Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 240546
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1045 PM MST Sun Feb 23 2020

.SHORT TERM...(This evening through Monday)
Issued at 158 PM MST Sun Feb 23 2020

Headline Changes...

Added new Zones Cheyenne and Eastern Platte County to a High Wind
Watch 5 am Monday to 5 pm Monday.

Adjusted snow and QPF down slightly for the ongoing Winter
Weather Advisories.

Discussion...

Afternoon WV imagery showed an elongated upper level low and well
defined subtropical jet across the southern 3rd of the CONUS. To
the north and west, a second upper low was spinning onto the
coast of northern washington and western BC. Closer to home,
northwest flow aloft behind the departing southern wave was noted.
Regional Radar and satellite showed several snow bands spiraling
out from the surface low across the Texas Panhandle through
southern Wyoming. At Cheyenne, temperatures have been fairly
steady in the upper 30s and low 40s with sw winds and overcast
skies over the last 6 hours.

Snow showers and high winds will be the primary forecast concern
over the next 48 hours. A large sub arctic area of high pressure
will develop across the central Rockies later this evening and
Monday concurrent with the southeastward movement of the remnant
surface low from the BC storm system. The combination of this
dipole will lead to a rapid increase in surface pressure gradients
late tonight through Monday. High Wind Warnings are in place
across the wind prone areas of WY through Monday evening. There is
also some indication that high winds will spill onto the plains
with some mountain wave activity. Thus, have included Cheyenne in
a High Wind Watch early Monday.

Monday will be cooler with the approach of the subarctic high and
the remains of the clipper. High Winds should peak in the late
afternoon and early evening before falling off slightly overnight.
Scattered snow showers are also expected to develop Monday with
light accumulations possible. More significant snow will develop
across the northern panhandle from late Monday through early
Tuesday as the main upper level low transits the area. Models have
been somewhat uncertain on the exact evolution of the
precipitation structures associated with the upper level low early
Tuesday. Some high-res window guidance has indicated locally
higher QPF along the northern panhandle. Meanwhile, ensembles
have trended lower with amounts. Thus with low confidence, have
trended toward lighter amounts and retained the previous Winter
Weather Advisories with few changes. What models do agree on are
the strong winds through Tuesday. Gusts of 30 to 45 mph in the
panhandle will turn northerly with time behind a passing front.
This may cause some issues with blowing snow and visibility.
However, the low confidence in snow amounts suggests a lower end
threat at this time.

Snow will exit the area by evening Tuesday as the upper low phases
with the deepening southern branch low over the mississippi
valley. Winds will weaken through late Tuesday but remain stiff
overnight. Temperatures will be cold for much of Tuesday evening
as high pressure and the associated sub arctic airmass settles in
over WyoBraska

.LONG TERM...(Tuesday night through Sunday)
Issued at 158 PM MST Sun Feb 23 2020

A chilly morning across the CWA Wednesday in the wake of the low
pressure system with mins in the single digits to lower teens.
Still on the cool side Weds and Thursday then warming to close
out the week. Mainly dry but another fast-moving shortwave should
bring some snow showers to mainly the mtns on Thursday but amounts
not a lot given the speed of the system. Breezy conditions with
the shortwave Thursday otherwise winds not looking too significant
through the period as well.

&&

.AVIATION...(For the 06Z TAFS through late Monday evening)
Issued at 1045 PM MST Sun Feb 23 2020

Next Pacific storm system and associated cold front will move across
the southeast Wyoming terminals between 08z and 13z Monday morning,
and then between 12z to 16z across western Nebraska with winds
shifting into the north or northwest. Snow showers are expected to
develop as the front slides southeast, impacting most terminals
through the day on Monday and possibly Monday night.

HAZARDS/WEATHER TRENDS: LLWS is the initial Aviation threat late
tonight as winds sharply increase out of the west or northwest near
the surface cold front. Moderate to strong turbulence expected after
07z once the cold front moves into the area. SNOW will begin once
the LLWS threat diminishes after 10z. VFR conditions until 10z, then
a brief period of IFR CIGS/VIS for KRWL and KLAR until the band of
snow pushes east into the high plains. Low confidence on how this
band will impact KCYS and KBFF with downslope winds, so kept VCSH
for those locations.  KCDR and KAIA are looking more likely to be
impacted by IFR conditions as early as 15z-18z Monday. Precip type
is uncertain at this time, but will likely fall as a mix of rain and
snow initially.

&&

.FIRE WEATHER...
Issued at 158 PM MST Sun Feb 23 2020

Cool temperatures and winter weather should keep fire weather
concerns low despite the strong winds through the next few days.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 5 AM Monday to 8 PM MST Tuesday for
     WYZ101-102-112-114.

     High Wind Warning from 8 PM this evening to 5 PM MST Monday for
     WYZ106-110-116-117.

     High Wind Watch from late tonight through Monday afternoon for
     WYZ107-118.

NE...Winter Weather Advisory from 5 AM Monday to 8 PM MST Tuesday for
     NEZ002-095.

&&

$$

SHORT TERM...AL
LONG TERM...RE/REC
AVIATION...TT
FIRE WEATHER...AL


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