Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 281155
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
555 AM MDT MON JUL 28 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY NIGHT)
ISSUED AT 428 AM MDT MON JUL 28 2014

UPPER-LEVEL RIDGING PERSISTS ACROSS THE WESTERN STATES THIS AM PER
THE LATEST WATER VAPOR SATELLITE LOOP. WE ARE ON THE EASTERN FRINGE
OF THIS FEATURE AS A VIGOROUS SHORTWAVE MOVES SOUTHEAST ACROSS THE
GREAT LAKES REGION. MODEST NORTHWEST FLOW ALOFT WILL REMAIN IN PLACE
OVER THE CWA TODAY AS MONSOONAL MOISTURE SPREADS NORTH. WEAK FRONTAL
BOUNDARY DRAPED FROM NORTHWEST TO SOUTHEAST ALONG THE LARAMIE RANGE
WILL PROVIDE A GENERAL FOCUS FOR SHOWER AND TSTM DEVELOPMENT BY THIS
AFTN AND EVE. SHOULD SEE ACTIVITY GRADUALLY SHIFT ACROSS THE REST OF
THE AREA LATER ON AS MIDLVL ENERGY TRAVERSES THE FLOW ALONG THE EDGE
OF THE RIDGE...BUT TIMING THESE WEAKER WAVES IS DIFFICULT. ABUNDANT
MOISTURE IN THE 700-300 MILLIBAR LAYER AND INCREASING UPPER-LEVEL
DIVERGENCE IN THE RIGHT REAR QUAD OF A 110 KT H25 JET STREAK TO OUR
NORTHEAST SHOULD CONTRIBUTE TO AT LEAST ISOLATED TO WIDELY SCATTERED
CONVECTION OVERNIGHT. DOUBT WE WILL SEE ANYTHING TOO STRONG IN THE
NEXT 24 HOURS WITH MODERATE CAPES AROUND 1000 J/KG CONFINED TO AREAS
ALONG AND JUST EAST OF THE SOUTH LARAMIE RANGE. WHILE INSTABILITY
MAY BE SUFFICIENT FOR STRONGER UPDRAFTS...15 KTS OF FLOW UPSTAIRS AT
H5 SUGGESTS INADEQUATE SHEAR FOR STORM ORGANIZATION. HEAVY RAIN PTNL
IS THERE WITH SLOW STORM MOTIONS...BUT DID NOT MENTION IN THE LATEST
FCST PACKAGE AS THERE IS STILL A LOT OF UNCERTAINTY WITH TIMING AND
PLACEMENT OF HEAVIER RAINFALL.

CONFIDENCE IS INCREASING ON A WIDESPREAD AND POTENTIALLY SIGNIFICANT
PCPN EVENT ACROSS THE AREA ON TUE AND WED. GFS/NAM/ECMWF EACH OFFER
VARYING SOLUTIONS CONCERNING HEAVY PCPN TIMING. HOWEVER...ALL AGREE
WITH STRONG EAST-TO-SOUTHEAST LLVL UPSLOPE FLOW SETTING UP ALONG THE
LARAMIE RANGE AHEAD OF A STRONGER SHORTWAVE PROGGED TO MOVE ACROSS
CENTRAL WY SOMETIME ON TUE AM. EXCELLENT MOISTURE FOR THIS EVENT GFS
PWAT VALUES INCREASE TO AROUND 1.5 INCHES WITH SFC DEWPOINTS AROUND
60F SOUTHEAST. SOUTHEAST LLVL FLOW QUICKLY VEERING TO THE NORTHWEST
ABOVE H7 SUGGESTS PTNL FOR TRAINING CONVECTION ALONG THE LARAMIE
RANGE...WHICH EXPLAINS SOME OF THE HIGHER QPF WE ARE SEEING IN THE
MODELS. WPC DAY 3 EXCESSIVE RAINFALL SHOWS A MDT RISK OVER THE CO
FRONT RANGE EXTENDING NORTHWARD INTO FAR SOUTHEAST WY. FUTURE SHIFTS
MAY NEED TO CONSIDER A FLASH FLOOD WATCH FOR PARTS OF THE AREA ONCE
MODELS COME INTO BETTER TEMPORAL AGREEMENT. MOST LIKELY AREA WOULD
BE THE SOUTH LARAMIE RANGE EASTWARD INTO CYS. TEMPERATURES THROUGH
THE PERIOD WILL BE COOL FOR THIS TIME OF YEAR. H7 TEMPS FALL TO
BETWEEN 5-8 C BY MIDWEEK...AND WITH WIDESPREAD CLOUDS AND PCPN SOME
AREAS MAY BE HARD PRESSED TO SEE 70S FOR HIGHS. STILL UNDERCUTTING
MOS GUIDANCE FOR TUE AND WED.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 428 AM MDT MON JUL 28 2014

