Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS65 KCYS 210536

Area Forecast Discussion
National Weather Service Cheyenne WY
1136 PM MDT Sun Aug 20 2017

.SHORT TERM...(This evening through Tuesday Night)
Issued at 235 PM MDT Sun Aug 20 2017

A few showers/thunderstorms are expected to continue through early
this evening for the southeast Wyo mountains, and adjacent valleys
including Laramie. There is potential for some additional activity
to develop over the high plains after 00z as a shortwave begins to
traverse the northern Rockies. The HRRR suggests this, but GFS/NAM
both remain mostly dry tonight. We introduced low-end PoPs along/E
of I-25 given decent low-level moisture with dew points in the 50s
for these areas. Light, moist southeast flow will allow stratus to
develop over the NE Panhandle overnight, possibly encroaching into
east central WY in the Platte River Valley. Forecast soundings are
suggesting some potential for fog, especially via the NAM. 12z GFS
quite a bit drier though, so opted to leave this out of the latest
forecast and let the evening shift re-evaluate. Any fog or stratus
over southeast Wyoming should erode very quickly by 15z as a front
causes winds to shift to the northwest. The Panhandle sites should
take longer to clear out on Monday AM, so Wyoming is looking quite
good for the Great American Eclipse. Precipitation chances will be
low with most of the energy aloft going to the north & east. Upper
level ridging will build into the area on Tuesday, keeping chances
for precipitation low outside of the high country.

.LONG TERM...(Wednesday through Sunday)
Issued at 320 PM MDT Sun Aug 20 2017

Models in good agreement for late this week and into next weekend
showing a strong upper level ridge to the south of Wyoming
dominating the weather pattern. As is typical with late August,
the polar jet will become a little more active along the United
States/Canada border. Models indicate that each Pacific upper
level trough will remain well north of southeast Wyoming with the
bulk of the cool air. Some cooler air may move into the High
Plains this weekend as the upper level high builds further to the
west, allowing northerly flow aloft to increase as a cold front
moves southward across the plains. Expect daytime temperatures to
be near or slightly above normal through the end of the week, and
then it may cool off a bit by Sunday as that cold front moves

As for precipitation, Wednesday and Thursday look to be
the most favorable days to see at least scattered showers and
thunderstorms in the afternoon and evening hours. Models continue
to show a weak upper level low near the Calif coastline ejecting
northeast, which will help advect subtropical moisture northward
into Wyoming and Colorado midweek. Kept POP between 25 to 35
percent during this period across most of southeast Wyoming and
western Nebraska. Models indicate less instability for Friday and
Saturday, but still can not rule out a few showers and
thunderstorms mainly in the mountains and near the Black Hills
north of Lusk and Chadron Nebraska. Most locations will be dry so
kept POP between 10 to 20 percent into the weekend.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1130 PM MDT Sun Aug 20 2017

Still expecting low stratus to affect the NE terminals after 09Z
with MVFR ceilings at KBFF and IFR for KSNY and KAIA. Short term
guidance has hinted at elevated convection over the Panhandle late
tonight which would serve to disrupt any low cloud formation but
so far do not see any evidence of this happening. Latest
indications are that the stratus will burn off rather quickly
Monday morning so have brought in VFR by 15Z and it may be even
earlier. Elsewhere, expect VFR to prevail with light winds. A
cold front will drop south across the plains Monday morning with
gusty north winds developing behind the front in the late morning.
Convective chances Monday should be minimal.


Issued at 235 PM MDT Sun Aug 20 2017

Fire weather concerns are expected to remain low over the next few
days with RH values generally above 15 percent and winds remaining




FIRE WEATHER...CLH is the U.S. government's official web portal to all federal, state and local government web resources and services.