214
FXUS65 KCYS 072050
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
250 PM MDT Mon Apr 7 2025

.KEY MESSAGES...

- Mild to seasonably warm temperatures this week, along with
  elevated to near critical fire weather conditions at times. A
  Fire Weather Watch is in effect for the southern Nebraska
  panhandle Tuesday afternoon.

- Elevated to high winds possible for the southeast Wyoming wind
  prones on Tuesday and Wednesday. Wind gusts over 50 MPH are
  likely.

- An isolated shower or thunderstorm is possible in the northern
  Nebraska panhandle Tuesday and Wednesday.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 238 PM MDT Mon Apr 7 2025

Currently a pleasant, sunny day across the area with mild
temperatures in the 50s and 60s for most locations. A little breezy
out west this afternoon with strong winds expected to spread
eastward through the overnight hours. Flow aloft tonight will
gradually turn more westerly as a shortwave moving along the
Montana/Canada border flattens the upper-level ridge. This will
strengthen 700 mb winds over the course of the night, and lead to a
prolonged period of windy conditions as the strong winds persist.

By Tuesday, winds aloft over the Laramie Range and usual southeast
Wyoming wind prones will reach 40 to 50 kts. Combined with decent
subsidence, some of these winds are likely to reach the surface
during the day Tuesday. Held off on any high wind headlines at this
time as both height and MSLP gradients are really lacking. A surface
low moving across the eastern half of the CWA tomorrow afternoon
will really dampen pressure gradients. In-house guidance is also not
too excited about high winds, showing 20 to 30 percent chances for
most wind prones. In-house guidance gives the highest probabilities
to Bordeaux, with almost a 40 percent chance of high winds. Would
agree that this location has the best chance just based off winds
aloft and subsidence alone. However, the lack of any sort of decent
gradient over the Laramie Range gives little confidence in high
winds here. Despite this, the wind prones will likely still see 50
to 55 MPH wind gusts during the day. Will let another model cycle go
through so later shifts can decide if any wind headlines are needed.
Strong winds across the area will also lead to fire weather concerns
during the afternoon hours. Downsloping winds and a dry surface will
lead to elevated fire weather conditions east of the Laramie Range.
Issued a Fire Weather Watch for Tuesday afternoon for the southern
Nebraska panhandle as fuels are ready and this location has the
strongest chance to see relative humidity drop below 15
percent. Models have been fairly consistent with showing mid-
level cloud cover as the aforementioned shortwave drops down
from the north Tuesday night. Increasing mid-level moisture
throughout the day will increase cloud cover and potentially
limit relative humidity from dropping below critical thresholds.
Hi-Res guidance like the HRRR and RAP are rather aggressive and
suggest downsloping winds will overcome the cloud cover. Due to
this and 40+ MPH winds expected in the panhandle, issued the
Fire Weather Watch. Opted to keep the northern panhandle out of
the Watch for now as there is a slight chance for an isolated
shower or two ahead of the incoming shortwave.

Wednesday will be virtually a repeat of Tuesday, but with slightly
better chances for high winds and fire weather. With the shortwave
diving down into the northern High Plains, the exit region of the
250 mb jet will be located over the CWA. Winds aloft over the South
Laramie Range will reach 50 to 55 kts with even stronger subsidence
than Tuesday. MSLP gradients remain unimpressive, but CAG-CPR 700 mb
height gradients do briefly climb over 50 meters, giving Arlington a
shot at high winds on Wednesday. In-house guidance shows just under
a 40 percent chance for high winds for these areas. Have more
confidence in high winds on Wednesday and for more locations, but
held off in case headlines are needed tomorrow. Strong winds will
again lead to fire weather concerns. Fire weather headlines may
likely be needed again during the afternoon hours with continued
gusts above 40 MPH. Relative humidity remains the limiting
factor, however model soundings show a very dry surface.
Combined with downsloping winds, humidity may be able to drop
below critical thresholds. With the shortwave off to the
northeast, the northern panhandle may still see an isolated
shower or thunderstorm during the day. Elevated CAPE values
could lead to a thunderstorm with gusty winds given the
inverted-V soundings.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Issued at 238 PM MDT Mon Apr 7 2025

The main weather story in the long range (Thursday and beyond) will
be a big warmup heading into the weekend. Upper westerly zonal flow
midweek transitions to northwest and eventually southwest as a ridge
builds over the Rockies. The ridge appears to be rather progressive
in only sticking around a couple days before breaking down to the
east, but will be rather anomalous. A closed low then dives into the
Dakotas during the latter half of the weekend while a trough digs
into the central Rockies. That system will bring the next potential,
albeit still rather limited (20-30%) of precip and temperatures
closer to normal.

Thursday through Saturday... The forecast area remains on the
periphery of the ridge on Thursday, but quickly falls under its
influence on Friday. NAEFS ensembles suggest H5-7 heights reach
99%ile of climo on Friday as the axis bisects the forecast area. The
magnitude of the ridge combined with decent southerly low level flow
over the Great Plains and westerly downslope flow along the
mountains will encourage well above normal temps to round out the
week. ECM EFI values indicate near certainty in abnormally warm max
temps (0.8-0.9/1) and potential for near records as SoT values >0.
H7 and H85 temps in the guidance also reflect the pattern as they
increase from -4C to +10C in eastern Wyo and from +7C to +25C in Neb
panhandle, respectively. As of now, official forecast highs range in
the lower/mid 60s Thu to mid/upper 70s Fri to lower/mid 80s Sat for
areas east of I-25. These values line up near the 25%ile of the NBM
envelope but closely resemble the MEX. Depending on cloud cover and
prevalence of downslope flow, current forecast may need bumped up.
Saturday`s highs surpass normal values as much as 25 degrees and
approach daily records, so any increase could very easily set new
records. Aside from the warmth, fire weather concerns are definitely
raised as humidity values drop into critical thresholds (<15%).
Thursday may feature the gustier winds, but relatively higher
humidity, but Saturday will need monitored as winds could increase
with the ridge breakdown.

Sunday and Monday... The next upper trough quickly fills in behind
the ridge as the low passes just to the north of the area. The
dynamics in the mid/upper levels appear rather impressive with an
organized H5 vort max and a streak in the H3 jet intensifying from
100 kts over Wyo to 130+ kts in Neb. The surface component features
a secondary low somewhere near the Black Hills driving the warm
front (passage Sat) and then the strong cold front on Sunday. The
primary low will be more closely associated with the upper low over
the Dakotas. Despite the increased forcing, moisture could be a
limiting factor in the overall setup. Low level vectors steer the
greatest flow and convergence east of the forecast area, and most of
the appreciable precip may stay concentrated along the northern tier
of the CONUS. Some wrap-around activity may work into Wyo and
western Neb as cooler air filters into the region. Thermal profiles
would suggest mountain and perhaps nighttime snow and valley/daytime
rain or mix.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1124 AM MDT Mon Apr 7 2025

VFR will continue for southeast Wyo and Neb panhandle terminals
through the forecast period. The primary aviation weather
concern is wind. West winds will gust around 20 kts in Wyo this
afternoon, taper tonight, then strengthen to around 30 kts by
midday tomorrow. Generally light and variable winds in Neb today
will become prevailing southeast by this evening, then
transition to southwest and finally west/northwest tomorrow
morning. Gusts to 25 kts are likely by midday for most of the
panhandle (lighter at CDR).

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...Fire Weather Watch from Tuesday morning through Tuesday
     evening for NEZ436-437.

&&

$$

SHORT TERM...SF
LONG TERM...DS
AVIATION...DS