Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 020005
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
605 PM MDT FRI MAY 1 2015

.UPDATE...
ISSUED AT 602 PM MDT FRI MAY 1 2015

OUR GRIDDED FORECASTS HAVE BEEN UPDATED PRIMARILY TO ACCOUNT
FOR SPATIAL COVERAGE OF SHOWERS AND THUNDERSTORMS...OVER
EASTERN LARAMIE COUNTY OF WYOMING...AND OVER KIMBALL AND WESTERN
CHEYENNE COUNTIES OF NEBRASKA. HAVE TOUCHED UP OTHER
METEOROLOGICAL VARIABLES FOR THE REST OF THE NIGHT BASED ON
TRENDS.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 354 PM MDT FRI MAY 1 2015

SHOWERS AND THUNDERSTORMS ARE ON THE UPTICK ALONG THE INTERSTATE 80
CORRIDOR IN SOUTHEAST WY THIS AFTERNOON. AS EXPECTED...THE GREATEST
COVERAGE HAS BEEN IN ALBANY IN LARAMIE COUNTIES WITH ENHANCED LOWER
LEVEL CONVERGENCE ALONG THE LARAMIE RANGE. THE KCYS RADAR LOOP ALSO
SHOWS NUMEROUS BOUNDARIES IN THE VICINITY OF CYS...LIKELY PLAYING A
ROLE IN CONVECTIVE EVOLUTION. CLOUDS CLEARED LATE THIS AM...HELPING
PUSH SFC TEMPS INTO THE 55-65 DEGREE RANGE AMID DECENT LLVL MOISTURE
WITH DEWPOINTS IN THE MID 40S F. THIS BENEATH STEEP MID LEVEL LAPSE
RATES ON THE ORDER OF 8-9 DEG C/KM IS CONTRIBUTING TO SBCAPES ON THE
ORDER OF 1500 J/KG PER THE 21Z SPC MESOANALYSIS. GFS AND NAM BUFKIT
SOUNDINGS BOTH SHOW H5 FLOW AROUND 30 KTS...WHICH COMBINED WITH GOOD
VEERING IN THE SFC-500 MILLIBAR LAYER IS CONTRIBUTING TO EFFECTIVE
BULK SHEAR VALUES FAVORABLE FOR ROTATING UPDRAFTS (35-45 KTS). COULD
SEE A HAIL THREAT EVOLVE WITH SOME CELLS...BUT DO NOT EXPECT TO SEE
MORE THAN ONE OR TWO SEVERE STORMS. OPTED TO MAINTAIN SMALL HAIL AND
GUSTY WIND WORDING IN THE OFFICIAL FORECAST. LATEST HRRR HAS CHANGED
VERY LITTLE FROM THIS MORNING...AND APPEARS TO BE ACCURATELY SHOWING
CONVECTIVE ELEMENTS BETWEEN LARAMIE AND CHEYENNE. FOR THAT REASON...
WILL MAINTAIN LIKELY POPS FOR THOSE AREAS. CONVECTIVE COVERAGE WILL
DWINDLE OVERNIGHT WITH THE LOSS OF DAYTIME HEATING/INSTABILITY.

QUASI-ZONAL FLOW ALOFT PERSISTS INTO SATURDAY. A SERIES OF MID LEVEL
DISTURBANCES WILL TRAVERSE THE FLOW OVER THE CENTRAL ROCKIES...ONCE
AGAIN PROMOTING AFTERNOON CONVECTION CHANCES. THE DAY 2 SPC OUTLOOK
HAS SHIFTED THE MARGINAL RISK EAST OF OUR CWA...WHICH MAKES SENSE AS
THE LATEST IN-HOUSE WRF PLACES THE BEST INSTABILITY AXIS EAST OF AN
ALLIANCE TO SIDNEY LINE BETWEEN 18-20Z SAT. POTENTIAL FOR WIDESPREAD
THUNDERSTORMS WILL DEPEND ON THE TIMING OF THE DRYLINE. GFS AND NAM
BOTH PUSH THIS FEATURE EAST OF THE CWA BY EARLY TO MID AFTERNOON...
BUT MODELS TEND TO MIX DRYLINES A BIT QUICKLY. LATER SHIFTS MAY NEED
TO ADJUST POPS ACCORDINGLY IF IT APPEARS THE LOW-LEVEL CONVERGENCE
ZONE WILL HANG ANY FURTHER WEST. A MUCH WARMER DAY APPEARS TO BE ON
TAP TOMORROW FOR THE PLAINS WITH WESTERLY DOWNSLOPE FLOW...AND 700
MILLIBAR TEMPS AROUND 8-10 DEG C.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 354 PM MDT FRI MAY 1 2015

