Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Cheyenne Wyoming
926 PM MST sun Nov 23 2014
issued at 925 PM MST sun Nov 23 2014
The evening water vapor loop showed the next Pacific upper level
trough progressing southeast across Idaho/western Montana. This trough
will continue to move across Wyoming tonight and early Monday morning.
The 00z GFS/NAM 700mb winds peak 40-45 knots between 06z and 12z
Monday. The 00z mesoeta Craig-Casper geopotential height gradient
at 850mb decreased from 59 to 55m with 700mb gradient 45-50m.
While a brief instance of high winds may occur...the threat for
a sustained period of 40 miles per hour or higher winds and/or gusts of 58
miles per hour or higher is marginal at best. Therefore...cancelled the high
wind watch for Arlington and southern Laramie range.
Snow has tapered off over the mountains of Carbon/Albany counties
since late afternoon. This will be short-lived as snowfall intensity
will increase once again later tonight and Monday morning with the
approach and passage of the upper trough. An additional 3 to 6
inches of snow is forecast. The combination of falling and blowing
snow will create very low visibilities and treacherous travel
conditions through the snowy/Sierra Madre mountain passes. The
Winter Storm Warning remains in effect.
Short term...(this evening through tuesday)
issued at 300 PM MST sun Nov 23 2014
Models in good agreement through Tuesday...with winds and high
elevation snows the primary forecast concern over the next 48 to
60 hours. For tonight and Monday...kept the Wind Advisory going
for the next few hours with winds gusting to 50 miles per hour across the
western Nebraska Panhandle. These winds will diminish around
sunset with breezy conditions expected through midnight. The
mountain snowfall continuing across the region today...and snotel
sites reporting over one foot storm total snow already...the
Winter Storm Warning looks good as well through Monday. Did adjust
snow accumulations a bit across the higher ridges since a few
places may see close to 30 inches by late Monday. Added blowing
snow to the mountains and surrounding valleys into Monday as the
next upper level disturbance moves into Wyoming late tonight.
After a brief lull in the snowfall rates this evening...snow
intensity will quickly increase after midnight with an additional
6 to 12 inches expected through Monday afternoon.
The main forecast challenge will be tonight and then again on
Tuesday with strong winds across portions of southeast Wyoming.
The next upper level disturbance...currently pushing southeast
across Idaho and western Montana...will move into Wyoming late
tonight. Low level winds will shift into the west by midnight and
gradually increase due to a strengthening pressure gradient along
the Continental Divide and the Laramie range. Wind gusts over 58
miles per hour are possible over the wind prone areas along i80.
Therefore...issued a high wind watch for the Arlington area and
the i80 Summit between Cheyenne and Laramie. Do not believe i25
will see the strongest winds this time around since models show
surface pressure remaining steady or increasing slightly across
the High Plains. Models do indicate pressure falls further south
across northern Colorado...so expect the southern Laramie range to
receive the higher gusts this time around. Otherwise...expect
another round of isolated to scattered snow showers across the
valleys and High Plains on Monday as this disturbance moves across
the area and into Colorado.
For Tuesday...a more widespread high wind event is possible as a
140 knot jet maximum pushes across the area while the jet stream
itself translates northeastward into Tuesday night. May need a
high wind watch for most of southeast Wyoming on Tuesday along
with wind advisories across western Nebraska. There is high
confidence that the wind prone areas will see gusts over 60 miles per hour by
early Tuesday morning.
Long term...(tuesday night through sunday)
issued at 300 PM MST sun Nov 23 2014
Winds are the primary forecast challenge in the long
term...followed by temperatures late in the extended. Not a good
travel time Tuesday night through Wednesday across southeast
Wyoming ahead of the Thanksgiving Holiday.
Starting off Tuesday evening...going to be really windy across
southeast Wyoming. GFS 700mb winds 75 to 80kts across southern
Albany County and the south Laramie range. European model (ecmwf) 700mb winds a
bit lower...but still in the 50 to 60kt range...so chances are
still really good for high wind highlights at least for our wind
prone areas continuing into Tuesday night and Wednesday morning.
Latest wrkhgt product ends at 00z Wednesday...but still shows both
850 and 700mb Craig to Casper height gradients well above 60mtrs.
Another uncertainty in Tuesday nights forecast...GFS sets up a
fairly robust band of precipitation over the Laramie range. Could be due
to upsloping of northwest winds on the west side of the Laramie
range along the frontal boundary thats going to lay in the area.
European model (ecmwf) much less on quantitative precipitation forecast amounts. We are going to need to watch this
development. Should the GFS solution come true...this snow
combined with the very strong winds will create blizzard
conditions for the south Laramie range over to probably Arlington
or so Tuesday night into Wednesday. Did add areas of blowing snow
into the forecast weather grids for that time frame. Later shifts
will need to determine what winter headlines to issue.
Both the GFS and European model (ecmwf) lift the frontal boundary northeast into
the far northern Nebraska Panhandle by Wednesday afternoon. Windy
conditions west of the Laramie range to continue as both the GFS
and European model (ecmwf) show 700mb winds well above 50kts.
For Thanksgiving...it looks dry across southeast Wyoming and
Nebraska Panhandle. Continued windy...but nothing near what we
will see Tuesday and Wednesday. Wind prone areas could still be
flirting with high wind criteria...especially out by Arlington on
Interstate 80. Fairly warm Thursday afternoon with low to middle 40s
Strong winds look to return Friday into Saturday as another
frontal boundary begins to sag south out of Montana. GFS much
faster on the southern movement of this boundary...driving the
front into the east slopes of the Laramie range by Saturday
morning. European model (ecmwf) has front still up over northern Wyoming by 12z
Saturday. So we could be looking at a 15 to 20 degree temperature
bust depending on which solution pans out. Did lower high
temperatures Saturday several degrees across the Panhandle and
eastern sections of southeast Wyoming as a hedge for now.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 925 PM MST sun Nov 23 2014
Northwest winds will remain breezy for the plains tonight...with
stronger and gusty west winds developing from the Laramie range
westward. A upper level disturbance will bring the stronger winds
and increase the snow intensity over the southern Wyoming mountains
with LIFR obscurations. MVFR ceilings/visibilities will be
possible outside the mountains west of the Laramie range including
Rawlins and Saratoga. West to northwest winds will remain breezy
to windy Monday with occasional snow showers affecting southeast
Wyoming and northern NE Panhandle terminals.
issued at 110 PM MST sun Nov 23 2014
Although winds will be strong early this week...no fire weather
concerns are anticipated due to cool temperatures and high
Wyoming...Winter Storm Warning until 5 PM MST Monday for wyz112-114.