Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 120455
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1054 PM MDT THU SEP 11 2014

.UPDATE...

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES
AREAS OF MVFR/IFR CIGS WILL GRADUALLY DISSIPATE THROUGH 10Z WITH
AREAS OF FOG OR LOWER LIFR/IFR CIGS DEVELOPING AS DRIER AIR MOVES IN
ALOFT.  THESE CONDITIONS WILL RAPIDLY IMPROVE BETWEEN 14Z-16Z WITH
MAINLY VFR/SKC CONDITIONS PREVAILING 16Z FRI-12Z SAT.   SFC WINDS
WILL GENERALLY BE FROM THE S-SE AT 5-10KTS THROUGH THE DAY FRIDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
THROUGH 15Z FRIDAY...SOME MVFR CIGS AROUND FL090 MAY PUSH INTO VCNTY
KRKS THROUGH 15Z. ELSEWHERE...THERE MAY BE SOME PATCHY FOG OBSCURING
THE WESTERN VALLEYS.  VFR/SKC CONDITIONS WILL PREVAIL AFTER 15Z WITH
MOSTLY LIGHT WIND OF 10 KNOTS OR LESS.


SNOW HAS TAPERED OFF ACROSS THE NORTH AND WINTER WEATHER
HIGHLIGHTS WERE ALLOWED TO EXPIRE. HEAVIER W-E ORIENTED SNOWBANDS
SLOWLY SAGGING SOUTH ACROSS NATRONA COUNTY AHEAD OF THE UPPER
TROUGH. THESE BANDS HAVE ALREADY DEPOSITED 4 INCHES OF SNOW ON
CASPER MOUNTAIN WITH MOST OF THE SNOW ACCUMULATION IN CASPER
CONFINED TO VEGETATION. MOST OF THIS ACTIVITY IS EXPECTED TO
CONTINUE TO SAG SOUTH OF THE AREA BETWEEN 7 PM AND 8 PM.

&&

.PREV DISCUSSION... /ISSUED 217 PM MDT THU SEP 11 2014/

SHORT TERM...TONIGHT THROUGH FRIDAY

A COLD MOIST UPPER LEVEL LOW PRESSURE CENTER OVER MONTANA THAT HAS
BROUGHT CLOUDS AND AREAS OF SNOW TO NORTH AND CENTRAL WYOMING...WILL
SHIFT EAST TONIGHT AS COLD DRY HIGH PRESSURE OVER THE PACIFIC
NORTHWEST MOVES INTO WESTERN WYOMING.  THIS WILL BRING AN END TO THE
SNOWFALL BUT WILL PRODUCE CONDITIONS FAVORABLE FOR FOG DEVELOPMENT...
WHICH WILL BE A THREAT THROUGH MID MORNING.  VERY COLD TEMPERATURES
FOR EARLY SEPTEMBER WILL BRING A HARD FREEZE TO THE AREA.  AS THE HIGH
PRESSURE CONTINUES TO MOVE IN...TEMPERATURES WILL WARM THROUGH THE
DAY.

LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

THIS PERIOD IS THE CALM AFTER THE STORM. AS DISCUSSED...THE
DEPARTURE OF THE STRONG AREA OF LOW PRESSURE WILL ALLOW FOR BUILDING
RIDGING AND NORTHWEST FLOW. THE HIGH PRESSURE RIDGE WILL LAST OVER
THE AREA THROUGH THE MIDDLE PORTION OF NEXT WEEK...WITH DRY
CONDITIONS. TEMPERATURES WILL STEADILY WARM...WITH SEASONABLE
TEMPERATURES ANTICIPATED BY EARLY NEXT WEEK.

A FEW VERY LIGHT DISTURBANCES ARE POSSIBLE IN THE RIDGING
PATTERN...BUT ARE NOT EXPECTED TO HAVE MUCH OF AN IMPACT ON THE
FORECAST AREA. THE NEXT POTENTIALLY SIGNIFICANT SYSTEM MAY ARRIVE
LATE WEDNESDAY AND INTO THURSDAY. A WAVE OF LOW PRESSURE IS
DEMONSTRATED ON THE GFS SOLUTION...BUT THE ECMWF HOLDS ONTO THE
RIDGE. BY THURSDAY THE SLIGHT VARIATION BECOMES MUCH MORE MASSIVE
WITH THE GFS PUSHING A MOIST WAVE THROUGH THE STATE WITH WIDESPREAD
PRECIPITATION...AND THE ECMWF MAINTAINING ITS DRY SOLUTION. TRENDING
TOWARDS THE DRIER SOLUTION..THOUGH SLIGHT CHANCE PRECIPITATION
AMOUNTS HAVE BEEN INCLUDED IN THE FORECAST FOR NOW.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

WIDESPREAD RAIN AND SNOW WITH MVFR/IFR CONDITIONS AND MTN
OBSCURATIONS WILL CONTINUE ACROSS THE AREA.  SNOW WILL DECREASE
FROM NW-SE THROUGH THIS EVENING AS A MUCH DRIER AIR MASS MOVES IN
ALOFT 06Z TO 12Z TONIGHT. AREAS OF MVFR/IFR CIGS AND AREAS OF FOG
WILL LIKELY PERSIST OVER MUCH OF THE AREA THROUGH 15Z FRIDAY AS
THE BOUNDARY LAYER AIR MASS WILL REMAIN NEARLY SATURATED.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR CONDITIONS WILL PREVAIL ACROSS THE FAR WEST THROUGH THE PERIOD.
A COLD FRONT WILL CONTINUE TO DEEPEN ALONG THE EAST SLOPES OF THE
DIVIDE WITH THIS FRONT PUSHING TO VCNTY KRKS.  AREAS OF MVFR CIGS
FL080-090 WILL LIKELY FILL IN BEHIND THE FRONT...OBSCURING HIGHER
TERRAIN. SOME OF THESE LOWER CLOUDS MAY ALSO SPILL OVER THE DIVIDE
INTO VCNTY KPNA. THOUGH A DRIER AIR MASS WILL PUSH IN ACROSS MOST
OF THE AREA TONIGHT...SOME OF THESE LOWER CIGS MAY LINGER VCNTY
KRKS AND EAST THROUGH 12Z FRIDAY.

FIRE WEATHER...

A COLD MOIST UPPER LEVEL LOW PRESSURE CENTER OVER MONTANA THAT HAS
BROUGHT CLOUDS AND AREAS OF SNOW TO NORTH AND CENTRAL WYOMING...WILL
SHIFT EAST TONIGHT AS COLD DRY HIGH PRESSURE OVER THE PACIFIC
NORTHWEST MOVES INTO WESTERN WYOMING.  THIS WILL BRING AN END TO THE
SNOWFALL BUT WILL PRODUCE CONDITIONS FAVORABLE FOR FOG DEVELOPMENT...
WHICH WILL BE A THREAT THROUGH MID MORNING.  VERY COLD TEMPERATURES
FOR EARLY SEPTEMBER WILL BRING A HARD FREEZE TO THE AREA.  AS THE HIGH
PRESSURE CONTINUES TO MOVE IN...TEMPERATURES WILL WARM THROUGH THE
WEEKEND.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FREEZE WARNING FROM 2 AM TO 9 AM MDT FRIDAY
WYZ004>006-013-016>020-023-025>030.

&&

$$

UPDATE...AEM
SHORT TERM...C.BAKER
LONG TERM...BRANHAM
AVIATION...AEM
FIRE WEATHER...C.BAKER







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