Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 031813
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1213 PM MDT SUN MAY 3 2015

.UPDATE...
ISSUED AT 1156 AM MDT SUN MAY 3 2015

CLOUDS ARE ALREADY STARTING TO INCREASE ACROSS MUCH OF THE AREA
PER RECENT WATER VAPOR SATELLITE IMAGERY. POTENTIAL FOR SHOWERS
AND THUNDERSTORMS LIKELY TO INCREASE CONSIDERABLY OVER THE NEXT
FEW HOURS...ESPECIALLY ALONG/EAST OF THE LARAMIE RANGE. A WEAK
SURFACE BOUNDARY WAS EVIDENT NORTHEAST OF CHEYENNE ON THE 18Z
RADAR LOOP. AS THIS FEATURE SHIFTS SOUTHWEST...HIGH-RES MODELS
TURN LLVL WINDS NORTHEAST AND UPSLOPE BY 18-19Z. THIS IS ALREADY
REFLECTED IN SURFACE OBS OVER WESTERN NE. THE LAST COUPLE RUNS OF
THE HRRR HAVE BEEN CONSISTENT WITH SHOWERS/TSTMS BECOMING FAIRLY
WIDESPREAD AFTER 21Z OVER FAR SOUTHEAST WY...SO DECIDED TO BUMP
POPS UP TO CATEGORICAL. ONLY OTHER CHANGE WAS TO INCREASE HIGHS
A FEW DEGREES OVER THE PLAINS. WE ARE ALREADY 67F IN CHEYENNE AT
NOON. ANOTHER DEGREE OR TWO OF WARMING IS POSSIBLE BEFORE CLOUDS
AND PCPN HELP TO COOL THINGS DOWN.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY NIGHT)
ISSUED AT 300 AM MDT SUN MAY 3 2015

STARTING OFF THIS MORNING...SURFACE ANALYSIS SHOWING A FRONTAL
BOUNDARY LAYING WEST TO EAST ACROSS NORTHERN WYOMING...VERY SLOWLY
MOVING SOUTH THIS MORNING. LOOKS TO LAY ALONG THE LARAMIE RANGE BY
18Z OR SO TODAY WITH NORTHEASTERLY WINDS BEHIND THE FRONT FOR
AREAS EAST OF THE LARAMIE RANGE. MEANWHILE...THE UPPER LEVEL LOW
THAT HAS BEEN SENDING US PIECES OF ENERGY THE PAST COUPLE DAYS
CONTINUES OVER THE DESERT SOUTHWEST.

BEST FOCUS FOR SHOWERS AND THUNDERSTORMS TODAY LOOKS TO BE WEST
AND SOUTH OF THIS FRONT...BASICALLY ALONG AND WEST OF THE LARAMIE
RANGE. BUT IT AL DEPENDS ON WHERE THIS FRONT ULTIMATELY ENDS UP BY
EARLY AFTERNOON. SHOULD IT HAPPEN TO TAKE A LITTLE LONGER TO GET
TO THE LARAMIE RANGE...SHOWERS AND STORMS COULD BE FURTHER EAST.

A LITTLE MORE UNSTABLE TODAY OVER YESTERDAY WITH NAM SHOWING A
POCKET OF 850MB CAPE AROUND 1000 J/KG NEAR LARAMIE OVER TO
SARATOGA AND 700MB CAPES AROUND 600 J/KG. LIFTED INDICES NEAR
-4C...SO DO BELIEVE THE STRONGEST STORMS WILL BE IN THIS AREA.
LOCATIONS BEHIND THE FRONT WILL MOST LIKELY EXPERIENCE COOLER
TEMPERATURES IN THE NORTHEAST FLOW...SO DID NOT STRAY TOO MUCH
FROM THE LOW CHANCE POPS WE HAD GOING EAST OF I-25. DID INCREASE
POPS THOUGH OUT WEST AS MODELS ARE IN GREAT AGREEMENT WITH THE
LARAMIE RANGE...CARBON AND ALBANY COUNTIES SEEING DECENT RAINFALL
THIS AFTERNOON.

SHOWERS AND THUNDERSTORMS COULD LAST INTO THE LATE EVENING HOURS
TONIGHT WITH THE FRONTAL BOUNDARY IN THE AREA AND FAIRLY GOOD
UPSLOPING WINDS.

SOME DIFFERENCES IN GFS AND ECMWF ON WHAT IS GOING TO HAPPEN
MONDAY. BOTH ARE SHOWING SOME ENERGY MOVING NORTH FORM THE DESERT
SOUTHWEST TO INTERACT WITH THE STALLED FRONTAL BOUNDARY. GFS KEEPS
HIGHER POPS WEST...WHILE ECMWF SHOWS THE SOUTH LARAMIE RANGE AND
POINTS SOUTH SEEING MOST OF THE POPS. WENT MORE WITH THE ECMWF/NAM
SOLUTION WITH THE HIGHER POPS ACROSS THE SOUTH AND EAST.

