Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 222035
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
235 PM MDT WED APR 22 2015

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 232 PM MDT WED APR 22 2015

TONIGHT...WEAK SHORTWAVE TROUGH ALOFT MOVING OVERHEAD NEAR PEAK
HEATING. COMBINED WITH DECENT SOUTHEAST LOW LEVEL WINDS PROVIDING
MECHANICAL LIFT...UPWARD VERTICAL MOTION AT MID LEVELS...DECENT LOW
LEVEL MOISTURE FUEL PROVIDED BY MELTING SNOWFIELD OVER THE SOUTHERN
LARAMIE RANGE...AND PROXIMITY OF NORTH TO SOUTH ORIENTED 850/700 MB
THETA-E RIDGE AXIS...EXPECT ISOLATED TO SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS THROUGH EARLY EVENING ACROSS SOUTHEAST
WYOMING...WITH GREATEST AREAL COVERAGE OVER OUR SNOWY RANGE...SIERRA
MADRE AND LARAMIE RANGES...AND POINTS NEARBY. EXPECT THUNDERSTORMS
TO DISSIPATE AND CESSATE BY MIDNIGHT WITH LOSS OF SOLAR INSOLATION.

LOOKS LIKE A LOW LEVEL JET MAY SETUP AFTER MIDNIGHT OVER THE WESTERN
HIGH PLAINS...WITH THE NAM INDICATING SOME DECENT LOW LEVEL MOISTURE
ADVECTION NORTHWARD INTO OUR EASTERN COUNTIES OF WESTERN NEBRASKA
LATE TONIGHT...AND WITH THE MODELS SUGGESTING THIS AND BOUNDARY
LAYER RELATIVE HUMIDITIES PROGGED TO INCREASE...HAVE PAINTED AREAS
OF FOG OVER PART OF OUR WESTERN NEBRASKA COUNTIES LATE TONIGHT.

THURSDAY...ANOTHER WEAK SHORTWAVE TROUGH ALOFT PROGGED TO MOVE
OVERHEAD DURING PEAK HEATING...AND MODELS...ESPECIALLY THE
NAM...PROG A NICE NORTH TO SOUTH ORIENTED SURFACE TROUGH AND
CONVERGENCE BOUNDARY TO SET UP ALONG INTERSTATE 25...WITH AN
IMPRESSIVE NORTH TO SOUTH ORIENTED 850/700 MB THETA-E RIDGE AXIS IN
THE SAME LOCALE. THUS...EXPECT ISOLATED TO SCATTERED AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS...WITH THUNDERSTORMS MOST NUMEROUS
AND CONCENTRATED ALONG THE LOW LEVEL CONVERGENCE BOUNDARY AND
SURFACE TROUGH ALONG INTERSTATE 25 FROM WHEATLAND TO CHEYENNE AND
ALONG THE INSTABILITY AXIS. ALSO BELIEVE BASED ON PRECIPITABLE WATER
AND WEAK STEERING FLOW...SOME OF THE STORMS ALONG AND NEAR
INTERSTATE 25 WILL BE HEAVY RAINERS.

THURSDAY NIGHT...WITH LOSS OF DAYTIME HEATING...EXPECT A DECREASE IN
AREAL SHOWER AND THUNDERSTORM COVERAGE...THOUGH WITH THE PASSAGE OF
A SHORTWAVE TROUGH ALOFT...WILL CONTINUE WITH ISOLATED TO SCATTERED
SHOWER COVERAGE WITH MESOSCALE LIFT ALL NIGHT FROM THE SHORTWAVE
TROUGH ALOFT.

FRIDAY...PRIMARY SHORTWAVE TROUGH ALOFT MOVES TO WESTERN NEBRASKA
AND WESTERN KANSAS BY LATE AFTERNOON...WITH A SURFACE TROUGH SETTING
UP OVER WESTERN NEBRASKA NEAR SUPPER TIME. STILL THOUGH...DESPITE
THE ABSENCE OF LARGE SCALE FORCING...STILL EXPECT SCATTERED TO
NUMEROUS AFTERNOON SHOWERS...AND ISOLATED TO SCATTERED
THUNDERSTORMS...WITH DIURNAL EFFECTS...LOW LEVEL MOISTURE...FUEL...
ADDED BY THE ABUNDANCE OF MELTING SNOWFIELD OVER OUR MOUNTAINS AND
LARAMIE VALLEY. PER THE STORM PREDICTION CENTER DAY TWO OUTLOOK...A
FEW STORMS OVER THE SOUTHERN NEBRASKA PANHANDLE MAY APPROACH SEVERE
LIMITS IN THE AFTERNOON PER PROGGED SHEAR AND INSTABILITY. NAM QPF
FOLLOWED PRETTY CLOSELY AS FAR AS AREAL SHOWER AND THUNDERSTORM
COVERAGE...THUS SCATTERED TO NUMEROUS SHOWERS AND SCATTERED
THUNDERSTORMS FROM LARAMIE TO CHEYENNE TO WHEATLAND TO TORRINGTON TO
LUSK IN THE AFTERNOON.

