Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 191730
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1130 AM CST Wed Nov 19 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 341 AM CST WED NOV 19 2014

Cold front continues to move southeast across the county warning
with with the main push of colder air well to the north of the
area...but should gradually filter southward into mainly the
northern portions of the CWA today where highs should only recover
back into the middle 30s from morning lows...especially near the
Nebraska border where some residual snow cover remains. Further
south across the CWA the uncertainty increases on high
temperatures as the snow free area along I 70 corridor will be
milder and warm better to start the day before cooler air tries to
advect into the area in the afternoon. Will therefore maintain an
area of lower 40s just south of the I 70 corridor with cooler
highs in the upper 30s again with snow cover across the southern
portions of Coffey and Anderson counties. However...offsetting
factors for the southern CWA with the snow cover will be weaker
cold air advection and less potential for clouds through the day.
Lighter winds and drier air tonight will allow better radiative
cooling and colder lows from the middle teens north to around 20
south. There is some potential for stratocu development within
weak warm air advection later in the night which could limit
cooling slightly...although confidence remains low on this
scenario at this time.

.LONG TERM...(Thursday through Tuesday)
Issued at 341 AM CST WED NOV 19 2014

There remains some questions with the forecast for Thursday
through Sunday. The main question is the strength of the low
level moisture return and whether some freezing drizzle will
develop by Friday morning. The models appear to have backed off
on the idea of freezing drizzle as they now show a surface ridge
nosing into northeast KS through the morning Friday with the warm
front set up to the south. This would allow a dry easterly or
northeasterly low level wind to persist. However this does not
make much sense with the synoptic pattern becoming more
progressive with a westerly or northwesterly flow at mid levels.
The only thing I can come up with as the reason for the models
surface pattern is that they want to hold onto the cold high
pressure because of snow cover, which is already shrinking
markedly over the forecast area. Since I expect much if not all of
the snow to be gone by Friday, think MSLP will be more likely to
fall in response to the flow aloft which should help southerly low
level flow advect moisture back in. For this reason, I have
maintained a slight chance for freezing drizzle. However it still
does not look like a forgone conclusion. While models saturate the
low levels late Thursday night and Friday morning, forecast
soundings show very little vertical motion within the saturated
stable layer which is necessary for drizzle to develop. Isentropic
surfaces show the potential for some weak upglide which may be
enough for the development of drizzle. This is definitely
something to watch over the coming days as the impact from
freezing drizzle could be significant. Models also wanted to lower
highs Friday. The forecast adjusted slightly down, but I`ve used
a lot of the previous forecast anticipating the models are to
cool.

There will be precip chances for Friday through Monday as a series
of waves affect the Great Plains. The first is progged to shear
out as it crosses the central plains on Friday. However moisture
with this system appears to be shallow with not a great deal of
forcing for vertical motion. Because of this have left POPs
generally in the 20 to 30 percent range for Friday and Friday
night. Think the better chances for precip will be Saturday night
into Sunday morning as a surface low lifts north through MO.
Models have been consistent in digging a more amplified shortwave
into TX on Saturday and lifting it to the east of the forecast
area through the weekend. On this track, the better forcing and
deeper moisture are likely to remain mainly to the east. But there
may be enough deformation or mid level frontogenesis for some
precip across far eastern KS. With this system lifting northeast
for Sunday, have trended POPs lower thinking dry air from the
northwest will move in with no obvious waves to force vertical
motion.

For early next week, there is good agreement in a closed low
developing over the upper Midwest. The ECMWF has a shortwave
rotating around the back side of the closed upper low and
clipping northeast KS on Monday generating some light QPF. Have
continued with a slight chance for rain and snow on Monday.
However the ECMWF has trended warmer on the back side of the
system with the upper jet coming more from the Pacific and keeping
the arctic air up north. So am not that excited just yet for
accumulating snowfall.

Still think there should be relatively mild temps for at least the
first half of the weekend with southerly winds advecting warm air
and moisture north. A winds shift to the northwest on Sunday
argues for a cooling trend, but there does not seem to be a really
cold airmass behind the front. With this in mind, have highs 50s
Saturday and Sunday and then cooing a little to to 40s for Monday
and Tuesday.

&&

.AVIATION...(For the 18Z TAFs through 18Z Thursday Afternoon)
Issued at 1124 AM CST WED NOV 19 2014

VFR conditions expected through the taf period. Only concern will
be the possibility of a scattered to broken cloud deck above 3 kft
for a brief period this evening.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...63
LONG TERM...Wolters
AVIATION...Sanders





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