823
FXUS65 KCYS 031728
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1128 AM MDT Mon Jun 3 2024

.KEY MESSAGES...

- Scattered showers and a few thunderstorms are expected this
  evening with gusty winds possible.

- Elevated to high winds are possible for the wind prone areas
  of southeast Wyoming late tonight through Wednesday.

- Above normal temperatures likely Wednesday and Thursday as
  temperatures climb into the mid to upper 80s across much of
  the region, with 90F possible across the Nebraska Panhandle.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 425 AM MDT Mon Jun 3 2024

After another active day of convection on Sunday we will be seeing
thunderstorm activity quiet down for a little bit. Today won`t be
totally clear though as another more potent upper level trough is
diving into the Pacific Northwest this morning. Abundant cloud cover
is streaming out ahead of this low, with some high clouds already
working into our western zones. WSW flow ahead of the trough will
lead to strong warm air advection across the area today though
temperatures may be held back by cloud cover west of the Laramie
range. Further east, westerly downslope winds should lead to a warm
to hot day with most of the area reaching the 80s. Some of the
typical hotter spots like Torrington, Scottsbluff, and Chadron may
have a chance at 90F. Isolated showers/storms are expected to kick
off mid afternoon, but instability will be quite limited.
Significant warming aloft is ongoing today, which will decrease
lapse rates and instability. While some thunder is likely, severe
weather is not expected today. The only concern is that dry
microburst type events can`t be totally ruled out with inverted-v
soundings and increasing wind speeds aloft. More widespread shower
activity will work in from the west after about 5PM, but this looks
more synoptically driven. Marginal instability will produce some
embedded thunder, but the primary mechanism is the approaching upper
level trough. The mountains may pick up a tenth or two of
precipitation (which could fall as snow on the very highest peaks
above about 11000 feet). The surface cold front will push through
the area Tuesday morning, and a few showers or thunderstorms are
possible along this in the US20 corridor through midday Tuesday.

As the storm threat falls, the strong winds will return. Expect a
breezy day today, but winds will be on the increase for Tuesday
through Tuesday night. The approaching trough is much stronger than
the previous troughs, and will increase the pressure gradient across
the area. The strongest winds through this event are expected
Tuesday morning just ahead of the surface cold front passage, when
cross-barrier pressure gradients reach their maximum. While a breezy
to windy period is all but guaranteed, there is some uncertainty
still in if this will actually attain high wind criteria. The GFS
and GEFS are very aggressive, showing widespread 700-mb wind speeds
of 50 to 60 knots Tuesday morning and sharp MSLP gradients across
the wind prone areas. GFS based in-house guidance shows
probabilities of high wind around 60 to 80% for the Arlington/Elk
Mountain area 40 to 50% for Bordeaux and the I-80 summit Tuesday
morning. Probabilities for the latter two increase to the 60 to 80%
range for Wednesday morning as the GFS shows a finger of even
stronger 700-mb winds creeping over the area. However, all other
global models and ensemble systems show considerably weaker winds.
While the systems are closer together for Tuesday morning (median
700-mb wind at KCYS is 46 knots in the GEFS and 36 knots in the
ECMWF ensemble), spread increases dramatically by 12z Wednesday.
Then, the median 700-mb winds over KCYS is 57 knots in the GEFS and
33 knots in the ECMWF ensemble. There is higher confidence in
elevated winds tonight through Tuesday morning, with a marginal
threat for high winds. Tuesday night could be stronger event, but
confidence is lower. For now, held off on High Wind headlines due
to the lack in model consistency, but the next shift will have to
take another look.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 425 AM MDT Mon Jun 3 2024

The long term forecast will feature a mixed bag of weather impacts
for much of SE Wyoming and the Nebraska Panhandle. Elevated to
potentially high winds will be ending across the Arlington wind
prone and the south Laramie Range and Foothills Wednesday afternoon.
This will giveaway to well above normal temperatures Wednesday and
Thursday for much of the region. Could see widespread 90F across the
Nebraska Panhandle with mid to upper 80s likely across much of SE
Wyoming. Heading toward the end of the week and into next weekend,
the pattern then shifts toward a more active pattern with daily
chances of thunderstorms, some in which could become strong to
severe, especially next Monday.

Elevated to high wind gusts will be still ongoing across Arlington
wind prone and area adjacent. Passing shortwave trough to the north
and increasing heights to the south will keep a tight MSLP gradient
across the region with localized areas of +65kt 700mb winds over
those aforementioned areas. In-house guidance continues to show high
probabilities (greater than 60%) for high wind gusts too occur and
the long range GFS model continues to backup this notion. Still some
uncertainty amongst the ensemble members and the ECMWF, so we will
continue to monitor for potentially issuing some wind highlights.
Nonetheless, it will be breezy through Wednesday afternoon before
wind diminish as the shortwave passes to the east and the MSLP
gradients begin to weaken.

On the heels of this departing trough, a large ridge axis begins to
develop across much of the Intermountain West and this will drive
temperatures to well above normal for some locations Wednesday and
again on Thursday. Moisture advecting into the region underneath
this ridge may be enough to allow for some diurnal convection to
develop by Friday afternoon and with the increase in both moisture
and cloud cover, temperatures may be slightly "cooler" on Friday.

Those daily chances for thunderstorms arrive Friday afternoon and
could persist into the weekend as ripples in the flow will bring
quick moving shortwaves through the area Saturday. We could see more
scattered to widespread thunderstorms on Saturday as this ripple
moves through and we stay rather warm and moist in the lower levels.
Could see lesser chances for convection on Sunday as the ridge
begins to shift eastward and parts overhead on Sunday as the next
storm system begins to move into the Pacific northwest. That system
is progged to move through on Monday and this could bring the best
chance for some organized strong to severe thunderstorms to much of
SE Wyoming and into the Nebraska Panhandle.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1125 AM MDT Mon Jun 3 2024

VFR for all terminals expected in the forecast period. A weak
weather disturbance will move across the area later this
afternoon, bringing a chance of VCSH and VCTS to the area for a
couple of terminals. The main concern will be gusty winds this
afternoon and overnight. Wind gusts of 20-35 knots can be
expected this afternoon and evening for most terminals. KRWL
will see isolated gusts approaching 40 knots at times this
afternoon. Tuesday morning will bring another round of gusty
winds near 40 knots to most terminals through 18Z Tuesday.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...AW
AVIATION...BW