RELATIVELY WEAK UPPER-LEVEL RIDGE AXIS CENTERED OVR WRN NOAM EARLY
IN THE PERIOD WILL AMPLIFY AND SURGE NORTH EARLY NEXT WEEK. BOTH THE
ECMWF/GFS SUGGEST SLOW-MOVING SHORTWAVE ENERGY WILL BE EMBEDDED
WITHIN THE FLOW AND WHEN COMBINED WITH AN INFLUX OF MONSOONAL
MOISTURE WILL CONTINUE TO SPARK PRIMARILY AFTERNOON/EVENING
THUNDERSTORM CHANCES. CHANCES WILL BE CONFINED TO LOCATIONS IN
CLOSEST PROXIMITY TO THE SUB-TROPICAL MOISTURE PLUME...WHICH WILL BE
ALONG AND WEST OF THE INTERSTATE 25. ALTHOUGH CONFIDENCE IN THE
TIMING OF INDIVIDUAL SHORTWAVES IS LOW THIS FAR OUT...BOTH THE
GFS/ECMWF SUGGEST THAT PERHAPS THE STRONGEST SHORTWAVE MAY MOVE THRU
ON FRIDAY. SO...HAVE THE HIGHEST CONVECTION CHANCES THEN.
OTHERWISE...LESSER SHOWER/THUNDERSTORM CHANCES EXIST THURSDAY AND
AGAIN ON SATURDAY. AT THIS POINT...SUNDAY LOOKS TO BE THE DRIEST DAY
OF THE PERIOD AS THE MONSOONAL MOISTURE PLUME BRIEFLY GETS SHUNTED
SOUTH. IT RETURNS FOR MONDAY AS ANOTHER POTENTIALLY STRONGER H5
TROUGH APPROACHES THE REGION. THURSDAY WILL BE THE COOLEST DAY OF
THE PERIOD...YET WARMER COMPARED TO WEDNESDAY. HIGHS WILL REACH INTO
THE 70S ABOVE 5KFT AND 80S BELOW. TEMPS WILL CONTINUE TO WARM INTO
THE WEEKEND AS THE UPPER-LEVEL RIDGE AXIS STRENGTHENS ACROSS THE
INTERMOUNTAIN WEST.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 553 AM MDT MON JUL 28 2014

PATCHY FOG HAS MATERIALIZED IN THE VICINITY OF THE SRN LARAMIE
RANGE...WHICH HAS BROUGHT CONDITIONS TO IFR AT KLAR. THIS PATCHY
FOG WILL QUICKLY LIFT BY 8-9AM. SCATTERED SHOWERS AND
THUNDERSTORMS WILL DEVELOP ALONG AND WEST OF THE SOUTHERN LARAMIE
RANGE MONDAY AFTERNOON. HEAVY RAIN MAY PRODUCE LOW VISIBILITIES
WITH SOME OF THE SHOWERS AND THUNDERSTORMS. SHOWER AND
THUNDERSTORMS ACTIVITY MAY LINGER A BIT MONDAY NIGHT...BUT WILL
LESSEN IN STRENGTH AND COVERAGE.

&&

.FIRE WEATHER...
ISSUED AT 428 AM MDT MON JUL 28 2014

MINIMAL FIRE WEATHER CONCERNS OVER THE NEXT FEW DAYS. TODAY WILL BE
THE WARMEST DAY WITH AFTERNOON HIGHS IN THE MIDDLE TO UPPER 80S OVER
WESTERN CARBON COUNTY. MINIMUM HUMIDITIES WILL BE IN THE TEENS...BUT
WINDS WILL BE LIGHT. WIDESPREAD SHOWERS AND THUNDERSTORMS ARE LIKELY
ON TUE AND WED AS MONSOON MOISTURE OVERSPREADS THE AREA. SEASONABLY
COOL TEMPERATURES AND WEAK FLOW ALOFT WILL KEEP FIRE PARAMETERS TAME
IN THE NEAR TERM.

&&

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

$$

SHORT TERM...HAMMER
LONG TERM...HAHN
AVIATION...HAHN
FIRE WEATHER...HAMMER






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