Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 191138
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
538 AM MDT TUE AUG 19 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 538 AM MDT TUE AUG 19 2014

RADAR AND SATELLITE IMAGERY THIS MORNING SHOWS QUITE A BIT OF
SHOWER AND TSTORM ACTIVITY FROM NEVADA...ACROSS UTAH...AND INTO
WESTERN COLORADO AS A POTENT UPPER LEVEL SHORTWAVE MOVES NORTHEAST
ACROSS THIS AREA. THIS SHORTWAVE WILL CONTINUE TO APPROACH THE
CWA FROM THE DESERT SOUTHWEST THIS MORNING ON THE NOSE OF A 70 KT
JET AND WILL TRAVERSE ACROSS THE FORECAST THROUGH THE AFTERNOON
AND EVENING. 00Z MODELS SHOW SOME DIFFERENCES AS TO WHEN THE WAVE
WILL BE OVERHEAD...WITH NAM AND GEM A BIT SLOWER THAN THE ECMWF
AND GFS. RESULTANT SFC PRESSURE...WIND...AND MOISTURE FIELDS WILL
FOLLOW SUIT...WITH THE GFS/EC SHOWING THE LEESIDE SFC TROUGH
SITUATED OVER THE PANHANDLE BY 00Z THIS EVENING AND THE NAM/GEM
TROUGH SITUATED MORE OVER THE SOUTHEAST WYO PLAINS. THE SLOWER
SOLUTION WOULD SUGGEST THAT INITIATION OF CONVECTION ON THE
LEADING EDGE OF THE LEE TROUGH WILL BE OVER THE EASTERN WYO
PLAINS WITH THE POTENTIAL FOR HIGHER INSTABILITY AND SHEAR EAST OF
THE TROUGH IN STRONGER...MOIST SOUTHEASTERLY SFC FLOW. THE FASTER
SOLUTION WOULD (OBVIOUSLY) PUSH MAXIMUM CONVERGENCE/SHEAR/INSTABILITY
FURTHER EAST IN NEBRASKA. TOUGH TO DISCERN EXACTLY WHICH SOLUTION
WILL PAN OUT BASED ON CURRENT WATER VAPOR TRENDS...SO WILL BASED
THIS FORECAST ON A BLEND OF MODEL SOLUTIONS WITH A SLIGHT BIAS
TOWARD THE FASTER GFS/ECMWF SOLUTION.

WITH THAT SAID...WILL SEE SHOWERS AND TSTORMS DEVELOP OVER THE
MOUNTAINS OF SOUTHEAST WYOMING AROUND 18Z AS BROADSCALE UVV INCREASE
WITH THE APPROACHING WAVE. DEVELOPMENT ALONG THE LEE TROUGH WILL
OCCUR SHORTLY THEREAFTER LIKELY NEAR THE WYO/NEB BORDER...WITH
CONVECTION TRACKING INTO THE PANHANDLE THROUGH THE LATE AFT AND
EVENING. SBCAPES WILL INCREASE TO BETWEEN 1000 AND 2500 J/KG FROM
WEST TO EAST ACROSS THE PLAINS AHEAD OF THE LEE TROUGH...WITH
MINIMAL CIN AND ROUGHLY 30 TO 40 KTS OF DEEP LAYER SHEAR IN
PLACE. THERE IS CONCERN THAT THE RATHER THICK CIRRUS BLOWOFF FROM
CURRENT CONVECTION OVER UT/CO MOVES OVERHEAD THIS MORNING AND
STRENGTHENS THE CAP MORE THAN MODELS ARE SUGGESTING RIGHT NOW. 4KM
WRF MODEL SUGGESTS THE AREA FROM NIOBRARA COUNTY INTO THE NORTHERN
PANHANDLE COUNTIES WILL REMAIN SOMEWHAT CLEAR OF THIS CIRRUS THRU
THE MORNING THO...SO THIS AREA COULD BE UNDER THE GUN FOR
STRONG/SEVERE STORMS...AND LOOKS LIKE THE MAIN THREAT WILL BE
BETWEEN 21 AND 02Z. WILL THEREFORE FOCUS MAIN SEVERE THREAT IN
THIS AREA...AS THE NOSE OF THE LLVL MOISTURE AXIS SHOULD BE
POSITIONED NEAR THE PINE RIDGE BY 00Z THIS EVENING AS WELL. LARGE
HAIL AND STRONG DOWNDRAFT WINDS WILL BE THE MAIN THREATS...HOWEVER
ANY LOCALIZED BACKING OF THE SFC WINDS ALONG THE PINE RIDGE DUE TO
TERRAIN INFLUENCES COULD INCREASE LLVL SHEAR ENOUGH FOR A BRIEF
WEAK TORNADO TO OCCUR AS WELL. THE MAIN AND MORE WIDESPREAD THREAT
FROM ANY STORMS WILL BE HEAVY RAIN AS PWATS LOOK TO INCREASE TO
0.75-1.25 INCHES BY 00Z FROM WEST TO EAST. SMALL HAIL IS ALSO A
POSSIBILITY FROM STORMS THAT DEVELOP FURTHER SOUTH AND WEST.

