Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 011734
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1134 AM MDT FRI MAY 1 2015

.UPDATE...
ISSUED AT 1048 AM MDT FRI MAY 1 2015

AREA WEBCAMS AND VISIBLE SATELLITE IMAGERY SHOW FOG AND/OR LOW
STRATUS RAPIDLY DIMINISHING ACROSS PORTIONS OF CARBON AND ALBANY
COUNTIES THIS AM. CLOUD COVER HAS BEEN SLOW TO ERODE OVER THE CO
FRONT RANGE WITH WEAK LLVL UPSLOPE...BUT CLOUDS ARE THINNING AND
LLVL MIXING SHOULD GIVE WAY TO AT LEAST PARTLY SUNNY SKIES AS WE
HEAD INTO THE AFTERNOON. OUR ATTENTION THEN SHIFTS TO CONVECTIVE
POTENTIAL LATER TODAY. FORCING IS NOT AS PRONOUNCED AS PREVIOUS
DAYS...BUT INSTABILITY SHOULD BE THERE WITH STEEP MIDLEVEL LAPSE
RATES AND GOOD LLVL MOISTURE WITH SURFACE DEWPOINTS IN THE MID
40S. IF WE CAN BREAK OUT OF THE CLOUDS...OUR LOCAL WRF SUGGESTS
SBCAPE NEAR 750-1000 J/KG. 0-6KM SHEAR VECTORS ARE WESTERLY AT
AROUND 40 KTS...SUPPORTING POTENTIAL FOR ROTATING UPDRAFTS AND
HAIL PRODUCTION. THE HRRR INITIATES CONVECTION AROUND 20Z OVER
ALBANY AND LARAMIE COUNTIES...SO WENT AHEAD AND INCREASED POPS
INTO THE LIKELY CATEGORY. ALSO ADDED SMALL HAIL AND GUSTY WINDS
GIVEN THE THERMODYNAMIC/KINEMATIC ENVIRONMENT. WE COULD HAVE A
SEVERE STORM OR TWO...BUT OPTED NOT TO MENTION IN THE GRIDS AS
UNCERTAINTIES REMAIN WITH HOW CLOUDS WILL IMPACT COVERAGE OF
STRONGER STORMS.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)

ISSUED AT 300 AM MDT FRI MAY 1 2015

PATTERN WILL BE CHARACTERIZED BY A ZONAL FLOW ALOFT WITH SEVERAL
WEAK IMPULSES PASSING ACROSS THE CWA IN THIS FLOW PATTERN. A SFC
BOUNDARY WILL REMAIN BANKED UP ALONG THE HIGHER TERRAIN OF SE
WYOMING TODAY BEFORE ERODING EASTWARD OVERNIGHT INTO SATURDAY.
THIS BOUNDARY SHOULD INTERACT WITH THESE WEAK DISTURBANCES AND
SOME INSTABILITY TO PRODUCE SCTD SHOWERS AND A FEW STORMS MAINLY
OVER SE WYOMING TODAY. CAPE VALUES RANGE FROM ABOUT 500-1000J/KG
AGAINST THE LARAMIE RANGE THIS AFTERNOON BUT SHEAR VALUES RATHER
LOW SO A FEW STRONGER STORMS POSSIBLE. ACTIVITY SHOULD MOVE
OUT/DISSIPATE THIS EVENING LEAVING A QUIET NIGHT TONIGHT. MORE OF
THE SAME EXPECTED FOR SATURDAY AND SUNDAY EXCEPT AFTERNOON AND
EVENING CONVECTION SHOULD MAKE MORE PROGRESS EASTWARD AS THE SFC
BOUNDARY SHIFTS EAST. CAPE VALUES MUCH LESS OVERALL EXCEPT OVER
PARTS OF THE PANHANDLE WHERE THEY EXCEED 1500 J/KG LATE IN THE
MORNING BEFORE SHIFTING EAST OF THE CWA. WARMER TEMPS FOR SATURDAY
THEN THE NEXT COOL FRONT WILL PASS ACROSS EARLY SUNDAY RESULTING
IN ABOUT 5-15 DEGREES OF COOLING...GREATEST OVER THE PANHANDLE.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 300 AM MDT FRI MAY 1 2015

MUCH OF THE LONG TERM REMAINS UNSETTLED AS GUIDANCE CONTINUES TO
SHOW ALMOST DAILY PRECIP CHANCES OVER THE CWFA.

