Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 120854
Area Forecast Discussion
National Weather Service Riverton WY
154 AM MST Thu Jan 12 2017
.SHORT TERM...Thursday through Saturday night
Well, it is now January 12th. And right now we have a wonderful
occasion. Can anyone guess what it is? Anyone? Bueller? It is the
first day of 2017 that we do not have any watches, warnings or
advisories in effect. That`s right. We had them in effect for 11 days
straight in some form. We still have the avalanche warning, but
that is issued by a separate entity. There will be some lingering
light snow in the north but amounts will be inconsequential
compared to earlier in the week.
We are now entering a quieter period right now. Notice how I said
quieter and not quiet. We have one more thing today. There is some
energy and a bit of moisture that is riding the left front quadrant
of a jet streak that will pass to the south of the area. The NAM is
the most bullish and brings a couple of tenths of precipitation as
far north as Casper. The GFS is further south and confines things
mainly to Sweetwater County. The European is somewhere in the
middle. At this point, the European and GFS have been fairly
consistent while the NAM has been flip flopping like crazy. At this
point, we brought slight POPS as far north as line from Kemmerer to
Farson to Jeffrey City to Casper Mountain. The NAM also seems
overdone with QPF with the system fairly moisture starved. There
could be a couple of inches of snow in spots in eastern and southern
Sweetwater County and a coating further north but amounts would fall
short of advisory levels. This a quick hitting system, exiting by
midnight tonight with dry weather returning after that. High pressure
will then control the weather and bring mainly dry conditions to the
area Friday and into Saturday as well. Another good thing, only light
to moderate winds are expected as well.
The big challenge will be high temperatures, especially in the
Basins and the Valleys. It will be quite cold in areas that received
a lot of fresh snow out west as well as across the north. The
question is further south, in places like the southern Big Horn
Basin and Wind River Basin. We did keep temperatures below guidance.
However, the air mass is not as cold as the one last week. In
addition, in some areas some of the snow has melted and it is older
as well. This will reduce albedo as well. So the result will be
chilly but not brutally cold conditions into the first part of the
.LONG TERM...Sunday through Thursday
Synopsis...An upper level low pressure system will lift out of the
southern Rockies into the Central Plains Sunday and Monday.
Precipitation with this system will stay south of the area; dry and
cool surface high pressure will prevail with light wind.
The first in the next series of Pacific storms will move onto the
west coast Tuesday and begin to spread chances of snow into the west
Tuesday night, with coverage and intensity of snow increasing
through Thursday. Warmer and breezy to windy conditions will
develop across central areas Wednesday and Thursday.
Discussion...12/00z ECMWF offers better consistency than GFS overall
during this forecast period, so no major changes were made to quiet
split flow through early next week transitioning to a more active
westerly flow mid to late in the week.
The culprit in this transition will be a 180+ knot jet translating
the Pacific along 40-45N and nosing into the west coast Tuesday and
Wednesday, digging across Arizona/New Mexico on Thursday. Slower
ECMWF brings initial shot of precipitation into the west on
Wednesday, with lee side surface trough cranking up the wind machine
east of the Divide. This will also bring good mixing, likely
scouring out colder air trapped in the lower central basins. Heavier
snowfall looks to push into the west with a Pacific cold front
Wednesday night and Thursday. On Friday, the heavier precipitation
is forecast to shift south into the southern and central Rockies.
West of the divide...KBPI/KJAC/KPNA/KRKS Terminals
VFR conditions will occur at most terminal sites through 12Z Fri.
A short duration of snow is forecast to develop over southern
Wyoming around 23Z through 07Z Fri. MVFR to IFR conditions will
occur and this includes the KRKS airport. VFR conditions will
return to KRKS after 07Z Fri.
East of the divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals
VFR conditions will prevail through the period. Patchy fog may
occur in the northern Big Horn Basin until 17Z with local MVFR or
IFR conditions. This may impact the KCOD airport. An area of snow
will develop in southern WY around 23Z. This snow will move
northeast into southern Natrona county this evening. Will have
VCSH at KCPR airport from 03Z-09Z Fri. MVFR conditions will be
found from KRKS to near KCPR in the snow area.
Fire Danger low for all of WY through, at least, the weekend. Cold
seasonal temperatures, good existing snow pack, and relatively light
winds will characterize the next several days. Smoke dispersion will
also remain poor for all locations through the weekend. &&