Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 151759
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1159 AM MDT Sun Apr 15 2018

.SHORT TERM...(Today through Monday Night)
Issued at 240 AM MDT Sun Apr 15 2018

Fairly quiet pattern setting up for the next 36 hours as an upper
ridge moves gradually eastward across the region. With upper
ridging we will see a warming trend through Monday with not a
whole lot of wind (at least by Wyoming and Nebraska standards)
today, and a bit breezier Monday afternoon during peak mixing
(late morning through mid afternoon)...especially across Carbon
county and into western Converse counties where gusts around 40
mph will be possible. RH values will also drop to around 15
percent for those areas Monday afternoon with deep mixing, but
for now no fire concerns due to some low elevation green-up as
reported by the fire district (see fire discussion below).

.LONG TERM...(Tuesday through Saturday)
Issued at 320 AM MDT Sun Apr 15 2018

Medium to Long Range models and ensembles indicate an unsettled
weather pattern Tuesday through the end of next week. Models
continue the trend of showing a progressive weather pattern
earlier in the week that will transition to a more amplified
blocking pattern by next weekend. The first upper level trough
will push across Wyoming and Colorado Tuesday afternoon, bringing
some shower activity and even some thunderstorms further east.
Models show a negatively tilted trough axis as it moves across the
area, so will need to monitor strong thunderstorm potential
across the High Plains this time of the year. There is potential
for strong winds across the area, mainly as the front moves across
the area in the morning and just behind the front across the
eastern plains in the afternoon. However, models are in poor
agreement with wind speeds with the GFS 15 to 20 knots higher
compared to the other models. The upper level jet will be
weakening further north as the core of the max winds stay over
Colorado and Kansas through Tuesday night, which is unfavorable
for persistent strong winds. At best, this appears to be a quick
Bora event. However, struggled to get sustained winds above 30
knots along the I-80 corridor on Tuesday, so headlines appear
unlikely if model trends remain the same. Otherwise some light
rain changing to snow is expected in the afternoon and evening
hours, so kept POP between 30 to 50 percent outside of the
mountains.

For Wednesday and Thursday, models show the Front Range in between
weather systems as a weak ridge axis quickly moves across the area
and then east of the region by early Thursday. A lingering cold
front will remain in the area and eventually strengthen and push
south across the I-80 corridor, keeping the area on the cool side
both days. Highs on Thursday will struggle to reach 50 degrees
across most of the area with east to southeast surface winds.

Attention then shifts towards the strong Pacific storm digging
southeast into the four corners region by late this week. Will
need to keep a close eye on this storm system since it takes a
very favorable track for significant snowfall for southeast
Wyoming and western Nebraska beginning as early as Thursday night
or Friday morning. Models show impressive lift and dynamic forcing
as the system slows down while moving into central-eastern
Colorado on Friday. Models have continued to be consistent with
this storm with very little variability in the positioning of the
storm in addition to the overall evolution. The only notable
inconsistency is the 12 hour timing difference between the GFS and
the ECMWF, which is shown to some degree in the ensemble
forecasts as well. 500mb and surface standard deviations are not
as high as they normally would be 5 to 6 days out, which results
in above normal confidence with the forecast. With that in mind,
increased POP between 60 to 80 percent for the mountains and
eastern plains along and east of the I-25 corridor beginning late
Thursday night. Based on the ensemble forecasts, would not be
surprised if this storm stalls across western Kansas and continues
impacting the weather here into early next weekend. At the very
least, expect temperatures well below normal Friday and Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1156 AM MDT Sun Apr 15 2018

VFR. Wind gusts to 30 knots at Wyoming sites through 00Z, then
wind gusts to 35 knots after 15Z Monday. Lesser winds at Nebraska
sites.

&&

.FIRE WEATHER...
Issued at 240 AM MDT Sun Apr 15 2018

No fire concerns today as winds and RH stay outside critical
thresholds. Meteorologically we note deeper mixing across our
western and northwestern zones Monday afternoon with RH values
dropping to between 10 and 15 percent and gusty west to
southwesterly winds at 25 to 40 mph. However, latest updates from
the fire districts indicate some low elevation green-up has
occurred and those zones (301, 303, and 304) are now in the no
category for fuel status. Therefore we do not plan on issuing any
Fire Weather Watches at this point for Monday.

&&

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

$$

SHORT TERM...JG
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...JG



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