Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 280955
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
355 AM CST Fri Feb 28 2014
.SHORT TERM...(Today and Tonight)
Issued at 355 AM CST FRI FEB 28 2014
Latest water vapor satellite loop at 08Z shows a compact
shortwave trough over southeast Colorado into the Texas Panhandle.
Regional radar showing precipitation breaking out from southern
Kansas south into Oklahoma. 00Z TOP and area soundings show quite
a bit of dry air in place. Initial precipitation will go into
moistening the column and forecast soundings from the RUC and NAM
suggest that this should start to occur between 12Z and 15Z when
precipitation should start making it to the ground. Initially
cooling to the wet bulb would give sleet at first then
transitioning over to all rain after 15Z, so not expecting much
ice accumulation this morning. Models are indicating good warm
advection today ahead of the arctic front which was just moving
into western North Dakota and Montana at 09Z. Mixing from 875 mb
today and factoring cloud cover will go lower than MOS temps with
highs in the lower to middle 40s.
Tonight the cold front will move south across the CWA with
temperatures falling back into the teens north to the middle 20s
southeast of Interstate 35. Chances of light rain will continue
early this evening as additional lift is expected as additional
shortwave energy moves through and also some low level frontogenetic
forcing along the cold front. precipitation still looks to be all
rain before ending early this evening, could not rule out a mix
along the Kansas and Nebraska border though.
.LONG TERM...(Saturday through Thursday)
Issued at 355 AM CST FRI FEB 28 2014
Rapid pressure rises underway in eastern Montana this morning with
surface temps near -30 F in central Manitoba and Saskatchewan with
water vapor showing northerlies over it. To the west, rather potent
upper low making eastward progress toward California with one
stronger embedded wave nearing the coast at 08Z. Although modifying
with time, these features come together over the Central Plains this
weekend for a potential winter storm.
Overall setup hasn`t changed a lot, but model differences remain
rather large in smaller scale features, leaving confidence much
lower than that in the days preceding the heavy snow event of early
this month. Differences throughout the troposphere in temperature
and moisture profiles as well as upper energy moving through, the
location and duration of frontogenesis, and the sharpness and
intensity of the warm nose lead the list of potential pitfalls to
how this storm plays out. 0Z models range from the slow NAM to the
fast ECMWF with GEM and GFS in between. The NAM and GFS are more
robust with the aforementioned lead wave passing just north Saturday
evening and then slower with the larger scale wave Sunday, with the
GEM and ECMWF opposing these ideas.
Still looking like much of Saturday will be spent moistening the mid
levels, but by late morning low level isentropic lift may be enough
for freezing drizzle and flurries to be generated. Chances for
measurable amounts increase quickly late in the day, though the NAM
and GFS would suggest a break overnight behind the lead wave. In
either event, fast mid level flow will bring the potential for
longer lived frontogenetic bands under CSI or perhaps brief CI in
the snow growth zone. Upper lift then picks up for much of Sunday as
the main wave passes. Didn`t alter precipitation types much given
uncertainty in the details of the warm nose and how saturated it may
be for at least early in the event. This still keeps the heavier
snow in the northern to central portions of the area with moderate
ice accumulations from freezing rain in the south, and periods of
sleet for most locations. Still not looking like a major ice event
in the very cold low levels and 850 mb front staying well south.
Overall trends suggested a bit stronger wind speeds and colder
temps, giving some concern for blowing snow and hazardous wind chills
as well. Actual air temps should fall to around record levels for both
highs and lows into Monday.
Zonal flow takes hold for the remainder of the forecast resulting in
moderating temps. Some decent agreement with a longer wavelength
trough passing around Wednesday though moisture values likely quite
limited for only light precip opportunities.
.AVIATION...(For the 06Z TAFs through 06Z Friday Night)
Issued at 1137 PM CST THU FEB 27 2014
Look for VFR conds to become MVFR by afternoon as moisture streams north
ahead of the disturbance now moving into the TX Panhandle. There
could also be sct -shra but coverage remains in question at the
TAF sites. Next issue becomes when CIGS drop to below 2kft as
another cold front pushes south through the area after 00z Sat.
There could also be patchy drizzle or freezing drizzle after 00z
Sat but confidence is low.
WINTER STORM WATCH from Saturday evening through late Sunday
night FOR KSZ008>012-020>024-026-034>040-054>056-058-059.