Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 230218
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
818 PM MDT FRI AUG 22 2014

.UPDATE...
ISSUED AT 807 PM MDT FRI AUG 22 2014

A PRONOUNCED MIDLVL SHORTWAVE CONTINUES TO LIFT NORTHEAST ACROSS
CENTRAL CO THIS EVENING PER RECENT WATER VAPOR IMAGERY. REGIONAL
RADAR MOSAIC SHOWS A BAND OF MODERATE RAIN AND EMBEDDED TSTMS HAS
DEVELOPED OVER THE WESTERN NE PANHANDLE...LIKELY SUPPORTED BY A
MESOSCALE VORTEX CURRENTLY IN THE VICINITY OF AKO. THIS AREA OF
PCPN IS EXPECTED TO SHIFT NORTH AND EAST WITH TIME...SO HAVE THE
CATEGORICAL POPS CONFINED TO AREAS ALONG AND SOUTHEAST OF A LINE
FROM IBM TO SNY IN OUR CWA. PCPN INTENSITY SHOULD NOT BE
PARTICULARLY HEAVY TONIGHT AS INSTABILITY WAS MITIGATED BY
EXTENSIVE CLOUD COVER EARLIER TODAY. THINKING ANY THREAT FOR FLASH
FLOODING IS RATHER LOW. NOT SURE HOW WIDESPREAD CONVECTION WILL BE
ELSEWHERE...BUT ENOUGH MOISTURE IN MONSOONAL FLOW COMBINED WITH
LARGER SCALE SUPPORT SUGGESTS A CONTINUED THREAT FOR ISOLATED TO
SCATTERED SHOWERS FOR MOST OF THE NIGHT. FOG COULD BE A CONCERN
TONIGHT...AND WEBCAMS HAVE ALREADY SHOWN THIS IN THE LARAMIE RANGE
FOOTHILLS. DO NOT THINK THIS WILL LAST LONG AS ALL MODEL GUIDANCE
SHOWS LLVL WINDS SHIFTING TO THE SOUTHWEST. FARTHER E...TRUE FOG
IS UNLIKELY WITH MODERATE PCPN. OPTED NOT TO INCLUDE IN THE GRIDS
ATTM BUT WILL CONTINUE TO MONITOR. ONLY OTHER CHANGE TO THE FCST
WAS TO BUMP LOW TEMPS UP A FEW DEGREES WHERE THE MAIN PCPN BAND IS
SETTING UP. DO NOT EXPECT MUCH FOR RADIATIONAL COOLING THERE.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 300 PM MDT FRI AUG 22 2014

PRETTY ACTIVE THE NEXT 24 TO 48 HOURS. TEMPERATURES AND POPS ARE
THE FORECAST CHALLENGES FOR THE SHORT TERM.

CURRENTLY...WATER VAPOR IMAGERY SHOWING A PRETTY PRONOUNCED WAVE
IN THE MONSOONAL FLOW MOVING NORTH THIS AFTERNOON OUT OF NEW
MEXICO INTO WEST CENTRAL COLORADO. MOSAIC RADAR SHOWING WIDESPREAD
SHOWERS OVER CENTRAL COLORADO EARLY THIS AFTERNOON WITH A GENERAL
NORTH NORTHEAST MOVEMENT ON THE CELLS. INFRARED RADAR SHOWING
COOLING CLOUD TOPS WITH THIS WAVE AND WE ARE SEEING AN UPTICK IN
LIGHTNING STRIKES ACROSS WESTERN COLORADO. UPPER LOW OVER IDAHO
FAIRLY DYNAMIC AS WELL WITH NUMEROUS LIGHTNING STRIKES DEVELOPING.
LATEST SPC MESOANALYSIS SHOWING A SLOW EROSION OF CIN OVER EXTREME
SOUTHEAST WYOMING INTO THE KIMBALL AREA...WITH CAPE VALUES
AROUND 1000 J/KG ABOVE. LOOKING AT CLOUD COVER OVERHEAD...IT IS
PRETTY DENSE AND WE HAVE BEEN HARD PRESSED TO GET MUCH WARMING SO
FAR TODAY. 1 PM TEMPERATURES HERE AT THE OFFICE AT 69 DEGREES WITH
LOW TO MID 70S OUT IN THE PANHANDLE.