FRIDAY NIGHT...GREATEST SHOWER AND THUNDERSTORM COVERAGE MOVES TO
WESTERN NEBRASKA IN THE EVENING WITH LESSER COVERAGE ELSEWHERE IN
THE DOWNWARD VERTICAL MOTION AREA IN THE WAKE OF THE SHORTWAVE
TROUGH ALOFT AND WITH LOSS OF SOLAR INSOLATION.

SATURDAY...PERFECT SETUP FOR SCATTERED TO NUMEROUS SHOWERS AND
SCATTERED THUNDERSTORM COVERAGE IN THE AFTERNOON. WELL AMPLIFIED
TROUGH ALOFT OVER THE PACIFIC NORTHWEST WITH INCREASING DIFFLUENT
SOUTHWEST FLOW ALOFT OVER OUR COUNTIES. IN RESPONSE...SURFACE LOW
DEVELOPS AND STRENGTHENS OVER SOUTHEAST COLORADO WITH LOW LEVEL
SOUTHEASTERLIES ADVECTING BEAUCOUP LOW LEVEL MOISTURE NORTHWESTWARD
INTO OUR COUNTIES. NAM PROGS IMPRESSIVE AND WELL PRONOUNCED 850/700
MB THETA-E RIDGE AXIS FROM NORTHWEST KANSAS INTO SOUTHEAST WYOMING
WITH LOW AND MID LEVEL SOUTHEAST WINDS. WITH ALL THESE FACTORS...AND
A LIKELY SHORTWAVE TROUGH PASSAGE AROUND PEAK HEATING...WILL PAINT
SCATTERED TO NUMEROUS AFTERNOON SHOWERS...WITH ISOLATED TO SCATTERED
THUNDERSTORMS...WITH 60 TO 100 PERCENT POPS OVER MOST OF SOUTHEAST
WYOMING AND WILL ADD MENTION OF LOCALLY HEAVY RAINERS DUE TO
EXPECTED PRECIPITABLE WATER VALUES AND WEAK STEERING FLOW ALOFT.
THINKING THAT HEAVY RAIN WILL BE THE MAIN IMPACTS FROM
THUNDERSTORMS...THOUGH COULD SEE SOME STORMS WITH HAIL AND STRONG
WINDS IN THE AFTERNOON.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 232 PM MDT WED APR 22 2015

THE WEEKEND WILL END ON A WET NOTE AS A SECOND STRONGER UPPER TROUGH
TRANSITS EASTWARD ACROSS WYOMING AND WESTERN NEBRASKA.  WE CONTINUE
TO CARRY LIKELY POPS MOST AREAS FOR SNOW SHOWERS IN THE HIGHER
ELEVATIONS ACROSS THE WEST AND MOSTLY RAIN SHOWERS EAST OF THE
LARAMIE RANGE SUNDAY INTO MONDAY.  THE GFS AND ECMWF ARE IN FAIR
AGREEMENT WITH THE PROGRESSION OF THE MAIN SYNOPTIC-SCALE FEATURES
SUNDAY INTO TUESDAY...MOVING THE UPPER TROUGH EAST OF OUR AREA
TUESDAY.  THE GFS IS GOING RATHER BULLISH ON SNOWFALL AMOUNTS SUNDAY
INTO MONDAY PRODUCING NEARLY A FOOT OF NEW SNOW OVER THE SNOWY AND
SOUTHERN LARAMIE RANGES...WITH THE ECMWF SIGNIFICANTLY LESS WITH 6
INCHES OR LESS.  RIGHT NOW THINKING A FEW INCHES OF SNOW
ACCUMULATION IN THE MOUNTAINS BUT MAY HAVE TO TREND HIGHER AS WE GET
CLOSER TO THE EVENT.  OTHERWISE...THE MODELS ARE IN AGREEMENT
BUILDING A LARGE UPPER RIDGE IN FROM THE WEST BY MID WEEK AND TEMPS
WARMING UP INTO THE 70S EAST AND 50S TO LOWER 60S WEST.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 232 PM MDT WED APR 22 2015

SATELLITE IMAGERY SHOWING SOME CONVECTIVE BUILDUPS FORMING OVER
THE SNOWY AND SOUTHERN LARAMIE RANGES AT MID-DAY. WE CONTINUED
PREVIOUS FORECASTS OF HAVING THUNDERSTORMS IN THE VICINITY OF
RAWLINS...LARAMIE AND CHEYENNE HERE THIS AFTERNOON...DIMINISHING
IN THE EARLY EVENING HOURS. STRONGER WINDS EXPECTED TODAY IN THE
EASTERN ZONES AFFECTING ALLIANCE AND SIDNEY...WITH GUSTS TO 25 KTS
FROM THE SOUTH. OTHERWISE...VFR CATEGORY IN THE FORECAST THROUGH
TOMORROW MORNING AT ALL SITES.

&&

.FIRE WEATHER...
ISSUED AT 232 PM MDT WED APR 22 2015

MINIMAL FIRE WEATHER CONCERNS INTO THE WEEKEND DUE
TO EXPECTED SHOWERS AND THUNDERSTORMS...RELATIVELY WET GROUND AND
EXPECTED HUMIDITIES AND WINDS.

&&

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

$$

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


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