STORM ACTIVITY LOOKS TO CONTINUE OVERNIGHT AS MOIST AND ENERGETIC
SOUTHWEST FLOW CONTINUES TO STREAM OVERHEAD. COVERAGE OF SHOWERS AND
TSTORMS WILL BE LESS ON WEDNESDAY AS OVERALL MOISTURE CONTENT
LESSENS AND MIDLEVEL ENERGY IS WEAKER. STILL LOOKING AT A GOOD
CHANCE FOR STORMS OVER THE MOUNTAINS WITH THE 70KT JET CORE MOVING
OVERHEAD...WITH A MORE ISOLATED THREAT OVER THE PLAINS WITH A DRIER
SFC AIRMASS IN PLACE IN THE WAKE OF THE LEE TROUGH THAT WILL BE
EAST OF THE FORECAST AREA BY WEDNESDAY MORNING.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 538 AM MDT TUE AUG 19 2014

THURSDAY...SOUTHWEST FLOW ALOFT PREVAILS WITH AN ASSOCIATED SURFACE
LEE TROUGH ACROSS SOUTHEAST WYOMING. LOW AND MID LEVEL THETA-E RIDGE
AXIS EXISTS FROM NORTHERN COLORADO ACROSS SOUTHEAST WYOMING WITH
DECENT POSITIVE THETA-E ADVECTION ACROSS OUR COUNTIES. AIRMASS MAY
BE TOO CAPPED FOR CONVECTION ALONG AND EAST OF INTERSTATE
25...THOUGH EXPECT ISOLATED TO SCATTERED LATE DAY THUNDERSTORMS
ALONG AND WEST OF INTERSTATE 25 WHERE CONVECTIVE INHIBITION...CIN...
WILL BE LESS PRONOUNCED.

FRIDAY...ISOLATED TO SCATTERED LATE DAY THUNDERSTORMS ON TAP AS WEAK
CYCLONIC FLOW ALOFT PREVAILS OVER THE ROCKIES...WHILE A LOW LEVEL
CONVERGENCE AXIS IS PROGGED TO BISECT OUR COUNTIES FROM SOUTHWEST TO
NORTHEAST.

SATURDAY...AT LEAST A SCATTERED AFTERNOON AND EVENING COVERAGE OF
SHOWERS AND THUNDERSTORMS IS EXPECTED AS MODELS PROG A LOW LEVEL
CONVERGENCE BOUNDARY ACROSS OUR COUNTIES NEAR PEAK HEATING...WITH
ENOUGH LOW AND MID LEVEL MOISTURE AND SHORTWAVE TROUGHS ALOFT MOVING
ACROSS OUR COUNTIES.

SUNDAY...DRYING TREND ON TAP AS THE FLOW ALOFT TURNS ZONAL AND
COOLER AND MORE STABLE LOW LEVEL SOUTH AND SOUTHEAST WINDS WILL
PREVAIL.

MONDAY...SLIGHT INCREASE IN LATE DAY SHOWER AND THUNDERSTORM
COVERAGE WITH INCREASE IN LOW AND MID LEVEL MOISTURE...AND A SURFACE
TROUGH BISECTING OUR COUNTIES ALONG AND NEAR THE WYOMING AND
COLORADO STATE LINE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 538 AM MDT TUE AUG 19 2014

VFR THIS MORNING...WITH INCREASING CLOUDINESS AND
ISOLATED TO SCATTERED THUNDERSTORMS DEVELOPING THIS AFTERNOON...
PRODUCING LOCALIZED MVFR AND TURBULENCE. DECREASING COVERAGE OF
STORMS TUESDAY EVENING.

&&

.FIRE WEATHER...
ISSUED AT 538 AM MDT TUE AUG 19 2014

AN UPPER LEVEL DISTURBANCE MOVING OVER THE DISTRICT TODAY WILL
PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS BEGINNING LATE THIS
MORNING OVER THE MOUNTAINS...WITH STORMS DEVELOPING OVER THE
EASTERN PLAINS THROUGH THE AFTERNOON AND EVENING AS WELL. MODERATE
TO HEAVY RAINFALL WILL ACCOMPANY THE STORMS AS MONSOON MOISTURE
INCREASES WITH THIS DISTURBANCE. SHOWERS AND THUNDERSTORMS WILL BE
MORE WIDELY SCATTERED OVER THE DISTRICT ON WEDNESDAY AND
THURSDAY...AND WILL BECOME MORE WIDESPREAD ONCE AGAIN FRIDAY AND
SATURDAY AS A STRONGER LOW PRESSURE SYSTEMS MOVES ACROSS THE
ROCKIES. TEMPERATURES WILL COOL AND HUMIDITIES WILL INCREASE WITH
THIS SYSTEM AS WELL.

&&

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

$$

SHORT TERM...RJM
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...RJM





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