Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 282158
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
358 PM MDT Thu Mar 28 2024

.KEY MESSAGES...

- High Wind Warning for central Carbon County as well as areas
  near Arlington and Elk Mountain until 6 PM MDT this evening
  for occasional wind gusts 55 to 60 MPH.

- Snow squalls are possible across Carbon and Albany Counties
  during the early to mid evening hours today. The heaviest
  bands could produce snowfall amounts in excess of 3 inches.

- A prolonged period of unsettled weather is expected Friday
  through Monday with daily chances for rain and snow, but the
  probability of a high impact winter storm is decreasing.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 230 PM MDT Thu Mar 28 2024

Wind gusts 55 to 60 MPH have developed across portions of Carbon
County (including both Rawlins and Arlington) this afternoon, in
response to strong low-level gradients and deep low-level mixing
across the region. Opted for the issuance of a High Wind Warning
in an earlier update, which is valid until 6 PM MDT this evening
with winds expected to diminish toward sunset. Snow showers will
begin to increase in coverage and intensity across western areas
by 00z this evening as a cold front blasts eastward across south
central and southeast Wyoming. Linear forcing along this frontal
zone, coupled with ample instability courtesy of very steep mid-
level lapse rates should support a convective precipitation mode
through the early to mid evening hours, with linear segments and
locally enhanced precipitation rates. Given 700-800 hpa flow at/
above 40 knots, this activity may also be accompanied by locally
enhanced wind gust and thus potential for snow squalls. Could be
a chance for a couple of lightning strikes as well. The majority
of areas should see fairly modest accumulations, but snow squall
activity or localized bands could produce a quick 2 to 4 inches,
perhaps more over the Snowys & Sierra Madres. After a brief lull
on Friday morning, models depict the next wave lifting north and
east across the CWA by late Friday afternoon in ahead of a deep/
vigorous upper-level low spinning off the CA coastline. This may
support a widespread shield of light to moderate snow across the
majority of the CWA w/ the best chance of more substantial snow-
fall accumulations over the Snowy and Sierra Madre mountains. We
may need to expand current Winter Wx Advisories in both time and
space with later updates, as another 6 to 12 inches appears very
possible with this next wave.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 230 PM MDT Thu Mar 28 2024

A messy storm system associated with a closed low dropping south
just off the California coast this weekend will lead to several days
of unsettled weather. Picking up on Saturday, the low will still be
just west of the San Francisco Bay, but moisture laden southwest
flow will be stretching out ahead of it, with deep moisture
streaming over our area in a strong and broad jet stream aloft.
Confluent flow on the eastern edge of this trough will keep a
frontal boundary stalled somewhere close to our area through the
weekend. Downstream amplification ahead of the trough will help to
lift the frontal boundary north through the day on Friday, allowing
for fairly strong warm air advection across most of the area.
Guidance shows fairly consistent isentropic lift overrunning the
frontal boundary, particularly strong when one of a series of vort-
maxes traverses overtop the boundary. The stratiform precipitation
should lift mostly north of our area during the day Saturday, but as
that occurs, showery type precipitation will develop in the narrow
warm sector of the storm system. Thus, still have decent PoPs across
the area Saturday afternoon and evening even as the frontal boundary
shifts north. A vort-max moves to the east late Saturday evening,
should allow the frontal boundary to sag southward slightly in its
wake.

Sunday looks like a fairly similar setup to Saturday, just with the
frontal boundary slightly further south. Another round of showery
type precipitation should develop in the warm sector, then focused a
little further south closer to the I-80 corridor and up to the
central portion of the forecast area. Ensemble means show a few
hundred J/kg of CAPE across the southern half of the area on Sunday
afternoon. Combined with frontogenesis and another round of
overrunning, we should see pretty good precipitation coverage Sunday
afternoon and evening, with some embedded thunder possible. Sunday
evening and overnight looks quite complex, with rapid cold air
advection as a surface cyclone over east central Colorado draws the
cold front back to the south and ejects to the east. Expect rain to
change over to snow rapidly as cold air spills southward. However,
the dynamics in the wrap-around flow don`t look that favorable for
widespread stratiform precipitation. This leaves some considerable
uncertainty in the cold phase of this system still, but the vast
majority of ensemble members are consolidating around a less-snowy
scenario at this time. Still looking at some fairly widespread light
accumulations Sunday night into Monday, and could see some
advisories being needed.

Much colder on Monday with 700-mb temperatures dropping to near -8C
for much of the area with brisk northerly winds. This cold snap
should be short-lived with a strong ridge pushing in on top of the
departing trough as we head into Tuesday. We should warm to near
average Tuesday, and then above average Wednesday and Thursday.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 230 PM MDT Thu Mar 28 2024

A period of MVFR to locally IFR/LIFR ceilings & visibilities may
occur across western terminals (KRWL/KLAR) after 00z w/ possible
snow squalls this evening, and potential for lingering -SN after
06z. Conditions are expected to improve after sunrise Friday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 6 PM MDT this evening for WYZ109-110.
     Winter Weather Advisory until 6 AM MDT Friday for WYZ112.
NE...None.

&&

$$

SHORT TERM...CLH
LONG TERM...MN
AVIATION...CLH


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