Area Forecast Discussion
Issued by NWS Topeka, KS

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453
FXUS63 KTOP 101740
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1140 AM CST Sun Dec 10 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 252 AM CST Sun Dec 10 2017

There is not a lot of change to the synoptic pattern per the 08Z
water vapor imagery. Northwest flow remained over the central plains
between ridging to the west and troughing over the eastern U.S. At
the surface, a trough was moving across the upper Midwest with the
axis of the surface trough about to move through northeast KS.

For today and tonight, the forecast calls for dry weather to persist
mainly due to a dry airmass in place with no real moisture advection
in sight. Models actually show a compact shortwave approaching
northeast KS after midnight tonight with reasonable forcing. But the
models are not generating any QPF near the area due to limited
moisture. So only an increase in high clouds is anticipated ahead of
this wave. Highs today are expected to be warmer with most areas
seeing highs around 60 given good insolation and some warm air
advection from the west. Out west across Dickinson and Ottawa
counties, highs should warm into the mid 60s. Lows tonight will
again be dependent on whether winds can stay up or if they drop off.
Looks like winds could become light in the evening before another
surface trough passes through after midnight. So temps are forecast
to fall into the 20s along the KS river valley while locations up on
hills are likely to see lows hold in the lower 30s.

.LONG TERM...(Monday through Saturday)
Issued at 252 AM CST Sun Dec 10 2017

On Monday a strong shortwave trough dives over the upper Midwest,
which is rather close to the amplified upper ridge across the
western US. Due to this proximity the pressure gradient will be
maximized over the plains. The low level jet is forecasted to reach
upwards of 50 kt as the wave passes to the north. Model soundings
show that most locations mix up to at least 850 mb therefore
allowing these high winds to transfer to the surface. This deep
mixing will be supported by a cold frontal passage that causes the
low levels to become unidirectional and abnormally warm temperatures
prior to the cold air advection. By the afternoon wind speeds are
expected to be around 20 to 30 mph with gusts up to 40 mph. Based on
this pattern the top 15 CIPS analogs show there is a greater than 50
percent chance for surface gusts over 40 kt across the entire area.
In the absence of return flow dew points remain low and highs are
forecasted to be in the 50s so minimum RH should range from 27 to 42
percent. Given these RH values and wind speeds the fire danger will
be very high and possibly extreme.

Tuesday highs will be about 10 degrees cooler behind the front. A
few more shortwaves track over the western ridge and dive over the
central US. As a result Wednesday warms into the 50s and Thursday we
are back into the 40s. By the weekend a strong shortwave crashes
into the western ridge, which should cause a temporary break
down. This less amplified pattern opens the door to more transient
shortwaves in the westerly flow. Although given that the eastern
trough has been fairly deep as of late the moisture recovery will
be limited.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1136 AM CST Sun Dec 10 2017

Expect VFR conditions for the next 24 hours. West-northwest winds
will increase to 30 KTS 1500 feet above the surface through the
night, and will cause moderate low-level windshear of 20 to 30 KTS
from the surface through 1500 feet. West-northwest surface winds
will increase to 15 to 20 KTS with gusts of 25 to 30 KTS after
15Z MON.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 4 PM CST this afternoon for KSZ008-009-
020>022-034>038-054.

&&

$$

SHORT TERM...Wolters
LONG TERM...Sanders
AVIATION...Gargan



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