Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 161743

Area Forecast Discussion
National Weather Service Topeka KS
1143 AM CST Fri Feb 16 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 311 AM CST Fri Feb 16 2018

Scattered snow bands associated with an elevated region of
negative EPV/broad frontogenetical forcing in the DGZ have been on
the decline over the last hour on radar and are expected to
dissipate before sunrise. Strong winds that accompanied the
passage of the cold front yesterday evening will likewise decrease
this morning as the pressure gradient relaxes and a 1030 mb
Canadian high slides southward. This high passes through during
the afternoon and despite clearing skies, will keep highs in the
mid-30s to near 40. IR satellite shows a long fetch of high
cirrostratus to the SW of the CWA and with little change in the
upper level flow pattern, have increased sky cover today across
the southern CWA (in line with RAP/NAM soundings). Return flow
sets in behind the departing high tonight, but little in the way
of WAA will keep lows in the 20s. A fast moving, mid-level impulse
will work into the region late tonight, with an increase in cloud
cover being the most notable sensible weather impact. Some light
snow is possible prior to 12Z in the far SE CWA as suggested by
the NAM/EC while the GFS timing of the H850 theta-e advection band
is slightly slower and after 12Z.

.LONG TERM...(Saturday through Thursday)
Issued at 311 AM CST Fri Feb 16 2018

Models are in agreement that a low amplitude wave within the
broad cyclonic flow aloft will help to bring a weak front through
the area on Saturday. Ahead of the front some weak warm air and
moisture could advect into east central KS with the possibility
for some light rain and snow. The NAM is the more aggressive
model in advecting moisture north and as a result suggests there
could be some freezing drizzle across a good portion of northeast
and east central KS. Since the GFS is not as aggressive with the
moisture return, it doesn`t show much of a saturated layer for
drizzle. So I haven`t included a mention of freezing drizzle, but
this will need to be monitored by later shifts.

Another surface wave is likely to pass through the plains Sunday
night. The low level warm air advection pattern appears to be much
stronger ahead of this wave with a strong low level jet helping to
bring 50 degree dewpoints into the forecast area. The model
consensus shows this strong moisture advection to be capped by a
strong elevated mixed layer through Monday. However this set up
does look like a reasonable setup for elevated convection given
steep mid level lapse rates. The only question is whether an
elevated parcel will could be lifted above the EML to initiate
convection. For the most part isentropic surfaces show the lower
condensation pressure deficits below the EML. Bur there is a hint
of some localized lift collocated with a narrow axis of moisture
that could reside just above the EML. Have opted to maintain a
slight chance for thunderstorms Sunday night into Monday morning
because of this.

For Monday through Tuesday, a slow moving frontal boundary is
progged to remain near east central KS with southwesterly flow
aloft. Weak perturbations within the flow along the boundary could
spark precip and have continued with some chances for precip
across east central KS. The ECMWF has trended a little slower with
the frontal boundary. If this trend continues, some chances for
precip may linger into Tuesday night or Wednesday morning. For now
with the GFS and GEM pushing the front well southeast of the area,
have a dry forecast by Tuesday night expecting cold and dry air
moving in from the north.

Temps Saturday are expected to remain mild even though a weak
front moves through. Warm temps in the 60s are expected for Sunday
with the increasing low level warm air advection, and ahead of the
cold front on Monday. However that cold front should bring colder
temperatures to the forecast area by Tuesday and through the end
of the period.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1135 AM CST Fri Feb 16 2018

Expect VFR conditions through most of the night. Lower stratus
may approach the KFOE and KTOP terminals after 10Z SAT. I included
3500-4000 feet OVC ceilings and some scattered MVFR ceilings.
Deeper mixing will scatter out the stratus after 15Z.




LONG TERM...Wolters
AVIATION...Gargan is the U.S. government's official web portal to all federal, state and local government web resources and services.