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000
FXUS65 KCYS 110950
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
350 AM MDT Thu Apr 11 2024

.KEY MESSAGES...

- Above normal temperatures expected across much of the region
  Friday and through the weekend. Afternoon highs in the 70s can
  be expected east of the Laramie Range and into the Nebraska
  Panhandle.

- Potential for a storm system to impact the region next week,
  but confidence on any expected impacts are low at this time.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 335 AM MDT Thu Apr 11 2024

Latest GOES imagery shows northwest flow remaining overhead as
a large scale upper level low continues to move across the
southeast CONUS. Looking farther west, a large scale upper level
system continues to churn south of the Gulf of Alaska and looks
to continue to move down the Pacific Coast late this week and
eventually be our next weather producer next week (see long term
discussion). The gradual warmup will begin today with height
rises across the CWA as an upper level ridge shifts east and
amplifies. Afternoon temperatures will mostly remain in the 50s
this afternoon with scattered cloud cover currently over
northwest WY moving our way later today.

Headed into Friday, the 500mb ridge axis will shift overhead as
700mb temps climb around 5C, which is around the climatological
90th percentile value for mid-April. This will support
afternoon temperatures reaching the upper 60s to 70s for most
across southeast WY and western NE, possibly pushing 80F degrees
Friday in the North Platte River valley near Torrington and
Scottsbluff. If not Friday, temperatures look to be a few
degrees warmer Saturday afternoon, especially east of I-25 into
the NE Panhandle. Decided to nudge temperatures towards the NBM
50th percentile as the deterministic NBM was on the lower end of
the distribution despite the high model certainty. With these
warmer temperatures, we could see elevated fire weather
conditions across portions of the area Friday and Saturday with
gusty afternoon winds possible in spots.

Precipitation chances are fairly minimal during the short term
period. There is a low chance (>15%) of isolated shower
development late Friday afternoon with a weak shortwave
traversing the central Rockies ahead of the larger scale upper
level low along the Pacific Coast. However, this will likely be
confined to the higher terrain and will result in little to no
measurable precipitation.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Issued at 335 AM MDT Thu Apr 11 2024

After a warm weekend, the weather pattern next week will
gradually trend cooler and more unsettled.

A vigorous closed low will dive towards the California coast this
weekend and start to inch eastward on Sunday. Downstream
amplification of the ridge over the central Plains in advance of
this system is expected to lead to further warm air advection on
Sunday. Ensemble mean 700-mb temperatures jump to around +8C near
Cheyenne by Sunday late afternoon, supporting another day of highs
some 10-20F warmer than average. Many locations in the Nebraska
panhandle will get another shot at 80F, if this wasn`t already hit
on Friday or Saturday, but this should be the warmest day of this
warm spell. Breezy conditions Sunday may also lead to increased fire
weather concerns with low afternoon RH expected. The closed low then
ejects east of the Rockies late on Monday or early Tuesday, and
brings the warm spell to an end. Monday`s highs will depend on the
timing of the front, but most guidance has trended slower, which
would give us one more day of above normal temperatures Monday, but
still about 10F cooler than Sunday. Over the last 24 hours, models
have trended towards a solution that keeps the initial shortwave
more progressive and open, which inhibits effective wrap-around
precipitation Monday night into Tuesday. While scattered rain and
snow showers driven by frontogenesis still look like a good bet, the
widespread stratiform precipitation scenario shown by the ECMWF
ensemble yesterday at this time is looking less likely. Despite the
more progressive nature, models are still showing a potent surface
low winding up over the High Plains and quickly ejecting to the
northeast. This leads to a period of gusty northwest winds Monday
night into Tuesday across the area. This doesn`t look nearly as
strong as last weekend`s wind event, but there is certainly
potential for another round of High Wind Warnings. Ensemble median
700-mb wind speeds are around 40 to 45 knots over Cheyenne, but
there are a few outliers showing a more potent event. Regardless,
looks cooler and breezy Tuesday with a few rain/snow showers around.

This first system will move off to the east quickly, but another
trough will sink into the northern Rockies on Tuesday into
Wednesday. This northern branch disturbance will be considerably
colder than the first, but the dynamics and precipitation potential
remain fairly uncertain. Ensembles are split between showing a more
progressive trough vs. stalling the trough and associated frontal
boundary over the area for a few days. The cluster showing the most
progressive solution still leads to fairly widespread QPF on
Wednesday but dries the area out quickly by Thursday. The more
stalled scenarios keep precipitation chances around for Thursday and
even longer. There is better confidence in temperatures returning to
below normal values for Wednesday and Thursday. While there is still
quite a bit of model spread, ensemble median 700-mb temperatures
plummet to -10C by Thursday, which is around the climatological 10th
percentile.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1130 PM MDT Wed Apr 10 2024

VFR conditions expected for the forecast period. There is a
slight (10-20%) chance for fog near KLAR and KCYS for a few
hours Thursday morning, but the probability is too low to add to
the TAF. Otherwise, quiet with NW winds gusting 20 to 25 knots
late morning through the afternoon. Some mid level clouds will
filter through during the day also.

&&

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

&&

$$

SHORT TERM...MB
LONG TERM...MN
AVIATION...MN