Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 250558
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1158 PM MDT Mon Apr 24 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 218 PM MDT Mon Apr 24 2017

The main concern with this forecast package is the timing of the
cold front moving through Niobrara and Converse counties tomorrow.

Tonight:
Latest radar loop was showing scattered showers continuing to
develop over portions of southeast Wyoming. This activity appears
to be associated with the left exit region of the upper level jet
which is enhancing the diffluence over the area. This activity
will continue to spread east this evening and may become a little
more widespread as cyclogenesis takes place across northeast
Wyoming. This will bring widespread snow to the mountains tonight
with some heavy accumulation especially during the evening due to
good mid level instability in place. Otherwise, gusty winds are
expected to develop along our wind prone areas of Arlington and
Bordeaux.

Tuesday:
Models are projecting the surface low to develop just north of
forecast area late tonight. The main question will be how far
south will this surface low will sink tomorrow before shearing
out. The models are showing this surface low hanging to the north
of the forecast through midday. This is a bit different than the
previous runs which had the surface low shift south a little
sooner. The ensemble members are showing some higher standard
deviations a little further south which could mean this may shift
south again. We will let the evening examine this further. If this
surface low does go further south a little faster, then we may be
looking at the potential for some accumulating snowfall in the
morning in Niobrara and Converse counties. Another concern is the
potential for frontogenesis behind the front which may cause high
snowfall rates for a couple of hours. If this pans out in the
morning the accumulation may be greater. However, if this boundary
and associated surface low moves through the afternoon, it may be
difficult to see the higher snowfall accumulations due to better
insolation and warmer road temperatures. The rain and snow mix
will shift south during the course of the day, but the
precipitation should begin wane during the afternoon as the
surface low begins to shear out.

Tuesday night-Wednesday:
Cooler temperatures are expected during this timeframe, but the
bulk of the precipitation will shift south into the southern
Rockies. This will be in response to the upper level trof moving
east into the plains and weak upper level ridging building over
the southwest.

.LONG TERM...(Wednesday night through Monday)
Issued at 218 PM MDT Mon Apr 24 2017

Models in pretty decent agreement in showing a rather cool and
moist pattern across the region for most of the period. Broad
upper cyclonic flow will be present across the western and central
part of the CONUS in the Thursday through Saturday time period
with a cool surface high pressure area settling south out of
Canada Friday and holding into Sunday. Inverted surface trough
will also exist over the high plains Thursday with several
shortwaves moving mainly south of the CWA. Put all together
looking like an extended period of rather wet conditions for the
CWA with the main difficulties being rain and snow areas.
Mountains snows a good bet with rain and snow showers across
lower elevations. Some drying should arrive Sunday and Monday
under northwesterly upper flow.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1158 PM MDT Mon Apr 24 2017

A band of rain with a few thunderstorms is currently situated
from the northern Nebraksa Panhandle southeast into eastern
Laramie County. Moderate to heavy rain and small hail is occurring
with the southern extent of this line, along with winds 40 to 50
mph. Expect this activity to impact KSNY after 07Z. MVFR cigs may
linger through the early morning hours before lifting. The next
round of rain and snow showers will occur late Tuesday morning
through the evening as a cold front drops south across the area.
MVFR to IFR conditions expected with this activity.

&&

.FIRE WEATHER...
Issued at 218 PM MDT Mon Apr 24 2017

No real major concerns during the next few days due to numerous
shortwaves bringing precipitation and the majority of the fuels
being moist.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 PM MDT Tuesday for WYZ112-114.

NE...None.
&&

$$

SHORT TERM...REC
LONG TERM...RE
AVIATION...RJM
FIRE WEATHER...REC



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