Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 011735
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1135 AM CST Sun Mar 1 2015
...Update to aviation forecast discussion...
.SHORT TERM...(Today and Tonight)
Issued at 257 AM CST SUN MAR 1 2015
Expansive upper trough axis continues to rotate off the CA coast
while weaker embedded areas of vorticity were lifting north and
east towards Colorado and Kansas. A stronger shortwave trough was
observed shifting southeast towards the northern plains later this
morning. Lows were starting out in the teens and lower 20s with
scattered light snow or flurries across northeast Kansas.
Main highlight of the forecast is expected snowfall from sunrise
through noon today. As the upper trough dives southeast, mid level
forcing is enhanced within the embedded vorticity maxima tracking
east over the state. Timing of this feature and area of weak
frontogenesis will place the snow band near the Interstate 70
corridor based on latest runs of the RAP and NAM or just south near
the Intestate 35 corridor based on the 4-KM WRF and HRRR solutions.
Duration of light snow is quick as well with lift diminishing
eastward by mid afternoon today. Main changes for the forecast
package were to remove precip chances for far north central Kansas
as dry air aloft increases after sunrise. Also adjusted highest
chances for snowfall in the above mentioned areas where an
additional one half to one inch of snow is expected. Will maintain
the advisory ongoing until noon and have the following shift remove
counties as the snowfall exits.
With the snowfall exiting quicker and the possibility of higher
cloud bases, increased highs today a few degrees in the lower to
possibly middle 30s. Weak high pressure shifts southeast this
evening as skies become partly to mostly cloudy. Calm winds and snow
covered ground hold lows in the upper teens to lower 20s.
.LONG TERM...(Monday through Saturday)
Issued at 257 AM CST SUN MAR 1 2015
For Monday models prog the mid level shortwave ridge to be over
the area with low level moisture remaining to the south of the
forecast. So with no real forcing expected to affect the area,
have a dry forecast through the day. With some cloud cover and the
surface ridge possibly influencing eastern KS still, have highs
only reaching the mid and upper 30s.
Monday night and Tuesday appear to be the next opportunity for
precip as low level return flow advects moisture north while a
shortwave kicks out from the base of the mid level trough over the
southwest. However chances appear to remain limited. The model
consensus shows the stronger Q vector convergence and PV anomaly
passing just north of the forecast area while a dry slot moves
into eastern KS by Tuesday morning. With the deeper moisture over
far eastern KS, have kept the higher POPs across the east during
the early morning hours Tuesday as the shortwave passes by. Prior
to this there could be some drizzle develop and spread northeast
through the area in response to the stronger low level moisture
return. Depending on temps, there could be a brief period of light
freezing drizzle. However I expect this to be short lived mainly
in the evening as warm air advection should cause temps to rise
through the night. Therefore any accumulations should be very
minor. Another arctic ridge of high pressure is set to move
through the forecast area Tuesday with the GFS trending a little
faster with the frontal passage. However with the dry slot in
place as the front moves through and upper level forcing likely to
the northeast of the forecast area, the front may move through
mostly dry through the early afternoon. The forecast anticipates
falling temps through the afternoon as cold air moves in behind
the front. But for the most part think that any precip on Tuesday
is likely to be out ahead of the front and in the form of rain.
There are still weak indications of some convective instability
Tuesday morning. Because of this have kept a mention for thunder
across east central KS. Lows Monday night are forecast to occur
early in the evening while highs Tuesday are likely to be measured
late in the morning.
Tuesday night may be the last chance for precip through the rest
of the week. There remains some indication for some mid level
frontogenesis along with enough moisture for mid level saturation.
The NAM is most bullish with this idea developing several
hundredths of precip. While less impressive, the ECMWF also spits
out some very light precip. Because of this have continued with a
slight chance for snow Tuesday night. However would not anticipate
the snow amounting to very much if at all.
The upper level trough axis is progged to finally move east of the
forecast area Wednesday night. But with dry air moving in with the
arctic airmass on Tuesday, precip chances Wednesday and Wednesday
night look to be less than 20 percent due to to much dry air.
Wednesday is shaping up to be another cold day with lows in the
teens and highs in the 20s.
Thursday through Saturday continues to look dry with moderating
temps as models keep a dry northwest flow over the central plains.
By Friday, highs are expected to be in the 50s. This could be a
little conservative with the GFS and ECMWF showing 925 MB temps
warming to between +5 and +10C. For now stayed with the model
consensus and have highs in the lower 50s.
.AVIATION...(For the 18Z TAFs through 18Z Monday Afternoon)
Issued at 1134 AM CST SUN MAR 1 2015
For the 12z TAFs, scattered to broken MVFR cigs will persist through
the day as the storm system exits east of the area. As surface high
pressure moves over the area tonight into Monday, northwesterly winds will
veer toward the northeast and eventually to the southeast by the end
of the TAF period.
WINTER WEATHER ADVISORY until Noon CST today FOR KSZ058-059.