Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 021823
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1223 PM MDT SAT MAY 2 2015

.UPDATE...

ISSUED AT 1025 AM MDT SAT MAY 2 2015

SUNNY SKIES WILL GIVE WAY TO SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS OVER MUCH OF SOUTHEAST WYOMING THIS AFTERNOON.
ACTIVITY WILL FIRST FORM WEST OF THE LARAMIE RANGE EARLY THIS
AFTERNOON AND THEN SPILL EASTWARD INTO THE PLAINS LATER IN THE
AFTERNOON AND EARLY EVENING. EAST CENTRAL WYOMING AND THE
NORTHERN NEBRASKA PANHANDLE WILL LIKELY STAY ON THE DRY SIDE WITH
MOST SHOWER AND THUNDERSTORM ACTIVITY REMAINING TO THE SOUTH.
SEVERE THUNDERSTORM POTENTIAL IS VERY LOW TODAY. A FEW STORMS WILL
LIKELY PRODUCE GUSTY WINDS AND SMALL HAIL BUT VERY MINIMAL CHANCE
FOR LARGER HAIL.

&&

.SHORT TERM...(TODAY THROUGH MONDAY NIGHT)
ISSUED AT 245 AM MDT SAT MAY 2 2015

FORECAST CHALLENGES DEAL WITH PRECIP CHANCES THROUGH THE SHORT
TERM.

CURRENTLY...WATER VAPOR IMAGERY CONTINUES TO SHOW AN AREA OF LOW
PRESSURE OVER THE DESERT SOUTHWEST THIS MORNING. CONVECTION HAS
PRETTY MUCH COME TO AN END AND MOSAIC RADAR ACROSS WYOMING AND
COLORADO. AT THE SURFACE...WE ARE SEEING ANOTHER COLD FRONT
PUSHING INTO THE PACNW.

FOR TODAY...INITIALLY DRY THIS MORNING. GUIDANCE GENERALLY AGREES
THAT CONVECTION WILL BEGIN BREAKING OUT ACROSS SOUTHERN WYOMING
AFTER 18Z. BEST CHANCES APPEAR TO BE ALONG AND SOUTH OF THE I-80
CORRIDOR FROM CHEYENNE TO RAWLINS AND HAVE OUR HIGHEST POP
FORECAST FOR THIS AREA. NAM...AND TO A LESSER EXTENT THE ECMWF HAS
SOME LIGHT PRECIP CHANCES FURTHER NORTH...SO WILL KEEP SOME LOW
CHANCE POPS GOING FOR NORTH OF I-80 FOR THIS AFTERNOON.

LESS UNSTABLE TODAY OVER FRIDAY AND SEE THE STORM PREDICTION
CENTER HAS MOVED THEIR MARGINAL RISK AREA FURTHER EAST TODAY
ACROSS CENTRAL NEBRASKA...SO DO FEEL CONFIDENT THAT SEVERE
THUNDERSTORMS WILL NOT BE AN ISSUE TODAY.

CONVECTION PICKS UP AGAIN SUNDAY AFTERNOON AND BECOMES A LITTLE
MORE WIDESPREAD...ESPECIALLY WEST OF THE LARAMIE RANGE AS THE
SURFACE FRONT MOVES TO NEAR THE WYOMING/COLORADO LINE. AREAS EAST
OF THE LARAMIE RANGE WILL SEE UPSLOPING EASTERLY TO NORTHEASTERLY
WINDS THAT COULD AID IN OROGRAPHIC CONVECTION ALONG THIS SIDE OF
THE LARAMIE RANGE. DO GET A PIECE OF ENERGY OFF THE DESERT
SOUTHWEST UPPER LOW THAT TRACKS ACROSS NORTHEAST COLORADO SUNDAY
EVENING.

BETTER CHANCES FOR MORE WIDESPREAD SHOWERS AND THUNDERSTORMS
MONDAY AS BOUNDARY REMAINS ALONG THE LARAMIE RANGE. DIFFERENCES
SEEN BETWEEN GFS AND ECMWF ON PRECIP PLACEMENT MONDAY WITH THE
ECMWF MORE WIDESPREAD AND GFS CONFINING SHOWERS TO CARBON COUNTY.
FOR NOW...WILL GO WITH THE ECMWF SOLUTION WITH HIGH CHANCE POPS
ACROSS MUCH OF THE CWFA. BUT WE WILL NEED TO MONITOR AND
CONVECTIVE COMPLEXES THAT FORM OVER CENTRAL KANSAS. THEY COULD
REALLY CUT OFF OUR LOW LEVEL MOISTURE TRANSPORT INTO NORTHEAST
COLORADO AND EXTREME EASTERN WYOMING MONDAY AFTERNOON/EVENING.

