Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 260341
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
941 PM MDT SAT APR 25 2015

.UPDATE...
ISSUED AT 941 PM MDT SAT APR 25 2015

CONVECTIVE STRENGTH HAS WANED OVER THE PAST FEW HOURS AS
INSTABILITY HAS DECREASED. AS OF 9 PM...THE ONLY AREA OF
ORGANIZED LIGHT TO MODERATE RAIN THAT REMAINED WAS ACROSS TEH
SOUTHERN NEBRASKA PANHANDLE. LATEST 00Z GUIDANCE SUGGEST THIS
PRECIP AREA WILL DISSIPATE ACROSS THE PANHANDLE...WHILE ANOTHER
DEVELOPS ASSOCIATED WITH A LEAD VORT LIFTING NORTH FROM THE
AMPLIFIED FLOW FROM NE COLORADO. ALTHOUGH STILL AWAITING THE 00Z
GFS DATA...THE NAM HAS SHIFTED THE ASSOCIATED AXIS OF HEAVIEST
PRECIP WEST ACROSS THE SOUTHEAST WYOMING PLAINS AND FAR WRN
NEBRASKA PANHANDLE AFTER MIDNIGHT. SUSPECT THAT THE NAM IS A BIT
HEAVY HANDED WITH AMOUNTS. HOWEVER...WOULD THINK THAT WIDESPREAD
ONE QUARTER TO ONE HALF INCH OF RAINFALL WILL CERTAINLY BE A
POSSIBILITY. SNOW LEVELS MAY DIP BRIEFLY TO AROUND 7 KFT LATE
TONIGHT WITH A MIX BELOW TO AROUND 6 KFT. WOULD NOT AT ALL BE
SURPRISED FOR A QUICK COUPLE OF INCHES ABOVE 7 KFT OVER THE I80
SUMMIT BETWEEN MIDNIGHT AND SUNRISE SUNDAY MORNING. FOG STILL
REMAINS ON TRACK AS EARLIER ANTICIPATED...SO WILL KEEP THE DENSE
FOG ADVISORY AS IS. H7 PROGS STILL HOVER BETWEEN 0C AND -2C DURING
THE DAY TOMORROW. DID PULL A MIXTURE A BIT LOWER ON SUNDAY TO
ACCOUNT FOR AT LEAST THE POTENTIAL OF A MODEL WARM BIAS AS WELL AS
WET- BULBING IN HEAVIER AND/OR CONVECTIVE SNOW BANDS.

&&

.SHORT TERM...(TONIGHT THROUGH MONDAY)

ISSUED AT 528 PM MDT SAT APR 25 2015

FOR TONIGHT...AN UPPER LEVEL TROUGH WILL STRENGTHEN AND WILL MOVE
ACROSS THE GREAT BASIN. MIDLEVEL PVA AND UPPER LEVEL DIFFLUENCE
WILL MOVE OVER THE ROCKIES ON THE EASTERN PERIPHERY OF THE TROUGH
IN SOUTHERLY FLOW. A SFC LOW LOOKS TO DEVELOP OVER UTAH/WESTERN
COLORADO IN THIS PATTERN...WITH EAST TO SOUTHEAST FLOW
STRENGTHENING IN THE SFC-700MB LAYER THIS EVENING AND OVERNIGHT
ACROSS THE FORECAST AREA. THE 700MB LLVL JET CORE OF 25-30 KTS
IS PROGGED TO MOVE UP INTO THE PLAINS FROM THE SOUTH...AND
FORECAST SOUNDINGS SHOW LAPSE RATES STEEPENING OVERNIGHT ACROSS
THIS AREA...ESPECIALLY EAST OF A LINE FROM LUSK TO TORRINGTON
KIMBALL. COUPLED UPPER AND LLVL DYNAMICS IN ADDITION TO LLVL
MOISTURE ADVECTION WITHIN THE JET WILL BRING RENEWED CHANCES FOR
SHOWERS AND THUNDERSTORMS OVERNIGHT. SOME STORMS... PARTICULARLY
THOSE THAT DEVELOP ON THE NOSE OF THE LLVL JET...WILL LIKELY
PRODUCE HEAVY RAIN. WITH ONGOING CONVECTION IN THIS AREA PRODUCING
DECENT AMOUNTS OF QPF...WILL HAVE TO MONITOR FOR LOCAL FLOODING.