AREA REMAINS UNDER EASTERLY TO SOUTHEASTERLY UPSLOPE FLOW SUNDAY
NIGHT INTO MONDAY AS A SURFACE HIGH OVER WESTERN SOUTH DAKOTA
REMAINS NEARLY STATIONARY.

EACH DAY THERE LOOKS TO BE PIECES OF ENERGY BEING DRAWN NORTH INTO
THE AREA FROM THE DESERT SOUTHWEST THAT INTERACTS WITH A BOUNDARY
THAT IS STALLED ALONG THE LARAMIE RANGE. MONDAY
AFTERNOON...CONVECTION IS CONCENTRATED MAINLY ACROSS OUR WESTERN
ZONES...BUT AS THE LOW PRESSURE SYSTEM MOVES INTO COLORADO
TUESDAY...OUR EASTERN ZONES GET SOME PRETTY GOOD RAINFALL. BEST
PRECIP CHANCES APPEAR TO BE ALONG THE WYOMING/COLORADO BORDER
ALONG INTERSTATE 80.

UPPER LOW SLOW TO MOVE OUT OF COLORADO AND WE SHOULD SEE
WIDESPREAD CHANCES FOR SHOWERS AND THUNDERSTORMS WEDNESDAY ACROSS
THE ENTIRE CWFA. FINALLY BY THURSDAY...UPPER LOW MOVES NORTHEAST
INTO THE DAKOTAS. NOT MUCH OF A BREAK IN PRECIP THOUGH AS A SECOND
SHORTWAVE MOVES IN BEHIND THIS ONE FOR FRIDAY. AREA WILL CONTINUE
TO SEE ABOVE NORMAL CHANCES FOR MUCH NEEDED RAINFALL INTO THE END
OF THE WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1134 AM MDT FRI MAY 1 2015

AVIATION CONCERNS CENTER AROUND TIMING AND PLACEMENT OF CONVECTION
THIS AFTERNOON AND EARLY EVENING...WHILE CAN ALWAYS BE A TRICKY.
ALL SITES WITH THE EXCEPTION OF KCYS WILL BEGIN THE PERIOD IN
VFR. PESKY STRATOCU DECK WILL KEEP BKN020-030 AGL IN PLACE AT KCYS
AT LEAST FOR THE NEXT HOUR OR TWO. LATEST HRRR INITIATE
-SHRA/-TSRA DEVELOPMENT ALONG THE DIFFERENTIAL HEATING AXIS (NR
THE LARAMIE RANGE W OF KCYS) BETWEEN THIS STRATOCU DECK AND THE
CLEARING TO THE WEST 20-21Z. CONFIDENCE HAS INCREASED ENOUGH TO
ADD A TEMPO -TSRA GROUP INTO KCYS. CONFIDENCE IS LOWER WEST OF
THIS AREA OF DIFFERENTIAL HEATING...SO HAVE KEPT VCTS IN KCYS.
HAVE ADDED VCTS TO THE NEBRASKA PANHANDLE SITES AS WELL LATER THIS
AFTERNOON AS WHATEVER CONVECTION DOES MANAGE TO DEVELOP TRANSLATES
EAST. IF THIS ACTIVITY DOES IMPACT AN AIRIFIELD...EXPECT MVFR
CIGS/VSBYS ALONG WITH BRIEF +RA...THE POTENTIAL FROM SMALL GS
ALONG WITH GUSTY WINDS. AM NOT CONFIDENT ENOUGH IN TIMING OR
PLACEMENT TO INCLUDE IN THE TAF...BUT WILL BE MONITORING RADAR
TRENDS CLOSELY THIS AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MDT FRI MAY 1 2015

CONCERNS TO REMAIN LOW THROUGH THE WEEKEND INTO EARLY NEXT WEEK
WITH NEARLY DAILY CHANCES FOR SHOWERS AND A FEW STORMS...BUT NO
DRY LIGHTNING.  WEATHER FACTORS REMAINING NON-CRITICAL.

&&

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

&&

$$

UPDATE...CLH
SHORT TERM...RE
LONG TERM...GCC
AVIATION...CAH
FIRE WEATHER...RE



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