407
FXUS65 KCYS 142332
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
532 PM MDT Tue May 14 2024

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms are expected
  today and tonight. Strong wind gusts 55-65 MPH will be the
  primary hazard, especially this afternoon and early evening.

- Cooler temperatures and unsettled weather continues on
  Wednesday with the chance for scattered showers and
  thunderstorms.

- Significant model disagreement persists with the evolution of
  the large scale pattern from late week through the weekend.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 226 PM MDT Tue May 14 2024

Fairly quiet across the area as the surface low tracks just north of
the CWA. Bulk of the precipitation has also remained just north of
the CWA, but there have been some returns across the far northern
parts of the forecast area. Scattered thunderstorms will continue
across these northern areas through the afternoon with the primary
threat in this area being hail. This evening, the storm threat
shifts further south to the rest of the forecast area. Model
soundings continue to show inverted-V profiles with dry low-
levels. Observations confirm dry surface conditions. Therefore,
the primary threat with storms this evening will be strong
winds. Could see gusts to 60 MPH, hence the marginal risk for
severe weather across the CWA.

The secondary shortwave pushes through later tonight, continuing
shower and thunderstorm activity overnight and into the day
Wednesday. Cooler temperatures behind the front will lead to a more
stable atmosphere. There will be some CAPE around the CWA Wednesday
afternoon which could lead to some rumbles of thunder. Overall, the
moister atmosphere on Wednesday will help limit the wind threat, but
small hail could still be possible in an isolated storm or two. The
shortwave will move out quickly Wednesday, so expect any showers
and storms to clear out by evening.

Looking at a warmer and drier day across the area Thursday as a weak
ridge axis parks itself over the CWA. 700 mb temperatures will warm
quite rapidly on Thursday with drier air infiltrating the mid-levels
of the atmosphere. Expect above average temperatures with minimal
chances for precipitation.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 226 PM MDT Tue May 14 2024

Models seem to be coming into better agreement with the overall
pattern, but still disagree and show poor run to run consistency
regarding the timing and evolution of a couple late season cold
fronts this weekend through early next week, and the potential
of a minor wind event for southeast Wyoming on Saturday.

Progressive west to southwest flow is expected through the
forecast period as the northern branch of the jet stream will be
over Idaho/Montana and Wyoming late this week and into the
weekend. By later in the weekend, all models show the northern
branch of the jet lifting north a bit as the southern branch
becomes more active late Sunday and into early next week.
Overall, this will result in the late season polar airmass
remaining pretty close to central and eastern Wyoming through
the weekend late on Friday with another push of polar air late
on Sunday. This is where model solutions are diverging, with the
12z GFS more aggressive and showing a colder solution with the
cold front moving across most of Wyoming, while the ECMWF and
Canadian show this front pushing east further north, barely
clipping far northern Wyoming and missing most of southern
Wyoming and western Nebraska. This is making temperature and
POP forecasts a headache this weekend. However, all models have
remained on the dry side with limited boundary layer moisture
and the 1st primary trough axis moving through the area early
Saturday morning when the low levels are at peak stability. Kept
POP pretty low through Saturday night, but can`t rule out some
shower activity and/or thunder showers across the area late
Friday and especially Saturday. Kept high temperatures on Friday
well into the 70s to mid 80s, warmest across western Nebraska.
Lowered temperatures Saturday, but kept them near the NBM 50th
percentile and close to ensemble (GEFS and ENS) mean. Would like
to note there is still a considerable spread in ensemble data
for Saturday and Sunday, but not as bad compared to a few days
ago. The difference in the location and evolution of the polar
front and polar airmass are also resulting in considerable
differences with wind speeds Friday night and Saturday. The GFS
maintains the potential for very windy conditions across
southeast Wyoming with 700mb winds of 50 to 60 knots. However,
all other models barely show 35 knots...and show the peak winds
much earlier in the day. Increased winds by about 5 knots, but
did not go too crazy at this time.

Expect a slow cool down late this weekend and early next week,
mainly due to increasing precipitation chances and increasing
cloud cover and not necessarily due to the colder airmass to the
north. Once the southern branch of the jet becomes more
dominant next week, the polar airmass across Montana and the
Dakotas should gradually erode or shift northeast into Canada.
A strong midlevel shortwave is forecast to lift northeast out of
the four corners region Monday and Monday night, with better
forcing and more favorable moisture profiles in the low to
midlevels. Models seem to be in better agreement with this
portion of the forecast, even though it`s a little further out
in time. Continued to increase POP for Monday and Tuesday of
next week. Due to cloud cover and cooler temperatures, the
probability of strong or severe thunderstorms looks rather low
early next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 523 PM MDT Tue May 14 2024

A weather disturbance and its associated cold front will move
across the terminals tonight, producing scattered showers and
some thunderstorms.

Wyoming TAFS...Ceilings will be near 10000 feet at Rawlins until
10Z, then will be near 3000 feet until 15Z, and then near
6000 feet. Thunderstorms will be in the vicinity until 05Z.
Occasional showers will occur from 10Z to 15Z. Winds will gust
to 20 knots until 01Z.

At Laramie and Cheyenne, ceilings will range from 5000 to
10000 feet until 07Z, then ceilings will vary from 1200 to
4000 feet until 15Z, then will be near 5000 feet. Thunderstorms
will be in the vicinity from 02Z to 12Z, with areas of fog and
visibilities near 4 miles at Laramie from 12Z to 15Z. Winds will
gust to 25 knots at Laramie until 07Z, to 25 knots at Cheyenne
until 02Z, and after 15Z Wednesday.

Nebraska TAFS...Ceilings will range from 6000 to 15000 feet,
with visibilities near 5 miles in showers and ceilings near
3000 feet at Chadron and Alliance from 10Z to 15Z. Ceilings
will be near 2500 feet at Scottsbluff from 13Z to 16Z. Winds
will gust to 30 knots at all terminals until 03Z, and to
23 knots after 15Z Wednesday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...SF
LONG TERM...TJT
AVIATION...RUBIN