Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 250542 AAC
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
1142 PM MDT SUN MAY 24 2015


.UPDATE...FOR THE MIDNIGHT AVIATION FORECAST PACKAGE UPDATE.

UPDATE...ISSUED AT 940 PM MDT SUN MAY 24 2015

SHOWERS CONTINUE TO DECREASE IN BOTH INTENSITY AND COVERAGE THIS
EVENING AS INSTABILITY WANES WITH SUNSET. INITIAL LOOK THRU 00Z
NAM/HRRR DATA SUGGESTS THAT THERE SHOULD BE SOME ADDITIONAL WEAK
CONVECTION DEVELOPING IN THE VICINITY OF THE UPPER LOW AS IT
PASSES NR THE WY/NE STATELINE AS WELL AS INTO THE WRN NEBRASKA
PANHANDLE BY SUNRISE ON MONDAY. THINK THAT THIS IS SOMEWHAT
OVERDONE...BUT STILL FELT IT WAS ENOUGH TO MAINTAIN AT LEAST
SCATTERED MENTION TO POPS THRU THE OVERNIGHT PERIOD. TEMPERATURES
LOOK FINE...THOUGH DID INCREASE OVERNIGHT LOWS A DEGREE OR TWO IN
SPOTS AS CLOUD COVER SHOULD PREVENT TEMPS/DEW POINTS FROM FALLING
MUCH FURTHER.

UPDATE ISSUED AT 631 PM MDT SUN MAY 24 2015

ALTHOUGH REGIONAL RADARS SUPPORT LIGHT TO PERHAPS OCCASIONALMODERATE
PRECIPITATION TONIGHT...NO LONGER ANTICIPATE IMPACTS ASSOCIATED
WITH FLASH FLOODING ACROSS NRN CARBON/ALBANY AND CONVERSE COUNTIES
TONIGHT. THEREFORE...WAS CONFIDENT ENOUGH TO LET THE FLASH FLOOD
WATCH EXPIRE FOR THESE AREAS AT 6 PM.

OTHERWISE...STILL MONITORING POCKETS OF CONVECTION ACROSS
PRIMARILY THE NRN NEBRASKA PANHANDLE WHERE LATEST SPC MESONALYSIS
SHOWS 500-1000 J/KG OF SBCAPE REMAINED. THIS WILL LIKELY BE THE
CASE FOR THE NEXT HOUR OR SO BEFORE CONVECTION STRENGTH IS
EXPECTED TO WANE CONSIDERABLY.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 408 PM MDT SUN MAY 24 2015

SHOWERS AND THUNDERSTORMS HAVE EXPANDED IN COVERAGE SINCE THE
EARLIER FORECAST UPDATE...WITH MODERATE RAINFALL  OBSERVED AT
TIMES ALONG WITH SMALL HAIL NEAR CHEYENNE. ACTIVITY IS INCREASING
OVER THE NORTHERN LARAMIE RANGE AND CENTRAL CONVERSE COUNTY AS
WELL...WITH SLOW MOVING THUNDERSTORMS OBSERVED ON RADAR. COULD
STILL SEE SOME HEAVIER RAINFALL TOTALS OUT OF THIS ACTIVITY SO
WILL MAINTAIN THE FLASH FLOOD WATCH. THE STRONGEST STORM SO FAR
THOUGH IS OVER NORTHERN SIOUX COUNTY WITHIN THE SLIGHTLY MORE
UNSTABLE ENVIRONMENT. IT CONTINUES TO TREK EAST TOWARD DAWES
COUNTY WITH FURTHER DEVELOPMENT TO THE SOUTH. EXPECT THESE TRENDS
TO CONTINUE THROUGH THE EVENING.

FOR TONIGHT...THE UPPER LOW WILL FINALLY MOVE NORTHEAST OVER THE CWA
AND WILL WEAKEN. SIMILARLY...THE SFC LOW WILL STEADILY TREK
NORTHEAST WITH  WINDS SHIFTING TO THE NNW BEHIND THE LOW. OVERALL
FLOW SHOULD REMAIN ON THE WEAKER SIDE TONIGHT...WITH AREAS OF FOG
REDEVELOPING OVERNIGHT ACROSS MUCH OF THE AREA. WITH THE NW FLOW
IN PLACE...DRIER AIR SHOULD BEGIN TO FILTER INTO THE CWA WHICH
WILL REDUCE OVERALL COVERAGE OF SHOWERS AND THUNDERSTORMS FOR
MONDAY. HOWEVER...COOLER AIR WITHIN THE UPPER TROUGH WILL REMAIN
OVERHEAD SO EXPECT AT LEAST SCATTERED COVERAGE OF SHOWERS WITH
ISO-T LATE MORNING THROUGH THE EVENING...ESPECIALLY OVER HIGHER
TERRAIN FEATURES.

