Area Forecast Discussion


007 
FXUS63 KTOP 130846
AFDTOP
Area Forecast Discussion
National Weather Service Topeka KS
246 AM CST Wed Dec 13 2017
.SHORT TERM...(Today and tonight)
Issued at 246 AM CST Wed Dec 13 2017
Currently, the persistent ridge trough pattern still exists over 
the CONUS with general northwest flow aloft over the northern 
plains into the central plains regions. Feature of note impacting 
northeast and east central Kansas weather today is that of a 
prominent shortwave trough translating into the northern plains. 
Reflection of surface low feature is evident over west central 
Minnesota. A surface pre- frontal trough is extending through 
eastern Nebraska into north central KS vicinity. Meanwhile a cold 
front is sharpening ahead of the aforementioned shortwave and is 
evident through central Nebraska and extending back up into 
Minnesota. 
Forecast for today is this boundary to arrive into the forecast area 
by mid morning.  With a southwest breeze still over the region ahead 
of the actual cold front tonight, overnight lows should be on the 
higher side of guidance and expected to settle into the mid and 
possibly upper 30s over north central KS areas.  Fire weather 
concerns come into the picture as the morning wears on (see Fire 
Weather section below for details).  Winds increase as the cold 
front tracks through the area and mixing increases eventually to the 
900-850mb level.  As the westerly LLJ speed max loses it's nocturnal 
influences, wind fields show some sign of not being as strong as 
previously forecast.  This will allow for winds to probably not be 
as strong over the area as the afternoon wears on (also surface 
pressure gradient not quite as strong since the surface low is 
further east of the area).  Therefore have a couple hours of wind 
gusts approaching 35 mph, but more common winds should be around the 
20-25 mph range. Again, this makes sense as the track of the surface 
low being pushed along by the upper wave moves into the Ohio Valley 
region by late afternoon. Forcing for ascent will influence the 
area, but the better forcing with associated PV anomaly will remain 
focused to the northeast of the area and then translate east during 
the day.  With a general lack of moisture, do expect another dry 
frontal passage today with some brief cloud cover.  High temps 
tempered a bit by timing of the front and CAA influence by 
afternoon.  Therefore, most areas should top out in the mid to upper 
50s.  Overnight lows Wednesday fall back into the 20s with cloud 
cover increasing as the next system round the western ridge and 
begins to finally break down its hold over the western CONUS.
.LONG TERM...(Thursday through Tuesday)
Issued at 246 AM CST Wed Dec 13 2017
There continues to be a small chance for precip Thursday afternoon
and evening as energy within the northwest flow aloft move over
the region. However forcing for precip looks a little less
organized from the latest model runs and indications are for the 
shortwave to shear out into more of an upper trough axis. The 
vorticity advection also looks like it tries to dig further west 
than last night and models show the better saturation across 
north central KS rather than near the MO river. So the main
changes to the forecast have been to shift the small POPs west.
Forecast soundings show all but the very lower part of the
sounding to be below freezing. So once temps begin to cool in the
evening, there could be some light snow. All of the guidance shows
QPF less than a tenth of an inch and much of the guidance is only
a couple hundredths. So any accumulations should be fairly light.
The next chance for precip looks to be Saturday night and into
Sunday morning. Once again energy within the northwest flow aloft
is progged to dig mainly west of the forecast area. However this
kicks a cutoff low out of northern Mexico which lifts across the
southern plains Saturday night. There is a nice PV anomaly with
this wave that looks to move from northern TX into southern MO.
There also looks to be a nice slug of moisture lifting northeast
with the wave. While the better forcing looks to pass to the
southeast of the forecast area and models keep the surface low
closer to the gulf coast, there may be some precip try to move
into east central and possibly northeast KS by Sunday morning. The
wild card will be a cold front that is forecast to slide through
the forecast area as the wave lifts northeast. This could
potentially push the deeper moisture and better precip chances to
the south and east depending on timing. Models have gone back and
forth with the expanse of precip to the northwest. With this in
mind have not gotten to cute with POPs and have some chances for
precip across the entire area early Sunday morning with better 
chances being across eastern KS. Given the timing of this system 
and models bringing the cold front into the area, it is possible 
for some light snow accumulations. But confidence in the track of
the wave and how far northwest the moisture gets is not high 
enough to get very excited about snow just yet.
After Sunday, The upper trough axis eventually shifts east with a
lower amplitude northwest flow developing. With the absence of an
obvious shortwave, the dry pattern is forecast to redevelop for
the first part of next week. 
For temps, generally above normal readings should continue. Highs
Thursday may be the coolest of the week with clouds and potential
for light precip keeping temps in the lower 40s, or right around
normal. Otherwise westerly low level winds and warm air advection
should warm temps back into the 50s for Friday and especially
Saturday. GFS and ECMWF are hinting at 925MB temps of +10C by
Saturday which may support highs near 60. A brief cool down is
forecast for Sunday as the southern wave passes through the 
region. Otherwise mild temps should redevelop for Monday and 
Tuesday. 
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1136 PM CST Tue Dec 12 2017
Expect VFR conditions for the next 24 hours. A westerly low-level
jet will strengthen to 40 to 45 KTS between 1000 and 1500 feet 
after 6Z. Therefore the low-level wind shear will be in the 30 to 
40 KTS range during the early morning hours of Wednesday at the 
terminals. After 14Z, the surface winds will increase due boundary
layer mixing. West-northwest winds will increase to 15 to 20 KTS 
with gusts of 25 to 30 KTS during the late morning and through the
afternoon hours of Wednesday.
&&
.FIRE WEATHER...
Issued at 246 AM CST Wed Dec 13 2017
Fire weather concerns today revolve around increasing winds mid 
to late morning. Minimum RH values drop only to the mid 20s over 
very southern counties in east central KS and western counties 
near central KS with lower dewpoints in place over those regions 
with higher temps. Winds should be in the range of 20-25 mph today
with gusts up around 35 mph and perhaps stronger for short 
periods of time. With cured fuels in place, all this yields high 
fire danger generally north I-70 and Very High Fire Danger south 
of I-70. Currently, no headline is expected, but general awareness
of the passing cold front should be considered with winds veering
during the morning from southwesterly to northwesterly.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Drake
LONG TERM...Wolters
AVIATION...Gargan
FIRE WEATHER...Drake