIS DEVELOPS FOR AT LEAST ISOLATED
THUNDERSTORMS OVER THE SOUTHERN LARAMIE RANGE...DRY ELSEWHERE.

.LONG TERM...(THURSDAY NIGHT THROUGH NEXT MONDAY)
ISSUED AT 233 AM MDT TUE SEP 1 2015

ALL MEDIUM RANGE MODELS INDICATE SOUTHWEST FLOW ALOFT OVER THE
CENTRAL AND SOUTHERN ROCKY MOUNTAINS INTO THE WEEKEND AS A STRONG
STORM SYSTEM FOR THIS TIME OF THE YEAR GRADUALLY MOVES EASTWARD
ACROSS THE PACIFIC NW AND THE NORTHERN GREAT BASIN REGION. THERE
WILL BE A PRETTY STRONG JET STREAM FOR THIS TIME OF THE YEAR OVER
THE AREA...WHICH MAY INFLUENCE THE POTENTIAL FOR DAYTIME
CONVECTION FRIDAY AND SATURDAY. INCREASED POP FRIDAY AND SATURDAY
BETWEEN 20 TO 25 PERCENT ACROSS MOST AREAS OUTSIDE OF THE
MOUNTAINS DUE TO DAYTIME INSTABILITY AND JET DYNAMICS
ALOFT. SOME COOLER AIR ALOFT WILL MOVE INTO THE AREA...BUT DO NOT
SEE A CLEARLY DEFINED COLD FRONT UNTIL LATER IN THE WEEKEND AS THE
UPPER LEVEL TROUGH OR LOW MOVES ACROSS WYOMING. KEPT HIGH
TEMPERATURES IN THE 70S TO MID 80S FRIDAY AND SATURDAY.

THERE IS SOME DISAGREEMENT BETWEEN MODELS ON SUNDAY WITH THE
PASSAGE OF THE UPPER LEVEL FEATURE AND THE SURFACE COLD FRONT. THE
00Z GFS MAINTAINS A NEGATIVELY TILTED OPEN WAVE WHICH LIFTS
NORTHEASTWARD THROUGH THE DAY. THE ECMWF IS MUCH SLOWER AND SHOWS
A CLOSED LOW OVER IDAHO AND WESTERN WYOMING WITH A MUCH MORE
DEFINED...AND STRONG...SURFACE COLD FRONT MOVING ACROSS THE AREA.
THE GEM ON THE OTHER HAND SHOWS THE CLOSED LOW MUCH FURTHER TO THE
WEST WITH WARMER TEMPERATURES OVER THE FORECAST AREA. ENSEMBLE
FORECASTS ALSO INDICATE A WIDE VARIETY OF SOLUTIONS. WITH
RELATIVELY LOW CONFIDENCE ON SUNDAY...KEPT TEMPERATURES NEAR
NORMAL AND GENERALLY IN THE MID 70S TO MID 80S. MOST OF THE
DYNAMIC FORCING WITH THIS STORM SYSTEM APPEARS TO STAY NORTH OF
THE FORECAST AREA REGARDLESS OF THE MODEL IN QUESTION...SO KEPT
POP BETWEEN 10 TO 15 PERCENT.

MODELS ARE IN GOOD AGREEMENT ONCE AGAIN BY EARLY NEXT
WEEK...SHOWING NEAR ZONAL FLOW AND COOLER TEMPERATURES BEHIND THE
COLD FRONT. HIGHS WILL BE NEAR OR SLIGHTLY BELOW NORMAL WITH
GENERALLY DRY CONDITIONS ON MONDAY. PRECIPITATION CHANCES MAY
INCREASE BY THE MIDDLE OF THE WEEK AS THE SUBTROPICAL JET STREAM
BECOMES MORE ACTIVE AND INTERACTS WITH SUBTROPICAL MONSOON
MOISTURE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH TUESDAY NIGHT)
ISSUED AT 233 AM MDT TUE SEP 1 2015

VFR CONDITIONS WILL PREVAIL TODAY WITH RELATIVELY LIGHT WEST TO
SOUTHWEST WINDS. ANOTHER ROUND OF SHOWERS AND TSTORMS ARE EXPECTED
IN THE AFTERNOON AND EVENING HOURS...MAINLY ACROSS SOUTHEAST
WYOMING IN THE AFTERNOON AND EVENTUALLY OVER WESTERN NEBRASKA
TERMINALS IN THE EVENING.

&&

.FIRE WEATHER...
ISSUED AT 233 AM MDT TUE SEP 1 2015

EXPECT AFTERNOON HUMIDITIES UNDER 20 PERCENT TODAY NORTH OF A
DOUGLAS TO CHEYENNE TO CHADRON LINE. FORTUNATELY...WINDS AND WIND
GUSTS WILL BE RELATIVELY LIGHT. THE FIRE WEATHER WATCH FOR LATE
WEDNESDAY MORNING AND AFTERNOON LOOKS ON TRACK OVER OUR NORTHERN
AND WESTERN DISTRICTS WITH HUMIDITIES UNDER 15 PERCENT AND WIND
GUSTS OVER 25 MPH...AND WE EXPECT THE WATCH TO BE UPGRADED TO A
RED FLAG WARNING LATER TODAY. LOW HUMIDITIES CONTINUE ON
THURSDAY... HIGHER HUMIDITIES FRIDAY AND SATURDAY...THEN LOWER
AGAIN FOR SUNDAY THROUGH TUESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
     EVENING FOR WYZ301-302-304-306.

NE...NONE.
&&

$$

SHORT TERM...RUBIN
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...RUBIN


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