Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 181721
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1121 AM MDT MON AUG 18 2014

.UPDATE...
ISSUED AT 1100 AM MDT MON AUG 18 2014

WATER VAPOR IMAGERY LOOP LATE THIS MORNING SHOWED A SHORTWAVE TROUGH
SLIDING SOUTHEAST FROM THE DAKOTAS TOWARD THE UPPER MIDWEST...A
CLOSED LOW DROPPING SOUTH ALONG THE NORTHERN CA COAST...AND A RIDGE
CENTERED OVER THE FOUR CORNERS REGION. WEST-NORTHWEST FLOW ALOFT HAS
PULLED SOME SUBTROPICAL MOISTURE INTO THE CWA TODAY. THE 12Z RIW
SOUNDING PRECIP WATER INCREASED A QUARTER INCH IN THE PAST 24 HOURS.
THIS MOISTURE COMBINED WITH A PASSING WEAK UPPER LEVEL IMPULSE AND
DAYTIME HEATING WILL RESULT IN AFTERNOON TSTORM DEVELOPMENT...WITH
SCATTERED COVERAGE OVER THE SOUTHEAST WY MOUNTAINS AND FOOTHILLS.
THE NAM SHOWS AN INSTABILITY AXIS FROM THE SOUTHERN NE PANHANDLE
NORTHWEST ALONG THE LARAMIE RANGE WITH SBCAPES OF 800-1500 J/KG.
UPSLOPE EASTERLY FLOW WILL ADVECT 50+ DEGREE DEW POINTS INTO
SOUTHEAST WY THIS AFTERNOON. 0-6KM SHEAR IS AROUND 30 KT...SO THE
POTENTIAL IS THERE FOR SOME STRONGER TSTORMS CAPABLE OF PRODUCING
SMALL HAIL AND WIND GUSTS OF 40 TO 50 MPH. WITH DRY AIR LINGERING
IN THE SUB-CLOUD LAYER...HEAVY RAINFALL IS NOT EXPECTED. FOR THE
MORNING UPDATE...TWEAKED CLOUD COVER AND POPS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 529 AM MDT MON AUG 18 2014

TODAY WILL BE ANOTHER VERY WARM DAY AS AN UPPER LEVEL HIGH REMAINS
CENTERED OVER THE FOUR CORNERS REGION AND MAINTAINS H7 TEMPS IN
THE MID TEENS OVER THE CWA. THE SFC FRONT THAT MOVED SOUTH THROUGH
THE EASTERN PLAINS LAST EVENING NOW LOOKS TO BE SITUATED NW-SE
MIDWAY ACROSS THE CWA...WITH WEAK EASTERLY SFC FLOW IN THE EAST
AND WEST-NORTHWEST FLOW TO THE WEST. DEW POINT DEPRESSIONS ACROSS
MANY SITES IN THE EAST ARE 4 DEGREES OR LESS SO WITH LIGHT WINDS
EXPECTED TO CONTINUE THRU THE MORNING...WILL LIKELY SEE PATCHY FOG
ACROSS THIS AREA.

