Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 121841
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1241 PM CST Tue Dec 12 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 237 AM CST Tue Dec 12 2017

Current WV imagery shows semi-permanent Pacific high pressure ridge
still in control over the Western 1/3 of the CONUS with broad
northwest flow spilling into the central US.  Meanwhile a deep
trough remains reinforced into the Ohio Valley and the east coast
region.  Over northeastern KS the pressure gradient continues to
relax with clear skies in place leading to a diurnal inversion
trying to take hold and thus allowing winds to decrease hour-by-
hour.  A plume of low level moisture is noted to be in place over
central into eastern portions of Nebraska.  This will be a player as
morning dawns and should allow for some cloud cover to increase over
portions of northeastern KS at least through part of the morning
time frame.  Over night lows tonight fall into the mid 20s with
radiational cooling partly offset by some light wind still helping
to mix areas a bit.

Today, dry conditions should be the story outside of early morning
cloud cover.  Heights begin to rise through the day into the evening
as the upper ridge from the west maintains its grip over the west
with the transition zone essentially over northeastern KS.
Therefore, a bit of a temperature gradient will exist over the area
with temps climbing into the low 50s from north central KS into
the mid to upper 40s over far eastern KS as a westerly to slightly
southwesterly return develops and H85 temps increase to about 5C
by the late afternoon. Surface ridge departs the area by late
afternoon. Prefrontal surface trough ahead of the next system
doesn`t arrive until the overnight period. As a result, still
expecting a slight breeze from the southwest which should hold
overnight low temps in the low to mid 30s.

.LONG TERM...(Wednesday through Monday)
Issued at 237 AM CST Tue Dec 12 2017

Several shortwaves are progged to move through the central plains
over the next week. However precip chances remain limited due to
a general lack of moisture. The first shortwave is expected to
pass overhead Wednesday. And the consensus among the models is for
there to be to much dry air for any measurable precip. Another
shortwave is expected to impact the area on Thursday. This time
there looks to be enough moisture for the column to become
saturated. Although the forcing with this wave could be better
and models don`t have much instability to speak of that could
help precip rates. There are some solutions that indicate the
forecast area gets mainly a glancing blow from this wave. So while
there is better moisture on Thursday, forcing could be better.
QPF progs are for a few hundredths of an inch during the afternoon
or early evening before the forcing passes to the east. There
could be a few snowflakes as temps cool during the evening, but it
appears unlikely there could be any significant accumulations to
create much of an impact. A third shortwave is expected to move
through the central plains over the weekend. However the GFS and
ECMWF show the bulk of the energy with this wave digging to the
southwest of the forecast area while moisture once again appears
to be limited. So except for some small POPs on Thursday, the
forecast calls for dry conditions to persist.

Temps will see some variability as these waves pass through the
area. Highs are forecast to be above normal with readings in the
50s on Wednesday, Saturday and again on Monday as low level warm
air advection occurs ahead of the shortwaves. Modified Pacific
airmasses with the shortwaves are expected to cool temps closer to
normal for the other days with highs in the 40s to around 50.
Even these temps are expected to be slightly above normal for this
time of year with no indication of an arctic airmass moving into
the plains through the next seven days.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1241 PM CST Tue Dec 12 2017

VFR conditions are expected through the period. A line of some
4kft clouds is moving west to east across the area and should
begin to scatter out as it reaches FOE/TOP. Winds gradually shift
from the southwest by 00Z, remaining there overnight. A surface
boundary moves through early morning, shifting winds once again
from the northwest through the end of the period. LLWS looks
likely at MHK after this passage near 12Z through 15Z. It looks
like more marginal LLWS conditions at TOP/FOE and have opted to
keep it out of this TAF issuance.

&&

.FIRE WEATHER...
Issued at 124 AM CST Tue Dec 12 2017

Elevated fire danger is possible Wednesday afternoon. Northwest
winds are forecast to strengthen again by the late morning with
gusts over 30 MPH likely. One question is how much low level
moisture there will be, and at this time forecast min RH values
remain around 30 percent.

&&

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

$$

SHORT TERM...Drake
LONG TERM...Wolters
AVIATION...Heller
FIRE WEATHER...Wolters



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