Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 271729
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1129 AM MDT Wed Mar 27 2024

.KEY MESSAGES...

- Strong wind gusts up to 60 MPH will be possible near Arlington
  and Elk Mountain from Wednesday evening through early Thursday
  morning. A High Wind Warning is in effect.

- We continue to monitor a strong weather disturbance which may
  impact southeast Wyoming and the western Nebraska Panhandle
  from Friday through Sunday. Specific details remain uncertain
  at this time.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 212 AM MDT Wed Mar 27 2024

Current Weather: Light snow showers are visible on radar as of 08Z
this morning in northwestern Laramie County and eastern Albany
County. These showers will slowly continue to drift to the
southeast, likely impacting Cheyenne in the next hour or two.
Minimal impacts are expected with these snow showers as they are
light in nature. Looking at webcams, snow showers over the I-80
Summit have lead to a layer of snow on the interstate with light
snow still falling at this time. It is another chilly night across
the region with 08Z temperatures ranging from 12F at Chadron to 27
in Rawlins and Laramie. Scattered clouds are drifting across
southeast Wyoming, with partly cloudy skies in the Nebraska
Panhandle, especially near Kimball.

Discussion: An upper-level ridge will begin to move in overhead
behind the departing upper-level trough that dropped temperatures
over the past few days. As this upper-level ridge builds in
overhead, northwesterly flow strengthens before turning more
westerly by the end of the day Wednesday. A strong swath of 500mb
vorticity will advect across the region as the ridge axis pushes
over Wyoming. The cyclonic vorticity advection associated with the
vorticity swath will increase lift across the region leading to
partly cloudy skies, despite the subsidence from the upper-level
ridge in place. Ample sunshine will still be visible throughout the
day and with 700mb temperatures warming back towards the -4 to -5C
range, temperatures will be warmer across the region. Expect high
temperatures in the 50s for many areas east of I-25 and temperatures
in the low-40s for areas west of I-25. Attention turns towards late
this evening into the overnight hours for a localized, marginal high
wind event along I-80 near Arlington. Craig to Casper height
gradients will increase towards the upper-50s by 06Z Thursday as
700mb height gradients tighten and a 50-55kt jet develops overhead.
In-house random forest guidance suggests a 55-60% chance for wind
gusts over 58mph between 03 and 06Z Thursday. Additionally, GFS
Omega fields suggest strong downward omega values off the Snowy
Range that continue to increase through the overnight hours and into
the early morning hours. With the strong 700mb jet, southwesterly
winds at the surface near Arlington, strong downward omega values,
and Craig to Casper height gradients approaching 60m, decided to
upgrade the High Wind Watch to a High Wind Warning. Gusts of 60mph
are possible during the warning timeframe, though this event will
likely be short-lived as dynamics weaken late in the High Wind
Warning timeframe.

High winds are expected to diminish Thursday morning, but will
likely remain elevated throughout the day. The upper-level ridge
will be directly overhead at this time with westerly winds aloft.
Several 500mb vorticity lobes will eject out ahead of an upper-level
trough off the West Coast as the upper-level jet strengthens across
the Four Corners region. These vorticity lobes will favor
precipitation to develop across western portions of the CWA,
especially the Snowy and Sierra Madre ranges. Cloud cover will
increase throughout the day Thursday ahead of the next system moving
towards the region (see Long Term discussion). Despite the cloud
cover, with the ridge axis directly overhead and 700mb temperatures
warming towards 0 and +1C , much warmer temperatures are expected
for Thursday with highs in the 50s to 60s area wide. Elevated winds
will be likely for much of the CWA west of I-25 due to a strong
700mb jet overhead. However, decided to not extend the current High
Wind Warning nor issue a separate High Wind Watch for Carbon County.
While GFS Omega fields are impressive throughout the day Thursday,
the 700mb jet does become more separated and decreases to around
40kts before completely dissipating late Thursday night. At this
time, confidence in a prolonged high wind event in low, but elevated
winds are likely to remain Thursday afternoon into the evening
hours. This setup should continue to be monitored as GFS downward
omega fields are currently maxed out across the mountains, but the
700mb jet remains weaker than needed for high winds, and Craig to
Casper gradients decrease towards the low- to mid-40s. In addition
to this, in house random forest guidance does not favor a high wind
event extending into Thursday afternoon/evening, as probabilities
remain around 20% for elevated winds. All these factors decreased
confidence in high winds continuing into the afternoon and evening
on Thursday, so did not extend the High Wind Warning past the
original 15Z ending time.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 300 AM MDT Wed Mar 27 2024

Upper shortwave moves through the area Friday. Some question on
where PoPs are going to develop. GFS has a more southern
solution on PoPs compared to the ECMWF. ECMWF has a petty solid
area of QPF along the I-80 Corridor through the day Friday.
ECMWF supported by SREF output...so generally followed its
guidance with PoPs Friday.

After brief ridging Saturday...next shortwave moves into the CWA
Sunday for another fairly widespread event. Both the GFS and
ECMWF are showing .1 to .25 inches qpf over much of the CWA
Saturday night into Sunday. Surface frontal boundary remains
along the I-80 Corridor through Sunday. SHould the GFS solution
hold true...we could be looking at heavy snow across
Laramie...southern Platte and Goshen Counties Sunday night into
Monday. ECMWF further north and east with QPF placement.

Precipitation ends from north to south Monday afternoon as upper
level ridging builds into the area from the north. As ridging
continues to build into the area...seeing warming 700mb
temperatures up above freezing Tuesday into Wednesday. Next
cold front set to move into the area Thursday as a strong
shortwave approaches from the west.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1126 AM MDT Wed Mar 27 2024

WNW to NW winds are beginning to develop across the area late
this morning. Expect gusts of 25 to 35 knots in WY through the
afternoon, and around 20 to 25 knots in NE. Another round of
pop-up rain/snow showers is expected along the I-80 corridor
this afternoon, but coverage and intensity will be much less
than yesterday. Can`t rule out a very brief VIS drop, but these
will be mostly virga producing temporary gusty or erratic winds
at terminals if they move nearby.

Winds will decouple from the surface after sundown, but
remaining breezy near KRWL. The flow will turn more southwest
overnight, leading to gusty SW winds at WY terminals by late
Thursday morning.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 6 PM this evening to 9 AM MDT Thursday
     for WYZ110.
NE...None.

&&

$$

SHORT TERM...AM
LONG TERM...GCC
AVIATION...MN


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