Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus65 kriw 070959 

Area forecast discussion
National Weather Service Riverton Wyoming
259 am MST Sat Dec 7 2019

Short term...(today through sunday)

Generally mostly clear skies were the rule over most of the forecast
area as of 09z this morning with the exception of some areas west
of the Continental Divide, especially over kbpi in Sublette
County. Patchy to areas of fog will also be predominant across
western sections of the forecast area in some valley locations.
Temps were in the teens to lower 20s with the exception of the
absarokas, extending south into Natrona County, where temps in the
mid to upper 30s were occurring.

A tight pressure gradient will result in winds picking up toward
morning at kcod, extending southeast into the kcpr area in Natrona
County. Will continue with a High Wind Warning across Natrona
County today until 01z early this evening due to the leeside
trough keeping winds gusty over especially the eastern portion of
the forecast area. The latest short term model runs continue to
indicate that 700 millibar winds will rise this morning to around
50 knots over Natrona County, so will continue with the High Wind
Warning until 01z this evening.

The lead ejecting short wave from an upper low off the Pacific coast
west of California will progressively move into Idaho today.
There will also be a consistent stream of Pacific moisture
expected, so will go along with the hrrr models depiction of light
to moderate snow expected into portions of western Teton/park
counties by around 19z today. Continue to expect that snow levels
will range from 7k-8kft this afternoon west of The Divide and fall
further after sunset. Have upgraded Winter Storm Watch to a
Winter Storm Warning for zones 12,13, 23 and 25 to account for
expected heavy snowfall into the western mountains starting by 22z

There will be a steady stream of Pacific moisture moving east-
northeast across the region from Yellowstone southward to the Star
Valley and the salt/Wyoming ranges, by tonight and through the day
on Sunday and into early Sunday evening. Have issued winter
weather advisories for western areas surrounding the Winter Storm
Warning for slightly lesser snowfall amounts through early Sunday
evening. From this afternoon through early Sunday evening,
snowfall totals up to 6 inches expected in the lower elevations
and 12 to 18 inches expected in the western mountains for this

Long term...Sunday through Friday

Snow east of The Divide will begin later Sunday afternoon
continuing through the evening hours. Snow amounts will only be
from a trace to around 2 inches, with most locations at or below 1
inch. Showers will end quickly Sunday night into early Monday
morning as a cold front moves through the region. This cold front
not only effectively cuts off all activity, but it also Ushers in
much colder air. High temperatures on Monday will be around 10 to
15 degrees cooler than on Sunday. Temperatures through the week
will slowly warm, but not substantially and will be similar to
this previous week. Monday will be mostly dry after the frontal
passage and winds decreased, though still breezy in the usual wind
prone locations.

Behind the front, northwest flow sets up and will bring some
moisture into the area that will give the northern mountains
isolated precipitation chances. Aside from a weak shortwave that
will pass through the area on Wednesday, northwestern flow
continues until the next significant system begins to impact
western Wyoming. Timing with this system is uncertain, but it
looks to be another decent weekend snow event across the
northwest. Snow may begin as early as Thursday afternoon and
persist through the weekend.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1140 PM MST Fri Dec 6 2019

Weak high pressure over the area tonight and tomorrow is allowing a
variety of weather to impact the terminals. Generally VFR
conditions can be expected, though some sites are likely to drop to
MVFR and IFR due to fog, starting now through 16z-18z/Sat. Likely
sites are kbpi, kpna, and kriw, with klnd a possibility too. Windy
conditions will persist at kcpr overnight and become stronger
Saturday, with gusts likely near 50 kts Sat afternoon. Breezy
conditions with gusts to 20-25 kts are also expected at kcod through
Sat. Moisture will move into western Wyoming Sat afternoon to bring snow
to the mountains around 18z, spreading to kjac between 21z/Sat-
00z/sun. Western Wyoming mountains are expected to be obscured through
much of the forecast period. Krks and sites east of The Divide will
be VFR Saturday with just some thick high clouds.


Fire weather...

Southwest winds will increase to 30 to 35 mph with gusts up to 60
mph by sunrise Saturday morning across zones 280 and 289. These
winds will continue through the day, before subsiding back down to
gusts of 35 mph by this evening. These gusty winds will continue
through tonight. Gusty winds will occur over the mountains during
this time through tonight. Otherwise, winds will generally be
light across the area.

Clouds and light snow will increase by this afternoon far western
portions, with generally mostly sunny conditions expected east of
The Divide. Moderate to heavy snow will occur over the far west
by this evening, continuing into early Sunday evening for tapering


Riw watches/warnings/advisories...
Winter Storm Warning from 3 PM this afternoon to 9 PM MST Sunday
for wyz012-013-023-025.

Winter Weather Advisory from 3 PM this afternoon to 9 PM MST
Sunday for wyz001-002-012>016-023>025.

High Wind Warning from 8 am this morning to 6 PM MST this
evening for wyz020-022.



National Weather Service Glossary of Abbreviations