IN ADDITION...THIS PATTERN IS QUITE CONDUCIVE TO UPSLOPE STRATUS
AND FOG ALONG THE SOUTHERN LARAMIE RANGE...SO WILL GO WITH A
DENSE FOG ADVISORY FOR THE SUMMIT AND EASTERN FOOTHILLS STARTING
LATE EVENING AND CONTINUING OVERNIGHT TO HIGHLIGHT INCREASINGLY
POOR VISIBILITIES FOR THOSE TRAVELING ALONG I-80. FOG COULD BOUNCE
AROUND A BIT IF SHOWERS DEVELOP OVER THE SUMMIT...BUT THINK
VISIBILITIES WILL REMAIN LOW ENOUGH ON THE WHOLE TO WARRANT THE
ADVISORY. DENSE FOG IS POSSIBLE FURTHER NORTH AND EAST LATER IN
THE NIGHT...BUT CONFIDENCE IS NOT AS HIGH AT THIS TIME HOW
WIDESPREAD IT WILL BECOME DUE TO HIGHER POTENTIAL FOR
SHOWERS/TSTORMS FOR THESE AREAS. ANY SHOWER ACTIVITY THAT OCCURS
OVER THE MOUNTAINS WILL LIKELY BE IN THE FORM OF SNOW...ESPECIALLY
ABOVE 9000 FEET.

THE FORECAST BECOMES QUITE COMPLICATED FOR THE REMAINDER OF THE
PERIOD...AND CONFIDENCE OVERALL REMAINS LIMITED ON SNOW LEVELS AND
TOTAL SNOW ACCUMULATIONS.  MODELS CONTINUE TO DIG THE TROUGH INTO
THE DESERT SOUTHWEST AND CLOSE OFF THE UPPER LOW SUNDAY AFTERNOON
OVER NEW MEXICO. THIS LEAVES THE MAIN ENERGY WELL SOUTH OF OUR
AREA...ALTHOUGH CANT RULE OUT A PIECE OF VORTICITY ROTATING UP
TOWARDS OUR AREA FROM THE SOUTH IN THE AFTERNOON AS SOME MODELS
DEPICT. DIFFLUENCE IS PROGGED TO STEADILY DIMINISH THROUGH THE
DAY AS THE MERIDIONAL JET WEAKENS AND SHIFT NORTH. AT THE
SFC...AN INVERTED TROUGH DEVELOPS OVER THE MOUNTAINS THROUGH THE
MORNING AND PERSISTS THROUGH MUCH OF THE DAY AHEAD OF THE COLD
FRONT THAT WILL SLOWLY MOVES FROM NORTHWEST TO SOUTHEAST ACROSS
THE AREA IN THE LATE AFTERNOON AND EVENING. DEEP SOUTHEASTERLY
FLOW THROUGH 250MB LOOKS TO PERSIST WITH PERSISTENT MOIST ISENTROPIC
LIFT OVER MUCH OF THE AREA. STRATUS/FOG MAY CONTINUE THROUGH MUCH
OF THE MORNING AND INTO THE EARLY AFTERNOON AS A RESULT. WITH THE
COMBINATIONS OF UPSLOPE FLOW...ISENTROPIC LIFT...AND SOME
MID/UPPER LEVEL DYNAMICS...WILL SEE WIDESPREAD PRECIP THROUGH THE
DAY. SOME INSTABILITY IS PROGGED OVER THE HIGH COUNTRY AS WELL
WHERE SOME BREAKS IN THE CLOUDS ALLOW SOLAR INSOLATION.
THUNDERSTORMS ARE THEREFORE A POSSIBILITY FOR THESE AREAS WHERE
INSTABILITY IS REALIZED.

ALL THE MODELS SHOW THAT 700MB TEMPS GENERALLY REMAIN AROUND 0 TO
MINUS 1 THROUGH THE DAY AND STEADILY COOL OVERNIGHT TO BETWEEN
MINUS 2 AND MINUS 3. THIS MAKES FORECASTING PRECIP TYPE QUITE
CHALLENGING THROUGH SUNDAY. AM LEANING TOWARDS SNOW MAINLY ABOVE
8000 FEET THROUGH THE DAY...ALTHOUGH ANY CONVECTIVE ACTIVITY COULD
BRING THOSE LEVELS DOWN TO 7000 FEET OR EVEN LOWER DEPENDING ON
THE STRENGTH OF THE ACTIVITY. IN GENERAL...NOT CONFIDENT IN THE
MODEL SOLUTIONS OF TEMPERATURES BASED ON THEIR PERFORMANCE IN LAST
WEEKS SYSTEM...BUT OVERALL UPPER LEVEL FORCING SEEMS TO BE PUSHED
FURTHER SOUTH SLIGHTLY THUS WILL TRY TO FIND SOME MIDDLE GROUND.
WILL KEEP A MIX OF RAIN AND SNOW IN THE FORECAST AROUND THAT 8000
FEET MARK...BUT AGAIN PRECIP COULD CHANGE TO ALL SNOW IN
CONVECTION. SNOW RATES OUTSIDE OF THE CONVECTION SHOULD REMAIN
FAIRLY LOW WITH LACK OF STRONG UPPER FORCING OVERHEAD...SO THAT
MAY HELP KEEP OVERALL SNOW ACCUMULATIONS DOWN. MODELS ALSO SHOW
THAT THE DEFORMATION ZONE MOVING OVERHEAD ON SUNDAY NIGHT WILL BE
FAIRLY WEAK AS UPPER LEVEL ENERGY SPLITS AND THE MERIDIONAL JET
WEAKENS. THUS DO NOT EXPECT SIGNIFICANT ACCUMULATIONS DURING THIS
TIME EITHER AS SNOW LEVELS DROP TO AROUND 6000 FEET OVERNIGHT.