SFC PRESSURE FALLS OUT WEST INDUCED BY HEATING OF THE HIGHER
TERRAIN WILL CAUSE SFC WINDS ACROSS THE PLAINS TO STRENGTHEN
SLIGHTLY AND BECOME AN EAST-NORTHEAST UPSLOPE COMPONENT AGAINST
THE LARAMIE RANGE THRU THE AFTERNOON. INCREASING MID LEVEL
MOISTURE WITHIN ENERGETIC FLOW OFF THE PACIFIC WILL INCREASE PWATS
TO BETWEEN 0.5 AND 1 INCH FROM WEST TO EAST ACROSS THE CWA. THE
COMBINATION OF HIGHER MOISTURE...MID LEVEL ENERGY...AND LLVL
UPSLOPE FLOW WILL BRING A RETURN OF ISO-SCT THUNDERSTORMS FOR MUCH
OF THE CWA THIS AFTERNOON AND EVENING. INITIATION WILL BE OFF THE
MOUNTAINS THRU THE AFTN...WITH A FEW STORMS EXPECTED TO MOVE OFF
THE HIGHER TERRAIN INTO THE PLAINS OF WYOMING AND SOUTHERN
PANHANDLE WHERE SBCAPES WILL INCREASE TO AROUND 700 J/KG BY LATE
AFTERNOON. CIN LOOKS TO BE MINIMAL ACROSS THIS AREA...BUT A
STRONGER CAP WILL BE IN PLACE FURTHER TO THE NORTH AND EAST AND
WILL REDUCE STORM CHANCES IN THAT AREA. BULK SHEAR WILL INCREASE
TO BETWEEN 30 AND 40 KT OVER MUCH OF THE CWA BY 00Z TUESDAY...SO
DO THINK A FEW STORMS WILL BECOME STRONG TO MARGINALLY SEVERE IN
THE LATE AFTERNOON/EVENING...ESPECIALLY WHERE STORMS TRAVERSE
ACROSS THE WYO PLAINS. GUSTY DOWNDRAFT WINDS AND HAIL WILL BE THE
MAIN THREATS FROM THE STRONGER STORM ACTIVITY. UPSLOPE ALONG THE
PINE RIDGE COULD INITIATE CONVECTION HERE IN THE EVENING DEPENDING
ON WHETHER THE CAP CAN BE OVERCOME AT TIME OF MAX HEATING. ADDED
IN A SLIGHT CHANCE FOR THUNDER HERE AS CONFIDENCE IS HIGH FOR AT
LEAST A STORM OR TWO DEVELOPING AROUND 00Z. THE LLVL JET LOOKS TO
STRENGTHEN TO ROUGHLY 20 KT OVERNIGHT WITHIN A WAA PATTERN OVER
THE CWA...WITH THE NOSE OF THE JET ROUGHLY OVER THE PANHANDLE JUST
BEFORE SUNRISE. THEREFORE...WOULD NOT BE SURPRISED TO SEE
REDEVELOPMENT OF A FEW ELEVATED SHOWERS/STORMS IN THIS AREA IN THE
EARLY MORNING ESPECIALLY ALONG THE HIGHER TERRAIN FEATURES.

A DEEPER PLUME OF MONSOONAL MOISTURE WILL STREAM UP FROM THE
SOUTHWEST ON TUESDAY ALONG WITH A STRONGER SHORTWAVE. PWATS WILL
INCREASE TO 0.75 TO 1.25 INCHES FROM WEST TO EAST BY LATE
AFTERNOON WITH THE HIGHER MID LEVEL MOISTURE MOVING IN AND ALSO AS
INCREASING SOUTHEASTERLY SFC FLOW IN ADVANCE OF THE WAVE ADVECTS
HIGHER LLVL MOISTURE INTO THE CWA AS WELL. BUT FIRST...THE
POSSIBILITY EXISTS AS TO WHETHER A STRATUS DECK WILL DEVELOP OVER
THE EASTERN PLAINS EARLY TUESDAY MORNING WITHIN INCREASING
SOUTHEAST FLOW IN THE LOW LEVELS. GUIDANCE DOES NOT SUGGEST A
WIDESPREAD EVENT WITH BL HUMIDITIES PROGGED TO BE ONLY AROUND 75
PERCENT...BUT STRATUS IS COMMON WITH THIS TYPE OF PATTERN SO KEPT
AT LEAST PARTLY CLOUDY SKIES IN THE FORECAST FOR THE POSSIBILITY
THAT STRATUS DOES DEVELOP. IF THE STRATUS DEVELOPS...THIS
COULD HINDER DEVELOPMENT AND STRENGTH OF AFTN TSTORMS. IF
NOT...THEN THE POSSIBILITY FOR A BROADER COVERAGE OF STRONG/SEVERE
STORM THREAT WILL BE HIGHER. SHEAR WILL OVERALL BE WEAKER BY ABOUT
10 KT BUT INSTABILITY WILL BE HIGHER ESPECIALLY IN THE PANHANDLE
WITH SBCAPES APPROACHING 2000 J/KG. FOR NOW...WILL JUST BUMP UP
POPS FOR TUE AFTERNOON AND EVENING AS THE STRONGER SHORTWAVE AND
INCREASING MOISTURE WILL NO DOUBT INITIATE TSTORMS ACROSS THE CWA.
AT THE VERY LEAST...SHOULD SEE MODERATE TO BRIEF HEAVY RAIN OUT OF
THIS ACTIVITY.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 529 AM MDT MON AUG 18 2014

