Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 061742
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1142 AM MDT SUN JUL 6 2014

.SHORT TERM...(TODAY THROUGH TUESDAY NIGHT)
ISSUED AT 418 AM MDT SUN JUL 6 2014

BROAD UPPER-LEVEL RIDGING REMAINS ANCHORED OVER MUCH OF THE WESTERN
CONUS THIS MORNING PER RECENT WATER VAPOR SATELLITE IMAGERY. AT THE
SURFACE...A BACKDOOR COOL FRONT WAS DRAPED FROM WEST TO EAST ACROSS
NORTHERN WY AND SOUTHWEST SD. LLVL WINDS WILL GRADUALLY SHIFT TO THE
NORTH AND NORTHEAST THROUGH THE DAY AS THIS FRONT BACKS IN TOWARD
THE LARAMIE RANGE FOOTHILLS. H7 TEMPS START OUT QUITE WARM WITH LAPS
SOUNDING ANALYSIS SHOWING +16C AT BFF AS OF 08Z. LATEST WATER VAPOR
SATELLITE LOOP SHOWS THE BEST MID AND HIGH LEVEL MOISTURE OVER THE
NORTHERN ZONES...SO WOULD EXPECT THE BULK OF ANY CLOUD COVER TO BE
THERE WITH AMPLE SUNSHINE ELSEWHERE IN THE AM. CONTINUED SUBSIDENCE
BENEATH THE RIDGE SUGGESTS ANOTHER HOT DAY FOR THE AREA. STILL THINK
THE NORTHERLY COMPONENT TO SFC WINDS AND DEVELOPING CUMULUS IN THE
AFTN WILL HOLD HIGHS BACK ABOUT 2 TO 4 DEG FROM THOSE OBSERVED ON
SAT. LOOK FOR MID 90S TO NEAR 100 FROM TOR SOUTHEAST INTO THE
CENTRAL NEBRASKA PANHANDLE. CONCERNING PCPN CHANCES...MOST MODELS
SHOW MOIST UPSLOPE FLOW BECOMING ESTABLISHED OVER THE LARAMIE RANGE
BY 21Z SUN WITH SFC DEWPOINTS APPROACHING 50F AT CHEYENNE. THE NAM
CONTINUES TO ADVERTISE SOME WEAK DISTURBANCES TRAVERSING THE FLOW
ALONG THE EDGE OF THE RIDGE...BUT THE LACK OF ANY LARGER SCALE
FORCING MECHANISM AND VERY WARM TEMPERATURES ALOFT SHOULD KEEP
ACTIVITY CONFINED TO THE MOUNTAINS. CANNOT RULE OUT ONE OF THESE
STORMS CREEPING OUT ONTO THE PLAINS...SO OPTED TO MAINTAIN SCHC POPS
EASTWARD INTO CYS AFTER 21Z. CAPES LESS THAN 500 J/KG AND WEAK FLOW
ALOFT WILL LIMIT STORM INTENSITY AND ORGANIZATION.

MOIST NORTHWEST FLOW ALOFT RETURNS TO THE NORTHERN ROCKIES ON MON
WITH A FLATTENING UPPER RIDGE. THIS OFFERS SOME RELIEF FROM THE HEAT
AS H7 TEMPS ON BOTH THE GFS AND ECMWF FALL TO BETWEEN 10C AND 12C
OVER THE HIGH PLAINS BY 00Z TUE. STILL QUITE WARM THOUGH. COULD SEE
SOME CONVECTION ONGOING AT 12Z MON ACROSS OUR NORTHEAST ZONES OWING
TO LLVL CONVERGENCE AND WARM ADVECTION ASSOCIATED WITH A SHORTWAVE
OVER THE NORTHERN PLAINS. FASTER / MORE ENERGETIC MIDLVL FLOW SHOULD
SHIFT SOUTH ACROSS MOST OF THE CWA BY EARLY AFTN ATOP PRONOUNCED
LLVL UPSLOPE FLOW. QG ASCENT BECOMES ESTABLISHED DURING THIS TIME AS
WELL...SO WOULD EXPECT GREATER PCPN COVERAGE. INCREASED POPS INTO
THE CHANCE CATEGORY DURING THE AFTN AND EARLY EVE HOURS. H5 FLOW OF
35 TO 45 KTS BOOSTS 0-6 KM SHEAR VALUES TO 40+ KTS. A BIT SURPRISED
THAT BOTH THE GFS AND NAM SHOW CAPES GENERALLY LESS THAN 1000 J/KG
WITH COOLING ALOFT AND MOIST LLVLS...SO THINKING THAT COULD BE A BIT
UNDERDONE. WILL NEED TO WATCH FOR THE POTENTIAL FOR ORGANIZED SEVERE
STORMS ON MON AFTN AND EVE. SPC DAY 2 CONVECTIVE OUTLOOK HAS A SLGT
RISK JUST TO OUR EAST OVER THE SOUTHERN PANHANDLE...AND MOST AREAS
EAST OF THE LARAMIE RANGE IN 5 PERCENT SEVERE PROBS. MODELS SHOW
CONTINUED NORTHWEST FLOW ALOFT ON TUE...BUT BETTER FORCING FOR
ASCENT SHIFTS TO THE NORTHEAST WITH THE DEPARTING SHORTWAVE OVER THE
GREAT LAKES REGION. THIS SHOULD KEEP MOST OF THE SHOWER AND TSTM
ACTIVITY RESTRICTED TO THE MOUNTAINS. TUE WILL BE THE COOLEST DAY OF
THE SHORT TERM PERIOD WITH 1000-500 MILLIBAR THICKNESS VALUES AROUND
577 DM.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 418 AM MDT SUN JUL 6 2014

