Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KCYS 210313 AAB
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
913 PM MDT WED MAY 20 2015

.UPDATE...
ISSUED AT 913 PM MDT WED MAY 20 2015

NO MAJOR CHANGES FOR THE EVENING UPDATE. MOST OF THE LIGHT SHOWER
ACTIVITY FROM LATE AFTERNOON EARLY EVENING HAS DISSIPATED WITH THE
EXCEPTION OF SOME LIGHT TO MODERATE SHOWERS PERSISTING IN
SOUTHWESTERN CARBON COUNTY WY. AREAS OF DENSE FOG HAVE REDEVELOPED
OVER THE SUMMIT BETWEEN CHEYENNE AND LARAMIE...AND WILL CONTINUE
THE DENSE FOG ADVISORY THROUGH THURSDAY MORNING FOR THAT PART OF
THE SOUTH LARAMIE RANGE.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY NIGHT)
ISSUED AT 243 PM MDT WED MAY 20 2015

SFC ANALYSIS SHOWS THE HIGH PRESSURE CENTER LOCATED NEAR THE PINE
RIDGE WITH EAST TO NORTHEAST UPSLOPE AND PERSISTENT LOW CLOUDS
ACROSS THE REGION.  IT HAS BEEN ANOTHER COOL DAY WITH TEMPS A GOOD
20 DEGREES BELOW NORMAL.  EXPIRED THE DENSE FOG ADVISORY FOR THE
SOUTH LARAMIE RANGE WITH WYDOT OBS SHOWING MOST VIS ABOVE 1 MILE.
THE HRRR DOES INDICATE VIS DROPPING BELOW ONE HALF MILE OVER THE
SOUTH LARAMIE RANGE BY 03Z.  THIS MAKES SENSE WITH SFC WINDS
REMAINING SOUTHEAST TO SOUTH OVERNIGHT.  HAVE AREAS OF FOG FROM
BUFORD TO THE SUMMIT BY EARLY TONIGHT AND CONTINUING THROUGH
THURSDAY MORING. WILL LET THE EVENING/NIGHT SHIFT MONITOR THE OBS
AND WEBCAMS OVER THE SUMMIT...AS DENSE FOG IS DEFINITELY POSSIBLE IN
THIS PATTERN.  SHOWERS DEVELOPING THIS AFTN ALONG AND WEST OF THE
LARAMIE RANGE HAVE BEEN STRUGGLING TO STAY TOGETHER IN THE VERY
STABLE AIRMASS OVER THE PLAINS.  KEPT ISOLATED TO SCATTERED SHOWERS
CONFINED TO MAINLY THE LARAMIE RANGE AND POINTS WEST THROUGH THE
EVENING.

PATTERN DOES NOT CHANGE A WHOLE LOT BY THURSDAY.  LOW CLOUDS WILL BE
STUBBORN TO CLEAR YET AGAIN WITH MOIST SOUTHEAST LLVL FLOW.
SLIGHTLY BETTER INSTABILITY WILL EXIST ALONG THE LARAMIE RANGE (CAPE
VALUES OF 100-200 J/KG) BUT THIS IS LARGELY DEPENDENT ON SOME AFTN
CLEARING...WHICH IS QUESTIONABLE.  INSTABILITY REALLY DROPS OFF TO
THE EAST OF CHEYENNE SO EXPECTING STORMS TO REMAIN CONFINED IN
VICINITY OF THE LARAMIE RANGE.  A SHORTWAVE WILL EJECT NORTHWARD
FROM COLORADO BY LATE THURS NIGHT AND FRI MORNING.  WITH GOOD UPPER
LEVEL DIFLUENCE...MODELS HAVE BEEN CONSISTENT AT SHOWING WIDESPREAD
RAIN DEVELOPING OVER THE PLAINS BY FRI MORNING AND CONTINUING
THROUGH MUCH OF THE DAY.  THIS IS LOOKING LIKE ANOTHER 0.25-0.75
INCH MAINLY STRATIFORM RAIN EVENT FOR LOCATIONS TO THE EAST OF THE
LARAMIE RANGE.  DID LOWER HIGHS A FEW DEGREES ON FRI WITH HIGHS
STRUGGLING TO GET ABOVE THE MID 50S.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 243 PM MDT WED MAY 20 2015

THE MAIN CONCERN WITH THIS PORTION OF THE FORECAST IS THE SEVERE
WEATHER POTENTIAL SATURDAY.

SATURDAY-SATURDAY NIGHT:
LATEST LOOK AT THE GEM/GEFS ENSEMBLES AND ECMWF ARE SHOWING
REALLY GOOD AGREEMENT IN THE TRACK OF THE UPPER LEVEL TROF THIS
WEEKEND. THE MODELS ARE ALSO IN AGREEMENT IN SHOWING THIS CLOSED
UPPER TROF OPENING UP IN NORTHWEST COLORADO AND SENDING ITS FIRST
PIECE OF ENERGY INTO OUR REGION SATURDAY. HOWEVER...THERE IS QUITE
A BIT OF STANDARD DEVIATION IN THE PLACEMENT OF THE SURFACE LOW
AROUND 00Z SUNDAY. THE MEAN ENSEMBLES ARE SHOWING THE SURFACE LOW
DEVELOPING IN EASTERN COLORADO. HOWEVER...THERE IS SOME HINTS THAT
THIS SURFACE LOW MAY ACTUALLY DEVELOP FURTHER NORTH IN NORTHEAST
COLORADO AND LIFT NORTHEAST THROUGH THE NEBRASKA PANHANDLE. IF
THIS SURFACE LOW DEVELOPS FURTHER NORTH...WE MAY SEE WARMER
TEMPERATURES AND HIGHER LOW LEVEL MOISTURE BEING DRAWN INTO AREAS
EAST OF THE LARAMIE WHICH WILL RESULT IN HIGHER INSTABILITY. THIS
COULD SET THE STAGE FOR SEVERE WEATHER IN AREAS EAST OF THE
LARAMIE RANGE SATURDAY AFTN/EVE...ESPECIALLY WITH 0-6KM SHEAR
VALUES APPROACHING 40 TO 50 KTS. ANOTHER CONCERN IS WHETHER OR NOT
WE WILL SEE LOW CLOUDS. AT THIS POINT...IT DOES NOT APPEAR THAT
THE LOW CLOUDS WILL BE PRESENT...BUT WE WILL HAVE TO SEE HOW THAT
EVOLVES. IF THE LOW CLOUDS ARE NOT PRESENT...TEMPERATURES SHOULD
BE ABLE TO CLIMB TO THE 60S.