WEDNESDAY...NEGATIVELY TILTED SHORTWAVE TROUGH ALOFT MOVES INTO THE
WESTERN DAKOTAS IN THE AFTERNOON...WITH DRYING WEST AND NORTHWEST
WINDS ACROSS OUR COUNTIES...THUS ONLY ISOLATED LATE DAY
THUNDERSTORMS ON TAP OVER AND NEAR OUR MOUNTAINS.

THURSDAY...SOUTHWEST FLOW ALOFT PREVAILS WITH THE BULK OF THE
MONSOONAL MOISTURE PROGGED TO REMAIN OVER COLORADO...THUS ONLY
EXPECT ISOLATED LATE DAY THUNDERSTORMS OVER AND NEAR THE HIGHER
TERRAIN.

FRIDAY...NEXT SHORTWAVE TROUGH ALOFT MOVES ACROSS OUR COUNTIES NEAR
PEAK HEATING...SPARKING LATE DAY ISOLATED TO SCATTERED THUNDERSTORMS
PRIMARILY NORTH AND EAST OF A DOUGLAS TO KIMBALL LINE.

SATURDAY...ZONAL...WEST TO EAST...FLOW PREVAILS. LOOKS LIKE ENOUGH
LOW AND MID LEVEL...AND LOW LEVEL MOISTURE CONVERGENCE TO PRODUCING
ISOLATED TO SCATTERED LATE DAY THUNDERSTORMS...MOST COMMON OVER THE
HIGHER TERRAIN.

SUNDAY...FLOW ALOFT BACKS TO THE SOUTHWEST...AND WITH THE LOW LEVEL
BOUNDARY ASSOCIATED...OVER OUR NORTHEASTERN COUNTIES...WILL GO WITH
ISOLATED LATE DAY THUNDERSTORMS EAST OF A LUSK TO SIDNEY LINE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY MORNING)
ISSUED AT 1121 AM MDT MON AUG 18 2014

VFR EXPECTED OVERALL THROUGH THE PERIOD AT ALL TERMINALS.
EXCEPTIONS WILL BE SHORT PERIODS OF MVFR VSBYS FROM WIDELY SCTD
AFTERNOON AND EARLY EVENING SHOWERS/TSTMS MAINLY IN THE VCTY OF KLAR
AND KCYS.

&&

.FIRE WEATHER...
ISSUED AT 529 AM MDT MON AUG 18 2014

INCREASING MOISTURE IN THE MID AND LOW LEVELS OF THE ATMOSPHERE
WILL KEEP HUMIDITIES ACROSS THE EASTERN PLAINS AROUND 20 PERCENT
OR HIGHER TODAY...WITH MID TEEN READINGS EXPECTED IN THE LOWER
ELEVATIONS WEST OF THE LARAMIE RANGE. WINDS ACROSS THE DISTRICT
WILL OVERALL BE MUCH WEAKER THAN OVER THE WEEKEND...SO NOT
EXPECTING ANY FIRE WEATHER CONCERNS TODAY. IN ADDITION...WILL
SEE WIDELY SCATTERED T-STORMS DEVELOP OVER THE HIGH COUNTRY THIS
AFTERNOON WITH A FEW STORMS MOVING OVER THE PLAINS AS WELL. THIS
ACTIVITY WILL LIKELY PRODUCE WETTING RAINS. A BETTER CHANCE FOR
MORE WIDESPREAD SHOWERS/STORMS WITH WETTING RAINS WILL OCCUR FOR
THE DISTRICT ON TUESDAY.

&&

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

$$

UPDATE...JAMSKI
SHORT TERM...RJM
LONG TERM...RUBIN
AVIATION...RE
FIRE WEATHER...RJM





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