Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Topeka Kansas
1129 PM CST Fri Feb 27 2015
..update to aviation forecast discussion...
Short term...(this evening through Saturday night)
issued at 356 PM CST Friday Feb 27 2015
An upper level trough along the Washington coast line will dig
south-southeast into central California by late Saturday afternoon. The
southern branch of the jet stream will begin back to the southwest
across the Southern Plains late tonight and Saturday.
After 12z Saturday, a deep layer of isentropic lift from 280k
through 300k will spread northeast across eastern Kansas. The lift will
coincide with ascent ahead of a weak 500 mb trough embedded in the
southern stream of the mid level jet-stream. The combined ascent
will cause light to at times moderate snow to develop during the mid
morning hours and continue into the early evening hours across much
of the County Warning Area. The strongest lift will occur across the southern
counties of the cwa, where as much as 3 to 4 inches of snow will
fall during the day on Saturday. The north central counties may only
see 1 to 2 inches of snow during the morning hours and into the
early afternoon hours. Forecast soundings from all numerical models
show that the precipitation will be in the form of snow as the
entire temperature profile in the vertical remains below 0 degrees c.
Later Saturday evening the stronger isentropic lift will shift
northeast of the County Warning Area and the dendritic growth zone south of I-70 may
unsaturate enough to cause the light snow to end for several hours.
There may continue to be enough weak isentropic lift within the
lowest levels of the atmosphere for some patchy freezing drizzle. If
patchy freezing drizzle develops only a slight glaze will result on
surfaces. The 12z and 18z runs of the NAM model show the best chance
for the potential for some patchy light freezing drizzle. The GFS
and European model (ecmwf) show enough lift to keep very light snow through the late
Early Sunday morning, an upper level trough currently in central
Canada will dig southeast into the Central Plains by 6z sun and
begin to phase with the southern stream mid and upper level jet. The
GFS shows strong frontogenetical forcing developing ahead of the
digging 500 mb trough along with increasing instability (mostly csi with
some ci) from 700-500mb. This may cause another band of moderate to
heavy snow across much of east central and northeast Kansas late
Saturday night and through the morning hours of Sunday. If the GFS
solution were to verify, then much of the County Warning Area would see an
additional 4 to 6 inches of snow. At this we are leaning more
towards the NAM and European model (ecmwf) solutions which are not as amplified with
the lift across eastern Kansas Sunday morning. Both the NAM and European model (ecmwf)
develop a band of light to moderate snow across east central and
northeast Kansas. Thus another 1 to 3 inches of snow may fall along the
The combined snow accumulations on Saturday and then again Sunday
morning will cause most areas to receive a total snowfall of 4 to 6
inches. North central Kansas may only see 2 to 4 inches.
Therefore a Winter Weather Advisory has been issued for the entire
County Warning Area from 800 am Saturday through 12 noon Sunday.
It will continue to be cold with lows tonight in the lower to middle
teens. Highs on Saturday will only reach the mid to upper 20s. Lows
Saturday night will only drop back into the lower to mid 20s.
Long term...(sunday through friday)
issued at 356 PM CST Friday Feb 27 2015
An active weather pattern will persist through the middle of next
week as several systems are expected to impact the region.
By Sunday morning, models show the mid-level trough axis extending
from Canada into the northern plains with a warm front stretching
from southwest Kansas into east central Kansas. There are some
discrepancies with regards to the strength of this warm front and the
amount of frontogenetical forcing that will be present Sunday
morning to enhance precipitation totals. At this time, the GFS
continues to be the most aggressive with this forcing across east
central Kansas, resulting in higher precipitation estimates.
Confidence is low with how much forcing will be available, but in
general have the best chances for precipitation focused along and
south of I-70. Models seem to be trending faster with the advection
of drier air by late Sunday morning/early afternoon as they show
surface high pressure quickly surging into the area, resulting in
precipitation ending from northwest to southeast. With the cloud
cover in place, have trended a bit on the cooler side for
temperatures on Sunday with highs in the low/mid 30s. When comparing
model soundings, most keep the temperature profiles below freezing
for the area, keeping precipitation in the form of snow. However a
few soundings show the potential for enough of a warm nose to
develop across east central Kansas for sleet to briefly mix in with
snow, so have this mention of a mix focused along and south of I-35.
At this time, 0.5 to 1.5 inches of snow accumulation will be
possible Sunday morning, but these amounts will be very dependent on
the location and strength of the forcing.
Surface high pressure will quickly track over the region Sunday night
through Monday with models showing a few weak embedded shortwaves
possibly skimming portions of the forecast area through the day.
Due to the low confidence in these initial weak waves, have only
slight chance pops in for Monday. Better chances for precipitation
look to move in Monday night through Tuesday as the next low
pressure system moves into the area from the west and as the
mid-level trough deepens across the northern U.S. Models show an
associated warm front extending into north central Kansas by Tuesday
morning with a cold front quickly tracking eastward over the area
during the late morning and afternoon hours. With winds increasing
out of the southwest Monday night, temperatures should rise
overnight into Tuesday with most locations along and south of I-70
expected to reach into the 50s for high temperatures. There is some
uncertainty with the timing of the cold front and how quickly the
cold air will surge into the region behind the front. Expect that
there will be a decent temperature gradient present from northwest
to southeast across the area, but it's difficult to fine-tune the location
at this time. Northern portions of the forecast area should see
falling temperatures Tuesday afternoon behind the front with low
temperatures plunging into the teens. Due to the warmer temperatures
initially with this system, expect much of the precipitation to be in the
form of rain initially, with some freezing rain possible across far
northern Kansas Monday night. As temperatures fall Tuesday
afternoon and evening, expect rain to transition over to snow from
northwest to southeast. There is some uncertainty with how quickly
the precipitation will end Tuesday night into Wednesday morning.
Once this system exits the area, we can finally expect a stretch of
dry weather through Friday. Wednesday temperatures will be cold as
surface high pressure moves over the area, with highs only in the
20s. As this high shifts east of the area and winds move around to
the southwest, expect a moderating trend with highs in the 30s/40s
Thursday and into the 40s/50s for Friday.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1128 PM CST Friday Feb 27 2015
Only minor adjustment to last taf issuance. Still bring in
prevailing snow with lowering cigs by the noon hour. May be able
to taper off late in the forecast period but too far out for
another group at this time.
Winter Weather Advisory from 7 am Saturday to noon CST Sunday