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000
FXUS63 KTOP 031743
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1143 AM CST Tue Mar 3 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 336 AM CST TUE MAR 3 2015

Latest water vapor imagery showing one shortwave lifting east
northeast across Co with a positive tilt northern stream trough in
its wake extending from MT into UT. The initial shortwave will
lift into the northern plains and will push a dry slot into the
CWA effectively ending light rain/drizzle chances across the far
east by mid morning. At the same time a cold front will also
steadily progress southeast across the county warning area through
the day...entering the northwest corner of the CWA by late morning
and exiting the southeast counties by mid to late afternoon. This
will produce morning highs in the lower 40s in the north central
with midday highs across the remainder of the CWA except the far
southeast corner. With a slightly slower arrival have edged highs
to around 50 in the southeast half of the CWA.

Tonight...the trailing portion of the shearing positive tilt
shortwave trough may push a band of light snow or flurries into the
northwest half of the CWA with frontogenesis and lift slowly across
the southern portions of the CWA...although saturation looks better
further south. Will therefore go with a low end chance pop late
tonight for light snow in the far north central and far southern
counties and only a slight chance for light snow elsewhere as drier
air in the low levels will be advecting in from the northeast. This
could play a significant role in determining the areal extent of any
light snow across the CWA through sunrise. With strong cold air
advection...will continue with lows in the teens all areas.

.LONG TERM...(Wednesday through Monday)
Issued at 336 AM CST TUE MAR 3 2015

The main question for Wednesday is how fast will dry air advect
into the region as the surface high builds south. The
NAM/GFS/ECMWF all have similar solution in their synoptic patterns
and with mid level frontogenesis moving through eastern KS.
However the GFS shows much dryer low level air moving in by
Wednesday morning while the NAM doesn`t. Unfortunately there could
be quite a difference in sensible weather between the dry GFS and
moist NAM. Both models indicate there will at least be some
conditional symmetric instability (CSI) with the NAM showing up
right or convective instability Wednesday morning. The models also
suggest snow to water ratios should be above normal given the cold
temperatures. So it is not out of the question given the
instability and high ratios that a quick couple of inches of snow
could accumulate across east central KS. The NAM is a wet outlier
compared to the other deterministic models and the WPC does not
favor its solutions at all. However with the ECMWF also bringing
some QPF into east central KS and there being similarities between
the NAM and GFS, am hesitant to completely discount it. With the
surface front expected to move through the area today, one would
think there is plenty of time for the low level dry air to advect
in. So have increased POPs across east central KS to account for
the model progs of frontogenesis and instability, but confidence
is low because of the potential for dry low level air to win out.
Highs Wednesday are expected to be in the mid to around 30 due to
limited insolation and cold air advection through the day. Left
Wednesday evening dry thinking the dry air will eventually win
out.

The main upper trough should finally move east of the forecast area
Wednesday night, and by Friday models are in agreement that
northwest flow aloft redevelops with southwesterly low level winds
bringing warmer air into eastern KS. Therefore have maintained a
dry forecast for Thursday through Monday with temps trending
warmer and above normal through the weekend. Have highs in the
upper 50s by Monday, but this may be to conservative of a warming
trend since the ECMWF is warmer than the GFS at 925 MB by about
3C. The ECMWF and GFS show a couple low amplitude shortwaves
moving through the central plains for the weekend. Moisture is
expected to remain to limited to add a chance for precip at this
time.

&&

.AVIATION...(For the 18Z TAFs through 18Z Wednesday Afternoon)
Issued at 1142 AM CST TUE MAR 3 2015

For the 18z TAFs, MVFR cigs will persist through early/mid afternoon
before scattering out to VFR cigs this evening and overnight. With
the passage of the cold front, winds will continue to veer to the
northwest and eventually north northeast by Wednesday morning.
Short-range models have been hinting more at the potential for some
light snow to clip the TAF sites Wednesday morning so went ahead and
added a mention for a couple of hours. Any snow accumulations should
be less than one-half inch. Wind gusts should diminish by Wednesday
morning with a return to VFR cigs by late morning.

&&

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

$$

SHORT TERM...63
LONG TERM...Wolters
AVIATION...Hennecke