Area Forecast Discussion
Issued by NWS Topeka, KS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KTOP 261747
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1147 AM CST Thu Feb 26 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today through Friday)
Issued at 227 AM CST THU FEB 26 2015

Broad upper trough this morning across most of the central and
eastern CONUS while a series of embedded waves impact eastern and
central portions of the U.S. Here in northeast Kansas, much of the
scattered flurries has cleared to the east. Skies remain mostly
cloudy with north winds continuing to gust near 30 mph. Wind chill
readings this morning may easily fall between 3 and 11 degrees below
zero.

For today and tonight, 1040 mb sfc ridge slowly slides southeast
across the western high plains, calming winds this evening. For the
afternoon, pressure gradient gradually wanes with the strongest
winds occurring during the morning and early afternoon. Cloud cover
dissipates by the afternoon as highs struggle to the upper teens and
low 20s. Current models still on track for this evening with the
ridge center over far northeast KS to northern MO by 12Z Friday.
Most of the CWA fall to the single digits for lows. Wind chill
readings for the morning commute range from 5 to 10 degrees below
zero.

Flow veers to the southeast Friday as a shortwave trough dives
southward over the western high plains overnight, pivoting eastward
over Nebraska during the day. Dry airmass precludes any
precip, however increasing mid level moisture results in mostly
cloudy skies during the afternoon. Lack of warm advection and ample
sunshine translate to highs once again in the lower 20s.

.LONG TERM...(Saturday through Wednesday)
Issued at 227 AM CST THU FEB 26 2015

Saturday through Saturday Evening:
Several inches of snow are expected during this time frame with
very high confidence most of the area will have 3-6 inches by 9
PM with a small chance of slightly higher amounts. There remains
outstanding model-to-model and run-to-run agreement regarding
this period of the forecast, and this is with good reason as
several ingredients will come together. First, steering winds are
very favorable to direct an upper short wave almost straight over
the forecast area. Second, deep persistent isentropic lift ahead
of, and during passage of the trough will provide a consistent
lift and saturation mechanism in tandem with the forcing of the
trough itself. Third, a lead short wave on Friday night should go
a long way toward saturating much of the dry air in place early
on, allowing the previously mentioned ingredients to devote much
of their energy to snow. Fourth, temperature profiles support snow
ratios on the order of 13:1 to 17:1 through this period with the
bulk of the snow probably falling on the higher end of that
spectrum. There will also be periods of weak frontogenesis and
even some weak instability or CSI to help enhance the snowfall at
times.

Saturday night through Sunday:
This period remains very difficult and has a substantial boom-or-
bust potential. The forecast continues to hinge on the strength and
track of a strong short wave trough diving south out of Canada
into the Northern Plains, and sending a cold front into the local
area. The GFS is just slightly weaker with this northern trough
and does not take it on such a meridional trajectory as some other
models, which causes the front to come in a bit weaker. While the
GFS is different in this regard, it is not as different from other
models as it`s much more robust QPF would make it seem. That is
because all available model guidance develops an east-to-west band
of mid level frontogenesis on Sunday and it persists into Sunday
night. Most all guidance locates this band in eastern KS, and
generally within 100 miles of I-70. Most all guidance suggests
that the lift associated with the frontogenesis will be sufficient
to produce precipitation. Where they differ is in the strength and
persistence of the frontogenesis and its interaction with drier
post-frontal air advecting in from the north. In some ways, would
maybe prefer to lean toward the robust GFS solution as its model
resolution should be able to resolve a greater magnitude of
frontogenesis than some other models, and while the other guidance
is still strong with the northern trough...they have trended
weaker with an earlier eastward turn than previous runs. However,
while maintaining the spirit of this band of precip developing,
did not have high enough confidence in the GFS solution of such
high precipitation to take the forecast to such an extreme amount
of precip at this time. One other note is that a weaker frontal
passage would promote chances for a mix of snow/sleet/freezing
rain/rain south of I-70 on Sunday...although again the GFS is
pretty much the only model suggesting this. Have kept a mention of
a mix in the forecast as it was already there but believe snow
will probably be the main precip type.

All told for this period, foresee a lull immediately in the wake
of the short wave trough passage on Saturday night, but this
should fill back in with a band of snow across the area. There is
plenty of uncertainty regarding the location and intensity of this
snow band so have included additional snow amounts in the forecast
but have kept them toward the conservative side of model guidance.
A weaker snow band would end earlier on Sunday while a stronger
band could persist into the evening. See a good chance for an
additional 1-3 inches of snow during this period with some small
potential for quite a bit more than that. With all of this in
mind, a winter storm watch was strongly considered but held off
for now as the initial wave of snow is primarily forecast to
remain just below the criteria of 6" in 12 hours, and there is too
much uncertainty regarding Sunday precip to have confidence in
meeting the 8" in 24 hour criteria. Hopefully future model runs
can provide increased confidence in the details of the storm
system. Regardless of official products, have high confidence that
this will be the most impressive snowfall of this winter season.

Monday through Wednesday:
By Monday into Monday night, models continue to agree on bringing
a neutral to negatively tilted short wave across the Central
Plains. The details of this system are very much in question but
it initially appears to surge a warm nose of air just off the
surface above sub-freezing surface temperatures. This could lead
to a period of sleet or freezing rain at onset of precip Monday
night. The good news is that warm advection beyond that time is
primed to bring temperatures above freezing during the period of
heaviest precipitation early Tuesday. This is all subject to
change, but appears to be the going thought at this time. The
interesting thing about this is that it could result in a fair
amount of rain falling on top of several inches of snowpack with
frozen ground underneath. This would result in quite a bit of
runoff and could see rises in creeks, streams, and rivers if it
plays out this way.

The main trough axis remains to the west even after this short
wave passage, and warrants a continued mention of small precip
chances through the end of the forecast period on Wednesday.

&&

.AVIATION...(For the 18Z TAFs through 18Z Friday Afternoon)
Issued at 1143 AM CST THU FEB 26 2015

Expect VFR conditions the next 24 hours. Northerly surface winds
of 12 to 15 KTS with gusts of 18 to 24 KTS will gradually diminish
late this afternoon and early this evening to 6 to 9 KTS. High and
mid level clouds will increase late Tonight with ceilings greater
than 120 KFT.

&&

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

$$

SHORT TERM...Bowen
LONG TERM...Barjenbruch
AVIATION...Gargan





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.