Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 172204
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
404 PM MDT FRI APR 17 2015

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 323 PM MDT FRI APR 17 2015

A WILD AND CRAZY WEATHER DAY CONTINUES ACROSS MUCH OF SOUTHEAST WY
AND THE WESTERN NE PANHANDLE. PTYPE HAS BEEN AND CONTINUES TO BE A
HUGE CHALLENGE WITH RAIN...SNOW...HAIL AND THUNDER ALL OBSERVED AT
KCYS OVER THE LAST COUPLE OF HOURS. FARTHER WEST...SNOW IS DOMINANT
AS THERMAL PROFILES ARE MORE THAN COLD ENOUGH WITH VDW SITTING AT 28
DEGREES AT 21Z. HIGH-IMPACT WINTER WEATHER CONDITIONS CONTINUE FOR
THE INTERSTATE 80 CORRIDOR BETWEEN RWL AND CYS. ONGOING WINTER STORM
WARNINGS AND ADVISORIES REMAIN IN EFFECT. DOWNGRADED CHEYENNE TO AN
ADVISORY AS SNOW LEVELS HAVE CLIMBED TO AROUND 6250 FEET...
RESULTING IN RAIN CUTTING BACK ON ADDITIONAL SNOW ACCUMULATIONS.
LATEST WATER VAPOR SATELLITE LOOP SHOWS A VIGOROUS UPPER LOW
SPINNING OVER THE 4 CORNERS REGION. A MID LEVEL DRY SLOT CONTINUES
TO PUSH NORTH ACROSS EASTERN CO INTO THE SOUTHERN PANHANDLE. THIS
IS HELPING TURN THINGS MORE SHOWERY BUT IS ALSO CONTRIBUTING TO
MODERATE INSTABILITY WITH SEVERAL HUNDRED J/KG SBCAPES PER SPC
MESOANALYSIS. COULD SEE A FEW STRONG STORMS ALONG THE I80 CORRIDOR
EAST OF CHEYENNE IN THE LATE AFTN AND EARLY EVE...SO WILL KEEP
MENTION OF SMALL HAIL/GUSTY WINDS GOING. A LITTLE CONCERNED ABOUT
THIS WARM FRONTAL SETUP WITH REALLY GOOD LLVL CONVERGENCE OVER OUR
SOUTHEAST. EAST-TO-NORTHEAST FLOW AT THE SFC IS CONTRIBUTING TO
AROUND 15 KTS OF 0-1 KM SHEAR...SO WOULD NOT BE SURPRISED TO SEE
AN ISOLATED WEAK TORNADO NEAR BOUNDARIES OR CELL MERGERS.

ON THE WINTER SIDE...EXPECT MOST OF THE SNOW IN THE NEAR TERM TO BE
ALONG AND WEST OF THE LARAMIE RANGE. IT IS IN THAT LOCATION THAT THE
BEST H7-H3 MOISTURE AND DYNAMIC FORCING COINCIDE. DO NOT EXPECT MUCH
ADDITIONAL ACCUMULATION WITH DRIER AIR MOVING IN...BUT ROAD SURFACES
ARE LIKELY TO REMAIN TREACHEROUS ESPECIALLY OVER THE I80 SUMMIT. THE
MODELS BRING THE MAIN VORT LOBE NORTHWARD AFTER 00Z. GFS/NAM/ECM ALL
SHOW LLVL WINDS TURNING EASTERLY/UPSLOPE BY 06Z...SO WOULD EXPECT AN
UPTICK IN PCPN ALONG/EAST OF THE LARAMIE RANGE OVERNIGHT. BEST GUESS
IS WE WILL NOT SEE A LOT OF ADDITIONAL ACCUMULATION...BUT WITH A LOT
OF RAIN/SLUSH AND POTENTIAL FOR SUB FREEZING TEMPS / ESPECIALLY WITH
A PRONOUNCED DRY SLOT AND SOME CLEARING / ROADS COULD BE QUITE NASTY
FOR THE MORNING COMMUTE. THAT WAS OUR REASONING FOR KEEPING A WINTER
WEATHER ADVISORY GOING FOR THE CITY OF CHEYENNE. EXTENDED ALL OTHER
WARNINGS THROUGH 12Z SAT AS ACCUMULATING SNOW WILL CONTINUE THROUGH
AT LEAST THAT TIME. THE LAST FEW RUNS OF THE NAM HAVE BEEN MORE THAN
A LITTLE BULLISH WITH DEFORMATION BANDING ON THE BACK SIDE OF THIS
SYSTEM ON SAT AFTN/EVE. PRECIP SHOULD BE ALL SNOW AS A KICKER SYSTEM
DIVES ACROSS EASTERN MT AND FORCES H7 TEMPS BELOW -3 C WITH A COLD
FROPA. WILL LET LATER SHIFTS EVALUATE HOW SIGNIFICANT THIS PCPN WILL
BE AND IF WINTER HEADLINES NEED TO BE EXTENDED FURTHER. ALL MODELS
DO PAINT AT LEAST 0.5 TO 1.0 INCHES OF QPF BETWEEN 12Z SAT AND 12Z
SUN THOUGH...SO THIS WILL DEFINITELY BE INTERESTING TO WATCH.

