Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 181242
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
642 AM MDT Wed Apr 18 2018

.SHORT TERM...(Today through Thursday night)
Issued at 345 AM MDT Wed Apr 18 2018

Relatively quiet weather over the next 36 to 48 hours across
southeast Wyoming and western Nebraska. Winds will continue to
dissipate this morning and this afternoon as llvl pressure
gradients relax. It will be dry today and cooler than average with
highs in the mid 40`s to mid 50`s due to cool northwest flow
behind yesterdays cold front.

For Thursday, models show an amplifying ridge axis over the
Rockies as it slides eastward into the plains in the afternoon.
Expect temperatures during the day to respond as 700mb
temperatures briefly increase above 0c. High temperatures in the
mid 50`s to low 60`s are forecast which will be around average for
this time of the year. It will be a little cooler than models
indicate due to a strengthening south to southeast winds, which
is typically upslope flow in this area. It may actually become
windy in the afternoon with southeast winds around 25 to 30 mph
sustained and some higher gusts. Attention will shift towards the
west in the afternoon and evening as the next Pacific storm system
across the southern Great Basin region moves eastward to a
position near the four corners region by late Thursday night.
Some rain shower activity is expected Thursday night as the first
bands of precip begin moving from south to north across the area.
Expect mainly rainfall with snowlevels starting off over 8500
feet.

.LONG TERM...(Friday through Tuesday)
Issued at 242 AM MDT Wed Apr 18 2018

The main forecast concern/highlight in the extended period remains
the potential for a significant spring storm affecting the Central
Rockies on Fri/Sat. The GFS/ECMWF remain in excellent agreement w/
a vigorous upper low tracking across the Four Corners after 12z on
Friday. Still a few minor model differences to work out here, with
the GFS being slightly further north with the storm track and more
favorable for more widespread precipitation in this CWA. The ECMWF
focuses the highest precipitation chances over southern areas. The
precipitation type is the other issue to address here. Models have
not been particularly cold with H7 temperatures only around -2C to
-4C from late Friday through early Saturday. We still wonder if we
will see a trend toward colder thermal profiles in the next 24 hrs
as the mid-level cold pool becomes better sampled when the culprit
storm system comes on-shore. However, one thing to note is that we
are seeing this system close off quite early, effectively limiting
any substantial supply of arctic air. Southwesterly 500-mb flow in
the Pacific Northwest on Friday is not a good sign for a potential
arctic intrusion. Still believe the models are a bit on the warmer
side, but with a split flow pattern aloft we just do not see where
the cold air is going to come from to support widespread snow fall
accumulations. NAM/GFS soundings suggest the highest potential for
accumulating snow will be at 6000+ feet elevation. Still certainly
something to monitor closely, but for the time being this is still
looking like a fairly low-impact event.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 638 AM MDT Wed Apr 18 2018

VFR with generally SKC conditions expected. Gusty winds are likely
to persist for most terminals across southeast Wyo and the western
Neb Panhandle through this afternoon, with winds becoming light by
01z.

&&

.FIRE WEATHER...
Issued at 242 AM MDT Wed Apr 18 2018

Minimal Fire Weather concerns for the rest of the week and into
the weekend with cool temperatures and higher relative humidites
compared to the last few days. Humidities will lower near 15 to 20
percent on Thursday across the lower elevations of Carbon county,
but winds will be pretty light. Otherwise, rain and snow will
spread across the area for Friday and early Saturday with a
wetting rain likely, especially near the Colorado border.

&&

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

$$

SHORT TERM...TJT
LONG TERM...CLH
AVIATION...CLH
FIRE WEATHER...TJT



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