448
FXUS65 KCYS 231145
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
445 AM MST Sat Nov 23 2024

.KEY MESSAGES...

- Elevated to Red Flag fire weather conditions are expected today
  for portions of Southeast Wyoming, with above average
  temperatures, low humidity, and gusty winds.

- Strong winds are also expected for portions of the I-80
  corridor between Laramie and Rawlins from late this morning
  through the late afternoon hours. Wind gusts to 50-60mph
  expected.

- Colder temperatures will return Sunday and last through next
  week. Chances for snow will be greatest on Sunday and
  Wednesday.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 305 AM MST Sat Nov 23 2024

A busy short term forecast period is in store for the area.
Model guidance for the short term package has really come
together quite well in the past 24 hours regarding strong winds
and fire weather concerns. On the heels of those weather
hazards, we will be ushering in much colder temperatures by
Sunday behind a strong cold front. This will result in localized
snow showers in the highest elevations of the Snowy and Sierra
Madre Mountains through early Monday.

Strong wind gusts will begin to ramp up in the wind prone and
gap areas of southeast Wyoming after daybreak today. There will
be multiple weather features to discuss. There will be a semi-
stationary frontal boundary draped on a transect line from
northwest WY to northern NE this morning into the early
afternoon hours. This will waffle back and forth throughout the
day, by propagating southward towards the North Platte River
Valley early on, and then receding back toward the Black Hills
of SD by the late afternoon hours as a weak warm front. This
will create quite the temperature gradient as areas near the
SD/NE state line of western NE will struggle to get out of the
40s today, but further south and southwest, temperatures will
surge into the low to middle 60s along and south of HWY 26 back
to the I-25 corridor.

Further west, the nose of a 140-150 knot jet streak will
propagate off the North CA coastline toward the northern Great
Basin area this morning. As this does so, upper level winds at
H5 and H3 will subsequently increase across western and central WY.
Short term model guidance, particularly the HRRR, has southwest
winds really picking up after daybreak today, with wind gusts of
30-50mph becoming prevalent across Albany and Carbon County. By
this afternoon, 700mb winds will spill north and east into the
Laramie Range, and Converse/Niobrara County. There is a very
dry air mass in place over the region courtesy of a departing
upper level ridge. In fact, RH recoveries have been very poor
for areas in the thermal belt overnight as they have struggled
to reach 20 percent. Surface pressure tendencies will tighten
across the majority of the cwa by late morning and this
afternoon, with 6 hour surface pressure changes progged to be
5-10+ mb, which is sufficient for marginal high wind concerns.
All of this being said, Red Flag Warnings have been issued due
to the gusty winds anticipated later today when combined with
the very low RH forecast numbers of sub 10% in some areas.
Additionally, have gone with a short-fused High Wind Warning for
the I-80 corridor forecast zones between Laramie and Rawlins
from mid-morning to late afternoon. Will likely see multiple
areas reach 55mph with a couple areas up to 60mph briefly for
wind gusts.

As we reach the nighttime hours of late Saturday night and
Sunday morning, there will be a strong cold front sweeping
through the area from the northwest. Model guidance is not
hinting at all that much moisture for the entire cwa for Sunday,
due to the weather system being progressive overall. However,
the mountain zones of the Snowy and Sierra Madre may pick up a
half inch of melted liquid water equivalent for areas above 9000
feet elevation. Light to moderate snowfall accumulations are
forecast there, with 2-5 inches forecast between elevations of
7500-9000 feet, and higher localized amounts from there. As we
wind down the wind and fire weather headlines later today,
wouldn`t be surprised to see a transition to winter headlines
for the Snowy and Sierra Madre Mtn zones from midday Sunday to
late Sunday night by the next forecast package, but will
certainly need to monitor trends to make sure confidence
remains moderate to high for the snowfall forecast in the
mountain zones. Further east, accumulations look to be a
dusting from the Laramie Range toward the western NE forecast
zones. Temperatures will be much cooler for Sunday and Sunday
night, as daytime highs in the 30s and 40s are likely, with
overnight lows in the teens. Stay tuned for any short term
updates.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 305 AM MST Sat Nov 23 2024

Cold front looks to have almost cleared the CWA Sunday evening.
It will certainly be through the Nebraska Panhandle and here to
Cheyenne as it hangs up in the Laramie Range. ECMWF drives the
front through southeast WYoming with precipitation ending Sunday
evening. GFS on the other hand...hangs up the front and keeps
some precipitation going through the evening hours.
Monday and Tuesday look dry as a shortwave ridge moves through.

Need to by on the lookout for Tuesday night into Wednesday as an
upper shortwave moves through northern Colorado. ECMWF back to
painting pretty hefty QPF over the Snowy and Sierra Madre
Ranges...while the GFS has the precipitation further south. Its
only going to be a matter of 50 to 100 miles on the track of
that shortwave on whether we get a good amount of snow out
west...or just a dusting. Probably won`t know that until we get
a little closer to the event. Drier weather for Thanksgiving
Thursday into Friday as an upper level ridge begins to build
into Wyoming.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 442 AM MST Sat Nov 23 2024

Strong winds today across parts of southeast Wyoming after 15Z.
Did increase winds at KRWL to gusts 42kts. Day shift will need
to continue monitoring TAF to increase speeds if needed. Broken
high clouds and VFR conditions otherwise across southeast
Wyoming and Nebraska Panhandle.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from 9 AM this morning to 6 PM MST this
     evening for WYZ418>423.
     High Wind Warning from 9 AM this morning to 6 PM MST this
     evening for WYZ109-110.
     Red Flag Warning until 6 PM MST this evening for WYZ427.
NE...None.

&&

$$

SHORT TERM...BW
LONG TERM...GCC
AVIATION...GCC