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Area forecast discussion 
National Weather Service Cheyenne Wyoming
458 am MST Thursday Jan 29 2015

Short term...(today through saturday)
issued at 404 am MST Thursday Jan 29 2015

Today...positively tilted shortwave trough aloft from southwest
Minnesota southwestward to southeast Wyoming around dawn...will move
quickly southeast after daybreak...with ridging aloft prevailing
over our counties...and light return south winds near the surface.
Compromised between the NAM and GFS MOS maximums for our high
temperatures. Boundary layer forecasts and current temperature and
dewpoint spreads suggest areas of fog through middle morning across
Carbon...Converse and portions of Albany counties of Wyoming.

Tonight...will see increasing middle and high cloud shield...mostly
opaque...approach over our Carbon and Albany counties in advance of
the approaching shortwave trough aloft from the southern rockies and
southwest United States. May see isolated snowy and Sierra Madre
range snow showers late...otherwise dry. Saturated boundary layer
suggests areas of fog again developing again over Carbon County of
Wyoming...especially where middle and high cloud shield is not as
pronounced. Again...compromised between the NAM and GFS MOS for low

Friday...although both the NAM and GFS keep the quantitative precipitation forecast over Colorado...
associated with the approaching shortwave trough aloft over the
Desert Southwest and southern rockies...we may see some orographic
snow showers over our snowy and Sierra Madre ranges of southern
Carbon and southwest Albany counties...dry elsewhere. Based on
projected thicknesses and 700 mb temperatures...a compromise between
the NAM and GFS MOS looks decent for our high temperatures. The
traditional work week will end with relatively mild maximum

Friday night...weak shortwave trough energy and a decently saturated
airmass suggests scattered coverage of light snow developing over
and near our snowy...Sierra Madre and southern Laramie ranges along
with low level north winds developing...though the bulk of quantitative precipitation forecast will
lie south of our counties over western Colorado. moving Alberta type clipper shortwave trough will
slide down through Montana and northern Wyoming...sending the next
plunge of cold Arctic air...and a piece of the
motherlode...southward across Montana and Wyoming into our northern
half of our counties in the afternoon. In fact...the strength of the
impressive cold air advection...may be enough to produce falling
afternoon temperatures north of a Rawlins to Scottsbluff line.

Most of our counties will lie in between the southern stream
shortwave trough aloft and approaching northern stream shortwave
trough aloft...thus limited chances for precipitation...though will
maintain a slight chance of snow in the afternoon south of a Rawlins
to Kimball line which blends well with our neighboring offices at
Grand Junction and Denver...though believe the bulk of the snow will
lie over Colorado.

Long term...(saturday night through wednesday)
issued at 404 am MST Thursday Jan 29 2015

00z models differ somewhat with how deep the shortwave trough
in the plains will dig on Saturday night. GFS and NAM tend to
favor a slightly deeper solution vs the European model (ecmwf) and previous
solutions...meaning more favorable lfq jet energy and moisture
will move over the County Warning Area with a better coverage of precipitation. In
addition...the associated cold front looks to move south across
the region late Saturday afternoon/evening and will add to the
overall will expand the slight chance probability of precipitation further
west over the County Warning Area through Sunday morning for this possibility.
Temperatures will be cooler in the 20s-30s for Sunday in the Post
frontal environment...and northerly winds will be a bit windy
Sunday morning as surface high pressure builds into the north-Central
Plains. This wave will quickly shift to the southeast Sunday night
with additional pieces of vorticity prognosticated to move across the Pacific
northwest and into The Rockies Monday through Wednesday within the
northern stream jet. Periods of rain/snow showers and wind will
occur through this time although models are struggling to handle the
fine details due to the weak and disorganized nature of these
systems. Winds look to be strongest on Monday with the initial
deepening of the Lee trough under the energetic northwest flow. GFS/ec 700 mb
winds are prognosticated to increase rapidly by 12z Monday to 50-55 kts
and look to remain around 50 kts through the early evening.
Thus...could be dealing with a marginal high wind event late
Sunday night through Monday mainly for the wind prone areas. Temperatures
will also warm back into the 40s and 50s Monday afternoon. Another
cold front looks to be on the horizon for late Monday/early
Tuesday with chances for light precipitation through Tuesday as the front
hangs up within the High Plains. Wednesday looks to be drier and
breezy as the front shifts back to the east.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 457 am MST Thursday Jan 29 2015

A line of snow showers will persist through sunrise just south of
the I-80 corridor from krwl to kcys...with MVFR to brief IFR
conditions expected here. Low ceilings are lurking in the northern
Panhandle as well this morning...but satellite pictures show these
clouds shifting steadily eastward so should not be a major impact
at kcdr and kaia. Otherwise...VFR conditions will prevail through
the period with generally light winds expected today. West-
northwest winds will shift to the south late this afternoon and
evening and will become gusty at times through the night in the
Panhandle...and for kcys and klar.


Fire weather...
issued at 404 am MST Thursday Jan 29 2015

No fire weather issues expected. A relatively strong
Arctic cold front will plunge south across the district on Saturday
ushering in colder temperatures for late Saturday and Sunday.


Cys watches/warnings/advisories...


Short term...Rubin
long term...rjm
fire weather...Rubin

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