000
FXUS65 KCYS 131518
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
918 AM MDT THU JUN 13 2013

.UPDATE...
ISSUED AT 852 AM MDT THU JUN 13 2013

TRICKY AND CHALLENGING FORECAST FOR TODAY. LOW LEVEL CLOUDS
HOLDING FIRM UNDER SOUTH TO SOUTHEAST LOW LEVEL FLOW ALONG AND
EAST OF THE LARAMIE RANGE. LOOKING AT WEB CAMS...THE FOG IS BEGINNING
TO LIFT OVER THE SUMMIT. WILL CONTINUE TO SEE FOG ERODE OVER THE
NEXT FEW HOURS AND SHOULD SEE LOW CLOUDS ERODE ALSO AS LOW LEVEL
MIXING AND WESTERLY FLOW ALOFT EAT AWAY AT THE LOW LEVEL MOISTURE.
THE QUESTION IS HOW MUCH WILL THIS AFFECT SURFACE TEMPERATURES AND
THE CHANCES FOR THUNDERSTORMS. GIVEN THE LONG LENGTH OF DAY AND
HIGH SUN ANGLE...WONT TAKE MUCH TO WARM TO NEAR THE CONVECTIVE
TEMPERATURE...ALTHOUGH CERTAINLY STRUGGLING TO WARM AT THIS TIME
WITH UPSLOPE FLOW AND CLOUD COVER. IT STORMS DO DEVELOP LATER THIS
AFTERNOON...SHEAR AND CAPE PROFILES SUGGESTIVE OF SEVERE
THUNDERSTORMS WITH LARGE HAIL AND DAMAGING WINDS AND CANT RULE OUT
ISOLATED TORNADOES. WILL HAVE TO MONITOR TRENDS THE REST OF
TODAY TO GUAGE SEVERE THREAT.



UPDATE ISSUED AT 600 AM MDT THU JUN 13 2013

WE HAVE SENT A QUICK UPDATE TO THE FCST PACKAGE TO BETTER REFLECT
THE EVOLUTION OF LOW CLOUDS ACROSS THE AREA. PATCHY DENSE FOG HAS
DEVELOPED FROM THE INTERSTATE 80 SUMMIT EASTWARD INTO CHEYENNE AS
PER AREA WEBCAMS DESPITE SFC FLOW IN EXCESS OF 10 MPH. DO NOT
EXPECT THIS TO LAST LONG AS FCST SOUNDINGS SHOW SOME LLVL DRYING
AFTER 13Z...AND SFC WINDS SHOULD HELP TO MIX THINGS OUT SHORTLY.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 514 AM MDT THU JUN 13 2013

WATER VAPOR SATELLITE IMAGERY AND OBJECTIVE UPPER AIR ANALYSIS SHOWS
STRONG UPPER-LEVEL RIDGING OVER THE CENTRAL HIGH PLAINS THIS MORNING
IN ADVANCE OF DEEP TROUGHING OVER THE PACIFIC NW. THIS RIDGE SHOULD
SHIFT EWD THROUGH THE DAY TODAY...GIVING WAY TO WARM SOUTHWEST FLOW
ALOFT AND CONTINUED MIDLVL WARM ADVECTION. THE 00Z MODEL SUITE WAS
INDICATIVE OF 700 MILLIBAR TEMPS SOME 3-4 DEG C WARMER THAN THOSE
SEEN ON WED...SO WOULD EXPECT ANOTHER WARM AFTN. LIMITING FACTOR
WILL BE AN INCREASE IN CLOUD COVER AND POSSIBLE ISOLATED SHOWERS
AND STORMS AS MIDLVL MOISTURE PLUME MOVES OVERHEAD...BUT STRATUS
SHOULD CLEAR EARLY ENOUGH TO ALLOW FOR STRONG SFC INSOLATION. AM
A LITTLE CONCERNED THAT EXPANDING CLOUD COVER UPSTREAM PER LATEST
IR SATELLITE COULD LIMIT MIXING...BUT WILL MENTION AREAS WEST OF
THE LARAMIE RANGE WHICH EXPERIENCE LESS CLOUD COVER CAN EXPECT
VERY WINDY CONDITIONS THIS AFTN. BUFKIT SOUNDINGS FOR KRWL SHOW A
DRY ADIABATIC PROFILE TO ALMOST 400 MILLIBARS WITH AT LEAST 40 KTS
AVAILABLE TO MIX FROM NOT TOO FAR OFF THE SFC. CANNOT RULE OUT A
FEW GUSTS NEAR 50 MPH IN THIS REGIME.

