Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 231804 AAB
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
1204 PM MDT THU APR 23 2015

.UPDATE...FOR NOON AVIATION FORECAST RELEASE.

UPDATE ISSUED AT 1129 AM MDT THU APR 23 2015

THE MAIN CONCERN THIS AFTERNOON WILL BE THE POTENTIAL FOR
STRONG CONVECTION IN THE SOUTHERN PANHANDLE THIS AFTERNOON.

LATEST VISIBLE IMAGERY WAS SHOWING A BOUNDARY APPROACHING THE
CHEYENNE RIDGE WITH THE LEE TROF EXTENDING JUST EAST OF THE
LARAMIE RANGE. LATEST RADAR LOOP WAS ALREADY STARTING TO SHOW
CONVECTION DEVELOPING IN THE SNOW RANGE. 17Z LAPS DATA IS SHOWING
SOME INSTABILITY WITH SURFACE BASED CAPE VALUES AROUND
500-1000J/KG. THEREFORE...IT APPEARS THERE SHOULD BE ENOUGH
INSTABILITY FOR SOME THUNDERSTORMS IN THAT REGION. AIR MASS BELOW
THE LFC IS CERTAINLY VERY DRY WHICH MAY FAVOR THE POTENTIAL FOR
GUSTY WINDS UNDERNEATH ANY SHOWERS AND THUNDERSTORMS THIS
AFTERNOON.

THE SOUTHERN PANHANDLE WILL CERTAINLY NEED TO BE WATCHED THIS
AFTERNOON. SURFACE DEWPOINTS HAVE CLIMBED TO THE MID 40S MAINLY
EAST OF A HARRISON TO KIMBALL LINE. THE MODELS ARE POINTING TO THE
HIGHEST 0-6KM SHEAR VALUES BEING IN THE SOUTHERN PANHANDLE WHERE
VALUES COULD REACH 30 TO 40KTS THIS AFTERNOON. SURFACE BASED CAPE
VALUES MAY ALSO APPROACH 1500 J/KG WHICH WILL BE SIGNIFICANT ENOUGH
TO PRODUCE A FEW STRONG/SEVERE STORMS MAINLY IN THE SOUTHERN
PANHANDLE. AS A RESULT...WE BUMPED UP PRECIPITATION CHANCES IN
THIS REGION THIS AFTERNOON AND HIT THE POTENTIAL FOR STRONG
THUNDERSTORMS WITH GUSTY WINDS AND SMALL HAIL.

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 330 AM MDT THU APR 23 2015

SHOWERS AND A FEW THUNDERSTORMS WILL BE POSSIBLE THE REST OF THIS
WEEK AND INTO THE WEEKEND. INSTABILITY WILL INCREASE THIS
AFTERNOON WHICH ALONG WITH SUPPORTIVE UPPER LEVELS OF THE
ATMOSPHERE WILL PRODUCE SOME SHOWER AND THUNDERSTORM ACTIVITY
TODAY. CONCERNS FOR SEVERE THUNDERSTORM POTENTIAL IS ON THE LOW
SIDE BUT IS NOT ZERO. TYPICAL INVERTED V SOUNDING OVER SOUTHEAST
WYOMING IS SUPPORTIVE FOR ISOLATED STRONG WIND GUSTS THIS
AFTERNOON AND EVENING...OTHERWISE NOT EXPECTING SEVERE
THUNDERSTORMS FOR SOUTHEAST WYOMING.

THE GREATER RISK FOR SEVERE WEATHER WILL BE OVER THE NEBRASKA
PANHANDLE IN CONJUNCTION WITH THE MAIN INSTABILITY AXIS THIS
AFTERNOON AND EARLY EVENING. MU CAPES SHOULD BE BETWEEN 1000-1500
J/KG WHICH MAY MAKE FOR FAIRLY ROBUST UPDRAFTS. 0-6 KM BULK SHEAR
VALUES WILL RANGE BETWEEN 30 AND 40 KTS WHICH WILL BE ENOUGH FOR
MARGINAL SEVERE THUNDERSTORMS. CONSIDERING WETBULB ZERO HEIGHTS
AROUND 5000 FT AGL...COULD VERY EASILY SEE A FEW THUNDERSTORMS
CAPABLE OF PRODUCING 1 INCH DIAMETER HAIL AS THERE WILL BE VERY
MINIMAL MELTING POTENTIAL. TORNADO THREAT IS VERY LOW BUT NOT
COMPLETELY IMPOSSIBLE SHOULD A STRONGER THUNDERSTORM UPDRAFT
ENCOUNTER HORIZONTAL VORTICITY...SUCH AS ALONG AN OUTFLOW
BOUNDARY.