.LONG TERM...(WEDNESDAY THROUGH SATURDAY)
ISSUED AT 300 AM MDT SUN MAY 3 2015

THE MODELS ARE STILL SHOWING A RATHER UNSETTLED EXTENDED PERIOD.
ON WED THE SHORTWAVE TROUGH WILL BE LOCATED OVER CENTRAL NEBRASKA.
GOOD LLVL MOISTURE IS INDICATED BY THE GFS WITH DEWPOINTS IN THE
MID 40S TO LOW 50S ACROSS THE PLAINS AND PW VALUES ARE QUITE HIGH
FOR EARLY MAY (0.75-1.0 INCHES). WITH MORE SUNSHINE ON WED
COMPARED TO PREVIOUS DAYS...THERE WILL BE BETTER INSTABILITY. SO
SCATTERED TO NUMEROUS SHOWERS AND TSTMS WILL DEVELOP BY WED
AFTN...SOME WITH HEAVY RAIN. WHILE THE MODELS YESTERDAY WERE
SHOWING A BRIEF BREAK IN THE PRECIP ON THURS...THIS IS REALLY NO
LONGER THE CASE. AN UPPER LOW WILL BE CUT OFF ACROSS NORTHERN
CALIFORNIA WITH EAST TO SOUTHEAST WINDS ACROSS THE CWA. THE GFS
INDICATES ANOTHER AFTN OF DECENT CAPE (600-800 J/KG) SO DID RAISE
POPS SOME INTO THE 30-40 PERCENT RANGE BY THURS EVENING. IT WILL
LIKELY BECOME EVEN WETTER AS WE HEAD INTO FRI. THE UPPER LOW MOVES
EASTWARD INTO THE GREAT BASIN ON FRI WITH UPPER LEVEL DIFFLUENCE
INCREASING ACROSS SOUTHEAST WY. THERE IS ALSO GOOD LLVL
UPSLOPE WITH A SFC HIGH OVER THE NORTHERN PLAINS...SO THE
POTENTIAL EXISTS FOR SOME PRETTY HIGH RAINFALL AMOUNTS FROM FRI
AFTN INTO SAT. BOTH THE GFS AND ECMWF SHOW WIDESPREAD QPF AMOUNTS
OF 0.5-1.5 INCHES. WILL ALSO HAVE TO MONITOR THE POTENTIAL FOR
SOME STRONG TO SVR STORMS AS THE EVENT DRAWS CLOSER...ALTHOUGH AT
THIS TIME THE THREAT LOOKS MARGINAL WITH LIMITED INSTABILITY (MORE
OF A STRATIFORM EVENT WITH EMBEDDED CONVECTIVE CELLS).

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1213 PM MDT SUN MAY 3 2015

CONCERNS ARE TWO-FOLD FOR THIS TAF CYCLE. THE INITIAL CONCERN WILL
BE DEVELOPING CONVECTION NR KRWL AND KLAR AND PROBABLY GETTING
INTO KCYS AFTER 20Z. FAVORED VCTS AT ALL THESE SITES UNTIL
INDIVIDUAL CELLS CAN BE IDENTIFIED AND TIMED. PANHANDLE SITES WILL
SEE LESS OF A CHANCE TO SEE THIS THUNDERSTORM ACTIVITY...ALTHOUGH
KBFF MAY GET INTO IT AFTER 22Z. LATEST MODELS SUGGEST THIS
ACTIVITY WILL LINGER INTO THE OVERNIGHT AND MORNING HOURS AS WELL
AND EXPECT AVIATION CONDITIONS TO WORSEN AFTER 03-06Z AS WINDS
TURN UPSLOPE FLOPPING AROUND TO THE SOUTHEAST. THIS IS A FAVORABLE
DIRECTION FOR THE DEVELOPMENT OF LOW STRATUS/FG. ALSO EXPECT
ANOTHER BAND OF SHOWERS TO LIFT NORTH ACROSS PRIMARILY PANHANDLE
SITES AFTER 06Z. ANY STRATUS OR FOG THAT DOES EXIST WILL LIKELY
LIFT IF THESE SHOWERS MATERIALIZE. FOR NOW HAVE TRENDED CONDITIONS
DOWNWARD AFTER 06Z TO ACCOUNT FOR THIS ACTIVITY.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MDT SUN MAY 3 2015

DAILY CHANCES FOR WETTING RAINS FOR MOST LOCATIONS AS A COLD FRONT
MOVE SOUTH OUT OF MONTANA AND STALLS NEAR THE LARAMIE RANGE. THIS
FRONT WILL INTERACT WITH ENERGY FROM A DISTURBANCE OVER THE FOUR
CORNERS AREA AND WILL FOCUS SHOWERS AND THUNDERSTORMS ACROSS
SOUTHEAST WYOMING. COOLER TEMPERATURES AND WETTING RAINS WILL AID
IN ONGOING GREENUP OF FUELS...SO NO FIRE WEATHER CONCERNS ARE
ANTICIPATED THROUGH MUCH OF THE UPCOMING WEEK.

&&

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

$$

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



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