Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 131738

Area Forecast Discussion
National Weather Service Cheyenne WY
1138 AM MDT Fri Oct 13 2017

.SHORT TERM...(Today through Saturday)
Issued at 330 AM MDT Fri Oct 13 2017

Pretty quiet weather this morning under mostly clear skies as the
surface cold front, which moved through the area yesterday, has
pushed into central Colorado and is weakening. Strong jet energy
aloft and weak dynamic forcing is producing some light
sprinkles/showers from near Lusk eastward towards Alliance and
Chadron, Nebraska. This 140 knot jet max will likely drift north
through the day with any remnant sprinkles diminishing across the
eastern plains. Temperatures will be cooler today compared to
yesterday with highs in the mid 50`s (west) to mid 60`s (east).
Outside of some Fire Weather concerns (see below), dry conditions
are expected with winds picking up in the afternoon along and west
of I-25. Winds may gust over 40 MPH over the high valleys west of
I-25 and western Converse county.

IR Satellite loop shows the next upper level trough currently
moving into Washington and Oregon early this morning. This
positively tilted trough will dig southeast today into eastern
Oregon and Idaho and then move eastward tonight into Wyoming. The
associated cold front, which will be stronger compared to the
previous frontal passage, will rapidly move across the area
Saturday morning. Expect highs to be mid to late morning across
the area with temperatures falling into the low/mid 30`s in the
afternoon across southeast Wyoming and portions of the northern NE
panhandle. Models show the trough moving through the area pretty
quick, which will limit upslope flow potential and precipitation.
However, models do show the potential of a brief period of
moderate to heavy rain/snow showers given forecast soundings and
dynamic lift along and just behind the front. Winds should shift
into the north and northwest by the afternoon instead of due west,
so a strong bora is not expected at this time. Windy and even
very windy conditions are still expected, but this time across the
high plains where gusts up to 50 MPH are possible mainly east of
I-25. Kept POP between 30 to 50 percent across most of southeast
Wyoming and the northern NE panhandle Saturday. Do not expect high
QPF amounts, but there is a one to three hour window where
moderate to heavy rain/snow mix, gradually changing over to snow,
is expected through the afternoon. This may be enough to impact
travel briefly along and west of I-25, especially in the mountain

.LONG TERM...(Saturday night through Thursday)
Issued at 218 AM MDT Fri Oct 13 2017

Saturday night...Progressive shortwave trough aloft moves from
western Nebraska into the Mississippi Valley with strong Northwest
flow aloft over our counties. Progged gradients suggest breezy
conditions over and near our wind prone locations.

Sunday...Flow aloft remains northwest with breezy to windy
conditions expected due to deep unidirectional flow aloft. Decent
warming trend as 700 mb temperatures and 1000-500 mb thicknesses
rise significantly.

Monday...Nice warming trend continues with rising mid level
temperatures and thicknesses. Continued dry with minimal low and mid
level moisture.

Tuesday...Ridge aloft moves overhead, inducing a surface lee trough
to develop across far eastern Wyoming. Warming trend continues with
700 mb temperatures continuing to rise and with airmass modification.

Wednesday...Mild temperatures continue with zonal, west to east,
flow aloft. Downslope warming will also help high temperatures.

Thursday...The flow aloft turns southwest in advance of the next
approaching shortwave trough aloft. Continued dry with lack of low
and mid level moisture.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1129 AM MDT Fri Oct 13 2017

SKC to FEW/SCT sky conditions can be expected for most areas today
with the exception of areas along/E of US 85, where conditions are
more likely to be SCT to BKN around 5000 feet AGL. A cold front is
expected to sweep across the area early Saturday, with snow shower
activity developing west of the Laramie Range after 09z. Terminals
most likely to experience this activity prior to 18z include RWL &
LAR. Strong winds will also develop in the wake of the front, with
gusts over 30 knots spreading east through Saturday AM.


Issued at 218 AM MDT Fri Oct 13 2017

Although Fire Weather concerns will be low this weekend and early
next week, elevated Fire Weather conditions are possible later
today, mainly west of I-25, based on trends in relative
humidity and gusty winds. Expect minimum afternoon humidities
around 15 percent west of a line extending from Laramie northward
to Lusk. Combined with gusty west to southwest winds up to 35 MPH,
this may result in a few hours of critical fire weather
conditions. Because of the time of the year, confidence is too low
to issue a Watch or a RFW at this time.




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