SHOWER AND THUNDERSTORMS WILL MAINLY DIE OUT THIS EVENING BUT
THERE WILL BE ANOTHER CHANCE BY FRIDAY AFTERNOON. AT THIS TIME THE
SET UP FOR SEVERE THUNDERSTORM ARE NOT EXPECTED WITH COOL AIR IN
PLACE. ALSO LOOKING FOR EXTENSIVE HIGH CLOUDS WHICH WILL INHIBIT
SURFACE HEATING AND INSTABILITY.

MODELS ARE TRENDING SLOWER WITH THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS SATURDAY AS THE UPPER LEVEL THROUGH IS A BIT SLOWER
SPREADING INTO THE ROCKIES. MOST PRECIPITATION WILL HOLD OFF UNTIL
SATURDAY EVENING AND MAY SEE PRECIPITATION BECOME WIDESPREAD.
SEVERE THUNDERSTORMS ARE NOT EXPECTED AT THIS TIME.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 350 AM MDT THU APR 23 2015

MAIN FORECAST CONCERN FOR THE LONG RANGE PERIOD WILL BE THIS
WEEKEND AND EARLY NEXT WEEK AS AN UPPER LEVEL LOW DEVELOPS NEAR
THE FOUR CORNERS REGION AND MOVES EASTWARD ACROSS THE
CENTRAL/SOUTHERN ROCKY MOUNTAINS. MODELS ARE IN PRETTY GOOD
AGREEMENT WITH NOT ONLY THE POSITION OF THE UPPER LEVEL LOW...BUT
ALSO WITH THE TIMING AND TRACK OF A POTENT SHORTWAVE LIFTING
NORTHWARD AHEAD OF THE MAIN LOW ON SUNDAY. ALL MODELS SHOW BETWEEN
ONE HALF TO ONE INCH OF QPF ON SUNDAY DUE TO THE COMBINATION OF
UPSLOPE FLOW...INSTABILITY...AND NEARLY SATURATED MODEL SOUNDINGS
UP TO 500MB. CONTINUED TO INCREASE POP BETWEEN 50 TO 70 PERCENT
ACROSS THE HIGH PLAINS AND THE MOUNTAINS. SNOW LEVELS WILL BE
RELATIVELY HIGH WITH THIS SYSTEM INITIALLY...UP AROUND 9000 FEET
INTO EARLY SUNDAY. HOWEVER...SOME COOLER AIR WILL ENTER THE
FORECAST AREA BY LATE SUNDAY. SNOWLEVELS MAY LOWER TO NEAR 6500
FEET BY EARLY MONDAY MORNING WITH RAIN/SNOW MIX DOWN TO 6000 FEET.
THANKFULLY...ANY SNOW WILL NOT LAST TOO LONG AS THE UPPER LEVEL
LOW WILL THEN PUSH SOUTH TOWARDS THE MEXICAN BORDER. LOOKS LIKE A
DECENT RAIN EVENT FOR THE HIGH PLAINS...BUT OTHERWISE A MODERATE
IMPACT OVER SOUTHEAST WYOMING AT MOST DUE TO HIGH SNOW LEVELS AND
A LOW CHANCE OF STRONG TSTORMS ACROSS THE HIGH PLAINS INCLUDING
WESTERN NEBRASKA. COOLER THAN AVERAGE TEMPERATURES ARE EXPECTED
SUNDAY AND MONDAY WITH HIGHS IN THE 40S AND 50S.

