000
FXUS65 KRIW 281824
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 AM MST FRI FEB 28 2014

.SHORT TERM...FRIDAY THROUGH SUNDAY NIGHT

THE STORM EVENT IS NOW STARTING TO GET UNDERWAY IN PORTIONS OF THE
AREA. ONE PIECE OF THE STORM WITH SOME WARM ADVECTION IS ONGOING
ACROSS THE WEST. ONE INTERESTING WRINKLE IS THAT TEMPERATURES ARE
BORDERLINE IN SOME AREAS SO THERE COULD BE SOME RAIN MIXING WITH
SNOW IN SOME LOCATIONS IN THE WEST. MEANWHILE...THE ARCTIC COLD
FRONT IS STARTING TO DROP SOUTHWARD ACROSS NORTHERN PORTIONS OF THE
STATE...HAVING MOVED THROUGH BUFFALO...POWELL AND CODY BY 1 AM. THIS
FRONT WILL CONTINUE TO DROP SOUTHWARD THROUGH THE DAY AND BRING IN
MUCH COLDER TEMPERATURES TO AREAS EAST OF THE DIVIDE. AT THIS SAME
TIME...SOME OVERRUNNING WILL DEVELOP AND BRING SOME SNOW TO AREAS
MAINLY FROM AROUND NATRONA COUNTY INTO THE BIG HORN BASIN. A JET
STREAK WILL LIFT ACROSS THE AREA TODAY...SO THERE COULD BE SOME
LOCALLY HEAVY SNOW. THE OTHER DILEMMA WILL BE FOR HIGH TEMPERATURES
AS A LOT DEPENDS ON WHEN THE FRONT MOVES THROUGH. FOR NOW...WE LEFT
THEM ALONE FOR THE MOST PART. MEANWHILE...OUT WEST THERE COULD BE A
LULL IN THE PRECIPITATION THIS AFTERNOON AS THE AREA WILL BE IN
BETWEEN SYSTEMS.

THE MAIN EVENT FOR MOST AREAS STILL LOOKS TO BE TONIGHT INTO
SATURDAY...ESPECIALLY LATER TONIGHT INTO AROUND MIDDAY SATURDAY. THE
SURGE OF MOISTURE NOW OVER CALIFORNIA WILL BEGIN MOVE OVER THE AREA.
IN ADDITION...THERE SHOULD BE SOME ADDITIONAL UPPER LEVEL DIVERGENCE
FROM THE REGION BEING IN THE FAVORED LEFT FRONT QUADRANT OF A JET
STREAK APPROACHING FROM THE SOUTHWEST. THE BEST DYNAMICS STILL LOOK
TO BE FROM AROUND 6Z TO 18Z SATURDAY SO THIS SHOULD BE THE TIME OF
THE HEAVIEST SNOW. ONE WORD OF CAUTION...THE 6Z NAM HAS COME IN WITH
THE JET MOVING FURTHER SOUTH AND KEEPING THE BEST DYNAMICS OVER
COLORADO....WHICH WOULD KEEP THE HEAVIEST PRECIPITATION TO THE
SOUTH. IT IS ONLY ONE RUN AND THE 6Z AND 18Z RUNS ARE NOTORIOUSLY
UNRELIABLE...BUT SOMETHING TO KEEP IN MIND. THE HEAVIEST
PRECIPITATION SHOULD BE OVER BY LATER SATURDAY AFTERNOON.
HOWEVER...SOME LIGHTER SNOW SHOULD CONTINUE THROUGH THE AFTERNOON.
SNOW SHOULD REALLY BEGIN TO TAPER OFF SATURDAY NIGHT EXCEPT FOR IN
THE WESTERN MOUNTAINS WHERE MOIST FLOW AND UPSLOPE WILL KEEP SNOW
GOING. TEMPERATURES WILL BE A SHOCK TO THE SYSTEM AFTER TOADY`S MILD
HIGHS IN MANY PLACES. HIGHS MAY REMAIN BELOW ZERO IN THE FAR
NORTHERN AND NORTHEASTERN PORTIONS OF THE COUNTY WARNING AREA AND
MOST AREAS EAST OF THE DIVIDE STRUGGLING TO REACH DOUBLE DIGITS
ABOVE ZERO.

AS FOR SUNDAY...WITH THE ONGOING STORM WE DID NOT MAKE A TON OF
CHANGES. ONE CHANGE WAS TO REMOVE THE POPS FROM MOST LOWER
ELEVATIONS EAST OF THE DIVIDE. WE KEPT TEMPERATURES BELOW MOS WITH
THE FRESH SNOW COVER PROVIDING GOOD ALBEDO. MEANWHILE...WEST OF THE
DIVIDE SOME SNOW WILL CONTINUE WITH CONTINUED FAVORABLE OROGRAPHIC
FLOW.

.LONG TERM...MONDAY THROUGH FRIDAY

DISTURBED ZONAL FLOW THROUGH MOST OF THE LONG TERM PERIOD WILL
KEEP THINGS ACTIVE...ESPECIALLY ACROSS THE WEST. THIS FLOW WILL
PRODUCE DOWNSLOPE WARMING WINDS ALONG AND NEAR THE EAST SLOPES OF
THE MOUNTAINS. THE AMOUNT AND TIMING OF THE WARMING WILL LIKELY
BE MODIFIED BY THE AMOUNT AND LOCATION OF SNOW COVER LEFT FROM THE
CURRENT STORM. ALSO WITH THIS FLOW PATTERN...STRONGER WINDS MAY
OCCUR EAST OF THE ABSAROKA MOUNTAINS AND THROUGH THE WIND CORRIDOR
FROM EASTERN SWEETWATER COUNTY THROUGH NATRONA COUNTY INCLUDING
THE CASPER AREA. THERE ARE SOME INDICATIONS THAT THERE COULD BE A
DIGGING TROUGH ON THURSDAY BRINGING SNOW EAST OF THE DIVIDE
AGAIN...BROUGHT AT LEAST SLIGHT CHANCE POPS TO THE ENTIRE FORECAST
AREA FOR THURSDAY NIGHT AND FRIDAY ALONG WITH COLDER TEMPERATURES.