THE MAIN CONCERN ON THU WILL BE THE CONVECTIVE POTENTIAL DURING THE
LATE AFTN AND EARLY EVE HOURS. ALTHOUGH THIS THREAT WILL MAINLY BE
CONFINED TO AREAS ALONG/E OF THE LARAMIE RANGE...ADDED SOME SLIGHT
CHANCE POPS TO OUR WESTERN ZONES AS INCREASING MOISTURE ALOFT AND
UPPER-LEVEL DIVERGENCE COULD TRIGGER A SHOWER OR TWO OVER CARBON
COUNTY IN THE AM AS INDICATED BY THE HRRR. FARTHER E...DEVELOPING
SFC TROUGH AXIS WILL ENHANCE LLVL CONVERGENCE ALONG THE FOOTHILLS
BENEATH INCREASINGLY DIFFLUENT FLOW ALOFT. SOUTH-TO-SOUTHEAST LLVL
FLOW WILL HELP TO REINFORCE LOW TO MID 50S DEWPOINTS OVER EAST WY
INTO THE WESTERN PANHANDLE...WHICH COMBINED WITH VERY STEEP MIDLVL
LAPSE RATES EXCEEDING 8 DEG C/KM SHOULD YIELD MODERATE INSTABILITY
WITH MLCAPES NEAR 2000 J/KG. SOUTHEAST LLVL WINDS VEER TO WESTERLY
AND INCREASE TO 40 KTS AT H5...YIELDING DEEP LAYER VERTICAL SHEAR
VALUES NEAR 50 KTS AND 0-3 KM HELICITIES AROUND 150 M2/S2. STORMS
DEVELOPING IN THIS AIR MASS COULD BECOME SUPERCELLS...CAPABLE OF
PRODUCING LARGE HAIL AND DAMAGING WINDS.

STRONG CAPPING WILL KEEP A MAJORITY OF THE CONVECTION AT BAY UNTIL
AT LEAST LATE AFTERNOON WHEN MODELS SHOW A LOCALIZED WEAKNESS IN
SFC BASED INHIBITION NEAR THE LARAMIE RANGE...ON THE WESTERN FRINGE
OF LLVL THETA-E RIDGE AXIS. DYNAMICS AND TERRAIN EFFECTS SHOULD
PROVIDE ENOUGH SUPPORT TO INITIATE AT LEAST ISOLATED TSTMS AFTER 21Z
EVEN IF CLOUD COVER YIELDS A COOLER...AND THUS MORE STRONGLY CAPPED
BOUNDARY LAYER. THIS ACTIVITY WILL SPREAD EAST INTO THE PANHANDLE
DURING THE EVENING AND POSSIBLY DURING THE OVERNIGHT...FUELED BY
LLVL MOISTURE TRANSPORT AND WARM ADVECTION WITH A STRENGTHENING
H85 JET. WRF SIMULATED REFLECTIVITIES SUPPORT THIS...AND THE SPC
HAS PLACED THE EASTERN HALF OF THE CWA IN A SLGT RISK FOR SEVERE
CONVECTION. WENT AHEAD AND ADDED MENTION OF LARGE HAIL AND DAMAGING
WINDS TO THE GRIDS.

