Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241808
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1208 PM MDT Wed May 24 2017

.UPDATE...
Issued at 1040 AM MDT Wed May 24 2017

Winds are currently gusting between 50 and 60 mph in the wind
prone areas along I-80 late this morning including a peak gust of
57 mph at ARL. Height gradients per the GFS look to peak at around
50m at 18z and then slowly decrease through the afternoon. Some
evidence of mtn wave activity on latest low and mid level WV
imagery which may be serving to enhance the winds at times. SFC
gradient remains strong through early afternoon and then becomes
more westerly as the trough over NE WY and W MT slides east. Went
ahead with an SPS for the Arlington through early afternoon for
these gusts. May see a rogue gust to high wind criteria but think
overall winds will remain below warning levels.

&&

.SHORT TERM...(Today - Thursday Night)
Issued at 310 AM MDT Wed May 24 2017

It is shaping up to be a nice day across southeast Wyoming, and the
western Nebraska Panhandle with the development of pronounced upper
level ridging over the central Rockies. H7 temperatures in the +10C
to +12C range and mostly sunny skies would suggest widespread highs
in the 70s with a few 80s over the plains. The pre-dawn water vapor
satellite loop shows a vigorous upper-level disturbance now digging
from BC/AB into WA/ID/MT. Increasingly difluent flow aloft ahead of
this feature will induce surface cyclogenesis over northeast Wyo in
the next few hours with most models showing a 985-987mb surface low
just northeast of Gillette at 00z Thu. This will result in a strong
pressure gradient across southeast the area, with the low-level CAG
to CPR height gradients even exceeding 50 meters. This, combined w/
deep mixing and a ribbon of 30-40 knot 700 mb flow suggests strong/
gusty winds along/west of I-25 today. The models also suggest a bit
of a ripple in the flow across southeast Wyo in the afternoon. This
weak disturbance could be enough to touch off high-based showers or
thunderstorms out west today, but the dry environment, and warm air
aloft makes for low confidence in measurable precipitation. We went
ahead and added slight chance PoPs along/w of the Laramie Range for
this possibility as the HRRR also supports the idea. The Inverted-V
look to forecast soundings around KRWL suggests any convection will
likely be associated with gusty winds.

Large scale blocking downstream over the Ohio Valley should help to
force a cold front south across the CWA on Thursday. Northeast low-
level upslope will support an increase in pcpn chances, possibly in
the form of thunderstorms depending on the timing of the front. The
potential for severe weather is low as the model continue to show a
considerable amount of cold air infiltrating the CWA. Also, the SPC
Day 2 outlook has shifted the MRGL risk further southeast into east
central CO and western KS. Continuing cool/unsettled into Fri given
persistent troughing over the north central US.

.LONG TERM...(Friday through next Tuesday night)
Issued at 400 AM MDT Wed May 24 2017

Medium and Long Range models continue to show a relatively cool
weather pattern across southeast Wyoming and western Nebraska.
Northwest flow aloft will continue across the northern and central
Rockies and will be responsible for the cool temperatures through
the Memorial Day weekend. An upper level low in southern Canada
will move very little through the weekend, keeping the forecast
area on the western flank of this low as it drifts south into the
northern plains/Great Lakes region. Upper level disturbances and
jet energy will dig southward out of Canada resulting in periods
of rain showers, widely scattered thunderstorms, and high
elevations rain/snow across the mountains. Saturday look to be the
most unsettled day of the holiday weekend with high temperatures
struggling to reach the mid 50`s along and west of I-25, with
highs around 60 further east. Kept POP between 40 to 60 percent
across the region for scattered to numerous showers and widely
scattered thunderstorms. Models shows a lower coverage of showers
and thunderstorms by Sunday and Monday as the upper level low
begins moving northeast across the Great Lakes area. However, the
ECMWF shows the cooler temperatures and a daily chance of showers
and isolated thunder continuing through early next week, including
Memorial day. Although temperatures should moderate by Tuesday
and Memorial day, not confident enough to remove weather and POP
during each afternoon. With llvl moisture present along with
instability and northwest flow aloft, it will not take much
forcing to produce isolated to widely scattered showers and a few
thunderstorms, especially over southeast Wyoming. Kept POP around
20 percent along and west of I-25 through Tuesday. High
temperatures should moderate into the 60`s to low 70`s across the
forecast area by Tuesday afternoon.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1203 PM MDT Wed May 24 2017

VFR conditions through the taf period. West winds will gust to
25-35 kts through the early evening at the southeast WY sites.
Southerly winds will prevail through around 03Z across much of the
western Nebraska Panhandle.

&&

.FIRE WEATHER...
Issued at 310 AM MDT Wed May 24 2017

Warm, dry, and/or windy conditions are expected today w/ widespread
RH values under 25 percent. However, fire weather concerns are very
low given recent heavy precipitation. A cool/unsettled pattern into
Thu/Fri will continue to keep concerns minimal.

&&

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

$$

UPDATE...DEL
SHORT TERM...CLH
LONG TERM...TJT
AVIATION...ZF
FIRE WEATHER...CLH



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