MODELS THEN SHOW A HIGH AMPLITUDE RIDGE OF HIGH PRESSURE ALOFT
MOVING EASTWARD INTO WESTERN COLORADO AND WYOMING FOR THE MIDDLE
OF NEXT WEEK. TEMPERATURES WILL MODERATE TO NORMAL WITH A LOW
CHANCE OF PRECIPITATION (BELOW 10 PERCENT) EXPECTED BY WEDNESDAY
OF NEXT WEEK.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 330 AM MDT THU APR 23 2015

SHOWERS AND A FEW THUNDERSTORMS WILL BE POSSIBLE THE REST OF THIS
WEEK AND INTO THE WEEKEND. INSTABILITY WILL INCREASE THIS
AFTERNOON WHICH ALONG WITH SUPPORTIVE UPPER LEVELS OF THE
ATMOSPHERE WILL PRODUCE SOME SHOWER AND THUNDERSTORM ACTIVITY
TODAY. CONCERNS FOR SEVERE THUNDERSTORM POTENTIAL IS ON THE LOW
SIDE BUT IS NOT ZERO. TYPICAL INVERTED V SOUNDING OVER SOUTHEAST
WYOMING IS SUPPORTIVE FOR ISOLATED STRONG WIND GUSTS THIS
AFTERNOON AND EVENING...OTHERWISE NOT EXPECTING SEVERE
THUNDERSTORMS FOR SOUTHEAST WYOMING.

THE GREATER RISK FOR SEVERE WEATHER WILL BE OVER THE NEBRASKA
PANHANDLE IN CONJUNCTION WITH THE MAIN INSTABILITY AXIS THIS
AFTERNOON AND EARLY EVENING. MU CAPES SHOULD BE BETWEEN 1000-1500
J/KG WHICH MAY MAKE FOR FAIRLY ROBUST UPDRAFTS. 0-6 KM BULK SHEAR
VALUES WILL RANGE BETWEEN 30 AND 40 KTS WHICH WILL BE ENOUGH FOR
MARGINAL SEVERE THUNDERSTORMS. CONSIDERING WETBULB ZERO HEIGHTS
AROUND 5000 FT AGL...COULD VERY EASILY SEE A FEW THUNDERSTORMS
CAPABLE OF PRODUCING 1 INCH DIAMETER HAIL AS THERE WILL BE VERY
MINIMAL MELTING POTENTIAL. TORNADO THREAT IS VERY LOW BUT NOT
COMPLETELY IMPOSSIBLE SHOULD A STRONGER THUNDERSTORM UPDRAFT
ENCOUNTER HORIZONTAL VORTICITY...SUCH AS ALONG AN OUTFLOW
BOUNDARY.

SHOWER AND THUNDERSTORMS WILL MAINLY DIE OUT THIS EVENING BUT
THERE WILL BE ANOTHER CHANCE BY FRIDAY AFTERNOON. AT THIS TIME THE
SET UP FOR SEVERE THUNDERSTORM ARE NOT EXPECTED WITH COOL AIR IN
PLACE. ALSO LOOKING FOR EXTENSIVE HIGH CLOUDS WHICH WILL INHIBIT
SURFACE HEATING AND INSTABILITY.

MODELS ARE TRENDING SLOWER WITH THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS SATURDAY AS THE UPPER LEVEL THROUGH IS A BIT SLOWER
SPREADING INTO THE ROCKIES. MOST PRECIPITATION WILL HOLD OFF UNTIL
SATURDAY EVENING AND MAY SEE PRECIPITATION BECOME WIDESPREAD.
SEVERE THUNDERSTORMS ARE NOT EXPECTED AT THIS TIME.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 350 AM MDT THU APR 23 2015

MAIN FORECAST CONCERN FOR THE LONG RANGE PERIOD WILL BE THIS
WEEKEND AND EARLY NEXT WEEK AS AN UPPER LEVEL LOW DEVELOPS NEAR
THE FOUR CORNERS REGION AND MOVES EASTWARD ACROSS THE
CENTRAL/SOUTHERN ROCKY MOUNTAINS. MODELS ARE IN PRETTY GOOD
AGREEMENT WITH NOT ONLY THE POSITION OF THE UPPER LEVEL LOW...BUT
ALSO WITH THE TIMING AND TRACK OF A POTENT SHORTWAVE LIFTING
NORTHWARD AHEAD OF THE MAIN LOW ON SUNDAY. ALL MODELS SHOW BETWEEN
ONE HALF TO ONE INCH OF QPF ON SUNDAY DUE TO THE COMBINATION OF
UPSLOPE FLOW...INSTABILITY...AND NEARLY SATURATED MODEL SOUNDINGS
UP TO 500MB. CONTINUED TO INCREASE POP BETWEEN 50 TO 70 PERCENT
ACROSS THE HIGH PLAINS AND THE MOUNTAINS. SNOW LEVELS WILL BE
RELATIVELY HIGH WITH THIS SYSTEM INITIALLY...UP AROUND 9000 FEET
INTO EARLY SUNDAY. HOWEVER...SOME COOLER AIR WILL ENTER THE
FORECAST AREA BY LATE SUNDAY. SNOWLEVELS MAY LOWER TO NEAR 6500
FEET BY EARLY MONDAY MORNING WITH RAIN/SNOW MIX DOWN TO 6000 FEET.
THANKFULLY...ANY SNOW WILL NOT LAST TOO LONG AS THE UPPER LEVEL
LOW WILL THEN PUSH SOUTH TOWARDS THE MEXICAN BORDER. LOOKS LIKE A
DECENT RAIN EVENT FOR THE HIGH PLAINS...BUT OTHERWISE A MODERATE
IMPACT OVER SOUTHEAST WYOMING AT MOST DUE TO HIGH SNOW LEVELS AND
A LOW CHANCE OF STRONG TSTORMS ACROSS THE HIGH PLAINS INCLUDING
WESTERN NEBRASKA. COOLER THAN AVERAGE TEMPERATURES ARE EXPECTED
SUNDAY AND MONDAY WITH HIGHS IN THE 40S AND 50S.