SUNDAY-SUNDAY NIGHT:
THE MODELS ARE SHOWING THE MAIN UPPER LEVEL TROF MOVING INTO THE
AREA ON SUNDAY IN ITS WEAKENED STATE. THERE IS A LITTLE MORE
UNCERTAINTY ON HOW THIS TROF WILL IMPACT THE AREA ON SUNDAY
AFTERNOON INTO SUNDAY EVENING. AT THIS POINT...IT APPEARS LIKE THE
MAIN CONVECTION SHOW WILL BE ON SATURDAY AFTERNOON/EVENING.
HOWEVER...IF WE DO NOT SEE MANY STORMS DURING THAT TIME...THEN
SUNDAY MAY BE A DAY TO WATCH AS WELL. IF WE DO SEE WIDESPREAD
CONVECTION ON SATURDAY THEN SUNDAY CHANCES MAY BE MUCH SMALLER.
FOR NOW...WE WILL STAY WITH THE MODEL BLENDS FOR CONSISTENCY SAKE.

MONDAY-WEDNESDAY:
MODELS/ENSEMBLES ARE IN PRETTY GOOD AGREEMENT IN SHOWING THE UPPER
LEVEL RIDGE BUILDING OVER THE AREA AHEAD OF THE NEXT UPPER LEVEL
TROF MOVING INTO THE NORTHERN ROCKIES. THIS TROF WILL INDUCE UPPER
LEVEL DIFFLUENCE OVER THE AREA ON MONDAY AND TUESDAY WHICH COULD
SPARK SOME CONVECTION OVER THE MOUNTAINS WITH SOME OF THIS
CONVECTION POSSIBLY SPILLING OVER INTO THE PLAINS. OVERALL...IT
DOES NOT LOOK LIKE A REAL WET PATTERN...BUT WE CANNOT RULE OUT THE
AFTERNOON AND EVENING CONVECTION CHANCES OVER OUR AREA EITHER.
ALTHOUGH...TEMPERATURES WILL NOT BE TOO COOL WITH HIGHS CLIMBING
TO NEAR NORMAL READING WITH HIGHS MAINLY IN THE 60S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 616 PM MDT WED MAY 20 2015

STARTING TO SEE CEILINGS LIFT TO VFR FLIGHT CATEGORY AT
CHADRON...SCOTTSBLUFF AND ALLIANCE WITH SIDNEY STILL IN MVFR A BIT
LONGER THROUGH 03Z. UPSLOPE FLOW AT CHEYENNE AND LARAMIE WILL
RESULT IN PROLONGED MVFR CEILINGS AROUND 1500 FT AGL THROUGH 03Z
THEN WE DROP THE CEILINGS TO IFR OR BELOW 1000 FT AGL AS UPSLOPE
FLOW STRENGTHENS A BIT OVERNIGHT...AND WE ALSO BRING IN SOME LIGHT
FOG FOR THOSE SITES TOWARD MORNING. A BIT MORE DRIER AIR WORKING
INTO RAWLINS AND THEY SHOULD STAY VFR THROUGH THE FORECAST PERIOD.


&&

.FIRE WEATHER...
ISSUED AT 243 PM MDT WED MAY 20 2015

NO FIRE WEATHER CONCERNS THROUGH THE WEEKEND.  TEMPERATURES WILL
REMAIN BELOW NORMAL AND AFTERNOON HUMIDITY VALUES WILL BE ABOVE 50
PERCENT.  THE BEST CHANCE OF WIDESPREAD WETTING RAIN WILL COME
THURSDAY NIGHT AND FRIDAY.

&&

.HYDROLOGY...
ISSUED AT 243 PM MDT WED MAY 20 2015

LARAMIE RIVER AT FORT LARAMIE AND LARAMIE WILL CONTINUE TO RUN AT
RELATIVELY HIGH LEVELS THROUGH THIS WEEK...BUT AT THIS TIME IS
EXPECTED TO REMAIN WITHIN ITS BANKS. ANOTHER ROUND OF MODERATE TO
HEAVY RAINFALL IS EXPECTED OVER THE HIGH PLAINS AND POSSIBLY THE
LARAMIE VALLEY ON FRIDAY...SO WILL NEED TO CONTINUE TO MONITOR
THE LARAMIE RIVER THROUGH LATE THIS WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...DENSE FOG ADVISORY UNTIL 10 AM MDT THURSDAY FOR WYZ116.

NE...NONE.
&&

$$

UPDATE...JG
SHORT TERM...ZF
LONG TERM...REC
AVIATION...JG
FIRE WEATHER...ZF
HYDROLOGY...ZF



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.