WITH ALL THAT SAID...ANTICIPATE SNOW TOTALS TO RANGE FROM 5 TO 10
INCHES IN THE SNOWY AND SIERRA MADRE MOUNTAINS WITH 2 TO 5 INCHES
IN THE LARAMIE RANGE FROM LATE SUNDAY MORNING THROUGH MONDAY
MORNING. LOCALLY HIGHER AMOUNTS ARE POSSIBLE AT THE MOUNTAIN
PEAKS. ACCUMULATIONS IN THE LOWER ELEVATIONS DOWN TO 6000 FEET
WILL BE GENERALLY 1 TO 3 INCHES OR LESS. WITH LACK OF HIGH SNOW
RATES OUTSIDE OF CONVECTION...WILL SEE QUICK COMPACTION AND
MELTING OF THE SNOW ON ROAD SURFACES AND PERHAPS GRASSY AREAS AS
WELL THAT ARE CURRENTLY BARE. BELOW 6000 FEET...ANTICIPATE LIGHT
TO MODERATE RAINFALL AMOUNTS.

MONDAY WILL SEE LIGHT RAIN AND HIGH ELEVATION SNOW SHOWERS
CONTINUE AS A SECONDARY UPPER LEVEL TROUGH MOVES OVERHEAD...BUT
IMPACTS FROM THIS WAVE WILL BE MINIMAL.

.LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 PM MDT SAT APR 25 2015

UPPER SHORTWAVE LOOKS TO MOVE THROUGH THE AREA MONDAY NIGHT INTO
TUESDAY MORNING. MOUNTAIN SHOWERS LOOK TO COME TO AN END MONDAY
EVENING. GET SOME WARMING TUESDAY AS 700MB TEMPERATURES CLIMB FROM
-3 TO 0C MONDAY AFTERNOON UP TO 0 TO +5C TUESDAY AFTERNOON.

EST OF THE WEEK LOOKS PRETTY DRY WITH BREEZY WEST WINDS. GFS 700MB
WINDS INCREASE TO 30KTS WEDNESDAY AND THURSDAY...SO WOULD THINK
DOWNSLOPING OFF THE LARAMIE RANGE WILL KEEP THINGS DRY. VERY WARM
TOWARDS THE THURSDAY/FRIDAY TIME FRAME AS 700MB TEMPERATURES
CLIMB TO +10C. TEMPERATURES SHOULD BE WELL INTO THE UPPER 70S/LOW
80S IN THE PANHANDLE WITH UPPER 60S/LOW 70S ACROSS SOUTHEAST
WYOMING.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 544 PM MDT SAT APR 25 2015

SCATTERED SHOWERS AND THUNDERSTORMS COULD RESULT IN BRIEF MVFR TO
IFR CIGS/VSBYS AND GUSTY/ERRATIC WINDS THROUGH EARLY EVE...MAINLY
OVER THE WESTERN NE PANHANDLE. VFR CONDITIONS ARE EXPECTED THROUGH
THE EVENING OUTSIDE OF THUNDERSTORMS. LATER ON TONIGHT...EAST TO
SOUTHEAST UPSLOPE FLOW SHOULD RESULT IN IFR/LIFR CONDITIONS ALONG
AND EAST OF THE LARAMIE RANGE. THESE CONDITIONS ARE EXPECTED TO
PERSIST WELL INTO THE DAY ON SUNDAY.


&&

.FIRE WEATHER...
ISSUED AT 330 PM MDT SAT APR 25 2015

MINIMAL FIRE WEATHER CONCERNS AS A SLOW MOVING LOW PRESSURE SYSTEM
TRACKS THROUGH COLORADO OVER THE NEXT COUPLE DAYS. THIS SYSTEM
WILL BRING WETTING RAINS AND MOUNTAIN SNOWS TO MOST AREAS IN
SOUTHEAST WYOMING AND NEBRASKA PANHANDLE. RAIN/SNOW COULD PERSIST
INTO MONDAY BEFORE WINDS SHIFT WESTERLY AND PRECIPITATION ENDS.
WARM AND DRIER WEATHER FROM TUESDAY ON.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...DENSE FOG ADVISORY UNTIL NOON MDT SUNDAY FOR WYZ116-117.

NE...NONE.
&&

$$

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



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