034
FXUS65 KCYS 091129
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
529 AM MDT Wed Apr 9 2025

.KEY MESSAGES...

- Mild temperatures this week, along with breezy weather
  resulting in elevated fire weather conditions at times.

- An isolated shower or thunderstorm is possible in the northern
  Nebraska panhandle Wednesday with some gusty winds possible.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 1245 AM MDT Wed Apr 9 2025

Fast flow aloft is expected to continue through the short-term
period as southeast Wyoming and western Nebraska remain in-
between a ridge of high pressure over the southwestern CONUS and
a broad trough over the northern plains. The gradient between
these two pressure systems will result in gusty winds over much
of the Wyoming high country and high plains today. Previously
issued High Wind Watches have been upgraded to High Wind
Warnings for the Snowy Range Foothills and I-80 summit in
southeast Wyoming where gusts over 60 mph are possible by midday
on Wednesday. Farther east, humidity values are expected to drop
into the mid and upper teens aided by adiabatic compression from
the general downsloping wind pattern. As a result of this low
RH combined with gusty winds over 30 mph in the southeast NE
panhandle, a Red Flag Warning is now in effect for Wednesday
afternoon. Consideration was given to extending this RFW farther
west into southeast Wyoming as well as the northern NE
panhandle. However, forecast guidance has inched upward somewhat
with regard to RH at the surface and we will hold off for now
in these locations. There is a very slight chance of a shower or
two clipping the far northern portions of Niobrara, Sioux and
Dawes county later in the afternoon as weak convection once
again fires off the Black Hills region and drops southeast. Have
added very slight PoPs for weak thunderstorms in the Chadron
area as a result of this low-probability outcome shown in some
HREF ensemble guidance members.

Winds will drop back considerably on Wednesday night into
Thursday morning as the gradient relaxes aloft and the
associated jet in northwest flow pushes east into the central
plains. Expect a mainly sunny day on Thursday with lighter
northwest breezes during the afternoon and a completely dry
weather forecast. Despite height rises over the region,
afternoon high temperatures will run similar to on Wednesday
given the loss of strong downslope flow. Forecast confidence is
high throughout the short-term with only slight adjustments to
wind and humidity grids in this forecast package.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 132 PM MDT Tue Apr 8 2025

The main weather story in the long range still revolves around the
big warmup to round out this week, then a storm system to start the
new one. Northwest flow aloft transitions to southwest as a highly
amplified ridge spreads across the Rockies. The ridge breaks down
over the weekend and is replaced by a trough that digs into the
Northern Plains. A closed low also spins up over the Dakotas and
quickly moves over the Great Lakes. That system will bring the next
potential of precip, albeit still limited (20-30%) and temperatures
closer to normal.

Friday and Saturday... The forecast area becomes split by the upper
ridge axis on Friday and experiences the low level thermal ridge on
Saturday. NAEFS ensembles continue to suggest H5-7 heights and temps
reaching 99.5%ile of climo each day. The magnitude of the ridge
along with strengthening southerly low level flow over the Great
Plains and increasing westerly downslope flow near the mountains
will support the abnormally warm temps. ECM EFI values also continue
to indicate near certainty in well above normal max temps (0.8-
0.9/1) and the potential for near records with SoT values >0. Long
range guidance reflects this pattern as H7 temps increase to +10C in
eastern Wyo and H85 temps surpass +25C in the Neb panhandle.
Official forecast highs range in the mid 70s to lower 80s Fri and
upper 70s to mid 80s Sat for areas along and east of I-25. Guidance
has been fairly consistent in keeping these values near the 25%ile
of the NBM envelope, but close to the MEX. Saturday`s highs surpass
normal values as much as 25 degrees and approach daily records, so
any increase in the forecast could easily set new records. Fire
weather conditions will need monitored during this stretch as
humidity values drop into critical thresholds (<15%). At this time,
the risk of red flag does not appear overly significant with the
gusty winds primarily being confined to the mountains and toward
central Wyo.

Sunday through Tuesday... The upper trough quickly follows the
ridge, while the closed low passes just to the north of the forecast
area. The dynamics with this system are fairly impressive, but
remnant dry air and the lack of moisture advection should keep
moisture amounts low. An organized H5 vort max and a 120+ kt jet
streak at H3 jet cross the Great Plains. At the surface, the first
low develops around the Black Hills and drags a warm front through
the area (likely Sat). A strong cold front follows on Sunday as a
potentially deeper low more closely associated with the upper low
slides across the Dakotas. Some post-frontal and wrap-around showers
are possible as cooler air filters into the region. Thermal profiles
suggest mountain and nighttime snow and valley/daytime rain or mix
as highs drop into the upper 40s to lower 50s on Monday.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 525 AM MDT Wed Apr 9 2025

VFR conditions will dominate at all terminals today. A dry day
is expected however very gusty winds out of the west to
northwest are expected at all terminals, particularly in the 16z
to 23z timeframe. Gusts over 40 mph are possible at RWL and LAR
in the afternoon hours. Winds will drop back after 02z at most
locations this evening.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 6 PM MDT this evening for WYZ110-116-
     117.
NE...Red Flag Warning from 11 AM this morning to 7 PM MDT this
     evening for NEZ436-437.

&&

$$

SHORT TERM...MAC
LONG TERM...DS
AVIATION...MAC