Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 230917
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
317 AM MDT SAT APR 23 2016

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 206 AM MDT SAT APR 23 2016

POTENT UPPER LOW MOVES FROM NORTHWEST UTAH THIS MORNING TO
WESTERN WYOMING THIS AFTERNOON...WHILE ASSOCIATED LOW PRESSURE
DEVELOPS OVER NORTHEAST WYOMING WITH A COLD FRONT ENTERING OUR
WESTERN ZONES IN THE LATE AFTERNOON. DIFFLUENT FLOW ALOFT ALONG WITH
FRONTAL LIFTING WILL HELP PRODUCE ISOLATED TO SCATTERED SHOWERS THIS
AFTERNOON...MOSTLY WEST OF INTERSTATE 25 WITH THE GREATEST AREAL
COVERAGE OVER CARBON COUNTY WYOMING. ENOUGH INSTABILITY FOR ISOLATED
THUNDERSTORMS...SOME PRODUCING WIND GUSTS OF 50 TO 55 MPH. CONTINUED
QUITE MILD IN THE WARM SECTOR...ESPECIALLY EAST OF I-25...AND HAVE
COMPROMISED BETWEEN THE NAM AND GFS MOS FOR MAXIMUM TEMPERATURES.

TONIGHT...UPPER LOW MOVES TO NORTHEAST WYOMING WITH THE PACIFIC
ORIGIN COLD FRONT BLASTING WEST TO EAST ACROSS OUR COUNTIES. MAIN
CHALLENGE WILL BE WINDS. NAM FORECASTS 700 MB WINDS PEAKING AROUND
45 KNOTS WHILE THE GFS PEAKS AROUND 65 KNOTS. WITH NOCTURNAL
TIMING...DECENT COLD AIR ADVECTION IN THE LOW LEVELS AND 500-300 MB
AND 700-500 MB QG DOWNWARD MOTION...EXPECT SOME OF THE STRONGER
WINDS TO MIX DOWN TO THE SURFACE...ESPECIALLY OUR TYPICALLY WIND
PRONE LOCALES. HOWEVER...WITH STILL SOME UNCERTAINTY...WILL LEAVE
OUR INHERITED HIGH WIND WATCH INTACT SO OUR DAY SHIFT TEAM CAN
ASSESS THE 12Z MODEL RUNS AND MAKE A BETTER FINAL CALL ON POSSIBLE
UPGRADING OF THE HIGH WIND WATCH...AND IF IT MAY EVEN NEED TO BE
EXPANDED TO INCLUDE OTHER LOCATIONS ACROSS SOUTHEAST WYOMING.

DECENT OROGRAPHICS WILL PRODUCE WIDESPREAD SNOW ACROSS OUR SNOWY AND
SIERRA MADRE RANGES AFTER MIDNIGHT WITH SCATTERED TO NUMEROUS
SHOWERS NORTH OF A LARAMIE TO ALLIANCE LINE. STRONG DOWNSLOPING IN
THE LOW AND MID LEVELS WILL PRODUCE A RAIN SHADOW EFFECT DOWNWIND OF
THE LARAMIE RANGE...AFFECTING MUCH OF FAR SOUTHEAST WYOMING AND THE
SOUTHERN NEBRASKA PANHANDLE.

SUNDAY...THE COMPACT UPPER LOW MOVES SLOWLY INTO WESTERN SOUTH
DAKOTA WITH PLENTY OF WRAPAROUND SHOWERS IN THE CYCLONIC FLOW
ALOFT...ESPECIALLY NORTH OF A RAWLINS TO SCOTTSBLUFF LINE. MOISTURE
DEPTH MORE SHALLOW ACROSS OUR SOUTHERN COUNTIES THUS MORE ISOLATED
SHOWER COVERAGE IN THE CYCLONIC FLOW ALOFT. CONSIDERABLY COOLER IN
THE WAKE OF THE COLD FRONT. STRONG WINDS LIKELY CONTINUE ACROSS OUR
WIND PRONE LOCALES BASED ON 700 AND 850 MB HEIGHT DIFFERENCES
BETWEEN CRAIG AND CASPER. POSSIBLE WIND ADVISORY ACROSS WESTERN
NEBRASKA.

SUNDAY NIGHT...SHOWERS WILL DECREASE MARKEDLY IN COVERAGE AS THE
UPPER LOW MOVES TO EASTERN SOUTH DAKOTA AND RIDGING ALOFT DEVELOPS
OVER WYOMING.

