Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 192358

Area Forecast Discussion
National Weather Service Cheyenne WY
558 PM MDT Thu Apr 19 2018

Issued at 232 PM MDT Thu Apr 19 2018

Winter headlines issued for southeast Wyoming Friday and


.SHORT TERM...(This evening through Saturday night)
Issued at 245 PM MDT Thu Apr 19 2018

Forecast challenges deal with critical fire weather concerns today
around the Saratoga area, followed by accumulating snow Friday
into Saturday.

Currently...Surface low centered over central Utah this afternoon.
High clouds ahead of the system starting to move into northwest
Colorado and southwest Carbon County. Was getting Red Flag
criteria at Skyline that started spreading into the Saratoga area.
Saratoga starting hitting with 27 mph winds and 10 percent
humidity. Then the clouds moved in and the winds eased off. There
is a large break behind this first band of clouds and we could
start mixing out there again, so will keep the Red Flag Warning
going for FWZ 306. Later shifts can cancel if needed early.

Models coming in a little colder for Friday with GFS dropping
700mb temperatures to -5C by Friday evening. NAM still the colder
of all guidance with -7 to -8C temperatures, but other guidance
closing in on the NAM. So, this will increase snow amounts across
southern Wyoming. Getting 10 inches in the Sierra MAdre and 14-15
inches in the Snowy Range. Decided to issue an Advisory for the
Sierra Madre and a warning for the Snowies. Summit is going to see
4-5 inches of snow, so will have an advisory for them as well.

Latest guidance showing system slowing with precip not ending now
until Saturday afternoon. Later shifts need to watch the southern
Panhandle. If the NAM solution comes true, we will need something
out there as well.

.LONG TERM...(Sunday through Thursday)
Issued at 245 PM MDT Thu Apr 19 2018

Latter part of the weekend will see a warming trend as high
pressure builds east across the region. A fast moving shortwave
will carve into the upper part of the ridge Monday bringing a
cold front south across eastern Wyoming and western Nebraska, and
our next chance at precipitation. The system late Monday into
Tuesday does not look to be a significant precipitation producer
as the system is fairly progressive moving through.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 535 PM MDT Thu Apr 19 2018

The main concern with this TAF issuance is the timing of the
low cloud cover and associated shower activity.

Latest water vapor loop was showing upper level low spinning over
southern Nevada. This feature will continue to creep east-
northeast during the next 24hrs. As this low approaches, upper
level diffluence will be on the increase along with energy from
the upper level jet. This main impacts will occur near KRWL TAF
site overnight with the potential rain/snow mix mainly after 10z.
However, this should not last too long after the trof axis shifts
east and allows for northerly flow and some cold air advection to
move in. The other concern will be in the panhandle TAF sites
where strong isentropic lift/moisture transport (295-305k) kicks
in towards daybreak. The models have been advertising this during
the past day or two with a fairly distinct band of rain/snow
showers. Being on the warm sector side of this upper low, I would
expect it to be mainly rain. However, we will need to watch
profiles as time gets closer. The rest of the TAF sites will
mostly be in the warm sector through much of the day. The main
question will be when the low (mvfr) ceilings develop. We brought
these lower ceilings mainly after 16z, but some higher elevations
may actually see some sun tomorrow.


Issued at 245 PM MDT Thu Apr 19 2018

Looking like winds may be coming down in FWZ 306 this afternoon as
clouds move over the Saratoga area. Is a break behind this band of
clouds over extreme northwest Colorado, so will keep the Red Flag
Warning going for FWZ 306 through the afternoon. After today, fire
weather concerns should be on the decrease as a low pressure
system moves across Colorado, bringing widespread rain and
mountain snow. This precipitation should continue through
Saturday afternoon before ending from northwest to southeast.
ANother low pressure system for Monday should bring more rain and
mountain snow as a cold front moves through the area Monday night.


WY...Winter Storm Warning from 6 AM Friday to 9 AM MDT Saturday for

     Red Flag Warning until 8 PM MDT this evening for WYZ306.

     Winter Weather Advisory from 6 AM Friday to 9 AM MDT Saturday
     for WYZ112.

     Winter Weather Advisory from noon Friday to noon MDT Saturday
     for WYZ116.



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