Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 310427
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1027 PM MDT SAT AUG 30 2014

.UPDATE...
ISSUED AT 826 PM MDT SAT AUG 30 2014

CONVECTION IS STARTING TO WIND DOWN ACROSS THE CWA THIS EVE. WIND
GUSTS IN EXCESS OF 45 MPH WERE COMMON WITH LARGE SFC TEMP-DEWPOINT
SPREADS AND RESULTANT INVERTED-V SOUNDING PROFILES. WE HAD ONE
STORM KICK OUT SOME INTENSE OUTFLOW AS IT MOVED OVER CYS AROUND
500 PM WITH GUSTS TO 60 MPH REPORTED AT THE INTERSTATE 80 PORT OF
ENTRY EAST OF CHEYENNE. MORE WIDESPREAD PCPN AND A GENERAL LOSS OF
DIURNAL HEATING HAS STABILIZED THINGS FOR THE REST OF THE NIGHT SO
DO NOT EXPECT ANYMORE BIG WIND GUSTS. SHOULD ALSO SEE LESS IN THE
WAY OF LIGHTNING STRIKES WITH MAINLY SHOWERS OVERNIGHT. WATER
VAPOR SATELLITE SHOWS THE LEAD SHORTWAVE MOVING ACROSS FAR EASTERN
WY AS OF 02Z. THIS IS RESPONSIBLE FOR ONGOING NUMEROUS SHOWERS AND
WEAK TSTMS OVER THE PANHANDLE. CLEARING/SUBSIDENCE IN THE WAKE OF
THIS FEATURE SHOULD SHUT PCPN OFF FOR A LITTLE WHILE. WENT AHEAD
AND KEPT ISOLATED POPS IN FOR MOST OF THE NIGHT AS THE MAIN COLD
FRONT IS STILL HANGING BACK OVER CENTRAL WY. FROPA OVERNIGHT AND
LARGER SCALE ASCENT ASSOCIATED WITH A LARGER PIECE OF SHORTWAVE
ENERGY CURRENTLY UPSTREAM WILL RESULT IN AN INCREASE IN SHOWERS
FROM WEST TO EAST BY DAYBREAK SUN. UPDATED POPS AND CLOUD TRENDS
BASED ON CURRENT RADAR/SATELLITE IMAGERY. OTHERWISE THE INHERITED
FCST IS IN GOOD SHAPE TONIGHT BASED ON OBS AND NEAR TERM HIGH-RES
MODELS.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 418 PM MDT SAT AUG 30 2014

WATER VAPOR IMAGERY FROM THIS AFTERNOON SHOWS THE LEAD IMPULSE IN
A QUASI-ZONAL FLOW PATTERN ENTERING SOUTHWEST WYOMING THIS
AFTERNOON...WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
DEVELOPING OVER THE CWA OUT AHEAD OF THIS WAVE. THE FOCUS FOR
CONVECTIVE INITIATION WAS OVER THE MOUNTAINS EARLY THIS AFTERNOON...AND
ALONG VARIOUS BOUNDARIES THAT SET UP ALONG LARAMIE AND CONVERSE
COUNTIES THIS AFTERNOON. MLCAPES ARE UP TO 500 J/KG ACROSS THE
PLAINS ACCORDING TO SPC MESOANALYSIS...WITH DEEP LAYER SHEAR 20
KTS OR LESS. THEREFORE...EXPECT CONVECTION TO CONTINUE THROUGH
THIS EVENING INCLUDING LOCATIONS ACROSS THE NEB PANHANDLE AS THE
UPPER WAVE APPROACHES. BUT WITH LACK OF SIGNIFICANT INSTABILITY
AND SHEAR...STORMS SHOULD REMAIN RELATIVELY WEAK WITH GUSTY AND
ERRATIC WINDS THE MAIN IMPACT. WITH MODERATE SOUTHWEST WINDS ALREADY
IN PLACE OVER MUCH OF THE FORECAST AREA DUE TO 3MB/3HR PRESSURE
FALLS OVER THE HIGH PLAINS...TSTORM DOWNDRAFTS COULD AUGMENT THE
CURRENT WINDS SPEEDS...WITH GUSTS OF 50 TO 55 MPH GUSTS POSSIBLE
FROM ANY STORMS.

