Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
000
FXUS65 KRIW 180523
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1023 PM MST Tue Jan 17 2017

.SHORT TERM...Tonight Through Friday

TEMPERATURES ARE THE BIGGEST CHALLENGE IN THE FORECAST ATTM. THE
TEMPERATURE INVERSIONS CONTINUE TO BE TOUGH TO SCOUR OUT OF THE
BASINS AND VALLEYS NOW THAT WARM AIR ADVECTION IS TAKING PLACE 1000
FEET OR SO ABOVE THE BASIN FLOORS. CURRENTLY THE TEMPERATURE ALONG
THE LITTLE WIND RIVER, 2 MILES SOUTH OF RIVERTON, IS 4 DEGREES
ABOVE ZERO, WHILE AT THE SAME TIME, THE TEMPERATURE AT THE WIND
RIVER RAWS AT AN ELEVATION OF OVER 9K ON THE EAST SLOPE OF THE
WIND RVR MTNS IS 50 DEGREES. THE TEMPERATURE AT MOXA IS NOW MINUS
12F BUT AT GRASS CREEK AT 7127 FEET IT IS 54F DEGREES. THE
TEMPERATURES AT THE HIGHER ELEVATIONS WILL LIKELY MAX OUT LATE
TODAY WITH THE H7 TEMPS PROJECTED TO GO ALL THE WAY UP TO 7C BY
THIS EVENING, SO THAT WITH A DRY ADIABATIC LAPSE RATE, ASSUMING NO
INVERSION, THESE TEMPS WOULD BE WHERE ONE WOULD EXPECT THEM TO BE.
THE INVERSIONS SHOULD STICK AROUND TONIGHT THROUGH WEDNESDAY AND
INTO WEDNESDAY NIGHT BEFORE SOME COOLER AIR ALOFT SEEPS IN FROM
THE NORTHWEST WITH THE NEXT UPSTREAM TROUGH. SO WE CAN EXPECT AT
LEAST TWO MORE CHILLY NIGHTS IN THE VALLEYS AND BASINS AND ONE
MORE CHILLY DAY. HOWEVER, INCREASING CLOUDS IN THE WEST WILL KEEP
TEMPS FROM DROPPING OUT THERE AS MUCH WEDNESDAY NIGHT. TEMPS WILL
BE COLD IN THE BASINS EAST OF THE DIVIDE WEDNESDAY NIGHT, BOT ONLY
A FEW DEGREES MILDER. THE GRADIENT WILL INCREASE AS THIS TROUGH
APPROACHES WITH THE INCREASING SOUTHWEST STEERING WINDS WEDNESDAY
NIGHT BACKING TO A MORE SOUTHERLY TRAJECTORY BY THURSDAY THROUGH
FRIDAY, AN INDIRECT FEED OFF THE PACIFIC. BY THE END OF THE WEEK,
MOST OF THE ENERGY FROM THIS TROUGH WILL BE DIVERTED WELL TO THE
SOUTHWEST OVER CA, SOUTHERN NEVADA, AND ARIZONA SO WESTERN WY IS
ONLY EXPECTED TO RECEIVE LIGHT SNOWFALL THU THROUGH FRI. THE
TEMPERATURE GRADIENT OF 12-14C FROM THE ABSAROKA MTNS TO THE CODY
FOOTHILLS SHOULD BE ENOUGH TO CRANK THE GAP WINDS UP TO SUB HIGH
WIND NUMBERS SO HAVE ISSUED AN SPS FOR TONIGHT AND WED MORNING,
PRIMARILY FOR THE CLARK AREA WITH ISOLD GUSTS OF 60 MPH. SOUTHWEST
WINDS ARE ALREADY CRANKING OVER THE CASPER AREA, BUT CURIOUSLY,
ALTHOUGH THE WIND SHAVE BEEN GUSTING TO 43 MPH AT THE NATRONA
COUNTY AIRPORT, THEY ARE ONLY GUSTING TO 24 MPH ON OUTER DRIVE.
ALSO HAVE AN SPS OUT FOR THE GREEN/GRANITE MTNS AS THESE WINDS
WILL LIKELY CONTINUE THROUGH WED AS SUGGESTED BY MOS GUIDANCE IN
SPITE OF THE FACT THAT THE 700MB WINDS ARE RELATIVELY WEAK.

.LONG TERM...Friday Night Through Tuesday

Models start to differ more in the big picture by the end of the
period. The Euro is holding together a better mean trough over the
Intermountain west while the GFS is now flattening the flow by early
next week. End result is a more potent looking system in the Euro
early next week with a chance of decent snow in at least the far
srn/sern zones from near RKS to CPR. The GFS splits this system and
is much further south with just some snow from the northern piece in
the mtns and far south. Low confidence at the end of the medium
range right now. For the first few days, there is reasonable
agreement still. Friday night and Saturday we get a splitting system
with some light snow expected in the west and far south with mainly
just clouds elsewhere. We start up with a little trough/caa light
snow out west (Fri ngt/Sat) and finish off with some warm advection
snow Saturday night. On Sunday, we should see a transitory ridge
before our system early next week. Snow should begin in the far west
by late in the day Sunday, increasing Sunday night as trough
dynamics (QG/Jet) support increase. SW favored wind areas will
respond east of the divide ahead of this trough. Could see some
decent advisory amounts in the west from this system Sunday night
and Monday. Depending on how this system evolves, we`ll then have to
watch the area from Sweetwater County ne to Natrona County late
Monday into Tuesday morning.

&&

.AVIATION.../06Z ISSUANCE/

Low confidence in fog development impacting terminals this morning
across the basins and valleys as well as Sweetwater County as
boundary layer moisture remains limited. As of 05Z the satellite fog
product and area webcams show little fog development. Have decided
to go with persistence to less fog than what occurred Tuesday
morning with mainly only tempo groups for fog right now. Will let
the night shift monitor conditions, and decide if fog needs to be
prevailed or not. Otherwise VFR conditions are expected with windy
conditions in SE Fremont into Natrona County impacting KCPR...and
low-level wind shear impacting KCOD through the period. Also an
approaching storm system will bring in some lower clouds over the
west after 00Z Thursday.

&&

.FIRE WEATHER...

STRONG TEMPERATURE INVERSIONS ALONG WITH POOR SMOKE
DISPERSAL AND HEAVY SNOW COVER WILL BE THE RULE FOR MOST LOWER
ELEVATIONS FOR THE NEXT COUPLE OF DAYS. VERY MILD TEMPERATURES ARE
EXPECTED AT THE HIGHER ELEVATIONS. EXPECT BRISK WEST SOUTHWEST WINDS
IN THE CLARK AREA NORTH OF CODY AS WELL AS ACROSS ZONES 289 AND 280.
LIGHT SNOW IS EXPECTED THURSDAY AND FRIDAY IN THE FAR WEST ALTHOUGH
HIGHER MOUNTAIN PEAKS WILL EXPERIENCE LESS WIND.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...WM
FIRE WEATHER...Lipson



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.