THIS PERIOD WILL BE DOMINATED BY GENERALLY CONSISTENT SOUTHWEST
FLOW ACROSS THE INTERMOUNTAIN WEST AS YET ANOTHER LARGE SCALE
TROUGH IS CARVED INTO THE WRN CONUS. MOISTURE ADVECTION ALONG WITH
DIFFICULT TO TIME SHORTWAVES EMBEDDED WITHIN THIS FLOW WILL SET
THE STAGE FOR A RELATIVELY UNSETTLED PERIOD. THIS BEGINS ON
SUNDAY/MONDAY AS WEAK SFC BOUNDARY SETTLES SOUTH ACROSS THE PLAINS
HANGING UP AROUND THE FRONT RANGE. MEANWHILE...RELATIVELY WEAK
SHORTWAVE ENERGY WILL LIFT ACROSS THIS BOUNDARY AND WHEN COMBINED
WITH WEAK INSTABILITY PROGS (SBCAPE 300- 500 J/KG) WILL PRODUCE
AFTERNOON/EVENING CONVECTION BOTH DAYS. A STRONGER EJECTING TROUGH
WILL MOVE THROUGH THE CWFA TUE/WED. BUT WITH MORE MOISTURE AND
THICKER CLOUD CANOPY...INSTABILITIES ARE PROGD TO BE LESS.
SOUTHWEST FLOW PERSISTS INTO THURSDAY WITH THE NEXT TROUGH
SWINGING OUT OF THE DEEPENING WEST COAST TROUGH FOR FRIDAY OR
FRIDAY NIGHT...DEPENDING ON THE MEDIUM RANGE GUIDANCE OF CHOICE.
ISOLATED TO SCATTERED LATE DAY SHOWERS AND THUNDERSTORMS ARE HARD
TO ARGUE WITH REALLY ANY DAY NEXT WEEK. SO HAVE KEPT PRECIP
CHANCES FAIRLY BROAD BRUSH BUT NOT WIDESPREAD NEXT WEEK. SUNDAY
WILL BE THE WARMEST DAY OF THE WEEK WITH HIGHS REACHING THE
60S/70S. HIGHS WILL FALL BACK INTO THE 60S GENERALLY MON-FRI.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 536 PM MDT FRI MAY 1 2015

SHOWERS AND THUNDERSTORMS WILL DIE OFF ACROSS FAR SOUTHEAST
WYOMING AND SOUTHERN NEBRASKA PANHANDLE OVER THE NEXT FEW HOURS.
OTHER THAN LOCAL MVFR NEAR SHOWERS AND THUNDERSTORMS MAINLY
LOOKING AT VFR THROUGH THE TAF PERIOD...ALTHOUGH PATCHY RADIATION
FOG IS POSSIBLE LATE TONIGHT WITH LIGHT WINDS. ANOTHER ROUND OF
SHOWERS AND THUNDERSTORMS SATURDAY AFTERNOON...SOME WITH GUSTY
WINDS AND SMALL HAIL.


&&

.FIRE WEATHER...
ISSUED AT 354 PM MDT FRI MAY 1 2015

FIRE WEATHER CONCERNS WILL BE ON THE LOW SIDE WITH DAILY CHANCES FOR
SHOWERS AND THUNDERSTORMS. WHILE ANY GIVEN STORM MAY PRODUCE GUSTY
AND ERRATIC WINDS...NO DRY LIGHTNING IS EXPECTED. AFTERNOON RELATIVE
HUMIDITY VALUES SHOULD REMAIN ABOVE 15 PERCENT.

&&

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

$$

UPDATE...RUBIN
SHORT TERM...CLH
LONG TERM...CAH
AVIATION...SML
FIRE WEATHER...CLH


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