Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 121122

Area Forecast Discussion
National Weather Service Cheyenne WY
422 AM MST Sun Nov 12 2017

.SHORT TERM...(Today through Tuesday)
Issued at 104 AM MST Sun Nov 12 2017

Not a whole lot going on in the short term, but there could be an
increase in winds Tuesday.

Currently...Weak frontal boundary that has been laying along the
east slopes of the Laramie Range has begun its move to the east
this morning. As of 1AM, the front lays roughly along a line from
Gillette to Lusk to just north of Bayard. Westerly winds to the
west of the front providing downslope conditions and mostly clear
skies. 11-3.9u satellite imagery showing a small area of stratus
near Lusk just east of the front. Last couple shots show the area
starting to retreat eastward as the front edges eastward.

Ridge of high pressure to build over the CWFA through the day with
westerly winds and warming 700mb temperatures. Looks like a sunny
day with warm temperatures.

Keep this pattern into Monday with GFS 700mb temperatures climbing
to +4C Monday afternoon. Continued sunny skies and dry weather.
Start to see an increase in winds Monday evening into Tuesday as
ridge gets flattened by an upper disturbance moving through
Montana. GFS 700mb winds increase to 40-45kts Monday evening and
up to 45-50kts Tuesday morning as the shortwave tracks to our
north. Did increase winds over our higher terrain in southeast
Wyoming over guidance. Got us pretty close to high wind criteria
in our wind prone areas of southeast Wyoming Tuesday morning
through the afternoon. Later shifts can adjust as needed.

.LONG TERM...(Tuesday night through Saturday)

Issued at 104 AM MST Sun Nov 12 2017

Shortwave trough will exit to the east on Tuesday night.
Associated surface cold front will cross the region early in the
evening. Gusty NW winds will accompany the front but deep layer
westerly flow and associated downsloping will make this a dry
frontal passage. Ridging reasserts itself over the Rockies on
Thursday as yet another deep trough digs into the Pacific NW.
Latest operational runs of the GFS and EC have trended a bit
stronger with this system as it ejects to the east over the
Rockies Thursday night into Friday. At the same time this happens,
subtropical ridging will build over the desert SW and southern
plains. This will intensify the WSW`ly jet over the central
Rockies. Low level thermal gradient will also tighten in response
to this increased jet energy setting the stage for a significant
mountain snow event with ideal orographics and plenty of dynamic
lift. Additionally, a strong surface gradient will develop on
Thursday as a surface low takes shape invof western SD.
Operational models and ensembles also indicate a second surface
low will likely develop on Thursday night somewhere in the
vicinity of eastern CO which will serve to accelerate a strong
cold front southward through SE Wyoming. This has the potential to
be a rather high impact but quick moving frontal passage with a
period of snow and high winds west of the Laramie Range along with
a bora type wind event east of the range.

Ridging begins to rebuild on Friday evening into Saturday.
Residual cold air to the west, deep layer NW flow, and lee
troughing should continue the windy conditions into the weekend.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 419 AM MST Sun Nov 12 2017

VFR will prevail through the TAF period. Some patchy early morning
fog still possible around KAIA but latest satellite imagery shows
the more widespread visibility reduction will likely stay to the
north. Breezy conditions will develop west of the Laramie Range
this afternoon with west winds gusting to 30kt near KRWL.


Issued at 230 AM MST Sun Nov 12 2017

Breezy winds over the next few days becoming strong Tuesday. Ridge
of high pressure over Wyoming will keep skies mostly clear and the
weather dry. Wind gusts during the morning and afternoon along and
west of the Laramie Range look to get as high as 35-40mph each
day. Fortunately afternoon humidity expected to stay well above
critical levels. Stronger winds Tuesday afternoon that could be
more widespread. But again, humidity expected to be well above
critical levels, so fire weather concerns are minimal.




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