Area Forecast Discussion
Issued by NWS Riverton, WY

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758
FXUS65 KRIW 130606
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1106 PM MST FRI FEB 12 2016

.UPDATE...

.AVIATION.../06Z ISSUANCE/

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

FOG WILL NOT BE AS EXTENSIVE AS THE LAST FEW NIGHTS...BUT PATCHY FOG
MAY PARTIALLY OBSCURE TERRAIN IN THE WESTERN VALLEYS THROUGH 15Z SAT.

A COLD FRONT WILL PUSH ACROSS THE AREA 16Z-20Z BRINGING NMRS MTN
SHSN AND FQT MTN OBSCURATIONS VCNTY AND NORTH OF A KJAC-KDUB LINE
WITH MAINLY SCT MVFR SHSN OVER THE WESTERN VALLEYS AND FURTHER SOUTH
ALONG THE DIVIDE.  AREAS OF LLWS WILL ALSO ACCOMPANY THE COLD FRONT
VCNTY KJAC WHERE SFC WINDS WILL REMAIN SW WHILE W-NW SFC WINDS
INCREASE TO 20-30KTS AT OTHER TERMINALS.

AN INCREASINGLY MOIST NW FLOW WILL BRING WIDESPREAD MVFR/IFR -SN
INTO FAR WEST...VCNTY KJAC-KAFO 06Z-12Z SUNDAY WITH MTNS ALONG AND
WEST OF THE DIVIDE BECOMING MOSTLY OBSCURED.

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

VFR CONDITIONS WITH MAINLY SOME SCT-BKN MID AND HIGH CLOUDS WILL
PREVAIL THROUGH SATURDAY MORNING.  A COLD FRONT WILL PUSH ACROSS THE
AREA 19Z-22Z SATURDAY BRINGING SCT-NMRS MVFR/IFR SHSN VCNTY AND
NORTH OF A KBYG-KPOY LINE ALONG WITH THE BIGHORN AND ABSAROKA RANGES
BECOMING MOSTLY OBSCURED.  AREAS OF SFC NW WINDS AT 20-30KTS WITH
GUSTS NEAR 40KTS WILL FOLLOW THE FRONT...WITH THE STRONGEST WINDS
EXPECTED VCNTY KDUB-KRIW AND KSHR-KBYG THROUGH EARLY SATURDAY
EVENING.  WINDS WILL DIMINISH AFTER 02Z SUNDAY ALONG WITH SHSN
ENDING ACROSS NORTHERN WYOMING.  INCREASING MOISTURE IN WESTERLY
FLOW WILL RESULT IN THE HIGHER PEAKS OF THE WIND RIVER AND ABSAROKA
RANGE BECOMING MOSTLY OBSCURED AFTER 06Z SUNDAY.

&&

.PREV DISCUSSION... /ISSUED 110 PM MST FRI FEB 12 2016/

SHORT TERM...TONIGHT THROUGH SATURDAY

AN HIGH PRESSURE RIDGE OVER THE WESTERN U.S. WILL PRODUCE
NORTHWEST FLOW WITH LIMITED MOISTURE OVER WESTERN AND CENTRAL
WYOMING TONIGHT AND SATURDAY MORNING. SOME LOW STRATUS CLOUDS AND
FOG WILL BE A THREAT IN JACKSON HOLE AND STAR VALLEY LATER TONIGHT
AND SATURDAY MORNING.  VARIABLE MID AND HIGH CLOUDS WILL BE OVER
THE AREA AS WELL. A LOW PRESSURE TROUGH WILL BRING INCREASED
MOISTURE AND LIFT INTO THE NORTHWEST BY EARLY AFTERNOON WITH
INCREASING COVERAGE OF LIGHT SNOW SHOWERS OVER THE NORTHERN AND
WESTERN MOUNTAINS.

LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

WITH DIFFERENT WEATHER PROBLEMS...WE WILL DIVIDE THE DISCUSSION INTO
WEST AND EAST OF THE DIVIDE.

WEST OF THE DIVIDE...AFTER A BRIEF BREAK BETWEEN SYSTEMS FOR
SATURDAY EVENING...THE NEXT ONE WILL ARRIVE LATER SATURDAY NIGHT AND
INTO SUNDAY. THIS SYSTEM HAS DECENT ISENTROPIC LIFT AND MOISTURE
ASSOCIATED WITH IT SO THERE COULD BE A DECENT AMOUNT OF SNOW. NOT
WARNING LEVEL...BUT POSSIBLY ADVISORY. SINCE IT IS STILL A WAYS
AWAY...WE WILL LET FUTURE SHIFTS MAKE THAT DECISION. THE HEAVIEST
SNOW LOOKS TO BE SUNDAY MORNING AS THE TROUGH AXIS SWINGS
THROUGH...ALTHOUGH PERIODS OF SNOW WILL CONTINUE INTO THE AFTERNOON
AND EVENING WITH THE FAVORABLE WEST TO NORTHWEST OROGRAPHIC FLOW.
THE MODELS THEN DIFFER ON THE STRENGTH OF THE NEXT SYSTEM FOR
MONDAY WITH THE NAM WEAKER AND THE GFS HAVING A BIT MORE MOISTURE.
THE MODELS DO KEY IN ON NORTHWESTERN WYOMING WITH THIS SYSTEM
HOWEVER. MONDAY NIGHT INTO TUESDAY SHOULD THEN SEE A DRYING TREND AS
HIGH PRESSURE AND RIDGING BUILD ACROSS THE AREA...ALTHOUGH THE
EUROPEAN IS SLOWER THAN THE GFS IN BUILDING THE RIDGE. FOR NOW...WE
SPLIT THE MIDDLE. TUESDAY AND WEDNESDAY AT THIS POINT LOOK LARGELY
DRY WITH RIDGING OVER THE AREA. THE NEXT IN THE SERIES OF SYSTEMS
THEN MOVES IN FOR THURSDAY ALTHOUGH THE MODELS DO HAVE IT SPLITTING
SOMEWHAT. TEMPERATURES WILL REMAIN ABOVE NORMAL THROUGH MUCH OF THE
PERIOD.

EAST OF THE DIVIDE...ANY SHOWERS ON SATURDAY SHOULD END EARLY
SATURDAY EVENING WITH A BALANCE OF THE NIGHTTIME HOURS LARGELY DRY.
ANOTHER SYSTEM WILL SPILL OVER THE DIVIDE ON SUNDAY THOUGH. WITH
UNSTABLE NORTHWEST FLOW...THERE COULD BE SOME SHOWERS AND BANDS OF
SNOW AND RAIN. AND AS USUAL...THIS FAR OUT IT IS IMPOSSIBLE TO
PINPOINT THEM. WE KEPT THE HIGHER POPS ACROSS EASTERN AND NORTHERN
PORTIONS OF THE AREA WHERE THE MODELS ARE SHOWING MORE QPF.
HOWEVER...GIVEN THE WARMER TEMPERATURES ANY THAT FALLS DURING THE
DAY MAY HAVE TROUBLE STICKING..ESPECIALLY ON PAVED SURFACES. IT WILL
BE ANOTHER BLUSTERY DAY AS WELL. EXPECT THE SAME ON MONDAY WITH
ANOTHER SYSTEM MOVING ACROSS THE AREA WITH ADDITIONAL
SHOWERS...AGAIN SOME AS RAIN GIVEN THE WARM TEMPERATURES. A DRYING
TREND THEN MOVES IN FOR TUESDAY AND WEDNESDAY AS RIDGING BUILDS
ACROSS THE AREA WITH LIGHT TO MODERATE WINDS. THIS TIME
HOWEVER...GIVEN THE WARMER WEATHER THAT WILL BRING SNOW MELT...THERE
IS MUCH LESS CHANCE OF INVERSIONS NOW. ABOVE NORMAL TEMPERATURES
WILL CONTINUE INTO NEXT WEEK. THURSDAY COULD BE QUITE WINDY. A
PRESSURE GRADIENT WILL TIGHTEN AHEAD OF AN APPROACHING PACIFIC
SYSTEM WITH THE MODELS SHOWING 700 MILLIBAR WINDS AS HIGH AS 60
KNOTS...ESPECIALLY ACROSS THE SOUTHWESTERN WIND CORRIDOR. THIS
SYSTEM THEN CROSSES THE AREA THURSDAY NIGHT INTO FRIDAY. THE GFS
SPLITS THE SYSTEM WHILE THE EUROPEAN IS A BIT MORE ROBUST. STILL
PLENTY OF TIME TO WATCH IT THOUGH. EVEN BEHIND THIS SYSTEM...IT DOES
NOT LOOK TERRIBLY COLD SINCE THE AIR MASS IS PACIFIC IN ORIGIN.

