Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 171152

Area Forecast Discussion
National Weather Service Cheyenne WY
552 AM MDT Mon Oct 17 2016

.SHORT TERM...(Today through Tuesday)
Issued at 238 AM MDT Mon Oct 17 2016

Today...Inherited gridded forecasts and highlights are in good shape
with some minor adjustments. As far as strong winds go, fast moving
shortwave aloft and cold front will quickly sweep west to east
across our counties with an 80 to 90 knot 500 mb speed max zipping
across, along with a 100 to 140 knot 300 mb jet max. Models,
including their soundings, show enough subsidence and dry adiabatic
layer to help the stronger 50 to 55 knot 700 mb winds mix down to
the surface, especially across southeast Wyoming. We have decided to
expand the high wind warning to include Converse, Niobrara and
Goshen counties based upon the NAM and GFS numerical guidance and
progged soundings. Winds across western Nebraska may get close or
even exceed high wind criteria, though with it being a borderline
situation, we have opted to continue the inherited wind advisory and
advise the day shift to monitor closely. Scattered to numerous
showers expected along and west of I-25 in moist flow aloft.
Guidance high temperatures close on the models and have compromised
between the models. Local wind models also suggest a decent chance
of high winds at Bordeaux and Cheyenne.

Tonight...Fortunately, winds aloft will decrease and surface winds
will mostly decouple, though it will remain breezy at times, with
relatively mild overnight minimum temperatures due to mixing.
Precipitation will end as the low and mid levels dry out.

Tuesday...Next fast moving, low amplitude shortwave aloft moves into
western Wyoming, spreading increasing clouds and rain and snow
showers across our Snowy and Sierra Madre Ranges in the afternoon.
Much less wind expected based on low and mid level gradients and
more cloud cover that will limit mixing. Cooler in the wake of the
cold front, especially east of I-25, and again have compromised
between the NAM and GFS MOS maximum temperatures for highs.

.LONG TERM...(Tuesday night through Sunday)
Issued at 238 AM MDT Mon Oct 17 2016

Tuesday night-Wednesday:
The models are in fairly good agreement in showing a progressive shortwave
moving through the northern Rockies. This shortwave will bring
scattered rain/snow showers to the forecast area. The best focus
at this point appears to be along the sierra/snowy mountain
ranges, but there may be a good chance along the mid level frontal
boundary as it surges southeast through Southern Wyoming and the
southern Panhandle Tuesday night. Not real confident that it will
yield to much precipitation, but there will be some instability
which may yield to some banded rain/snowfall. Colder temperatures
will also accompany this front as it pushes through the area
Tuesday night. These colder temperatures will persist through the
day on Wednesday along with the potential for a few instability

Wednesday night-Sunday:
A strong surface high is expected to settle over western Wyoming
Wednesday night which will allow for a cold start for most of the
area with lows mostly in the 20s. Beyond this timeframe, we should
see a warming trend as the upper level ridge builds across the
southwest U.S. This may keep us in a breezy pattern, but it should
be fairly mild with afternoon highs climbing from the 50s and 60s
on Thursday to the 60s and 70s this weekend.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 539 AM MDT Mon Oct 17 2016

The main concern with this taf issuance is the how the cloud cover
will affect wind speeds today.

Latest ir loop was showing a mid level cloud deck continuing to
hang on to areas mainly northwest of a Rawlins to Lusk line. This
area also appears that it is undergoing subsidence as well due to
the surface high building across the western half of the state. If
this subsidence ends up being the dominant factor, then wind
speeds should have no trouble mixing out today. However, if these
lower clouds persist, the mixing may be closer to the surface and
limit the strong wind speeds. However, another concern is the
potential that the subsidence may push those stronger >50kt winds
closer to the surface, and it may not matter how much mixing we
see and winds could be strong across most of the taf sites. At
this point, we are favoring the latter scenario. Timing of this
trof passage will generally range from 15z (KCYS), 17z (KBFF), and
18z- 19z Nebraska Panhandle sites. The good news is that these
wind speeds should subside by midnight.


Issued at 238 AM MDT Mon Oct 17 2016

Inherited Red Flag Warning for today looks good especially with
expected winds and humidities nearing 15 percent. Fortunately,
humidities will be higher Tuesday through Thursday, limiting
concerns. Humidities will again lower Friday and Saturday, and we
will closely monitor this.


WY...Red Flag Warning from 11 AM this morning to 7 PM MDT this
     evening for WYZ310.

     High Wind Warning from 9 AM this morning to 7 PM MDT this
     evening for WYZ101-102-104-105-107>109-115-117>119.

     High Wind Warning until 7 PM MDT this evening for WYZ106-110-116.

NE...Wind Advisory from 11 AM this morning to 7 PM MDT this evening
     for NEZ002-003-019>021-054-055-095-096.

     Red Flag Warning from 11 AM this morning to 7 PM MDT this
     evening for NEZ313.



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