Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 120943
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
343 AM MDT SAT JUL 12 2014

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 330 AM MDT SAT JUL 12 2014

CURRENT PREDAWN WATER VAPOR/H5 COMPOSITE ANALYSIS DEPICTED A MID/UPPER
LEVEL RIDGE FROM THE SOUTH CENTRAL CONUS TO THE PACIFIC NORTHWEST. POLAR
VORTEX RESIDED OVER NORTH CENTRAL CANADA. CLOCKWISE FLOW ALOFT WAS
ADVECTING SUBTROPICAL MOISTURE NORTHEASTWARD FROM THE CENTRAL AND
SOUTHERN ROCKIES INTO THE CENTRAL GREAT PLAINS. THE SHORTWAVE RESPONSIBLE
FOR THE STRONG CONVECTION FRIDAY EVENING MOVED INTO NEBRASKA AND IOWA
OVERNIGHT. RESIDUAL OUTFLOW BOUNDARIES COLLIDING IN THE WAKE OF THE
DISTURBANCE WAS PRODUCING ISOLATED SHOWERS ALONG THE COLORADO-WYOMING
BORDER. A COOL FRONT PUSHED SOUTH INTO NORTHEAST COLORADO AND EXTENDED
INTO CENTRAL WYOMING. NORTHERLY SURFACE WINDS PREVAILED BEHIND THE
FRONT. TEMPERATURES RANGED FROM THE MID 5OS TO MID 60S. POST-FRONTAL
UPSLOPE PRODUCED AREAS OF LOW CEILINGS.

00Z SHORT RANGE MODEL GUIDANCE IS CONSISTENT DEPICTING A PREVAILING
NORTHWEST FLOW ALOFT OVER THE CWA AS AN EXTENSION OF THE CANADIAN
POLAR VORTEX PROGRESSES SOUTHEAST INTO THE MIDWEST AND UPPER RIDGE
AMPLIFIES OVER THE INTERMOUNTAIN WEST. SUBTROPICAL MOISTURE COMBINED
WITH PASSING DISTURBANCES IN THE NORTHWEST FLOW WILL PRODUCE SCATTERED
MAINLY AFTERNOON AND EVENING SHOWERS/TSTORMS DURING THE PERIOD. MODEL
SOUNDINGS INDICATE PRECIPITABLE WATER VALUES OF ONE TO TWO STANDARD
DEVIATIONS ABOVE NORMAL /1.0 TO 1.25 INCHES/ TODAY. MUCAPES GENERALLY
RANGE FROM 500-1000 J/KG HOWEVER 0-6KM SHEAR PROFILES ARE NOT THAT
IMPRESSIVE /15-25 KT/. THE STRONGER TSTORMS WILL BE CAPABLE OF PRODUCING
HEAVY RAINFALL /0.5-1.O INCHES PER HR/...SMALL HAIL AND WIND GUSTS TO
40 KT. IT WILL BE COOLER TODAY WITH 700MB TEMPERATURES NEAR 10C.

SUNDAY WILL NOT BE AS CONVECTIVELY ACTIVE AS TODAY WITH PRECIPITABLE
WATER VALUES BETWEEN 0.75 AND 1.0 INCHES. MUCAPES ARE A BIT HIGHER
BUT SHEAR VALUES REMAIN LOW. TSTORMS WILL NOT BE AS EFFICIENT RAIN
PRODUCERS AS THEY WILL BE TODAY BUT STILL COULD PRODUCE BRIEF HEAVY
RAIN. 700MB TEMPERATURES ARE SIMILAR TO TODAY WITH HIGHS NEAR SEASONAL
NORMALS.

AS THE UPPER TROUGH DEEPENS TO THE EAST...IT WILL PUSH A FAIRLY STRONG
COLD FRONT SOUTHWARD THROUGH THE REGION MONDAY AFTERNOON WITH A SURGE
OF COOLER AND DRIER AIR ACROSS THE PLAINS. CONVERGENCE AND MOISTURE
ALONG AND AHEAD OF THE FRONT WILL GENERATE WIDELY SCATTERED AFTERNOON
CONVECTION FROM THE SOUTHERN NEBRASKA PANHANDLE INTO SOUTHEAST AND
SOUTH CENTRAL WYOMING. 700MB TEMPERATURES LOWER TO NEAR 6C EAST OF
THE LARAMIE RANGE.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 315 AM MDT SAT JUL 12 2014

