National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KCYS 160006
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
606 PM MDT WED MAY 15 2013

.SHORT TERM...(TONIGHT THROUGH FRIDAY)
ISSUED AT 251 PM MDT WED MAY 15 2013

TONIGHT...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS CONTINUE TO
DEVELOP THIS AFTERNOON...PRIMARILY ALONG THE SPINE OF THE LARAMIE
RANGE AND INTERSTATE 25 CORRIDOR. SHOWERS AND THUNDERSTORMS HAVE
BEEN SLOWER TO DEVELOP IN AREAL COVERAGE THAN EARLIER EXPECTED...
PERHAPS DUE TO A LACK OF SYNOPTIC AND MESOSCALE LIFT SINCE THE
SHORTWAVE TROUGH ALOFT IS STILL BACK ACROSS UTAH.

FOR THIS EVENING...THE SHORTWAVE TROUGH ALOFT MOVES ACROSS WESTERN
COLORADO. EXPECT A CONTINUOUS INCREASE IN AREAL SHOWER AND
THUNDERSTORM COVERAGE THROUGH EARLY EVENING AS A LOW LEVEL
CONVERGENCE AXIS DEVELOPS FROM RAWLINS TO SCOTTSBLUFF. WITH
PRECIPITABLE WATER VALUES SOME 120 TO 140 PERCENT OF NORMAL AND
STORM MOVEMENT ONLY TO THE NORTHEAST AT 10 MPH...A FEW HEAVY RAINERS
WITH UP TO ONE INCH PER HOUR ANTICIPATED.

SURFACE BASED CAPE FROM THE STORM PREDICTION CENTER MESOANALYSIS
PAGE SHOWS SOME 500-1000 J/KG WITH EFFECTIVE BULK SHEAR OF 20 TO 35
KNOTS. WITH PROJECTED CAPE AND SHEAR...A FEW STORMS THIS EVENING MAY
BE STRONG...PRODUCING SMALL HAIL AND WIND GUSTS TO 50 MPH. EXPECT
STORMS TO GRADUALLY SPREAD EASTWARD EAST OF I-25 THIS EVENING AND
INTO WESTERN NEBRASKA.

AFTER MIDNIGHT...THE SHORTWAVE TROUGH ALOFT MOVES ACROSS SOUTHEAST
WYOMING AND WITH ATTENDANT SURFACE LOW LEVEL CONVERGENCE...EXPECT AT
LEAST SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO AFFECT WESTERN
NEBRASKA WHILE LIKELY DECREASING IN COVERAGE ACROSS SOUTHEAST
WYOMING.

THURSDAY...TRANSITORY LOW AMPLITUDE SHORTWAVE RIDGE LIES OVER
EASTERN WYOMING. SURFACE TROUGH AND LOW LEVEL CONVERGENCE BOUNDARY
WILL LIE NORTH TO SOUTH FROM CASPER TO CHEYENNE...ACTING AS A FOCUS
FOR THUNDERSTORM INITIATION...THOUGH WITH LESS AREAL COVERAGE THAN
TODAY. EXPECT ISOLATED AFTERNOON AND EVENING THUNDERSTORMS.

THURSDAY NIGHT...EXPECT FAIRLY QUICK CESSATION AND DISSIPATION OF
THUNDERSTORMS WITH LOSS OF INSOLATION AND LACK OF LIFTING MECHANISMS.

FRIDAY...FLOW ALOFT BACKS TO SOUTHWEST AND STRENGTHENS IN ADVANCE OF
APPROACHING SHORTWAVE TROUGH FROM THE GREAT BASIN STATES. IN
RESPONSE...A WELL PRONOUNCED SURFACE TROUGH WILL DEVELOP NORTH TO
SOUTH ACROSS EASTERN WYOMING WITH A WELL PRONOUNCED THERMAL RIDGE
ACROSS OUR COUNTIES. WARM TEMPERATURES ALOFT...NEAR 12 CELSIUS AT
700 MB...WILL ACT TO PROVIDE SIGNIFICANT CONVECTIVE INHIBITION...OR
CIN...WHICH WILL EFFECTIVELY KEEP NEARLY ALL LOCATIONS THUNDERSTORM
FREE IN THE AFTERNOON. ONLY CAVEAT HOWEVER...WILL BE TO INCLUDE SOME
LOW TOKEN POPS FOR ISOLATED THUNDERSTORMS LATE IN THE AFTERNOON
ACROSS THE SNOWY AND SIERRA MADRE RANGES WHERE CONVECTIVE INITIATION
OCCURS MANY TIMES DESPITE STRONG CONVECTIVE INHIBITION ALOFT.

BACK TO WARM TEMPERATURES...AND HAVE BOOSTED MAXIMA A FEW DEGREES
FROM GUIDANCE BASED ON MODELS TENDING TO UNDERDO WARMING WITH THESE
SCENARIOS.

