Area Forecast Discussion
Issued by NWS Cheyenne, WY

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508
FXUS65 KCYS 200037
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
637 PM MDT TUE MAY 19 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 252 PM MDT TUE MAY 19 2015

UPPER LEVEL TROUGH AXIS IS CURRENTLY ALONG THE COLORADO BORDER AND
SWINGING NORTHWARD. CLOUD TOPS HAVE WARMED IN AREAS ALONG
INTERSTATE 80 AND THE PRECIPITATION IS BECOMING MORE
SHOWERY/CONVECTIVE IN NATURE. A HEAVIER SHOWER JUST MOVED OVER THE
INTERSTATE 80 SUMMIT WITH SOME SNOW ACCUMULATING BRIEFLY ON THE
ROAD. DECIDED TO CANCEL THE WINTER WEATHER ADVISORY FOR THE
SOUTHERN LARAMIE RANGE AS WIDESPREAD SNOW ACCUMULATION ON ROADS IS
UNLIKELY EXCEPT DURING THE BRIEF HEAVIER SNOW SHOWERS...WHICH ARE
EXPECTED TO BECOME LESS NUMEROUS DURING THE EVENING. MAIN REGION
OF PRECIP WILL SHIFT NORTHWARD INTO THE NORTHERN HALF OF THE CWA
BY LATER THIS EVENING...ALTHOUGH NOT EXPECTING RATES TO BE AS HIGH
AS THIS AFTERNOON. THE COLDEST AIR AT LOWER ELEVATIONS IS
CURRENTLY OVER THE NEBRASKA PANHANDLE WHERE SFC TEMPS ARE 32-35F
AND SNOW IS FALLING. CURRENT THINKING IS THAT LIGHT SNOW WILL
MAINLY ACCUMULATE ON GRASSY SURFACES THROUGH EARLY TONIGHT AS ROAD
TEMPS REMAIN RATHER WARM. LARGE SCALE LIFT REALLY BEGINS TO
DECREASE AFTER 06Z WITH LIGHT SNOW SHOWERS STILL POSSIBLE THROUGH
SUNRISE OVER CONVERSE/NIOBRARA COUNTIES AND INTO THE NORTHERN
PANHANDLE. WITH THE SFC HIGH REMAINING ANCHORED JUST TO THE EAST
OF THE CWA THROUGH THE NIGHT AND EAST TO SOUTHEAST SFC
WINDS...AREAS OF FOG WILL PROBABLY DEVELOP ONCE AGAIN FROM THE
SUMMIT TO CHEYENNE.

IT WILL BE COOL AND CLOUDY AND STABLE OVER THE REGION ON WED. LOW
CLOUDS WILL BE PERSISTENT IN THE LLVL UPSLOPE FLOW TO THE EAST OF
THE LARAMIE RANGE. THE MODELS SHOW ONLY VERY WEAK INSTABILITY OVER
CARBON AND ALBANY COUNTIES...SO WILL KEEP THUNDER OUT OF THE FCST.
WED COULD BE THE ONLY DAY OUT OF THE NEXT FEW WHERE PRECIP IS
ABSENT TO THE EAST OF THE LARAMIE RANGE. TEMPS WARM AROUND 10
DEGREES ON THURS AND SFC DEWPOINTS RISE SOME...SO INSTABILITY WILL
BE QUITE A BIT HIGHER. THE GFS SHOWS CAPE VALUES UP TO 500-750
J/KG ALONG THE LARAMIE RANGE DURING THE AFTN. CONVECTION WILL
STRUGGLE TO PUSH TOO FAR EASTWARD OFF THE LARAMIE RANGE AT THE
AIRMASS BECOMES MORE STABLE.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 252 PM MDT TUE MAY 19 2015

BY FRIDAY WE TREND BACK TO A WETTER PATTERN AS AN UPPER LOW ROLLS
UP OUT OF CALIFORNIA AND CROSSES WYOMING AND WESTERN NEBRASKA
BEFORE OPENING UP AND LIFTING NORTHEAST OF THE AREA. THIS NEXT
SYSTEM OVER THE WEEKEND LOOKS WARMER IN THE MODELS...AND MAIN
CONCERNS WILL BE COVERAGES OF SHOWERS/THUNDERSTORMS FRIDAY THROUGH
SUNDAY AS THE SYSTEM CROSSES THE REGION. THE GFS STILL POINTS TO A
POTENTIAL FOR A FEW SUPERCELLS EAST OF THE LARAMIE RANGE INTO
WESTERN NEBRASKA ON SATURDAY AFTERNOON AS A SURFACE LOW DEEPENS
OVER NORTHEASTERN COLORADO BACKING OF THE LOW LEVEL WINDS AND
INCREASING THE LOW LEVEL SHEAR PROFILES...SOMETHING WE WILL HAVE
TO MONITOR WITH SUBSEQUENT FORECASTS. OVERALL OUR HIGHEST POPS
WILL BE FRIDAY THROUGH SATURDAY WITH LIKELY POPS OVER THE EASTERN
2/3RDS OF THE AREA...AND MOSTLY CHANCE POPS OUT WEST. BY MONDAY WE
TREND POPS BACK DOWN TO SLIGHT CHANCE FOR MOST AREAS AS THE UPPER
SYSTEM LIFTS OUT TO THE NORTHEAST.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 626 PM MDT TUE MAY 19 2015

VERY POOR AVIATION CONDITIONS WILL PERSIST FOR THE FIRST 12-18
HOURS OF THIS TAF CYCLE AS A BROAD AREA OF LOW PRESSURE SPINS
ACROSS THE INTERMOUNTAIN WEST. MOISTURE ASSOCIATED WITH THIS LOW
PRESSURE AREA ALONG WITH LLVL UPSLOPE WILL CONTINUE TO PRODUCE
WIDESPREAD IFR/MVFR CIGS AND VSBYS THRU THE NIGHT. ADDITIONALLY...
POCKETS OF -SN AND -RA CAN CONTINUE TO BE EXPECTED AT LEAST
THROUGH AROUND 06-12Z. EXPECT SOME DRIER AIR TO BEGIN MOVING IN AT
THAT TIME AND SHOULD SEE CONDITIONS BEGIN TO SLOWLY IMPROVE 12-18Z
AND ESPECIALLY AFTER 18Z WEDNESDAY. MOUNTAINS WILL BE OBSCURED
THROUGH AT LEAST 18Z WEDNESDAY.

&&

.FIRE WEATHER...
ISSUED AT 252 PM MDT TUE MAY 19 2015

NO FIRE WEATHER CONCERNS THROUGH THE WEEKEND.  A COOL AND SOMEWHAT
WET PATTERN WILL REMAIN IN PLACE.  RAIN AND SNOW SHOWERS WILL COME
TO AN END BY LATE TONIGHT.  THE NEXT CHANCE OF WIDESPREAD WETTING
PRECIPITATION WILL COME THURSDAY NIGHT AND FRIDAY MORNING.  MINIMUM
AFTERNOON HUMIDITY VALUES WILL GENERALLY BE ABOVE 50 PERCENT.

&&

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

$$

SHORT TERM...ZF
LONG TERM...JG
AVIATION...CAH
FIRE WEATHER...ZF



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