Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 212153
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
253 PM MST Wed Feb 21 2018

.SHORT TERM...(This evening through Thursday)
Issued at 237 PM MST Wed Feb 21 2018

Complicated and potentially messy period of weather beginning this
evening. Currently large area of low level moisture moving in
from the south. This moves through the area tonight and slowly north
of the area on Thursday. Periodic pockets of mid and upper level
moisture moves across during this time. 12z soundings from DDC and
AMA show that saturated air mass with the potential for frozen or
freezing depending on how cold the near surface is. Tendency this
season so far has been to have a saturated low level air mass with
the ice appearing in the low levels.

Forecast soundings from the Nam and Gfs show the potential that
the upstream soundings have captured. Ran the builder and it gave
me more snow early on then trended toward the freezing
precipitation later in the night and overnight hours. This looks
reasonable. Best moisture and favorable theta-e combination appear
in the far eastern portion of the area, namely Norton and Graham
counties. A glaze, less than .05 of ice accumulation with up to an
inch of snow will occur in those counties which is the highest
anywhere in my forecast area. As a result of the above
collaboration have issued a Winter Weather Advisory for those
counties from mid evening tonight into mid afternoon on Thursday.

There is lower potential for freezing drizzle further west and did
not feel as confident about putting the advisory further east.
Evening and overnight shift will have to monitor this in case the
potential for freezing precipitation further west. Something also
the next couple shifts will have to watch will be the potential
for freezing fog. Did not feel totally confident about that, but
that is something that may develop in the overnight hours and
continue into tomorrow morning. This potentially could make the
situation even messier. No matter how this develops, conditions
should improve in the afternoon.

Kept close to the guidance for tonight and tomorrow due to the
cloud cover and the variable conditions.

.LONG TERM...(Thursday night through Wednesday)
Issued at 215 PM MST Wed Feb 21 2018

Main focus for this period is the precipitation Friday night and
Saturday morning.  During this timeframe a quick moving upper level
short wave trough moves across the Tri-State Area.  At the surface a
warm front will north to the I-70 corridor through the night.  As
the short wave trough approaches precipitation will form, but
consist of two different types of precipitation.  East/south of the
warm front the precipitation will be freezing drizzle.  West/north
of the front the precipitation will be snow.  As the front moves
east during the morning the precipitation will change from freezing
drizzle to snow.  Currently the best chance for freezing drizzle
will be east of Highway 25 by 6 AM CT before the front moves
through.

Have somewhat low confidence regarding the precipitation type for
the first few hours after midnight Friday night.  Models differ as
to whether the saturated layer will be deep enough to support
freezing drizzle or snow.  Have more confidence the precipitation
will start out as snow then change to all freezing drizzle around 3
AM CT east of Highway 25.  Once the precipitation changes to
freezing drizzle by 6 AM CT, it should remain that way until the
front moves through when it will change to snow.

Current snowfall amounts are in the one to two inch range. However
if the window for freezing drizzle is shorter then what is currently
forecast, the snowfall amounts will be higher.  Regarding amounts,
theta-e lapse rates in the saturated layer are convective along the
front and behind it.  This should lead to higher snowfall amounts.
However the quick movement of the snow band may counteract this. The
negative theta-e lapse rates are also in the freezing drizzle, which
may cause the ice accumulations to be slightly higher than currently
forecast.  However  the quick movement of the freezing drizzle may
negate the increased precipitation rates caused by the convective
lapse rates.  Bottom line, high confidence for precipitation, low
confidence for precipitation type for the first few hours after
midnight and when the precipitation will change to all freezing
drizzle, and moderate confidence for ice/snow accumulations.

The other lesser focus for interest is the fog potential Thursday
night and Friday.  Currently looks like fog will develop near the
warm front over Northwest Kansas after midnight Thursday night.  The
fog will expand in coverage through the night and into Friday
morning then lift in the afternoon.  Due to temperatures being below
freezing, this fog will create a thin glaze of ice on elevated
surfaces, mainly where visibilities are around a half mile or less.

Saturday afternoon mixing behind the front will allow the stronger
winds to reach the ground.  Current forecast may be underdoing the
winds during the early afternoon a few MPH.

After Saturday another upper level short wave trough moves through
Sunday night, but the lift with this trough is south of the forecast
area.  Mid next week a stronger upper level short wave trough
approaches from the southwest.  Currently the lift with this trough
will be south of the forecast area, but the track of this trough is
favorable for generating a bit more precipitation, if it shifts
its track slightly, than the trough Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1042 AM MST Wed Feb 21 2018

For Kgld, vfr conditions and southeast winds near 10 knots are
expected through 03z. At 03z, the southeast winds will continue
for the rest of the period. However, mvfr conditions should start
at that time and continue through the rest of the period. Freezing
fog and a mixture of freezing drizzle and snow are expected
near/at the site from near 11z through the end of the period.

For Kmck, vfr conditions and southeast winds are expected through
06z. From 06z, east southeast to southeast winds near 7 knots are
expected through the end of the period. As with Kgld, mvfr
conditions are expected to develop at this time and continue
through 15z on Thursday. At that time ifr conditions will move
into the site. Freezing fog and a mixture of freezing drizzle and
snow are expected near/at the site from 08z through the end of the
period.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Winter Weather Advisory from 9 PM this evening to 3 PM CST
     Thursday for KSZ004-016.

CO...NONE.
NE...NONE.
&&

$$

SHORT TERM...BULLER
LONG TERM...JTL
AVIATION...BULLER



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