A WEAK TRANSITORY RIDGE LOOKS TO MOVE OVERHEAD FOR TUESDAY
BRINGING WARMER TEMPS TO THE FORECAST AREA ALONG WITH SUBSIDENCE
ALOFT. SFC HIGH PRESSURE IS FORECAST TO SLIDE SOUTHEAST INTO THE
CENTRAL PLAINS THROUGH THE DAY...WITH SFC WINDS VEERING BACK TO
THE SOUTHEAST AND INCREASING LLVL UPSLOPE FLOW OVER THE CWA
THROUGH THE AFTERNOON. THE COMBINATION OF UPSLOPE AND HIGHER
TEMPS SHOULD MAINTAIN AT LEAST A CHANCE FOR AFTERNOON SHOWERS AND
THUNDERSTORMS...AGAIN ESPECIALLY NEAR TERRAIN FEATURES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 408 PM MDT SUN MAY 24 2015

AN ACTIVE PATTERN IS EXPECTED TO CONTINUE THROUGH THE WEEK AS LARGE
SCALE TROUGHING REMAINS INTACT ACROSS THE WESTERN US. A FEW EMBEDDED
DISTURBANCES WITHIN MOIST SOUTHWEST FLOW ALOFT COMBINED WITH PERIODS
OF LLVL UPSLOPE WILL PROMOTE DAILY CHANCES FOR CONVECTION THROUGH AT
LEAST THE END OF THE WORK WEEK. GENERALLY WEAK MID LEVEL FLOW / LESS
THAN 25 KTS AT H5 / WILL KEEP CHANCES FOR STRONG TO SEVERE STORMS ON
THE LOW SIDE...BUT THE GFS SUGGESTS SBCAPE AROUND 1500 J/KG ACROSS A
LARGE PART OF THE EASTERN PLAINS ON WED-THU. CANNOT RULE OUT A STRAY
SEVERE STORM...BUT ANYTHING ORGANIZED APPEARS UNLIKELY. EXPECT DAILY
HIGHS TO HOLD FAIRLY STEADY THROUGH THE EXTENDED GIVEN A PERSISTENT
UPPER LEVEL PATTERN IN PLACE. H7 TEMPS AVERAGING AROUND 5 C SUGGEST
HIGHS IN THE 65 TO 75 DEGREE RANGE FOR MOST AREAS. RIDGING ALOFT AND
A PUSH OF DRIER AIR ASSOCIATED WITH A CANADIAN SURFACE HIGH DIPPING
INTO THE UPPER MIDWEST MAY GIVE US A BREAK FROM PRECIPITATION AS WE
HEAD INTO THE WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1142 PM MDT SUN MAY 24 2015

KEPT TREND OF DROPPING VISIBILITIES AND CEILINGS INTO IFR CATEGORY
FOR CHADRON...ALLIANCE AND SIDNEY WHERE WRAP AROUND LOW CLOUDS AND
PATCHY LIGHT RAINS ARE INDICATED TO CONTINUE IN THE HRRR AND NAM
THROUGH MORNING...WITH CEILINGS AND VISIBILITIES DROPPING INTO
MVFR AT SCOTTSBLUFF...CHEYENNE...LARAMIE AND RAWLINS THROUGH
MORNING. FOR CHEYENNE...HRRR SEEMS TO HAVE A DECENT HANDLE ON
BATCH OF RAIN MOVING SOUTHWEST OUT OF THE SCOTTSBLUFF
AREA...MOVING IT TO NEAR CHEYENNE BY DAYBREAK...SO AROUND 10Z WE
BROUGHT IN SOME LIGHT RAIN FOR CHEYENNE BUT DID NOT FEEL CONFIDENT
ENOUGH TO GO IFR ON CEILINGS OR VISIBILITIES AT THIS TIME.
OTHERWISE...AS THE LOW CLOUDS START TO SHOW SOME BREAKS BY EARLY
AFTERNOON MONDAY WE EXPECT TO SEE SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOP AND EITHER HAVE VICINITY THUNDER OR CARRIED
THUNDER FOR ALL SITES IN THE MID AFTERNOON HOURS INTO EARLY
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 408 PM MDT SUN MAY 24 2015

SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH MUCH OF THE WEEK AND
WILL BRING MODERATE TO HEAVY RAINFALL AT TIMES ACROSS THE DISTRICT.
WITH PLENTIFUL MOISTURE ANTICIPATED...NO FIRE WEATHER CONCERNS ARE
EXPECTED.

&&

.HYDROLOGY...
ISSUED AT 408 PM MDT SUN MAY 24 2015

FORECAST RAINFALL FROM SHOWERS DURING THE NEXT 24 HOURS WILL AVERAGE
BETWEEN 0.25 AND 0.50 INCHES...WITH LOCALLY HEAVIER AMOUNTS POSSIBLE
WITH THUNDERSTORMS. RUNOFF FROM THIS RAINFALL WILL MAINTAIN HIGH
WATER LEVELS ALONG THE LARAMIE RIVER AT LARAMIE AND NEAR FORT
LARAMIE THROUGH EARLY NEXT WEEK. REFER TO THE LATEST RIVER AND FLOOD
STATEMENTS FOR SPECIFIC INFORMATION.

&&

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

$$

UPDATE...CAH
SHORT TERM...RJM
LONG TERM...CLH
AVIATION...JG
FIRE WEATHER...RJM
HYDROLOGY...MJ/RJM


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