A COLD FRONT WILL TRY TO MOVE SOUTH ACROSS THE CWA THIS
EVENING...BUT LOOKS TO STALL NW-SE ACROSS CONVERSE COUNTY INTO THE
NORTHERN NEB PANHANDLE TONIGHT THRU EARLY SUNDAY. THIS SHOULD
MAINTAIN SHOWER/TSTORM DEVELOPMENT OVER THIS AREA THIS EVENING AND
AS THE UPPER WAVE MOVES ACROSS THE FORECAST AREA. A SECOND AND
STRONGER PV ANOMALY WILL APPROACH FROM THE WEST EARLY SUNDAY
MORNING...WITH A RE-INTENSIFICATION OF CONVECTION EXPECTED THROUGH
THE MORNING IN RESPONSE TO THE INCREASED UPPER FORCING. THE LEFT
EXIT REGION OF A 105 KT JET WILL MOVE OVERHEAD BY THE AFTERNOON AS
WELL...WITH THE SFC FRONT MAKING A RUN SOUTH ACROSS THE PLAINS
THROUGH THE LATE AFTERNOON. SO ANTICIPATE A GOOD COVERAGE OF
SHOWERS AND STORMS THROUGH THE DAY WITH THE COMBINATION OF SFC AND
UPPER FORCING...AND INCREASED POPS ANOTHER 5 TO 10 PERCENT FROM
THE PREVIOUS FORECAST. LOOKING AT GUSTY WINDS...SMALL HAIL AND
BRIEF MODERATE RAIN TO BE THE MAIN THREATS AS INSTABILITY VALUES
ARE PROGGED TO BE BETWEEN 500 AND 1000 J/KG THRU THE AFTERNOON
WITH ROUGHLY 30 KTS OF SHEAR OVERHEAD. MUCH DRIER AIR WILL MOVE IN
SUNDAY EVENING WITH STORMS PUSHING TO THE EAST. ANOTHER
COLD FRONT WILL APPROACH FROM THE NORTH MONDAY AFTERNOON AND
SHOULD INITIATE A FEW SHOWERS AND T-STORMS ACROSS THE PLAINS IN
THE AFTERNOON. OTHERWISE...SUNDAY AND MONDAY LOOK TO BE MUCH
COOLER THAN TODAY WITH THE PASSAGE OF THESE COLD FRONTS.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 418 PM MDT SAT AUG 30 2014

