Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 251143

Area Forecast Discussion
National Weather Service Cheyenne WY
443 AM MST Sun Feb 25 2018

.SHORT TERM...(Today through Tuesday)
Issued at 304 AM MST Sun Feb 25 2018

Round #2 of strong winds appears to be on track for the wind prone
areas of southeast Wyoming today. Low-level gradients are expected
to increase markedly over the next few hours as a 996-998 millibar
surface low tracks across northern MT. H7/H85 CAG-CPR gradients of
60-70 meters, coupled with 50-60 knot flow in the 700-800 mb layer
should be more than sufficient for warning-criteria gusts. Already
seeing some wind gusts around 50 MPH over the I-80 summit, so will
not make any changes to inherited High Wind Warnings. Later shifts
may want to consider extending this beyond 3z, but at this time it
appears winds aloft will decrease sufficiently despite a lingering
CAG-CPR gradient around 50 meters through the night.

Blowing snow will likely be an issue again today around ARL. Temps
have not been particularly warm since yesterday, and were near 10F
at 330 AM MST at ARL. Webcams still show plenty of snow that could
potentially be blowable. Near-blizzard conditions were observed on
Saturday afternoon, and do not see any reason why we would not see
a similar thing take place today. That said, a Winter Weather Adzy
has been issued for the Arlington/Elk Mountain areas again for the
potential for significant blowing snow.

Lingering mountain snow showers through tonight, but do not expect
to see more than a few inches of additional accumulation. Although
the upper-level pattern through Tue should be quite energetic, not
much moisture to work with so PoPs remain low. Highs are likely to
remain on the cool side, but should generally be at least slightly
warmer than we have been seeing as of late.

.LONG TERM...(Tuesday Night through Saturday)
Issued at 304 AM MST Sun Feb 25 2018

An elongated shortwave is progged to transverse through the
Rockies on Wednesday which will cause a frontal boundary to push
through the region. This feature does not look like there will be
much moisture associated with it, but there may be enough moisture
and lift in the mountains to squeeze out some snowfall. However,
we are not looking at more than a couple of inches. We will then
see a milder day shaping up on Thursday and Friday as the upper
level ridge builds over the region. Although, it will be a bit
breezy over areas west of the Laramie Range.

The next concern will be when the upper level trof in the Pacific
northwest will start to impact our region. At this point, it
appears like the majority of the forecast area will stay dry next
Saturday, but there is concern towards the latter half of the
weekend and early next week on the evolution of the upper level
trof. The FV3/ECMWF/GEM splits this trof and jet energy, and
induces an upper level low over Colorado early next week. If this
occurs, much of the forecast area may see another round of
widespread snowfall.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 436 AM MST Sun Feb 25 2018

Latest water vapor loop was showing an area of subsidence moving
east along the foothills of the Laramie Range. This area of
subsidence has caused wind speeds to increase to nearly 50kts
along some points along I-80 this morning. This area of subsidence
may shift over the KCYS TAF site during the next hour or so and
may cause strong winds to develop. We did bump up wind speeds to
28025g35kt for the KCYS TAF around 13z. Otherwise, good low level
mixing is expected to develop by midday. VFR conditions will also
be the rule during the next 24hrs.


Issued at 304 AM MST Sun Feb 25 2018

No fire weather concerns. Despite periods of strong/gusty winds on
Sunday & Monday, minimum RH should remain well outside of critical


WY...High Wind Warning from 8 AM this morning to 8 PM MST this
     evening for WYZ106-110-116-117.

     Winter Weather Advisory from 8 AM this morning to 8 PM MST this
     evening for WYZ110.



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