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Area forecast discussion
National Weather Service Cheyenne Wyoming
611 am MDT Fri Apr 28 2017

Short term...(today through Saturday night)
issued at 325 am MDT Fri Apr 28 2017

In general, the forecast remains on track as a potent late Spring
storm will affect southeast Wyoming and west NE through tonight. There are a few
concerns, namely that convection over NE and Kansas last night may
have choked off some moisture to the northern warning areas. Thus
the precip has been slower to develop than earlier thought. Latest
satellite and radar trends to indicate moisture is starting to
surge back to the north and west and Alliance recently reported 1
mi visibility in snow. This trend should continue through the
early morning hours and all guidance continues to indicate a
period of rather heavy precip rates for Converse, Niobrara, and
Sioux counties this morning into the afternoon. Based on this,
left the warnings in place for now but day shift will have to
monitor this area in case the precip gets going a little too late
for warning criteria snowfall.

Other area of concern was the south Laramie range and the greater
Cheyenne area. Should be a pretty robust frontal passage early
this afternoon with temperatures hitting a mid morning high and
then cooling as precip develops. Additionally, steep mid level
lapse rates and cool air aloft, combined with low level
frontogenesis and upslope flow will provide ample support for the
potential for heavy banded snowfall this afternoon and evening. It
might not snow for a long time, but think it will come down pretty
hard when it does start snowing. Road temperatures near the I-80
Summit are already below freezing, and with falling temperatures
through the day, snow should have no problem sticking to the Road.
Elected to go with a Winter Storm Warning for the south Laramie
range and extend the advisory into the Cheyenne area due to
expected precip rates and the potential for travel impacts.

Snow should taper off late tonight and early Saturday. Saturday
will be quite chilly with temps struggling through the 30s for southeast
Wyoming and into the low 40s over NE. Breezy NE winds and lingering
cloud cover will make it a raw day.

Long term...(sunday through Thursday night)
issued at 325 am MDT Fri Apr 28 2017

The deep upper low will steadily track from the Southern Plains into
the Midwest Sunday and Sunday night, and heights over our area will
slowly but steadily rise as it does so. Will see only slightly
warmer temps on Sunday though as we'll still be in cool northwest
flow. The mountains could see a few light snow showers in the
afternoon within in a fetch of increasing midlevel moisture,
otherwise conditions will be mostly dry through the day. A clipper
system will be quick on the heels of the upper low in northwest
flow, moving over northern Wyoming through Monday. The associated
upper level jet core of roughly 85 kts will move over our forecast
area in the day, with a sfc cold front moving across the region as
well. Do think this is relatively good pattern to see a few rain and
high elevations showers occur through the day, although chances
would be higher if the shortwave trough and cold air aloft extended
into southern Wyoming and Nebraska. The next system in northwest
flow on Tuesday looks to track more over our forecast area, so
expect a broader coverage of rain/snow showers and even isolated
thunderstorms through the day. Wednesday will finally begin a trend
back to warmer and dry conditions as a high amplitude upper ridge
builds over the western Continental U.S.. should see temps back into the 60s by
Thursday under partly cloudy skies. Winds through the period will be
breezy, but not strong.

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 611 am MDT Fri Apr 28 2017

Widespread IFR conditions were observed overnight at many
locations, and these low conditions continue now at 12z. The
exception has been from klar-kcys-kibm which have remained VFR,
but expect conditions to deteriorate at these spots through the
day as the cold front dives south through the morning. Should see
snow begin for these southern locations between 15 and 18z. Snow
is expected to occur in heavy bursts at times through the
afternoon, and winds will be east-northeast behind the front and
gusting 20 to 25 kts. As the front races southward this evening,
snow should diminish from north to south overnight. Likely to see
MVFR to IFR cigs persist though in moist northerly upslope flow.

&&

Fire weather...
issued at 325 am MDT Fri Apr 28 2017

Cloud cover and ample precipitation today and tonight should
preclude any fire weather concerns through Sunday as fuels should
be quite damp. Early next week, seasonably cool temperatures and
scattered showers will persist and elevated or critical fire
conditions not expected.

&&

Cys watches/warnings/advisories...
Wyoming...Winter Storm Warning until 6 PM MDT this evening for wyz101-102.

Winter Weather Advisory until midnight MDT tonight for
wyz106>110-113-115-117-118.

Winter Storm Warning until midnight MDT tonight for wyz103>105-
112-114-116.

NE...Winter Storm Warning until 6 PM MDT this evening for nez095.

Winter Weather Advisory until 6 PM MDT this evening for nez002-
003-096.

&&

$$

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