THUNDERSTORMS COULD BE AN ISSUE TOMORROW AS WELL. THE NAM SHOWS CAPE
VALUES OVER 500 J/KG OVER THE PLAINS FOR MUCH OF THE DAY. H7-H3 HPA
RH PROGS SHOW CONSIDERABLE DRYING WHICH WOULD IMPLY POTENTIAL FOR
BETTER SURFACE HEATING THAN TODAY. THINK A FEW STRONG STORMS ARE A
POSSIBILITY WITH 0-6 KM SHEAR AROUND 50 KTS. OVERALL CONVECTIVE PTNL
WILL DEPEND ON THE TIMING OF THE MID LEVEL ENERGY FROM CO AND THE
EVOLUTION OF THETA-E RIDGING OVER THE WESTERN PANHANDLE. MODELS ARE
ADVERTISING THE STABLE AIR MOVING RIGHT OVER OUR EASTERN ZONES...SO
THIS COULD BE A LIMITING FACTOR FOR TSTMS. A NARROW RIBBON OF WARM
AND MOIST AIR ALOFT WILL BE PRESENT OVER WESTERN AREAS...ENHANCING
PCPN RATES IN THE DEFORMATION AXIS.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 343 PM MDT FRI APR 17 2015

SKIES WILL BEGIN TO CLEAR OUT SUNDAY AS THE UPPER LOW IS KICKED
INTO THE PLAINS BY THE NEXT NORTHWEST FLOW DISTURBANCE. SOME
LINGERING SHOWERS ARE A POSSIBILITY SUNDAY BUT OVERALL IT WILL BE
MUCH DRIER. THE KICKER DISTURBANCE WILL MOVE ACROSS SOUTHEAST
WYOMING SUNDAY NIGHT. THIS DISTURBANCE COULD PRODUCE ANOTHER SHOT
OF SNOW...MAINLY ALONG AND WEST OF THE LARAMIE RANGE. COULD SEE
SEVERAL INCHES OF SNOW INTO THE SNOWY AND SIERRA MADRE RANGES BUT
NOT EXPECTING MUCH IN THE WAY OF ACCUMULATION OUTSIDE OF THE
MOUNTAINS.

SUNDAY WILL BE THE BEGINNING OF A WARMING TREND. THE WARMING
TREND WILL CONTINUE THROUGH AT LEAST WEDNESDAY AND POSSIBLY
THURSDAY DEPENDING ON HOW FAST THE NEXT TROUGH PUSHES INTO THE
REGION. AT THIS TIME LATE THURSDAY INTO FRIDAY LOOKS LIKE IT WILL
BE THE NEXT UNSETTLED PERIOD.


&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1223 PM MDT FRI APR 17 2015

UPPER LEVEL LOW PRESSURE OVER THE SOUTHWEST CONUS WILL MOVE
NORTHEASTWARD TONIGHT AND SATURDAY. WIDESPREAD MVFR TO IFR WILL
CONTINUE THROUGH TONIGHT AND INTO SATURDAY AS FOG...RAIN...AND
SNOW AFFECT THE REGION. MOST SNOW WILL BE FOUND ALONG AND WEST OF
THE LARAMIE RANGE WITH RAIN TO THE EAST. A FEW THUNDERSTORMS ARE
POSSIBLE THIS AFTERNOON AND EARLY EVENING...MAINLY NEAR THE
INTERSTATE 80 CORRIDOR FROM ROUGHLY CHEYENNE TO SIDNEY.

&&

.FIRE WEATHER...
ISSUED AT 323 PM MDT FRI APR 17 2015

UPPER LEVEL LOW PRESSURE WILL PRODUCE ANOTHER DAY OF RAIN AND SNOW
ACROSS THE REGION SATURDAY. THE UPPER LOW WILL EJECT INTO THE PLAINS
SATURDAY NIGHT WITH MOST PRECIPITATION ENDING SATURDAY EVENING.
ANOTHER SHOT SNOW POSSIBLE OVER THE HIGHER ELEVATIONS OF WYOMING
LATE SUNDAY INTO SUNDAY NIGHT.

WARMING TREND THROUGH MID WEEK WITH DRY CONDITIONS MONDAY THROUGH
WEDNESDAY...THEN ANOTHER SYSTEM MAY MOVE ACROSS THE AREA LATE NEXT
WEEK. NO FIRE CONCERNS THIS UPCOMING WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...WINTER STORM WARNING UNTIL 6 AM MDT SATURDAY FOR WYZ114>117.

     WINTER WEATHER ADVISORY UNTIL 6 AM MDT SATURDAY FOR WYZ103-105-
     106-110-112-118.

NE...NONE.

&&

$$

SHORT TERM...CLH
LONG TERM...SML
AVIATION...SML
FIRE WEATHER...SML


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