.LONG TERM...(TUESDAY THROUGH FRIDAY)
ISSUED AT 245 AM MDT SAT MAY 2 2015

PRETTY ACTIVE EXTENDED PERIOD WITH PERIODS OF PRECIP POSSIBLE.
SHORTWAVE WILL SWING NORTHEASTWARD FROM NEW MEXICO INTO NORTHEAST
COLORADO ON TUES. LLVL MOISTURE IN SOUTHEAST WINDS WILL BE
PLENTIFUL AHEAD OF THIS FEATURE WITH THE GFS SHOWING PW VALUES
APPROACHING 1 INCH ACROSS THE NEBRASKA PANHANDLE AND 0.75 INCHES
BACK TOWARD CHEYENNE. THERE IS NOT MUCH INSTABILITY PRESENT WITH
WIDESPREAD LOW CLOUDS...SO WILL LIKELY BE MORE OF A STRATIFORM
RAIN EVENT WITH EMBEDDED ISOLATED TSTMS. BOTH THE GFS AND ECMWF
ARE TARGETING AREAS TO THE EAST OF THE LARAMIE RANGE (AND
ESPECIALLY THE NE PANHANDLE) ON TUES AFTN AND EVENING...SO HAVE
THE HIGHEST POPS OUT THERE. UPPER LEVEL WAVE PUSHES INTO NEBRASKA
BY WED WITH ANOTHER GOOD CHANCE OF RAIN OVER AREAS TO THE EAST OF
THE LARAMIE RANGE. MODELS INDICATE SOME DRYING ACROSS THE PLAINS
BY THURS AS LLVL WINDS BECOME MORE WEST TO SOUTHWEST. THURS WILL
PROBABLY SEE THE LEAST COVERAGE OF STORMS...ESPECIALLY TO THE EAST
OF THE LARAMIE RANGE...SO DROPPED POPS TO 20-30 PERCENT. UPPER
LEVEL LOW IS THEN PROGGED TO CLOSE OFF OVER THE GREAT BASIN BY
FRI. SFC DEWPOINTS INCREASE ACROSS THE CWA AS WINDS TURN TO THE
SOUTHEAST AND UPPER LEVEL DIVERGENCE IS GOOD BY LATE FRI...SO HAVE
POPS BACK UP INTO THE 30-40 PERCENT RANGE. CHANCES OF STRONG TO
SVR STORMS WILL BE MINIMAL THROUGH THE LONG TERM...EXCEPT FOR
PERHAPS FRI WHEN INSTABILITY AND DEEP LAYER SHEAR ARE SUFFICIENTLY
HIGH OVER THE SOUTHERN PANHANDLE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1222 PM MDT SAT MAY 2 2015

A VFR AVIATION PERIOD UPCOMING INTO SUNDAY MORNING. THERE IS A
SLIGHT POSSIBILITY FOR A BRIEF PERIOD OF MVFR IN -SHRA/-TSRA THIS
AFTERNOON...BUT AM NOT CONFIDENT ENOUGH TO ADD MORE THAN VCSH/VCTS
TO THE TAFS AT THIS TIME. WINDS WILL VARY BETWEEN WEST AND
SOUTHWEST THROUGH THE PERIOD...WITH PERHAPS A FEW EXTRA GUSTS THIS
AFTERNOON AND/OR EARLY EVENING IN ANY ERRANT -SHRA/-TSRA. ANY
CONVECTION CHANCE WILL DISSIPATE WITH SUNSET.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MDT SAT MAY 2 2015

MINIMAL FIRE WEATHER CONCERNS FOR THE WEEKEND AND UPCOMING WEEK
AS HIGH CHANCES FOR WETTING RAINS OCCUR ON AN ALMOST DAILY BASIS.
FIRE ZONE 301 COULD SEE AFTERNOON HUMIDITIES CLOSE TO CRITICAL
TODAY...BUT WINDS SHOULD STAY BELOW CRITICAL THRESHOLDS. LOW
PRESSURE OVER THE 4 CORNERS AREA WILL CONTINUE TO SPIN PIECES OF
ENERGY NORTHEAST INTO SOUTHERN WYOMING EACH DAY.

&&

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

&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...ZF
AVIATION...CAH
FIRE WEATHER...GCC



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