FOR THIS EVENING...SHORTWAVE BEGINS TO MOVE INTO SOUTHEAST WYOMING
SHORTLY AFTER 00Z WITH GUIDANCE INDICATING FAIRLY WIDESPREAD
CONVECTION DEVELOPING AS THIS HAPPENS. THE 16Z HRRR FORECAST HAS
CONVECTION DEVELOPING HERE AT CHEYENNE AROUND THE 22Z
TIME FRAME...THEN EXPANDING ACROSS SOUTHERN WYOMING INTO THE
PANHANDLE AFTER WARDS. BY 01Z...MOST LOCATIONS EAST OF THE LARAMIE
RANGE SHOULD BE SEEING MEASURABLE RAINFALL WITH SCATTERED SHOWERS
OUT WEST. NAM SOUNDINGS FOR THE PANHANDLE SHOWING PRETTY STRONG
SHEAR OUT IN THE PANHANDLE THIS EVENING. LOOKING AT EASTERLY WINDS
NEAR THE SURFACE OF 15 TO 20KTS WITH SOUTHWEST 40-45KTS AT 6KM.
EVENING SHIFT WILL DEFINITELY NEED TO BE WATCHING FOR SEVERE
THUNDERSTORMS. 0-3KM HELICITY FOR SIDNEY AT 386M2/S2 AT 00Z. GIVEN
THE THICK CLOUD COVER THOUGH...CHANCES ARE DIMMING THAT WE WILL
SEE SEVERE THUNDERSTORMS.

SOMETHING ELSE FOR THIS AFTN/EVE...PRECIPITABLE WATER VALUES
REALLY HIGH FOR THE PANHANDLE. SIDNEY SOUNDING SHOWING 1.42
INCHES...EXTENDING UP TO CHADRON AT 1.40 INCHES. FORECAST QPF
REALLY HIGH FOR THE PANHANDLE AND EXTREME EASTERN WYOMING TONIGHT.
GOOD NEWS IS FORECAST STORM MOTIONS ARE FROM THE SOUTHWEST AT
14-16KTS...SO THESE STORMS SHOULD BE MOVING FAIRLY FAST. WILL NEED
TO WATCH THOUGH FOR TRAINING THUNDERSTORMS AND THERE COULD BE SOME
FLASH FLOODING FOR SOME AREAS THIS EVENING.

GFS AND ECMWF HAVE COME INTO DECENT AGREEMENT WITH THE UPSTREAM
LOW ON THIS 12Z RUN. BOTH SHOWING THE CLOSED LOW MOVING PRETTY
SLOW THROUGH NORTHERN WYOMING THROUGH THE DAY SATURDAY. MOST OF
SATURDAY WILL SEE SHOWERS LASTING MOST OF THE DAY. WENT
SIGNIFICANTLY HIGHER ON POPS OVER GUIDANCE. DO BELIEVE THE MID
SHIFT WILL PROBABLY WANT TO GO HIGHER.

FINALLY SATURDAY EVENING...THE UPPER LOW MOVES OFF INTO SOUTH
DAKOTA WITH RAIN ENDING FROM WEST TO EAST. GOING TO BE PRETTY COOL
WITH 700MB TEMPERATURES DOWN TO +6C SATURDAY NIGHT. SHOULD SEE
WIDESPREAD 40S OUT WEST FOR LOWS...WITH LOW 50S EAST. CLOUD COVER
COULD PROVIDE SLIGHTLY WARMER TEMPERATURES...WE WILL HAVE TO SEE
AS THE EVENT GETS CLOSER. DID GO UNDER GUIDANCE FOR SUNDAY
LOWS...ESPECIALLY OUT WEST WHERE CLOUD COVER WOULD BE LESS.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 335 PM MDT FRI AUG 22 2014

MEDIUM RANGE MODELS IN GOOD AGREEMENT THROUGH EARLY TUESDAY...BUT
THEN SOLUTIONS BEGIN TO DIVERGE THROUGH WEDNESDAY...WITH POOR
CONSISTENCY BETWEEN THE 12Z AND 00Z MODEL RUNS APPARENT INTO LATE
NEXT WEEK. EARLY IN THE WEEK...MOIST SOUTHWEST FLOW AHEAD OF A
POSITIVELY TILTED UPPER LEVEL TROUGH WILL MOVE ACROSS ACROSS THE
IDAHO AND INTO WESTERN WYOMING. A WEAK BOUNDARY WILL DEVELOP AND
DRIFT WESTWARD ALONG THE LARAMIE RANGE...WHICH WILL RESULT IN
UPSLOPE FLOW AND ENHANCE LIFT ACROSS THE HIGH PLAINS. KEPT POP
BETWEEN 35 TO 60 PERCENT ACROSS THE AREA WITH A GOOD CHANCE OF AT
LEAST SCATTERED SHOWERS AND THUNDERSTORMS. ALL MODELS SHOW THIS
ACTIVITY LINGERING THROUGH MONDAY NIGHT AS WELL AS A WAVE OF LOW
PRESSURE DEVELOPS ALONG THE BOUNDARY...WHICH WILL EVENTUALLY
TRANSITION INTO A COLD FRONT. KEPT POP AROUND 50 PERCENT MONDAY
NIGHT. WILL HAVE TO WATCH FOR STRONG TO SEVERE THUNDERSTORMS
MONDAY EVENING WITH CAPE VALUES AROUND 1500 TO 2000 J/KG...HIGH
PW/S...AND INSTABILITY.