MODELS IN GOOD AGREEMENT THROUGH THE MIDDLE OF NEXT WEEK...SHOWING
A DEEP UPPER LEVEL TROUGH REMAINING OVER THE EASTERN HALF OF THE
UNITED STATES AND AN UPPER LEVEL RIDGE RETROGRADING SLIGHTLY
WESTWARD OVER THE EASTERN PACIFIC. THIS PATTERN WILL CHANGE VERY
LITTLE FROM THIS WEEKEND THROUGH AT LEAST WEDNESDAY OF NEXT WEEK.
THEREFORE...EXPECT SHOWERS AND TSTORMS TO CONTINUE EACH DAY WITH
GOOD UPSLOPE FLOW EXPECTED ALONG WITH DEEP MOISTURE AND DAYTIME
INSTABILITY. IN ADDITION...SEVERAL UPPER LEVEL DISTURBANCES AND AN
ACTIVE JET STREAM WILL PROVIDE THE NORTHERN AND CENTRAL ROCKY
MOUNTAINS AND ADJACENT PLAINS WITH FAVORABLE DYNAMICS TO PRODUCE
STRONG TSTORMS AND VERY HEAVY RAINFALL AT TIMES. SOME OF THIS
CONVECTIVE ACTIVITY WILL LINGER WELL INTO THE NIGHT THROUGH THE
MIDDLE OF THE WEEK. MODELS SHOW THE MAIN UPPER LEVEL DISTURBANCE
PUSHING SOUTHEAST ACROSS WYOMING SOMETIME BETWEEN TUESDAY NIGHT AND
WEDNESDAY AFTERNOON...PRODUCING WIDESPREAD RAIN SHOWERS AND
THUNDERSTORMS. WILL HAVE TO MONITOR THIS TIME PERIOD OVER THE NEXT
FEW DAYS DUE TO THE POTENTIAL FOR FLASH FLOODING IN ADDITION TO
STRONG TSTORMS. WITH NORTHWEST FLOW ALOFT...TEMPERATURES WILL BE 10
TO 15 DEGREES BELOW NORMAL FOR THIS TIME OF THE YEAR AND GENERALLY
IN THE 70S TO LOW 80S ACROSS THE HIGH VALLEYS AND HIGH PLAINS EAST
OF THE LARAMIE RANGE.

BY THURSDAY AND FRIDAY NEXT WEEK...MODELS DO INDICATE SLIGHTLY DRIER
AIR MOVING INTO WYOMING AS THE LOW TO MID LEVEL FLOW VEERS INTO THE
SOUTH...AND THEN WEST. LOWERED POP BETWEEN 15 TO 20 PERCENT ACROSS
SOUTHEAST WYOMING WITH JUST A SLIGHT CHANCE OF MOUNTAIN SHOWERS/TSTORMS.
HOWEVER...THIS BREAK IN THE ACTION MAY BE SHORT LIVED AS MODELS SHOW
ANOTHER COOL FRONT MOVING ACROSS THE AREA WITH A RETURN TO NORTHERLY
FLOW ALOFT BY NEXT WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH SATURDAY NIGHT)
ISSUED AT 230 AM MDT SAT JUL 12 2014

ISOLATED RAIN SHOWERS WILL CONTINUE EARLY THIS MORNING...MAINLY NEAR
THE COLORADO BORDER. A BRIEF LULL IS EXPECTED LATER THIS MORNING WITH
SHOWERS AND TSTORMS QUICKLY DEVELOPING ONCE AGAIN BY EARLY THIS
AFTERNOON. IFR CONDITIONS IN LOW VISIBILITIES AND HEAVY RAIN ARE
POSSIBLE THIS AFTERNOON AND THIS EVENING...ESPECIALLY EAST OF THE
LARAMIE RANGE. WINDS WILL GENERALLY REMAIN LIGHT TODAY...BUT GUSTY
ERRATIC WINDS ARE EXPECTED IN AND AROUND THUNDERSTORMS.

&&

.FIRE WEATHER...
ISSUED AT 230 AM MDT SAT JUL 12 2014

NON-CRITICAL CONDITIONS WILL CONTINUE FOR THE NEXT SEVERAL DAYS AS
MONSOONAL MOISTURE KEEPS GOOD CHANCES FOR MAINLY AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS IN THE FORECAST. LOCALLY HEAVY RAINFALL AND
GUSTY WINDS WILL BE THE PRIMARY THREATS FROM THUNDERSTORMS TODAY.
TEMPERATURES WILL GRADUALLY COOL TO BELOW SEASONAL NORMALS THROUGH
THE MIDDLE OF NEXT WEEK AS A FEW COLD FRONTS PUSH SOUTH ACROSS THE
DISTRICTS. WARMER AND DRIER CONDITIONS WILL RETURN LATE NEXT WEEK.

&&

.HYDROLOGY...
ISSUED AT 300 AM MDT SAT JUL 12 2014

SOUTHERN PORTIONS OF THE NEBRASKA PANHANDLE EXPERIENCED VERY HEAVY
RAINFALL FROM THUNDERSTORMS FRIDAY EVENING WITH ONE TO THREE INCHES
OBSERVED. FLASH FLOODING OCCURRED OVER EASTERN KIMBALL COUNTY WITH
STREET FLOODING IN GERING AND SCOTTSBLUFF.

THE AIRMASS WILL REMAIN MOIST TODAY WITH PRECIPITABLE WATER VALUES
OF 1 TO 1.25 INCHES. THERE IS A LOW RISK FOR FLASH FLOODING AS STORMS
MOVE AT 10 TO 20 MPH. THE HEAVIEST RAINFALL RATES WILL BE AROUND ONE
INCH IN 30 MINUTES...THOUGH MOST AREAS WILL BE LESS. THE AIRMASS WILL
BE SLIGHTLY DRIER SUNDAY BUT STILL FAIRLY MOIST WITH BRIEF HEAVY
RAINFALL POSSIBLE.

&&

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

$$

SHORT TERM...JAMSKI
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...JAMSKI
HYDROLOGY...JAMSKI




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