HIGH PRESSURE OVR THE FOUR CORNERS EARLY IN THE PERIOD WILL SLOWLY
SHIFT EAST TOWARDS THE SRN PLAINS BY WEEKS END. THIS WILL TURN WK
NORTHWEST FLOW OVR THE CWFA SOUTHWESTERLY. THIS PATTERN WILL BE
CONDUCIVE IN ADVECTING SUB-TROPICAL MOISTURE AROUND THE PERIPHERY OF
THE WK HIGH LATE IN THE WK. IN FACT...THE ONE INCH PWAT LINE WILL
BACK TO THE FRONT RANGE BY SATURDAY. BOTH THE ECMWF/GFS ARE
CONSISTENT IN STEERING A SERIES OF EMBEDDED SHORTWAVES THRU THE CWFA
FOR THE LATTER HALF OF THE WEEK AND UPCOMING WEEKEND. THIS WILL
YIELD DAILY AFTERNOON AND EVENING CONVECTIVE CHANCES ACROSS THE
AREA. MEDIUM RANGE MODELS ARE ALSO CONSISTENT IN TRACKING A
SHORTWAVE THRU LATE WEDNESDAY NIGHT AND THURSDAY MORNING...SO KEPT
CONVECTIVE CHANCES GOING THEN DESPITE THE NON-DIURNALLY FAVORABLE
TIMING. PROGD DEEP LAYER SHEAR VALUES WILL HOVER BETWEEN 20-30 KNOTS
THRU THE PERIOD. SO ALTHOUGH THERE WILL BE SOME POTENTIAL FOR
STRONGER CONVECTION...DO NOT SEE SIGNIFICANT SEVERE POTENTIAL. THE
GREATER CONCERN WILL UNDOUBTEDLY TURN TO HEAVY RAIN AS SKINNY CAPES
INTERACT WITH RELATIVELY LIGHT STEERING FLOW. DONT SEE MUCH
TEMPERATURE VARIATION IN THE PERIOD...WITH HIGHS REACHING THE 80S
ABOVE 5 KFT AND 90S BELOW.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY MORNING)
ISSUED AT 1141 AM MDT SUN JUL 6 2014

LATE THIS MORNING WE NOTE A COLD FRONT EXTENDING FROM JUST WEST OF
SHERIDAN ALONG THE LARAMIE RANGE THEN SOUTHEAST TO JUST SOUTHWEST
OF CHEYENNE. LATEST HIGH RESOLUTION RAPID REFRESH MODEL RUN FROM 9
AM MDT CONTINUES PREVIOUS NOTION THAT SCATTERED SHOWERS AND
THUNDERSTORMS WILL FORM UP IN THE NORTHERN COLORADO MOUNTAINS THIS
AFTERNOON...AND WE ARE ALREADY GETTING SOME TALLER CONVECTION
GOING DOWN THAT WAY HERE AT 1130 AM. BY 3 PM OR SO WE MIGHT SEE
ISOLATED SHOWERS/THUNDERSTORMS FORM UP NEAR THE BOUNDARY IN
WESTERN LARAMIE COUNTY AND THAT COULD PASS NEAR KCYS...AND THIS IS
WHERE WE HAVE THE ONLY VICINITY MENTION OF THUNDERSTORMS THIS
AFTENOON. OTHERWISE...WRF GOES-R SIMULATED SATELLITE IMAGERY FOR
MID TO LATE AFTERNOON IS SUGGESTING THAT WE WOULD SEE ISOLATED
STORMS FORM UP ALONG THE NORTHERN LARAMIE RANGE...WHEREAS THE HRRR
KEEPS THAT REGION DRY. AT ANY RATE...THE WRF GOES-R SIMULATION
SUGGESTS THAT CONVECTION WOULD DIMINISH BEFORE REACHING OUR
NEBRASKA FORECAST SITES. GFS IS HINTING AT SOME LATE NIGHT
CONVECTION MOVING DOWN THE NORTHWEST FLOW ALOFT POSSIBLY AFFECTING
KCDR TOWARD MORNING...BUT CONFIDENCE IN THAT IS FAIRLY LOW SO DID
NOT INCLUDE IN THE MID-DAY FORECAST PACKAGE. 02/GARMON

&&

.FIRE WEATHER...
ISSUED AT 418 AM MDT SUN JUL 6 2014

HOT AND DRY CONDITIONS WILL PERSIST THROUGH TUESDAY. AREAS ALONG AND
WEST OF THE LARAMIE RANGE WILL SEE AFTERNOON RELATIVE HUMIDITIES OF
10 TO 15 PERCENT...HOWEVER SURFACE WINDS WILL REMAIN BELOW CRITICAL
THRESHOLDS THROUGH EARLY NEXT WEEK. A WEAK COLD FRONT WILL DROP INTO
THE HIGH PLAINS OF SOUTHEAST WY AND THE WESTERN NE PANHANDLE ON SUN
AFTERNOON...BRINGING SLIGHTLY COOLER TEMPERATURES AND A WIND SHIFT
OUT OF THE NORTHEAST. SHOWERS AND THUNDERSTORMS ARE POSSIBLE OVER
THE HIGHER ELEVATIONS EACH DAY THROUGH TUE...WITH MORE WIDESPREAD
ACTIVITY EXPECTED OVER THE PLAINS ON MON AFTERNOON AND EVENING. A
FEW OF THOSE STORMS COULD BE STRONG TO SEVERE WITH HAIL AND STRONG
WINDS THE MAIN HAZARDS.

&&

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

$$

SHORT TERM...HAMMER
LONG TERM...HAHN
AVIATION...GARMON
FIRE WEATHER...HAMMER





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