Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 160524
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1124 PM CST Mon Dec 15 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Tuesday)
Issued at 314 PM CST MON DEC 15 2014

Stacked system was centered in northern Missouri early this
afternoon with west to northwest winds bringing cold air in behind
and surface temps 5 to 15F below those of the pre- dawn hours.
Area of precipitation in deformation band on immediate west to
north flank of the system has weakened and exited, but water vapor
imagery supports RAP analysis of a minor wave rotating south into
south central Nebraska with narrow band of cloud top cooling and
light snow reported at CNK.

Recent HRRR and RAP output shows a steady decline in precip this
evening as the system enter the Ohio Valley overnight and this seems
very reasonable with heights rising and steady drying aloft. The
latter brings at least minor difficulty in precip type, but in this
band expect RH deep enough into the ice crystal formation layer for
rain and snow to dominate. Any accumulations should be quite light
and localized. Low cloud looks to be rather persistent tonight into
early Tuesday however with temps in this layer approaching -10C for
flurry possibilities but moisture depth shouldn`t support more than
brief bouts at best. Continued drying should bring some sunshine to
much of Tuesday, but high cloud entering the Rockies just upstream
of the upper ridge axis should increase toward sunset. Went a bit
above MOS averages on low temps tonight with the cloud in place.

.LONG TERM...(Tuesday Night through Monday)
Issued at 314 PM CST MON DEC 15 2014

Shortwave ridging and a dry airmass is expected to keep the
weather quiet for Tuesday night through Wednesday morning. With
some weak cold air advection as high pressure builds in, lows
Wednesday morning are expected to be around 20. Moisture appears
to begin returning north Wednesday. However models show the
shallow cold air holding in place Wednesday, keeping an easterly
surface winds and not mixing the boundary layer very deeply.
Therefore highs are forecast to remain in the middle 30s because
of this as well as increasing cloud cover.

Wednesday night and Thursday continue to look a little tricky with
regard to precip type. Models continue to show a perturbation
moving across the area Wednesday evening and a second one Thursday
morning. The better Q vector convergence and vorticity advection
may pass over southeast KS and the NAM and GFS forecast soundings
suggest there may not be enough saturation in the mid levels for
precip to be all snow. The one solution that continues to produce
a fair amount of QPF (around 2 tenths) Wednesday night is the
ECMWF, but it is difficult to know if there is as much dry air at
mid levels in its solution due to less vertical resolution. In all
it appears there is the potential for a weak progressive wave with
modest vertical motion to affect parts of the area with light
precipitation and have maintained POPs in the 30 to 40 percent
range. Best chances for measurable precip would be across east
central KS where the forcing is likely to be a little stronger.
Given the uncertainty provided by the NAM and GFS forecast
soundings, have introduced some freezing drizzle to the forecast
thinking mid levels may not be saturated and there would be no ice
in the cloud. Right now I would expect a light precip event
possibly affecting motorists late Wednesday night and Thursday
morning.

For Thursday night through Friday night, models seem to be
converging on a southern solution with the upper level jet
remaining over the southern U.S. and a developing surface low
tracking along the gulf coast. Even the 12Z GFS has trended
further south. Because of this, have trended POPS down a little
more for the period. Considered removing them all together but the
GFS still tries to bring energy down from the northwest and kicks
out some light QPF. Therefore held onto some slight chances for
precip.

Temps do not appear to be trending warmer until maybe Monday as
models hang onto the shallow cold airmass through much of the
weekend. By Monday there are signs that some low level return flow
could develop helping to bring some warm air back north. As for
the weather, the models continue to try and figure out this
pattern with split flow and energy coming off the Pacific. With
no obvious forcing progged to affect the forecast area through
Monday, have continued with a dry forecast for the weekend and
into next week.

&&

.AVIATION...(For the 06Z TAFs through 06Z Tuesday Night)
Issued at 1120 PM CST MON DEC 15 2014

MVFR conditions expected to continue through the overnight and
into the late morning hours. As expected the timing of the cloud
departure is in question. Have extended the VFR timing a few hours
later.

&&

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

$$

SHORT TERM...65
LONG TERM...Wolters
AVIATION...Sanders






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