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102
FXUS65 KCYS 251731
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1131 AM MDT Tue Jun 25 2024

.KEY MESSAGES...

- Critical fire weather conditions are expected today over the
  High Plains, generally south of the North Platte River. See
  the Fire Weather section below for more details.

- Moisture will return to the High Plains on Wednesday and
  Thursday, leading to the potential for some strong
  thunderstorms and heavy rainfall in the afternoon and
  evening.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 400 AM MDT Tue Jun 25 2024

The hot and dry weather pattern continues for another day across the
area today. The shortwave that brought the gusty thunderstorms to
the area on Monday is moving out to the east across South
Dakota and Nebraska at this hour. Much drier air is visible on
water vapor satellite imagery moving into our area behind this.
We also have a weak surface low located roughly over the
northern NE panhandle, which has put another weak cross-barrier
pressure gradient in place. This is keeping winds going through
the night in some areas, leading to a very warm night once
again. Temperatures remain in the upper 60s to 70s for much of
the area aside for a few locations that managed to get inverted
and start cooling such as the Laramie Valley and Lodgepole Creek
drainage. The surface low is expected to gradually translate
southeastward as the day progresses but a trailing pressure
trough to its northwest will serve as a stalled boundary. Areas
north of the boundary will be 10+F cooler than yesterday with
better low-level moisture. Those to the southeast may be
slightly cooler than yesterday, but HiRes guidance has backed
off on the cool down. As a result, widespread 90s are expected
again for the High Plains along and south of the North Platte
River. The same areas around Scottsbluff, Torrington, and Sidney
will make a run for 100F again. We`ll have to watch for this
stalled boundary setting up a little further south, which would
bust the high temperature forecast anywhere to the northeast,
but right now it looks like models have a good handle on it.
Mid-level moisture will be lower than yesterday, so shower/storm
coverage will also be greatly reduced. Still can`t rule out
some isolated showers/storms causing gusty winds and dry
lightning along the I-80 corridor.

This evening, a surface high pressure sliding into the northern
Plains will help nudge the stalled boundary further west overnight.
Expect winds to gain an easterly component and push moisture-rich
low-level air back against the Laramie range by Wednesday morning.
The amplifying ridge over the Four Corners states will also nudge
eastward on Wednesday. Finally, a subtle shortwave rotating
over the top of the ridge will tap into the monsoon-like
moisture and pull it northward and then eastward into our area.
All of these components will set the stage for a much more
active day of convection across the area. It will be a
drastically different environment compared to today, with cooler
temperatures expected and PW values exceeding 1.0" all the way
to the Laramie range and perhaps even further west. Southeast
low level flow underneath decent westerly flow aloft will lead
to around 40 to 50 knots of 0-6km shear concurrent with SBCAPE
values above 1500 J/kg (and as high as 2500 in some models).
Lift also looks plentiful due to the vort-max arriving near the
time of peak heating and some modest isentropic lift in the 600
to 700-mb layer. There is a little uncertainty in storm mode.
Storms could have fairly rapid upscale growth, limiting the
period for discrete supercells despite the favorable parameters.
A few strong to severe thunderstorms are certainly in the cards
for Wednesday PM, but the magnitude is still a little
uncertain. Storms will also have a flash flooding threat due to
the plentiful moisture present and nearly saturated soundings.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 234 AM MDT Tue Jun 25 2024

We continue to see a subtropical moisture surge from the
southwest Thursday. Flat ridge in the upper levels with
disturbances moving through this ridge. PWATS across the CWA
range from .8 inches out near Rawlins to near 1.3 inches in the
southern Panhandle. Also seeing a low level southeasterly jet
advecting low level moisture into the Panhandle. Sure looks like
a good setup for fairly widespread rain showers and
thunderstorms for the CWA Thursday afternoon through the evening
hours. A Marginal Risk area has been identified for excessive
rainfall over Carbon and Albany Counties Thursday afternoon. A
Slight Risk area covers southern Carbon County during this time
as well. Should this trend continue...we may need a Flash Flood
Watch for the Mullen Burn Scar Thursday afternoon.

Another concern for Thursday is the possibility of severe
convection in the Panhandle where GFS forecast soundings are
showing afternoon MUCAPE of 1700-2000J/KG. Sfc to 6km shear not
all that strong...but enough for severe storms to form this time
of year at 35kts. DCAPE for Sidney Thursday afternoon around
1100J/KG...so strong downburst winds are possible. Will also need
to watch for flash flooding in these areas as well.

Upper shortwave tracks into North Dakota Thursday night into
Friday with associated surface front tracking east. Should lead
to drier conditions across the CWA. Also cooler conditions as
700mb temperatures fall into the single digits behind the front.

Upper ridging returning to the CWA into the weekend with warming
temperatures. Still some lingering low level moisture for
afternoon and evening showers/storms that could impact our
southern zones both days.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
-- Changed Discussion --
Issued at 1127 AM MDT Tue Jun 25 2024

VFR expected at all terminals through the forecast period. Wind
gusts of 20-30 knots can be expected at times this afternoon
through 2Z for terminals as well. VCSH for KRWL and KCYS has
been introduced due to weak rain showers moving through the
area. Overnight, light VRB to northeast flow will move across
western NE. This may create a few MIFG areas, but VIS reductions
are not expected between 6Z and 12Z Wednesday.
-- End Changed Discussion --

&&

.FIRE WEATHER...
Issued at 400 AM MDT Tue Jun 25 2024

Critical fire weather conditions are expected today across far
Southeast WY and the southern NE panhandle. The combination of low
RH between 10 and 15% and northwest winds occasionally gusting 20 to
30 MPH will lead to favorable conditions for rapid fire spread. With
fuels newly critical in the areas mentioned above, opted to issue a
Red Flag Warning for fire weather zones 430, 431, 432, 433, and 437.
Critical RH and wind are also expected along and west of the Laramie
range, but fuels are not critical there. Along and north of the
North Platte River valley, winds should remain sub-critical, but
elevated fire weather conditions are still expected. There is also a
slight chance for an isolated storm that may produce gusty winds and
dry lightning, mainly along and south of I-80 in Wyoming.

Low-level moisture will push back against the Laramie range tonight,
leading to good to excellent humidity recoveries, and reduced fire
weather concerns for Wednesday and Thursday. Showers and
thunderstorms on Wednesday and Thursday will have greater coverage
and a higher chance of wetting rainfall.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
WY...Red Flag Warning until 7 PM MDT this evening for WYZ430>433.
NE...Red Flag Warning until 7 PM MDT this evening for NEZ437.
-- End Changed Discussion --

&&

$$

SHORT TERM...MN
LONG TERM...GCC
AVIATION...BW
FIRE WEATHER...MN