Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 061913

Area Forecast Discussion
National Weather Service Goodland KS
1213 PM MST Tue Dec 6 2016

.SHORT TERM...(Today through Wednesday morning)
Issued at 338 AM MST Tue Dec 6 2016

Latest upper air analysis has a closed low digging south over the
Northern Plains within a long wave trough over the western half of
the CONUS.  Further west a short wave trough was moving on shore
over the Pacific Northwest.  These two troughs will be responsible
for bringing snow to the Tri-State Area tonight and tomorrow.

Main focus will be snowfall amounts and wind chills for the forecast.

Today will be dry and much cooler than yesterday as dry zonal flow
will setup over the Tri-State Area.  Winds will be light as a
surface highs moves through.

Tonight through Wednesday morning snow will move in from the west.
Two bands of frontogenesis will develop during the mid evening, one
near the Highway 36 corridor and another over Kit Carson and
Cheyenne Counties in Colorado.  The band of frontogenesis over the
north will move very little during the evening while it strengthens.
Overnight this band will slide east-southeast.  This movement will
cause the band to train over the northern half of the forecast area.
As the band shifts eastward it will weaken as the left exit and
right entrance regions of the couple 500mb jet streak shift
southeast of the Tri-State Area.  The band of frontogenesis over the
southwest part of the area peaks by midnight then weakens as it
moves southeast.

Am expecting the highest snowfall amounts to occur during the late
evening through the first half of the overnight period when the
large scale lift and frontogenesis are strongest.  Most of the snow
during the night will occur under the northern band where the
environment will be saturated the deepest.  Very little snow will be
expected under the southern band due to a much more shallow
saturated layer to work with.

During the morning the lift will shift southeast ahead of the
approaching 500mb trough axis.  While the frontogenesis will be
weaker, it will be deeper.  The majority of the snow for Wednesday
will occur before mid morning.  After mid morning the frontogenesis
will exit the Tri-State Area.  There will be some lingering snow in
the afternoon, but am not expecting much if any accumulation.

Regarding confidence for snowfall amounts, have fairly high
confidence snowfall amounts around 3 inches will occur over the
northern half of the Tri-State Area.  Have low confidence of
snowfall reports of six inches or greater.  Confidence decreases
regarding the snowfall amounts being 3-4 inches or 2-3 inches.
Looking at SREF ensemble the members snowfall amounts are well
spread for Goodland, Imperial, McCook and Hill City, with no clear
grouping discernible.  SREF members for Akron group in the 3-4 inch
range.  This spread of snowfall amounts from zero up to eight or ten
inches lowers confidence for a specific range of snowfall to
forecast.  In addition the model blend qpf and snowfall has had a
continued downward trend for the last few nights.  Am concerned this
downward trend will continue today causing snowfall amounts to be
more in the 2-3 inch range.  There has also been some shifting in
the placement of the frontogenesis band over the last couple of
nights which lowers confidence regarding where the band of snow will
develop.  CIPS analysis continues to show snowfall amounts more in
the 2-3 inch range.  With all this in mind decided to not issue an
advisory since confidence was not quite high enough that 3-4 inches
of snow would occur over the Tri-State Area.

Considering impacts with this snow event, am expecting the overall
impact to be minor.  The highest snowfall rates will occur during
the late evening, into the overnight hours.  This snow will be very
fluffy since the precipitable water values are around 25% of normal
for this time of year.  Winds will gust 20 to 25 mph for the
southwest edge of the higher snowfall amounts, with lighter winds
expected where the majority of the higher snowfall amounts will
occur. Overall expect the blowing snow to have a low impact. Roads
will become snowpacked tonight, but travel impacts will be more of
an inconvenience. Wind chills will fall to the single digits above
and below zero late tonight into early Wednesday morning.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 1213 PM MST Tue Dec 6 2016

During the extended period the big focus will be the very cold
temperatures that will impact the region Wednesday night into
Thursday morning. Due to the arctic air still impacting the region,
temperatures are expected to drop close to zero, if not just below.
Winds/wind gusts are forecasted to be 5 to 15 mph for a few hours
but otherwise below 10 mph. Despite this, wind chill temperatures
could reach 10 to 20 below zero during the overnight hours into the
early morning hours on Thursday. This could potentially be worthy of
a wind chill advisory.

The remainder of the period will be primarily dry. There is a small
potential for precipitation Saturday, but models are differing at the
moment so decided to remove any chances. For the most part the upper
level flow will be marginal with the trough moving east of the
region Thursday into Friday. Zonal flow will begin to move over the
region during the day on Friday with the development of a shortwave
trough in the Pacific Northwest. That trough is showing to move over
the region Saturday (hence the possible PoP chances). Sunday and
Monday will continue to be dry, with Tuesday showing slight chances
for rain/snow across the far northern portions of the region.

Temperatures will be in the low 20s Thursday but will begin to
increase Friday into the 30s and 40s. Saturday will be in the 40s
and low 50s. Sunday will see a decrease into the 30s with the passage
of a cold front. Monday and Tuesday will increase back up into the


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1038 AM MST Tue Dec 6 2016

VFR expected at both KGLD and KMCK through this afternoon and
early evening. Tonight...upper system will approach with lowering
ceilings and snow developing by midnight at KGLD and overnight at
KMCK. Expecting IFR at KGLD through Wednesday morning with
reduced visibility in snow and blowing snow...with MVFR/borderline
IFR at KMCK due to lighter snow and a little less wind. I would
not be surprised to see KMCK go down to IFR however at some point
Wednesday morning as the snow makes its way north.




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