Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus65 kriw 162058 
afdriw

Area forecast discussion
National Weather Service Riverton Wyoming
158 PM MST Sat Nov 16 2019

Short term...(this evening through Sunday night)

Storm system continues to move through the area this afternoon,
with the heaviest precipitation at 1 PM extending from around
Lander to Beaver Rim and eastward into Natrona County. Hrrr is
showing the bulk of the precipitation moving southeast out of the
area by around 4 PM. Certainly some heavier rain and snow occurred
today than expected, with more snow due to adiabatic cooling from
southern Johnson County into Natrona County and across southern
Fremont County. Next couple of hours will see precipitation
continue across central Wyoming and impact activities and travel.

Clearing and brisk north to northwest wind to the northwest of
the system is showing nicely on radar, satellite, and webcams,
though unstable mid layers with so-so moisture could give rise
some scattered showers. Skies will go from partly cloudy to mostly
clear overnight with mid-level northwest flow. Sounds like a good
pattern for areas of fog after midnight in the places that have
received the most precipitation. High- to mid-level clouds will
start moving back into northwest Wyoming by early Sunday morning as weak
energy overtops the upper level ridge over the western US. Models
are indicating that low- to mid-level moisture will increase
enough over northwest Wyoming for light snow showers Sunday morning. This
enhancement appears to be due to a shortwave trough moving through
the flow over Montana and NE Wyoming. Sunday afternoon will thus see
the surface pressure gradient increase from west to east and help
west to southwest wind increase across southern and south-central
Wyoming. The wave will also bring precipitation to northeast Wyoming where
the bighorns and Johnson County will see another round of
precipitation and wind shift to the north. With 700mb temperatures
back to around 0c, precipitation should be rain in the lower
elevations with snow levels around 8000 feet. Some showers may
make it down into eastern Natrona County as will late Sunday
afternoon. This moderately moist northwest flow will continue
Sunday night to allow light snow showers over the northwest
mountains through Monday morning.

Long term...(monday through saturday)

A weak ridge axis will build from west to northeast across the
forecast area to start out the work week. The southwest low to mid
level flow into the area will result in a couple of above normal
temp days with generally dry weather into Tuesday. Winds will pick
up again on Tuesday especially in the wind corridor from Sweetwater
into Natrona counties and will have to be watched to potentially
have to highlight these areas.

The next storm system will arrive late Tuesday and affect northwest
Wyoming first, as the upper flow splits over the Pacific northwest.
This will result in an upper low being pushed south to California,
while the main mid level trough moves to the north of Wyoming. An
associated cold front will move southeast into the forecast area by
late Tuesday night, and will spread widespread precipitation into
the region through Wednesday.

The GFS and European model (ecmwf) models continue to disagree involving the precip
amounts with the next system. The GFS model continues to produce
more overrunning precip along the cold front, compared to the drier
solution of the European model (ecmwf) model. Still leaning more toward the European model (ecmwf)
model solution, which is more in line also with wpc quantitative precipitation forecast guidance,
which would result in more of a snow/rain mixture in the valley
locations and higher snow amounts in the northern toward central
mountains. This storm system has more of a Pacific air component, so
do not expect very cold air in the wake of this system. High
pressure by Friday, the slow moving frontal boundary should finally
be south of the state, with weak high pressure expected to build
into the forecast area through the upcoming weekend.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)

West of the Continental Divide...krks, kjac, kbpi, kpna terminal
sites:

Skies will be clearing across the area to start tonight's forecast
period with all taf sites expecting VFR conditions through the
entire forecast period through Sunday afternoon. Winds should begin
to relax somewhat by tonight after 03z at most locations with the
exception of krks. Have increased winds at krks and kbpi after 17z
Sunday.

East of the Continental Divide...kcpr, klnd, kriw, kcod, kwrl
terminal sites.

Skies will be clearing across the area to start tonight's forecast
period with most locations expecting VFR conditions through the
entire forecast period through Sunday afternoon. Winds should begin
to relax somewhat by tonight after 03z at most locations with the
exception of kcpr. Due to the increased moisture available and
snowfall amounts especially at klnd and kcpr, will add in a mention
of fog overnight at these locations from 03z-14z Sunday.

&&

Fire weather...

Storm system exiting the forecast area this afternoon, with
precipitation continuing across Natrona County, southern Fremont
County, and eastern Sweetwater County through about 4pm. Behind
the system, winds are north-northwest about 10 to 15 mph with
higher gusts. Skies will be partly cloudy to mostly clear
overnight. A weak system in northwest flow will skim north-central
Wyoming from midday Sunday through Monday morning, bringing some
showers to the northwest mountains and the bighorns, along with
showers over Johnson and eastern Natrona counties. Sunday will
also see slight warming over southwest Wyoming with breezy west wind.
Weak high pressure will be over the area Monday and Tuesday for
continued breezy conditions and above normal temperatures.

&&

Riw watches/warnings/advisories...none.

&&

$$

National Weather Service Glossary of Abbreviations