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

000
FXUS65 KCYS 292208
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
408 PM MDT Wed Mar 29 2017

.SHORT TERM...(This evening through Friday night)
Issued at 245 PM MDT Wed Mar 29 2017

Main forecast concern will be the Pacific storm system that will
impact the region Friday, Friday night, and potentially Saturday.
This will be a tricky forecast over the next few days since
significant impacts are POSSIBLE due to snowfall. But given how
the last few events panned out, widespread significant impacts
appear UNLIKELY at this time. Will continue to closely monitor
this system over the next 48 to 60 hours.

For the next 24 hours, expect quiet weather with some potential
for patchy fog over the eastern plains tonight as winds become
light and variable east of the Laramie Range. Further west, winds
will become gusty as a weak lee-side surface trough slides
eastward near the Wyoming/Nebraska border. Do not expect these
wind to get too strong by Thursday morning since a cold front will
begin to impact the region, but can not rule out some gusts
around 45 to 50 MPH over the wind prone areas after midnight. For
Thursday, as this front moves across Wyoming, expect rain showers
to develop ahead of it along and west of I-25. Can not rule out a
few thunder showers as well with some boundary layer instability
present.

Southeast Wyoming and western Nebraska will begin to be impacted
by the storm system late Thursday night as the Pacific upper
level trough rapidly digs southeast into the four corners region
and then stalls. This storm will take its time moving eastward,
likely remaining near the four corners region through Friday night
and into early Saturday morning. How far south this system digs
before it stalls will be key in determining precipitation amounts,
temperatures, precipitation rates, and possibly snowfall amounts.
As of right now, confidence is not too terribly high with any
particular solution given how the last two systems have panned
out even though models are in pretty good agreement regarding this
storm. 12z models have trended colder with this storm, and now
show snow levels down to 5000 feet and maybe as low as 4000 feet
if the coldest solutions verify. Will note that ensemble plumes
are also trending colder as well during the last 4 runs. The 12Z
ECMWF is currently a little further south but less progressive
compared to the GFS, which is enough to limit the higher
precipitation rates across southeast Wyoming. At first, upslope
flow, coverage along the cold front, and upper level difluence
will be the primary dynamics to initiate moderate rainfall across
the area and maybe a few thunderstorms. Eventually dynamic forcing
will be dominated by deformation and upslope flow as well as some
instability by Friday night. For now, lowered snow levels and
included accumulating snow down to 5000 feet or so. Below 5000
feet, expect mostly rain. Above 9000 feet will be all snow and
locations between these two elevations will be the highly
uncertain areas which unfortunately includes most of Interstate 25
and Interstate 80. Increased accumulations above 5500 feet for 2-4
inches of snow for Cheyenne, Laramie, and Wheatland. The Laramie
Range may actually do the best with snowfall amounts so increase
accumulations over 6 inches in those areas. Will likely have a
better idea about precip type and amounts once this system pushes
onshore tonight, but with the last two events in mind, will likely
be more cautious with this one as it approaches.

.LONG TERM...(Saturday through Wednesday)
Issued at 151 PM MDT Wed Mar 29 2017

Saturday...Potent upper low pivots across northern New Mexico and
possibly into southeast Colorado in the afternoon. Precipitation
shield progged to extend into the southern half of our counties,
though this could change significantly based on the track of the
system. For now will match our neighbors and paint 20 to 60 percent
POPS. Quite cool for the first day of April with cloud cover and
precipitation.

Sunday...Upper trough progged to open up and move across western
Kansas with zonal flow over our counties helping the atmosphere to
dry out and producing a dry afternoon, along with a warming trend
based on thicknesses and 700 mb temperatures.

Monday...Next potent shortwave trough aloft progged to move into
Wyoming, along with its associated cold front, spreading increasing
chances for rain across our counties, especially in the afternoon.

Tuesday...Highest POPS look to be across our northern counties based
on the projected track of the closed upper low over our central
counties into southwest Nebraska by late in the day. Definitely a
windy, cold and raw day based on expected low and mid level
gradients and progged thicknesses and 700 mb temperatures.

Wednesday...Continued cool as flow aloft remains strong
northwesterly, limiting the warming trend, and also windy based on
low and mid level gradients. Drying trend as the low and mid levels
dry out.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 405 PM MDT Wed Mar 29 2017

Wyoming TAFS...VFR prevails, except for MVFR at Rawlins after 17Z
Thursday.

Nebraska TAFS...VFR prevails, except for MVFR at Chadron, Sidney
and Alliance until 02Z.

&&

.FIRE WEATHER...
Issued at 151 PM MDT Wed Mar 29 2017

No Fire Weather concerns this week and this weekend with
widespread wetting precipitation expected along with cool
temperatures and high humidities. Another storm system is possible
by early next week.

&&

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

$$

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


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