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 251 PM MDT WED MAY 15 2013

THE MEDIUM RANGE MODELS AND THEIR ENSEMBLES HAVE BEEN TRENDING
TOWARD A SLOWER...MORE AMPLIFIED SOLUTION FOR THE PAST FEW DAYS...
AND THE 12Z FORECAST CYCLE IS NO DIFFERENT. A RATHER DEEP UPPER
TROUGH OVER THE INTERMOUNTAIN WEST FRIDAY NIGHT MOVES SLOWLY EAST
THROUGH THE ROCKIES THIS WEEKEND. ADDITIONAL SHORTWAVE ENERGY DROPS
SOUTH FROM THE NORTHERN ROCKIES AND BROADENS THE TROUGH LATE SUNDAY
THROUGH MONDAY OVER THE NATION/S MID SECTION. A CLOSED LOW DEVELOPS
OVER THE NORTH CENTRAL GREAT PLAINS LATE IN THE WEEKEND AND DRIFTS
TOWARD THE UPPER MIDWEST EARLY NEXT WEEK. AS THE UPPER LOW AND
TROUGH PULL AWAY...A SHORTWAVE RIDGE WILL EXPAND EAST TO THE FRONT
RANGE BY WEDNESDAY.

EXPECT DRY AND MILD CONDITIONS FRIDAY NIGHT WITH THE UPPER RIDGE
MOVING INTO THE GREAT PLAINS. A PACIFIC COLD FRONT MOVES THROUGH
THE CWFA SATURDAY...GIVING WAY TO COOLER TEMPERATURES AND A SHOWERY
WEATHER PATTERN THAT WILL LINGER INTO EARLY NEXT WEEK. BEST CHANCES
FOR WIDESPREAD MEASURABLE RAINFALL WILL BE SUNDAY AND MONDAY WITH
THE PASSAGE OF THE UPPER TROUGH. THERE WILL BE ENOUGH INSTABILITY
FOR ISOLATED TO SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS.
A DRIER AND MORE STABLE AIRMASS RETURNS FOR TUESDAY AND WEDNESDAY
WITH WARMER TEMPERATURES.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY AFTERNOON)
ISSUED AT 601 PM MDT WED MAY 15 2013

RADAR IMAGERY SHOWS ISOLATED TO SCATTERED SHOWERS CURRENTLY ACROSS
SOUTHEAST WY. AN UPPER LEVEL DISTURBANCE WILL CONTINUE TO MOVE
ACROSS THE REGION OVERNIGHT...SO WOULD EXPECT THESE ISOLATED
SHOWERS TO SPREAD OVER THE WESTERN NEBRASKA PANHANDLE BY THE LATE
EVENING. THE SHOWER THREAT SHOULD END AFTER AROUND 09Z...HOWEVER
SOME OF THE FAR EASTERN SITES COULD SEE THE ACTIVITY CONTINUE
THROUGH THE MORNING ON THURSDAY. WINDS SHOULD GENERALLY BE LESS
THAN 15 KTS...EXCEPT NEAR SHOWERS WHERE GUSTY WINDS WILL BE POSSIBLE.

&&

.FIRE WEATHER...
ISSUED AT 251 PM MDT WED MAY 15 2013

COOLER AND MORE HUMID CONDITIONS WILL BE OVER THE DISTRICT TODAY
BEHIND THE PASSAGE OF A COLD FRONT. IN ADDITION...THERE WILL BE A
GOOD CHANCE OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS.
SOME OF THE STORMS WILL PRODUCE A WETTING RAINFALL ALONG WITH
BRIEF WIND GUSTS TO 50 MPH. WARMER AND DRIER CONDITIONS CAN BE
EXPECTED FOR THURSDAY AND ESPECIALLY FRIDAY AND SATURDAY OVER THE
REGION. WESTERLY SURFACE WINDS WILL GUST AS HIGH AS 40 MPH DURING
THE DAYTIME IN AREAS ALONG AND WEST OF THE LARAMIE RANGE. MINIMUM
RELATIVE HUMIDITY VALUES WILL BE AS LOW AS AROUND 15 PERCENT
THURSDAY AND FRIDAY OVER THE LOWER ELEVATIONS OF CARBON COUNTY.
CRITICAL FIRE WEATHER CONDITIONS MAY BE REACHED IN THE AFTERNOON
HOURS OF THURSDAY THROUGH SATURDAY OVER THE LOWER ELEVATIONS ALONG
AND WEST OF THE LARAMIE RANGE. COOLER TEMPERATURES AND A CHANCE
OF SHOWERS WILL RETURN TO THE DISTRICT SUNDAY AND EARLY NEXT WEEK
BEHIND THE PASSAGE OF ANOTHER COLD FRONT.

&&

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

$$

SHORT TERM...RUBIN
LONG TERM...JAMSKI
AVIATION...FINCH
FIRE WEATHER...JAMSKI