Area Forecast Discussion
Issued by NWS Topeka, KS

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838
FXUS63 KTOP 052110
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
310 PM CST FRI FEB 5 2016

.SHORT TERM...(This Evening through Saturday)
Issued at 310 PM CST FRI FEB 5 2016

20Z water vapor imagery shows an upper trough over the Great Plains
with a short wave over the TX panhandle and another one moving
through SD. At the surface a trough of low pressure stretched from
the TX Big Bend through the Dakotas with area observations showing
generally a dry airmass across the region.

For tonight the concern is whether there might be some ground fog or
stratus develop overnight. The NAM is the most aggressive solution
in saturating the low levels overnight, but also has a history of
being to aggressive with the low level humidity. Winds are expected
to shift to the west this evening as the surface trough axis moves
east. Therefore there shouldn`t be much in the way of moisture
advection unless there is higher dewpoints coming off the snow pack.
Dewpoint temps are slightly higher over the snow. The GFS and RAP
forecast soundings show any moisture to remain fairly shallow with
some wind just off the surface which could entrain dry air into the
boundary layer. Because of this I don`t have a great deal of
confidence in fog developing overnight and will not include it in
the forecast just yet. I would expect any fog to be immediately
downstream of the snow cover and the next shifts can monitor
conditions. With some weak low level warm air advection developing
overnight, lows should not be quite as cold and expect temps to
bottom out in the low to middle 20s.

For Saturday, the upper trough axis should be to the east with the
next trough moving into the northern Plains. This should lead to
shortwave ridging over the area. With relatively dry air still in
place, we should see more sunshine with only some high clouds.
Models also show warm air advection continuing through the day. With
this in mind, highs are forecast to trend warmer into the upper 40s
where there is no snow. Up around Republic CO, temps may struggle to
get into the lower 40s.

.LONG TERM...(Saturday Night through Friday)
Issued at 310 PM CST FRI FEB 5 2016

At this point, the most concerning weather is in the first few
periods of the long range forecast, but impacts still appear to be
low to most customers. Cold front still expected late Saturday night
into early Sunday morning as the upper wave approaching the coast of
British Columbia today digs southeast into the Middle Mississippi
Valley. Strong mixing develops through the day as cold air advection
persists, making for a challenging wind, temperature, and humidity
forecast as 850mb winds increase to the 35 to 50kt range. Have
trended a bit more extreme on all of these values, keeping fire
danger concerns elevated but Extreme values seem unlikely. Highs
could be warmer than Saturday in the deep mixing. Cold air advection
slowly backs off into Monday but a tightening pressure gradient
brings more wind potential. This day looking to be the more likely
day for Advisory speeds, with the boundary layer mixing into the
snow growth temperature zone with some stratus here to lead to some
snow shower potential. Have just mentioned flurries at this point
with anything more than trace amounts in this scenario unlikely,
with much cooler highs in the 30s.

Upper flow remains northwest but becomes a bit more zonal into the
mid-week periods for moderating temps and little opportunity for
precip. The next more significant front looks to come in around
Friday for perhaps some cooler temps but haven`t gotten too out of
hand at this range.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1113 AM CST FRI FEB 5 2016

VFR conditions are expected to persist due to dry low levels in
the atmosphere. Main concern is once the mid clouds clear to the
east overnight, forecast soundings try to saturate the low levels
due to radiational cooling. The NAM is most aggressive and has a
history of overdoing the boundary layer saturation. Since there
isn`t expected to be any moisture advection overnight and there
hasn`t been fog or stratus the last couple mornings, think the NAM
is an outlier and will keep a VFR forecast at this time.

&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Wolters



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