THE MODELS BRING A STRONG MIDLVL SHORTWAVE ACROSS THE NORTHERN HIGH
PLAINS ON FRI AFTN. COULD BE ANOTHER BREEZY DAY FOR AREAS WEST OF
THE LARAMIE RANGE WITH ENHANCED FLOW ALOFT. BOTH THE GFS AND NAM
SUGGEST SEVERAL MIDLVL IMPULSES WILL TRANSLATE EWD ACROSS THE CWA
AS AN ASSOCIATED SFC COLD FRONT MOVES ACROSS THE REGION. THIS
MAY PROVIDE THE NECESSARY SUPPORT FOR TSTM DEVELOPMENT ALONG THE
INTERSTATE 80 CORRIDOR BY EARLY FRI EVENING. DO NOT EXPECT THESE
STORMS TO BE PARTICULARLY WIDESPREAD...BUT THEY COULD BE STRONG
GIVEN SUFFICIENT INSTABILITY AND SHEAR. ISOLATED TO WIDELY SCTD
SHOWERS AND TSTMS WILL AGAIN BE POSSIBLE OVER THE HIGH PLAINS ON
SAT AFTN AS LLVL UPSLOPE RETURNS TO THE REGION. LLVL MOISTURE
SEEMS A BIT MARGINAL FOR WIDESPREAD STRONG TO SEVERE CONVECTION...
BUT THIS WILL NEED TO BE MONITORED AS SHEAR PROFILES ARE PROGGED
TO BE QUITE STRONG. TEMPERATURES WILL TREND COOLER THROUGH THE
END OF THE WEEK AND INTO THE WEEKEND...WITH UPPER 70S AND LOWER
80S COMMON.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 514 AM MDT THU JUN 13 2013

SATURDAY NIGHT...ISOLATED EVENING THUNDERSTORMS ON TAP MAINLY OVER
WESTERN NEBRASKA ALONG A LOW LEVEL TROUGH AXIS AND PASSING WEAK
SHORTWAVE TROUGH ALOFT.

SUNDAY...ISOLATED TO SCATTERED AFTERNOON AND EVENING THUNDERSTORMS
EAST OF A LUSK TO PINE BLUFFS LINE IN A LOW LEVEL CONVERGENCE AXIS
AND NEAR DEEPER LOW AND MID LEVEL MOISTURE.

MONDAY...RIDGING PREVAILS OVER WYOMING. WITH ADEQUATE LOW AND MID
LEVEL MOISTURE...AND UPSLOPE MECHANICAL LIFT...ISOLATED TO SCATTERED
AFTERNOON AND EVENING THUNDERSTORMS WILL ERUPT MAINLY ALONG AND EAST
OF INTERSTATE 25.

TUESDAY...RIDGE AXIS MOVES EASTWARD TO WESTERN NEBRASKA. ISOLATED
AFTERNOON AND EVENING THUNDERSTORMS ON TAP ALONG AND EAST OF A
SURFACE TROUGH FROM DOUGLAS TO LUSK.

WEDNESDAY...DRYING OUT DAY EXPECTED AS SOUTHWEST FLOW ALOFT
STRENGTHENS AND THE LOW AND MID LEVELS DRY OUT...LOSING THEIR
MOISTURE AVAILABILITY FOR THUNDERSTORM INITIATION.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 514 AM MDT THU JUN 13 2013

VFR PREVAILS. UPPER RIDGE AXIS MOVES EAST TO CENTRAL
NEBRASKA BY 12Z THURSDAY THEN SLOWLY EAST BY 00Z FRIDAY WITH
SOUTHWEST FLOW ALOFT OVER WYOMING STRENGTHENING. SURFACE LOW
PRESSURE STRENGTHENING OVER NORTHERN WYOMING THURSDAY AFTERNOON WITH
SOUTH AND SOUTHEAST WINDS INCREASING DURING THE DAYLIGHT HOURS.
ISOLATED THUNDERSTORMS DEVELOPING THURSDAY AFTERNOON AND EVENING
WEST OF INTERSTATE 25 AND FRIDAY EVENING OVER WESTERN NEBRASKA SOUTH
OF SCOTTSBLUFF. THUNDERSTORMS PRODUCING LOCALIZED MVFR ALONG WITH
GUSTY AND ERRATIC WINDS.


&&

.FIRE WEATHER...
ISSUED AT 514 AM MDT THU JUN 13 2013

NO FIRE WEATHER CONCERNS ARE EXPECTED OVER THE NEXT SEVERAL DAYS
AS FUELS ARE EXPECTED TO REMAIN NON-CRITICAL. HOWEVER...GUSTY
WINDS AND VERY LOW AFTERNOON RELATIVE HUMIDITY VALUES WILL BE
POSSIBLE OVER MAINLY CARBON COUNTY THROUGH THE WEEKEND. STRONG
TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ALONG AND EAST OF THE
LARAMIE RANGE ON THURSDAY AFTERNOON AND EVENING...WITH LARGE
HAIL AND DAMAGING WINDS THE PRIMARY THREATS.

&&

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

$$

UPDATE...LIEBL
SHORT TERM...HAMMER
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...HAMMER