Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 242055

Area Forecast Discussion
National Weather Service Cheyenne WY
255 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.

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

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...(Tuesday night through Monday)
Issued at 218 PM MDT Mon Apr 24 2017

Models point to an unsettled weather pattern featuring a persistent
frontal boundary, enhanced by several waves of low pressure, fed by
a rich supply of moisture.

Area will be in a dry southerly flow between two low pressure
systems on Wednesday, with no precip expected. That will change
starting on Thursday when a cold front is forecast to swing through
from the west, bringing the likelihood for showers and
thunderstorms. The frontal boundary will wash out briefly under high
pressure Thursday night, before redeveloping as a warm front and
lifting across the region Friday to Sunday. This scenario suggests a
prolonged period for showers and thunderstorms to develop, lasting
through the weekend. A strong cold front is expected to push through
Monday, accompanied by more rounds of showers and thunderstorms.

Temperatures will be above normal for most of the period. Highs in
the 80s Wednesday will be boosted by warm advection. Readings are
forecast to slide back into the 70s Thursday and Friday due to
precip and modest cold advection associated with the weakening cold
front. Mainly 80s are expected Saturday and Sunday with the area in
the warm sector. A retreat toward the near normal upper 60s will be
possible Monday behind the stronger cold front. &&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday morning)
Issued at 1126 AM MDT Mon Apr 24 2017

VFR initially this afternoon for the terminals with increasing
mid/high clouds.  Expect lowering cigs this evening from west to
east with some MVFR/IFR cigs and vsbys with rain and snow spreading
across the area.  Improving conditions Tuesday morning behind a cold


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.


WY...Winter Weather Advisory from 6 PM this evening to 6 PM MDT
     Tuesday for WYZ112-114.



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