ECMWF STILL TRENDING SLOWER WITH THE UPPER LEVEL TROUGH COMPARED
TO THE GFS. THE GEM HAS TRENDED TOWARDS THE ECMWF WHILE THE GFS
PUSHES THE TROUGH THROUGH THE FORECAST AREA AS EARLY AS TUESDAY
AFTERNOON. THE ECMWF AND GEM SHOW THE TROUGH AXIS MOVING ACROSS
THE AREA LATE TUESDAY NIGHT AND EARLY WEDNESDAY. THE GEM AND ECMWF
SOLUTIONS THEN DIVERGE WITH THE ECMWF SHOWING THE SYSTEM
ATTEMPTING TO CLOSE OFF ON WEDNESDAY. EITHER WAY...EXPECT TUESDAY
AND TUESDAY EVENING TO REMAIN UNSETTLED WITH COOLER THAN NORMAL
TEMPERATURES AND A GOOD CHANCE OF WIDESPREAD RAINFALL. HIGHS MAY
STRUGGLE TO REACH THE MID TO UPPER 60S ON TUESDAY AS 700MB
TEMPERATURES LOWER BELOW 5C AFTER THE FRONT MOVES THROUGH THE
AREA. LOW CONFIDENCE ON THE WEDNESDAY FORECAST DUE TO SIGNIFICANT
MODEL DIFFERENCES. KEPT A SLIGHT CHANCE OF SHOWERS AND TSTORMS FOR
NOW DUE TO TIMING DIFFERENCES...EVEN THOUGH THE ECMWF SOLUTION IS
UNLIKELY TO OCCUR.

MUCH DRIER AIR MOVES INTO THE REGION THURSDAY AND FRIDAY BASED ON
CURRENT MODEL RUNS AS THE RIDGE AXIS REDEVELOPS WEST OF THE ROCKY
MOUNTAINS AND DRIFTS EASTWARD. BASED ON 12Z MODELS...WARMER
TEMPERATURES AND DRY CONDITIONS ARE EXPECTED NEXT WEEK.
HOWEVER...THERE IS A LARGE CONTRAST BETWEEN THESE SOLUTIONS AND
THE PREVIOUS 00Z SOLUTIONS FROM LAST NIGHT WHICH SHOW A PACIFIC
SYSTEM MOVES INTO THE REGION WITH ANOTHER STRONG COLD FRONT
ENTERING WYOMING BY LATE FRIDAY. KEPT TEMPERATURES NEAR NORMAL FOR
NOW WITH POP BELOW 10 PERCENT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY AFTERNOON)
ISSUED AT 551 PM MDT FRI AUG 22 2014

A FEW ISOLATED THUNDERSTORMS WILL BE FOUND OVER SOUTHEAST WYOMING
AND THE NEBRAKSA PANHANDLE THROUGH EARLY THIS EVENING...BUT WILL
MOSTLY SEE RAIN SHOWERS. CONDITIONS WILL MAINLY REMAIN VFR THROUGH
EARLY THIS EVENING BUT MVFR WILL OCCUR WITH SOME HEAVIER SHOWERS
INTO THE SOUTHERN NEBRASKA PANHANDLE AND NEAR THE COLORADO AND
WYOMING BORDER IN FAR SOUTHEAST WYOMING. INTO THE LATE NIGHT HOURS
IFR CIGS WILL OCCUR OVER MUCH OF SOUTHEAST WYOMING AND NEBRASKA
PANHANDLE...MAINLY ALONG AND EAST OF THE LARAMIE RANGE. FOG IS
POSSIBLE LATE TONIGHT THROUGH MID MORNING SATURDAY WITH POCKETS OF
LIFR. ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS EXPECTED FOR
SATURDAY AFTERNOON AND EVENING.


&&

.FIRE WEATHER...
ISSUED AT 300 PM MDT FRI AUG 22 2014

MINIMAL FIRE WEATHER CONCERNS ACROSS THE AREA THROUGH THE NEXT FEW
DAYS. UPPER LOW PRESSURE OVER IDAHO THIS AFTERNOON WILL BRING
INCREASING MONSOONAL MOISTURE AND FAIRLY WIDESPREAD RAINFALL TO
MUCH OF THE AREA TONIGHT INTO SATURDAY. BEST CHANCES FOR WETTING
RAINS WILL BE ALONG AND EAST OF THE LARAMIE RANGE AS WELL AS THE
SNOWY AND SIERRA MADRE RANGES. THE UPPER LOW WILL GRADUALLY MOVE
INTO WESTERN SOUTH DAKOTA EARLY SUNDAY MORNING WITH RAINS ENDING
FROM WEST TO EAST. COOLER TEMPERATURES BEHIND THE LOW WILL KEEP
AFTERNOON HUMIDITIES FAIRLY HIGH WITH EXCELLENT OVERNIGHT

&&

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

$$

UPDATE...HAMMER
SHORT TERM...CLAYCOMB
LONG TERM...TJT
AVIATION...SML
FIRE WEATHER...CLAYCOMB






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