MONDAY...PROGRESSIVE SPRING PATTERN CONTINUES WITH THE FLOW ALOFT
QUICKLY BACKING TO SOUTHWEST IN ADVANCE OF THE NEXT APPROACHING
SHORTWAVE. IN RESPONSE SURFACE TROUGH DEVELOPS OVER CENTRAL WYOMING
AND CENTRAL COLORADO...WITH LOW LEVEL SOUTHEASTERLY WINDS HELPING TO
ADVECT LOW LEVEL MOISTURE WESTWARD ACROSS OUR FORECAST AREA. WITH
THE FRONT LEFT QUADRANT OF THE 300 MB JET APPROACHING OUR WESTERN
COUNTIES...DIFFLUENT FLOW ALOFT AND DECENT LOW LEVEL
CONVERGENCE...WE EXPECT ISOLATED TO SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS TO ERUPT IN THE AFTERNOON ALONG AND WEST OF I-25. WILL
STICK CLOSE TO THE NAM AND GFS GUIDANCE HIGH TEMPERATURES SINCE THEY
ARE QUITE CLOSE AND SEEM ON TRACK BASED ON THE PROJECTED 700 MB
TEMPERATURES.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 325 AM MDT SAT APR 23 2016

MEDIUM TO LONG RANGE MODELS CONTINUE TO SHOW AN ACTIVE WEATHER
PATTERN ACROSS SOUTHEAST WYOMING AND WESTERN NEBRASKA AS TWO
POTENTIALLY SIGNIFICANT STORM SYSTEMS IMPACT THE AREA. ANOTHER
SLOW MOVING UPPER LEVEL LOW IS FORECAST TO DIG SOUTHEAST INTO THE
FOUR CORNERS REGION EARLY NEXT WEEK. MOST MODELS AND ENSEMBLE
FORECASTS SHOW TWO DISTINCT UPPER LOWS MOVING ACROSS COLORADO AND
WYOMING AS THE SYSTEM DRIFTS EASTWARD. HOW THESE TWO UPPER LEVEL
LOWS INTERACT WITH EACH OTHER...AND WHICH ONE BECOMES THE DOMINANT
FEATURE...WILL BE THE MAIN FORECAST CONCERN AS STRONG
THUNDERSTORMS...HEAVY RAIN...AND EVEN SNOW APPEARS POSSIBLE
LATE MONDAY THROUGH WEDNESDAY. MODELS SHOW THE NORTHERN UPPER
LEVEL LOW IMPACTING THE REGION LATE MONDAY AND MONDAY
NIGHT...BRINGING WIDESPREAD SHOWERS WITH HEAVY RAINFALL TO THE
HIGH PLAINS. PRETTY CONFIDENT THAT IT WILL BE WARM ENOUGH FOR
RAIN...EVEN ON THE I80 SUMMIT WITH 700 MB TEMPERATURES BETWEEN 0C
TO 4C INITIALLY. HOWEVER...THE GFS AND ECMWF SHOW THE SOUTHERN
UPPER LOW MOVING NORTHEAST INTO COLORADO AND RAPIDLY INTENSIFYING
AS A 988MB SURFACE LOW FORMS ACROSS EASTERN COLORADO AND SLOWING
MOVES NORTHWARD. THE ECMWF IS MUCH FURTHER EAST WITH THIS
DEVELOPMENT EVEN THOUGH ENSEMBLES SHOW THE LOW SOMEWHERE OVER
NORTH CENTRAL TO EAST CENTRAL COLORADO. EITHER WAY...THIS NEEDS TO
BE MONITORED THROUGH THE WEEKEND. IT WILL BE TURNING COOLER FOR
EARLY NEXT WEEK WITH DAYTIME TEMPERATURES ONLY IN THE 40S TO LOW
50S. INCREASED POP BETWEEN 50 TO 70 PERCENT ACROSS THE HIGH PLAINS
THROUGH EARLY WEDNESDAY FOR THE POTENTIAL OF MODERATE RAINFALL AND
SOME SNOW.

PORTIONS OF WESTERN NEBRASKA WILL LIKELY STILL BE DEALING WITH
THIS FIRST STORM SYSTEM EARLY ON THURSDAY BEFORE IT GRADUALLY
WEAKENS WHILE MOVING SLOWLY NORTH AND EAST. ALL MODELS THEN SHOW
THE NEXT SYSTEM QUICKLY MOVING INTO THE FOUR CORNERS REGION FOR
LATE NEXT WEEK. NOT CONFIDENT WITH TIMING AND IMPACTS FROM THIS
STORM HOWEVER...SINCE MODEL SOLUTIONS DIVERGE SIGNIFICANTLY LATE
FRIDAY AND INTO NEXT WEEKEND. EXPECT COOLER THAN NORMAL
TEMPERATURES TO CONTINUE WITH HIGHS STRUGGLING TO REACH THE LOW TO
MID 50S LATE NEXT WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH TONIGHT)
ISSUED AT 206 AM MDT SAT APR 23 2016

VFR CONDITIONS EXPECTED TODAY AND TONIGHT WITH SOUTHWEST WINDS
INCREASING FROM WEST TO EAST...LIKELY BEGINNING ACROSS THE
SOUTHEAST WYOMING TERMINALS BY THIS AFTERNOON. GUSTS BETWEEN 40 TO
50 KNOTS ARE POSSIBLE LATE TONIGHT NEAR KRWL AND KLAR.

&&

.FIRE WEATHER...
ISSUED AT 206 AM MDT SAT APR 23 2016

MINIMAL FIRE WEATHER CONCERNS BASED ON PROJECTED
HUMIDITIES AND WINDS...ESPECIALLY AFTER TODAY IN THE WAKE OF THE
NEXT COLD FRONT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...HIGH WIND WATCH FROM THIS EVENING THROUGH SUNDAY AFTERNOON FOR
     WYZ106-110-116-117.

NE...NONE.
&&

$$

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



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