&&

.AVIATION.../18Z ISSUANCE/

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

FIRST FRONTAL BOUNDARY SURGE PUSHED ACROSS ALL TERMINALS BY 15Z
TODAY. BATCH OF ENERGY THAT PRODUCED EARLIER HEAVIER SNOW HAS PUSHED
OFF TO THE EAST PER IR IMAGERY. MVFR/VFR STILL POSSIBLE AT KCOD...
KWRL...AND KCPR THROUGH 00Z/SAT WHILE KLND AND KRIW REMAIN VFR.
MOISTURE PUSH TONIGHT COUPLED WITH A SOUTHWARD SURGE OF A SECONDARY
FRONTAL BOUNDARY WILL COMBINE TO PRODUCE WIDESPREAD SNOWFALL AFTER
ABOUT 03Z/SAT. BEST FRONTOGENETICAL FORCING...JET COUPLING...AND
MOISTURE ALL COMBINE TO PRODUCE A PERIOD OF IFR/LIFR CONDITIONS
KLND-KRIW-KCPR FROM 06Z-16Z/SAT. WE ARE NOT QUITE AS AGGRESSIVE WITH
LOWERING CONDITIONS AT KCOD AND KWRL BUT STILL EXPECT IFR AT THOSE
TERMINALS OVERNIGHT. DYNAMICS AND BEST MOISTURE BEGIN TO WANE AFTER
ABOUT 16Z/SAT WITH SLIGHT IMPROVEMENT IN SURFACE VISIBILITY AND
CEILING HEIGHTS. MOUNTAIN OBSCURATIONS WILL BE WIDEPSREAD AFTER
00Z/SAT.

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

LIGHT SNOW FALLING IN THE MOUNTAINS LATE THIS MORNING BUT VALLEYS
ARE LARGELY DRY WITH VFR CONDITIONS. THESE CONDITIONS ARE LIKELY TO
CONTINUE THROUGH ABOUT 00Z/SAT BEFORE THE NEXT BATCH OF MOISTURE
WILL BEGIN ARRIVING FROM OUR SOUTHWEST. KBPI AND KPNA WILL SEE
CONDITIONS BEGIN TO DETERIORATE SHORTLY AFTER 00Z/SAT WITH KJAC
COMING A FEW HOURS LATER AS MOISTURE SLUG LIFTS NORTHEAST ACROSS THE
STATE. IFR CONDITIONS WILL BE FREQUENT AT THESE THREE TERMINALS
BETWEEN ABOUT 06Z/SAT AND 16Z/SAT. CONDITIONS WILL START TO SLOWLY
IMPROVE TOWARD MVFR CONDITIONS AFTER THAT TIME. MOUNTAIN
OBSCURATIONS WILL BE WIDESPREAD ALONG AND WEST OF THE DIVIDE THROUGH
THE ENTIRE PERIOD. WARMER SOUTHWEST FLOW WILL REMAIN ACROSS KRKS
THROUGH THE NIGHT. INITIAL PUSH OF MOISTURE THIS EVENING MAY BRING A
BRIEF PERIOD OF LIGHT SNOW TO KRKS LATE THIS EVENING AND EARLY
SATURDAY ACCOMPANIED BY BRIEF PERIODS OF MVFR CONDITIONS. FRONTAL
BOUNDARY MAY HAVE ENOUGH PUSH TO SLIDE INTO KRKS SATURDAY MORNING
BRINGING WINDS AROUND TO THE EAST-NORTHEAST THROUGH ABOUT 18Z/SAT.

&&

.FIRE WEATHER...

THE WEATHER WILL BE DOMINATED BY A MAJOR WINTER STORM FOR MOST AREAS
OVER THE NEXT COUPLE DAYS. THE WEST WILL BE HIT BY THE SNOW THROUGH
SATURDAY NIGHT. THE NORTH CENTRAL AREAS WILL HAVE THE ARCTIC COLD
FRONT DROP DOWN THIS MORNING WITH SNOW BEGINNING AND CONTINUING
THROUGH SATURDAY NIGHT. THE CENTRAL ZONES WILL SEE SNOW DEVELOPING
IN NATRONA COUNTY IN THE MORNING AND IN FREMONT COUNTY FRIDAY
AFTERNOON...CONTINUING THROUGH AT LEAST SATURDAY EVENING. THE I80
CORRIDOR WILL SEE SIGNIFICANT WIND AT TIMES WITH RAIN OR SNOW
SHOWERS...ESPECIALLY FRIDAY NIGHT AND SATURDAY. DRIER CONDITIONS
WILL RETURN EAST OF THE DIVIDE ON SUNDAY WITH CONTINUING SNOW
SHOWERS ACROSS THE WESTERN MOUNTAINS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 5 AM MST SUNDAY
WYZ016>020-022-027.

WINTER STORM WARNING UNTIL 5 AM MST SUNDAY
WYZ001>004-008>015-023>025.

WINTER STORM WARNING UNTIL 5 AM MST SUNDAY WYZ005>007.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...ALLEN
AVIATION...AR
FIRE WEATHER...HATTINGS