Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 222327
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
527 PM CST Sun Feb 22 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Monday)
Issued at 315 PM CST SUN FEB 22 2015

Low level cold air advection continues today as 1047mb surface high
sinks south through the Upper Mississippi Valley. Zonal flow remains
aloft over the southern and eastern portions of the ConUS with upper
low cutting off over Central California. Continued drying of the
lower levels and weakening forcing allowing snowfall to end.

The strong surface high pushes on south into the Central Plains
tonight and Monday, dominating local conditions. North to northeast
winds should slowly subside tonight, but confidence in just how cold
surface temps get is not high. Model soundings showing boundary
remaining mixed through the night with periods of high cloud making
their way through. Am concerned that any longer-lived clearing could
quickly allow for a more decoupled scenario to unfold, but have seen
the more-mixed idea a few times this winter. Have raised lows a few
degrees, closer to NAM MOS values. Wind chills will have a somewhat
limiting situation in that colder temps should allow for lighter
winds and more mixing keeping temps up, with values for much of the
overnight into early Monday morning in the -5 to -10 range. Surface
high axis passes through Monday for light winds and decent
insolation with some westerly component developing. Have limited
highs to about a 20 degree rise, but again raised forecast values a
bit.

.LONG TERM...(Monday Night through Sunday)
Issued at 315 PM CST SUN FEB 22 2015

Monday night through Tuesday night should be dry with the upper
level jet remaining over the southern plains keeping the better
forcing and moisture south of the forecast area. We should see a
general warming trend through this period as westerly and
southwesterly low level flow develops. With some influences of the
arctic ridge possibly lingering into Monday night, have continued
with lows Tuesday morning in the teens. However think there could
be a good warm up for the daytime hours Tuesday as the models
indicate good insolation with a westerly downslope wind at the
surface. With model progs showing 925 MB temps warming to between
+1 and +5C, have raised max temps into the mid 40s for most areas
and this may still be a little conservative. Models don`t show a
great deal of cold air advection for Tuesday night with some highs
clouds beginning to increase. With this in mid, have Lows
Wednesday morning in the lower 20s.

For Wednesday and Wednesday night, there remains a chance for some
snowfall across the forecast area. All of the solutions pick up on
a subtle shortwave within the northwest flow during the day
Wednesday. This is seen in the MSLP field as a weak area of low
pressure moving through central KS and an increase in Q vector
convergence over northeast KS. Additionally there is forecast to
be increasing mid level frontogenesis Wednesday afternoon and
Wednesday evening as the next arctic airmass builds south. While
there is general agreement in the models of the overall pattern,
there remains some questions to answer before increasing POPs
significantly. First is how quickly will low level dry air be
overcome. The ECMWF is somewhat similar in timing of the forcing
but seems to be 3 to 6 hours slower in generating QPF, primarily
due to low level dry air. Second there is a chance that within the
northwest flow, the track of the wave could vary west to east. The
GEM has a more easterly track with the system placing much of the
QPF over MO. Given these uncertainties, have opted to keep POPs at
a chance. Did however speed up the timing that light snow could
develop as forcing for precip increases over the area through the
day Wednesday. Additionally removed the small POPs from Thursday
as all the solutions show the forcing to the south and east of the
area by 12Z. Overall there remains the potential for 1 to 3 inches
of snow with northeast KS in line for the higher amounts at this
time. Highs Wednesday should actually be above freezing as some
warm air looks to precede the surface low. Although forecast
soundings suggest that once precip begins, temps should wet bulb
down to or below freezing with snow the more likely type of
precip. Because of this have a non-diurnal temp trend for
Wednesday afternoon indicating falling temps.

Thursday and Friday should be cold and dry as the next arctic
ridge of high pressure moves through the central plains. Highs are
forecast to be in the teens and 20s while lows Friday morning
bottom out in the single digits.

Friday night through Sunday is turning into a mess as the GFS and
ECMWF are in reasonable agreement for an upper trough to develop
over the southwest. With the potential for pieces of energy
kicking out from the base of this trough, there looks to be a
chance for precip Friday night through Sunday. Initially temps
appear to be cold enough for snow to be the primary precip type
Friday night into Saturday. However there are indications of a
warm front lifting up into east central KS Saturday evening and
Sunday morning causing any precip to change form. The GFS is by
far the warmest solution, but even the ECMWF shows 925 MB temps
warming to +3 or +4C. Because of this have introduced a rain snow
mix over east central KS. This is still quite a ways out in time
and shifts in the surface low development out across the high
plains would have a significant impact of temps and precip type.
Nevertheless there appears to be chances for snow possibly mixing
with or changing to rain. We`ll have to stay tuned to see how
models handle this in later runs. Temps should moderate heading
into the weekend, but based on GFS bufr soundings and likely cloud
cover and possible precip did not get carried away with warming
things up and kept highs Sunday in the 30s to around 40.

&&

.AVIATION...(For the 00Z TAFs through 00Z Monday Evening)
Issued at 512 PM CST SUN FEB 22 2015

VFR conditions at all terminals are expected throughout the
period. Northeast winds will calm.  However, exact timing is lower
confidence, but should be generally around the 06z time frame. By
12z time frame, they should calm further. Outside of that, expect
stratus to be high and less coverage above 10kft.

&&

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

$$

SHORT TERM...65
LONG TERM...Wolters
AVIATION...Drake





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