Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 240140
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
740 PM MDT Thu Mar 23 2017

.UPDATE...
Issued at 731 PM MDT Thu Mar 23 2017

Made a few tweaks to this evenings forecast as thunderstorms have
lingered along and east of the Laramie Range. The surface cold
front has pushed through the whole forecast area and now into
Colorado as winds have shifted into the north and northeast.
Temperatures have responded behind the front, but have not
observed any snowfall at this time along and west of I-25. Believe
this will quickly change over the next hour or two as temperatures
have dropped to around 35 degrees west of I-25. The office here in
Cheyenne is now at 42 degrees, which is roughly 18 degrees cooler
compared to an hour ago. Will closely monitor this change over to
snow through late this evening and may need to extend the Winter
Weather Advisories. As of right now, everything looks on track.

Another concern is strong winds across the high plains. Gusts up
to 50 MPH have already been reported along I-80 east of Laramie.
With some snowfall expected tonight, there is some concern of
blowing snow and very poor visibilities along the I-80 corridor
from the summit eastward to Sidney.

&&

.SHORT TERM...(This evening through Friday)
Issued at 318 PM MDT Thu Mar 23 2017

A very active 18 hours ahead for the region as a strong storm system
spins across the Rockies bringing snow to parts of the area along
with gusty northerly winds, and cooler temperatures. Afternoon
satellite pix depict this system spinning across Utah currently with
KCYS 88D returning showers along with a few wk thunderstorms along
the Pine Ridge in the N panhandle west back towards Rawlins. 20Z SPC
mesoanalysis does show a few pockets of 500-1000 j/kg pooling across
parts of the area, but agree with the latest few SPC outlooks that
point to just mainly general thunderstorms across the region. At the
surface...pressures have been steadily falling all day in along the
front range with a well defined dryline located between Pine Bluffs
and Kimball with 20z Td`s of 12F and 40F, respectively.

Cold front was knocking on the doorstep of the northern zones
this afternoon and will drop south across the CWA through 9 PM.
Recent HRRR output, suggest area of shower and embedded
thunderstorm activity will expand across the eastern plains
through the rest of the evening along and ahead of this cold
front. Snow-levels will fall this evening turning rain to snow,
first over the I-80 summit and eventually into adjacent higher
elevations (above 5000 feet) by around midnight. At the same time,
with the cyclone deepening to the south, north winds will
increase with gusts of 30-45 mph for a time across the eastern
plains. The combination of these strong winds and 3-7 inches of
new snow has prompted the issuance of a Winter Storm Warning
across the southern Laramie Range. Areas from Arlington to Laramie
and in the vicinity of Cheyenne will be well positioned for 2-3
inches of snow late tonight and for the Friday morning commute.
Again the combination of strong winds and these accumulations has
led to the issuance of a Winter Weather Advisory for these areas.

Some question as to just how far east along I-80 snow will be able
to fall especially given just how dynamic this system is, but for
now have kept accumulations Kimball to Sidney to an inch or less
and don`t suspect to see significant impacts there. Evening shifts
will need to watch for the potential of a 3-6 hours of high wind
potential for Kimball-Sidney from 09-15z. The system departs as
quickly as it moves through, allowing for drying conditions by mid
morning Friday and clearing skies through the afternoon. High
temperatures on Friday only to reach the 40s above 5500 feet, with
5 0s for lower elevations. Winds will gradually subside thru
Friday afternoon.

.LONG TERM...(Friday night through Thursday)
Issued at 318 PM MDT Thu Mar 23 2017

As the main upper low moves to our southeast, precipitation will
taper off around Sidney by 6 PM Friday with upper ridging keeping
a short dry pattern in place for Friday night. The weekend leads
off a rather active period of passing upper systems bringing
chances of snow in the higher elevations and mostly rain or a mix
below 6000 ft across the eastern zones. Given that the position
of the passing shortwaves Saturday into Sunday, then again Tuesday
into Wednesday, we don`t tap any deep cold air. Overall impacts
from winter weather this next week doesn`t look overly impressive
with any of these systems. The only thing to pay attention to
initially will be potential for localized higher amounts of new snow
to near 6 inches in the higher elevations of the Snowy Range this
weekend, but that is about it for anything that would approach
significant snowfall accumulations.

&&

.AVIATION...(For the 00Z TAFS through Friday afternoon)
Issued at 550 PM MDT Thu Mar 23 2017

Scattered showers with isolated thunderstorms will continue across
parts of SE Wyoming and western Nebraska early this evening. Cold
front currently along a line from around KAIA to KCYS across the
high plains, and then extending northwest, north of KLAR toward KRWL
west of I-25. Behind the cold front we will see a cold rain
switching to snow overnight in Wyoming. We expect lowering
ceilings/visbilities across the entire area, but more impactful down
to LIFR for Cheyenne and Laramie late tonight.


&&

.FIRE WEATHER...
Issued at 505 PM MDT Thu Mar 23 2017

Conditions are improving this evening as a cold front rapidly moves
southward across the high plains, ending the fire weather threat.
Fire weather concerns will be low for Friday with widespread rain or
snow expected late tonight and early Friday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 9 AM MDT Friday for WYZ110-115.

     Winter Storm Warning until 9 AM MDT Friday for WYZ116-117.

     Winter Weather Advisory from midnight tonight to 9 AM MDT Friday
     for WYZ118.

NE...None.
&&

$$

UPDATE...TJT
SHORT TERM...CAH
LONG TERM...JG
AVIATION...TJT
FIRE WEATHER...TJT



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