AVIATION.../00Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS EXCEPT KJAC AND KAFO
WHERE LOW STRATUS CEILINGS AND VISIBILITY REDUCED IN FOG WILL
PRODUCE AREAS OF MVFR TO IFR CONDITIONS FROM 09Z SATURDAY TO 18Z
SATURDAY.

A LOW PRESSURE TROUGH IN NORTHWEST FLOW ALOFT WILL BRING SCATTERED
SNOW SHOWERS TO THE NORTHERN MOUNTAINS UNTIL AROUND 02Z SATURDAY.
LOCAL MVFR CONDITIONS WILL OCCUR IN THIS AREA ALONG WITH HIGHER
MOUNTAIN OBSCURATIONS. ANOTHER LOW PRESSURE TROUGH WILL MOVE
THROUGH SATURDAY AFTERNOON WITH A REPEAT OF SNOW SHOWERS AND MVFR
TO IFR CEILING OVER THE NORTHERN AND WESTERN MOUNTAINS FROM 18Z
SATURDAY TO 00Z SUNDAY.

FIRE WEATHER...

AN HIGH PRESSURE RIDGE OVER THE WESTERN U.S. WILL PRODUCE
NORTHWEST FLOW WITH LIMITED MOISTURE OVER WESTERN AND CENTRAL
WYOMING TONIGHT AND SATURDAY MORNING. SOME LOW STRATUS CLOUDS AND
FOG WILL BE A THREAT IN JACKSON HOLE AND STAR VALLEY LATER TONIGHT
AND SATURDAY MORNING.  VARIABLE MID AND HIGH CLOUDS WILL BE OVER
THE AREA AS WELL. A LOW PRESSURE TROUGH WILL BRING INCREASED
MOISTURE AND LIFT INTO THE NORTHWEST BY EARLY AFTERNOON WITH
INCREASING COVERAGE OF LIGHT SNOW SHOWERS OVER THE NORTHERN AND
WESTERN MOUNTAINS. GENERALLY...RELATIVE HUMIDITY WILL BE FAVORABLE
TO HIGH WITH LOW MIXING HEIGHTS PRODUCING POOR SMOKE DISPERSAL
EXCEPT ALONG THE WINDIER EAST SLOPES OF THE MOUNTAINS EAST OF THE
CONTINENTAL DIVIDE WHERE BREEZY TO WINDY CONDITIONS WILL PROVIDE
BETTER MIXING FOR FAIR TO LOW END GOOD SMOKE DISPERSAL.

RIW WATCHES/WARNINGS/ADVISORIES...NONE.

$$

SHORT TERM...C.BAKER
LONG TERM...HATTINGS
AVIATION...C.BAKER

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...C.BAKER
LONG TERM...HATTINGS
AVIATION...AEM
FIRE WEATHER...C.BAKER



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