Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 222129
AFDCYS

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

.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 18Z TAFS THROUGH 18Z SATURDAY MORNING)
ISSUED AT 1145 AM MDT FRI AUG 22 2014

A BAND OF RAIN SHOWERS AND ISOLATED THUNDER WILL CONTINUE OVER THE
SOUTHERN NEBRASKA PANHANDLE OVER THE NEXT HOUR OR TWO BEFORE
DISSIPATING BY EARLY THIS AFTERNOON. EXPECT A BRIEF BREAK...WITH
MAINLY VFR CONDITIONS THIS AFTERNOON. THE ONLY EXCEPTION WILL BE
KCDR WHICH WILL MAINTAIN A LOW STRATUS DECK. ALL MODELS INDICATE AN
AREA OF HEAVY SHOWERS AND STRONG THUNDERSTORMS DEVELOPING OVER THE
HIGH PLAINS SOMETIME LATE THIS AFTERNOON AS A STRONG UPPER LEVEL
DISTURBANCE LIFT NORTHWARD OUT OF NEW MEXICO...AND WILL CONTINUE TO
MOVE NORTHWARD ACROSS THE AREA TONIGHT. FAIRLY CONFIDENT OF MVFR OR
IFR CONDITIONS IN THESE HEAVY SHOWERS WITH THE POTENTIAL FOR FOG AND
LOW STRATUS RESULTING IN AN EXTENDED PERIOD OF BORDER-LINE IFR
CONDITIONS INTO SATURDAY MORNING ACROSS THE HIGH PLAINS. KRWL AND
KLAR SHOULD REMAIN VFR TONIGHT WITH MOST OF THE ACTIVITY FURTHER TO
THE EAST...BUT CAN NOT RULE OUT SOME SHOWERS AND TSTORMS OVER THOSE
AREAS AS WELL.

&&

.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
RECOVERIES THROUGH THE MIDDLE OF NEXT WEEK.
&&

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

$$

SHORT TERM...CLAYCOMB
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...CLAYCOMB













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