Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
234 PM MDT sun Mar 29 2015
Short term...tonight through Monday
Gentle ridging west west/ northwest flow aloft and surface front well to the east and
into the Missouri River basin this morning. High pressure building
in at the surface over the forecast area. Weak SW and associated middle to upper level
clouds riding over/through the ridge from northestern Idaho into central Montana.
Not much going on this forecast period other than the middle/upper cloud
riding into the west and across the north today. Precipitation should
remain at Bay for the most part everywhere except for a stray shower
possible this evening just north of the border near Silver Gate. Another
weak upper wave with some cloud...currently located near the coastal
interface west/ WA/OR...will make its way into the County Warning Area and kick through
Monday to no avail. Drying will continue today and tomorrow under
modest wrly ll flow...leading to potential fire weather problems on Tuesday
when both winds and convective instability increase.
Long term...Monday night through Sunday
Monday night warm dry high pressure ridge will move across western
and central Wyoming through the night with increasing cloud cover in
the far west. Breezy to windy conditions will develop and increase
over and near the East...Lee...slopes of the mountains. Overnight
lows will be mild...especially along the east slopes of the
Tuesday the high pressure ridge will shift east of the area with
stronger southwest flow aloft developing with strong downslope
winds...very warm temperatures and low relative humidity over and
near the east slopes of the mountains. Some clouds with isolated
showers and thunderstorms may develop over the far western mountains
in the afternoon. Some record highs may be reached with the Chinook
conditions in place.
Tuesday night isolated evening thunderstorms and showers with
increasing clouds will spread east through the night with cooling
in the west and mild overnight temperatures in the east. Some
showers will spread east of the Continental Divide after
Wednesday a cold front will sweep southeast across the area with
showers becoming more numerous..especially over the mountains.
Windy conditions will occur both ahead of the cold front and behind
the front. The strongest winds should occur between Rock Springs
and Casper...through the wind corridor. Temperatures will be
colder...especially in the north and west.
Wednesday night some drying will occur as the first cold front
moves south and east and a second cold front and stronger upper
level low pressure trough develops to the west of Wyoming over
western Montana and Idaho. Temperatures will continue to cool as the
cold air deepens and north northeast flow increases with strong
cyclogenesis occurring over the Great Basin.
Thursday strong divergence aloft will develop in the left front
quadrant of an upper level jet accompanied with a plume of Pacific
moisture overrunning the cold front which will be hung up along the
Continental Divide. As the surface to 700 mb low deepens rapidly to
the southwest...stronger cold upslope flow will result with
rain...rain and snow mix spreading across the lower elevations with
snow in the mountains...possibly heavy in places. Through the day
temperatures will continue to cool with rain changing to snow after
maximum heating in the later afternoon.
Thursday night the upper level and surface low shows signs of
bombing in response to strong upper divergence...strong middle level
deformation...frontogenesis and latent heat release. An occlusion
is expected to form on top of the strongest upslope areas along the
Wind River mountains and western Laramie range...Casper Mountain.
Areas of moderate to heavy snow may result. Surface temperatures
will continue to plunge.
Friday the upper level and surface low will eject rapidly eastward
as the upper level jet sweeps east into the Central Plains. Snowfall
will taper off from northwest to southeast through the day with
partial clearing...especially in the north and west of the
Continental Divide. The mountains and east will have some lingering
snows. Temperatures will be cold.
Friday night a few showers may linger over the mountains in north
northwest flow aloft. Temperatures will be cold across the region with
clearing through the night. Some fog can be expected in the valleys
Saturday a high pressure ridge aloft will develop and move over the
area through the day with warming and mostly sunny conditions.
Saturday night high pressure will continue to bring mostly clear
conditions with warming. West southwest winds will pick up across
Sunday southwest flow aloft will increase over the area ahead of
another Pacific low pressure trough. The leading edge of the
moisture from this trough will enter the west in the afternoon with
isolated showers and thunderstorms developing in the afternoon hours.
Warming will continue.
VFR conditions will prevail through the forecast period. A thin
smoke layer from a large wildfire in eastern Montana may linger
vicinity and east of Interstate 25 including vicinity kbuf to kdgw through
12z Monday. Otherwise...skies will tend clear to partly cloudy
with mainly middle to upper level cirrus across the west and north.
Winds will remain west to southwest at less than 15kts for most
locations through the forecast period.
Fire weather...fire danger to remain below critical levels for most
locations today and Monday as somewhat cooler temperatures and lower
wind speeds remain across most of the forecast area under building
high pressure. However...across the western Wind River basin...there
will be locations this afternoon and Monday where fire danger will
become critical with low relative humidity values combining with occasionally gusty
west to northwest wind to 25 miles per hour. A red flag warning has been issued
for this area. Otherwise...fire danger will be on the increase once
again across many areas with a lack of snow cover on Tuesday.
Portions of the Wind River basin...Natrona County and southern
Johnson County...where fuels are currently critical...will see the
best chance at returning to critical fire danger levels.
red flag warning until 7 PM MDT this evening wyz283.
Red flag warning from noon to 7 PM MDT Monday wyz283.