MODELS THEN SHOW A HIGH AMPLITUDE RIDGE OF HIGH PRESSURE ALOFT
MOVING EASTWARD INTO WESTERN COLORADO AND WYOMING FOR THE MIDDLE
OF NEXT WEEK. TEMPERATURES WILL MODERATE TO NORMAL WITH A LOW
CHANCE OF PRECIPITATION (BELOW 10 PERCENT) EXPECTED BY WEDNESDAY
OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1204 PM MDT THU APR 23 2015

MAIN FORECAST ISSUE FOR THE NOON PACKAGE CONCERNS THE AMOUNT OF
SHOWERS AND THUNDERSTORMS THAT WILL DEVELOP FROM LARAMIE EAST INTO
THE NEBRASKA PANHANDLE THROUGH THE AFTERNOON HOURS. DRY AIR IN THE
LOW LEVELS TODAY COULD RESULT IN THUNDERSTORM GUSTS TO NEAR 60
KTS IN DRY MICROBURST ENVIRONMENT AT OUR NEBRASKA FORECAST SITES
MID TO LATE AFTERNOON. NOON PACKAGE ADVERTISED VCTS FOR
SCOTTSBLUFF...CHADRON...ALLIANCE AND SIDNEY. LATEST HIGH
RESOLUTION MODELS INDICATE THAT COVERAGE MAY BE HIGHER EAST OF THE
LARAMIE RANGE TODAY...SO UPDATES FOR PREVAILING PERIODS OF
THUNDERSTORMS FOR SOME OF THE WESTERN NEBRASKA PANHANDLE AIRPORTS
MAY BE NECESSARY WITHIN THE NEXT COUPLE OF HOURS. TO THE
WEST...SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS EXPECTED FOR
RAWLINS...LARAMIE AND CHEYENNE...AND CARRIED VCSH THROUGH THE
AFTERNOON FOR THOSE SITES...BUT STILL CANT RULE OUT A STRAY
THUNDESTORM. VERTICAL PROFILES INDICATE DRY MICROBURST POTENTIAL
IS LESS FOR THE SOUTHEAST WYOMING AIRPORTS...BUT WE MAY STILL SEE
ANY STORMS THAT DEVELOP PRODUCE 30-40 KT GUSTS INTO THE EARLY
EVENING. EXPECT SHOWERS AND THUNDERSTORMS TO DISSIPATE BY 03Z WITH
VFR CATEGORY IN THE FORECAST OVERNIGHT INTO FRIDAY MORNING.

&&

.FIRE WEATHER...
ISSUED AT 303 AM MDT THU APR 23 2015

NO FIRE WEATHER CONCERNS OVER THE NEXT 7 DAYS. UNSETTLED WEATHER
PATTERN WILL BRING CHANCES FOR SHOWERS THROUGH AT LEAST MONDAY.
NEAR NORMAL TEMPERATURES THE NEXT FEW DAYS THEN COOL LATE THIS
WEEKEND THROUGH EARLY NEXT WEEK.

&&

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

$$

UPDATE...REC
SHORT TERM...SML
LONG TERM...TJT
AVIATION...JG
FIRE WEATHER...SML


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