THE LONGWAVE UPPER TROUGH SHOULD CONTINUE SHIFTING EAST OF OUR
REGION TUESDAY WITH A DEEPLY DRY AIRMASS IN PLACE WITH MOST OF ANY
STRONGER SHORTWAVE ENERGY COMING DOWN THE NORTHWESTERLY FLOW ALOFT
REMAINING TO THE NORTH THROUGH AT LEAST WEDNESDAY. THIS PATTERN
WILL KEEP OUR AREA DRY THROUGH WEDNESDAY...POSSIBLY SIGNIFICANTLY
DRY WITH GFS SUGGESTING BOUNDARY LAYER DEWPOINTS GETTING INTO THE
UPPER TEENS FOR SOME AREAS OUT IN THE HIGHER TERRAIN AND WESTERN
ZONES TUESDAY INTO WEDNESDAY. SYNOPTIC SCALE PATTERN INDICATED IN
THE GFS/ECMWF SUGGESTIVE THAT WESTERLY/SOUTHWESTERLY DOWNSLOPE
WINDS WILL COME UP A BIT TUESDAY INTO WEDNESDAY AND WE ARE
FORECASTING THEM A LITTLE HIGHER THAN WHAT THE RAW MODEL GUIDANCE
SUGGESTS MIDWEEK WITH DEWPOINTS A FEW DEGREES DRIER AS WELL
(PLEASE REFER TO FIRE WEATHER SECTION OF THE DISCUSSION FOR MORE
INFORMATION ON POTENTIAL IMPACTS). OTHERWISE...GFS AND NOW THE ECMWF
BOTH IN FAIR AGREEMENT DEEPENING AN UPPER TROUGH ALONG THE WEST
COAST THURSDAY INTO FRIDAY...INDUCING A MORE SOUTHWESTERLY
MID/UPPER FLOW ACROSS OUR AREA GOING INTO LATE WEEK. THIS
PATTERN...IF IT DEVELOPS...SHOULD HELP US TAP INTO ANOTHER ROUND OF
PACIFIC MOISTURE COMING UP THROUGH THE 4 CORNERS REGION INTO
SOUTHERN WYOMING AND WESTERN NEBRASKA...SO WE CONTINUED PREVIOUS
FORECAST TREND OF BRINGING SLIGHT CHANCE TO LOCALLY CHANCE POPS
(HIGHER TERRAIN) FOR SHOWERS/THUNDERSTORMS BY LATE IN THE NEXT
WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY EVENING)
ISSUED AT 1025 PM MDT SAT AUG 30 2014

COLD FRONT CONTINUES TO SLOWLY MOVE INTO THE AREA LATE THIS
EVENING. STILL KICKING OFF SOME THUNDERSTORMS OVER THE MOUNTAINS
TO THE WEST...BUT ELSEWHERE...RADAR SHOWING CONVECTION COMING TO
AN END. VFR CONDITIONS EXPECTED AT ALL TAF SITES OVERNIGHT. RETURN
OF GUSTY WINDS AND ISOLATED THUNDERSTORMS FOR SUNDAY AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 418 PM MDT SAT AUG 30 2014

WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL
CONTINUE THIS AFTERNOON AND EVENING FOR MUCH OF THE DISTRICT AS A
STRONG WEATHER DISTURBANCE MOVES THROUGH THE AREA. A WEAK COLD
FRONT WILL MOVE SOUTH ACROSS ZONES 301 AND 311...AND WILL STALL
ACROSS THIS AREA TONIGHT THROUGH EARLY SUNDAY. GUSTY WEST TO
SOUTHWEST WINDS OCCURRING THIS AFTERNOON SOUTH OF THE FRONT WILL
EASE TONIGHT...AND WILL INCREASE ONCE AGAIN THROUGH SUNDAY MORNING
WITH GUSTS BETWEEN 30 AND 40 MPH EXPECTED ALONG AND WEST OF THE
LARAMIE RANGE THROUGH THE AFTERNOON. WINDS ACROSS THE PLAINS WILL
BE GUSTING 25 TO 30 MPH IN THE LATE MORNING UNTIL THE FRONT
FINALLY PUSHES SOUTH ACROSS THIS AREA BETWEEN 1200 AND 1900.
SHOWERS AND T-STORMS WILL OCCUR ALONG THE FRONT AND AS ANOTHER
STRONG WEATHER DISTURBANCE MOVES OVER THE AREA THROUGH SUNDAY.
DRIER CONDITIONS WILL DEVELOP BY MIDDLE OF NEXT WEEK WHILE GUSTY
WEST WINDS CONTINUE IN AREAS ALONG AND WEST OF THE LARAMIE RANGE.
LOOKING FOR FIRE WEATHER CONCERNS TO INCREASE ACROSS THIS AREA AS
A RESULT.

&&

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

$$

UPDATE...HAMMER
SHORT TERM...RJM
LONG TERM...GARMON
AVIATION...CLAYCOMB
FIRE WEATHER...RJM






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