Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
100 am EST Sat Jan 31 2015
high pressure will build into the area tonight through Saturday.
A developing low pressure system will move through the Ohio Valley
Sunday into Monday bringing widespread snow and rain to the
region. A much colder air mass will move in behind the low pressure
system for Monday.
Near term /until 6 am this morning/...
winds are light and variable as surface high pressure builds into
the region. Skies have become mainly clear after cumulus
dissipated with loss of daytime heating...while cirrus begins to
invade from the west ahead of developing low pressure. Lows
tonight will generally be in the teens...although single digits
will be possible across the north in areas that still have some
Short term /6 am this morning through Sunday night/...
focus in the short term period is on the developing low pressure system
forecast to move through the Ohio Valley Sunday into Sunday night.
The 06z and 12z NAM have trended considerably farther north with
the low track and as a result are now pulling quite a bit of more
warm air up ahead of it into our area. Meanwhile...both the 12z
GFS and 12z European model (ecmwf) are still farther south but both have been
nudging slightly northward with each run over the last couple of
days. The models tend to have a northwest shift with time in the
surface low track in these digging middle/upper level short wave
situations. As a result...think the NAM may very well be latching on
to something...but am hesitant to completely ignore the European model (ecmwf) and
GFS which have been more consistent. As a result...have taken more
of a blend of the NAM and GFS/European model (ecmwf) but would not be surprised if
the NAM ends up verifying better.
Ahead of the system...developing isentropic lift will allow for
snow to overspread the area Saturday evening...continuing into
Saturday night. With the more northward shift...it looks like the
best snow Saturday night will likely set up across northern
portions of our forecast area. As the low approaches and better frontogenesis
forcing develops...expect precipitation to increase in intensity Sunday
afternoon into Sunday evening. However...thermal fields off the NAM
are supporting a change over to rain up to at least I-70 through
the afternoon...while cooler European model (ecmwf)/GFS keeps the rain snow line
down closer to the Ohio River through much of the day. Taking more
of a blend of the NAM/GFS/ECMWF...will allow for just a little bit
of a mix through the I-70 corridor and keep it all snow across our
far northern areas. As a result...will go with 6-8 inches along
and north of the I-70 corridor with up to around 10 inches not out
of the question across our far northern counties. Moving
south...snow amounts/headline decisions become more problematic due
to the rain mixing in/changeover and the fact that our
watch/warning criteria drops off to 4 inches right about where the
rain/snow transition line is expected to set up. Since it is just
a watch and we are still a ways out...have opted to err on the
side of caution and include the northern tier of our lower
criteria counties in the watch...running from Franklin County
Indiana to Fairfield County Ohio. Confidence is not all that high
that we will actually reach warning criteria in those counties but
wanted to build in a little wiggle room in case the GFS/European model (ecmwf) end
up being closer to the final solution.
Long term /Monday through Friday/...
the winter storm will be coming to an end on Monday morning...with
some light additional snow accumulations possible in the Scioto
valley between 12z and 18z. On the back side of the strengthening
surface low...gusty north-northwest flow will lead to strong cold advection
through the Great Lakes and Northern Ohio valley. This will lead to
a few complications with the forecast. For one...temperatures will be
falling rapidly going into the early morning hours. With the
potential for some blowing snow...and refreezing on roads...this
could allow hazardous conditions to continue through beyond the end
of the snowfall. Also...the diurnal range for Monday will be quite
small...even with some breaks in the clouds expected to develop. Maximum
temperatures are unlikely to rise more than a few degrees from the morning
Cold and dry high pressure will move over the region by Tuesday
morning. Although some clouds may still persist...radiational
cooling conditions will be otherwise favorable...allowing for
temperatures in snow-covered areas to approach or even drop below
zero degrees. Combined with some wind (generally increasing slightly
by 12z)...wind chills appear likely to drop into advisory criteria
for the northern sections of the forecast area.
Forecast specifics become much more uncertain for Tuesday and
beyond. Quick west-northwest flow aloft will be set up across the northern tier
of the Continental U.S....with several weather disturbances expected to move
through. An initial shortwave will weaken as it moves into the Great
Lakes on Tuesday...with another cold front expected to move through
sometime between Wednesday night into Thursday. In advance of the
front...temperatures appear likely to be somewhat mild...and values
were raised in the forecast for this time period. However...behind
the front...another lengthy period of cold conditions is expected to
continue through the weekend. Precipitation with the cold front will
likely be mainly snow...but current model forecasts are fairly
subdued on accumulation potential.
Aviation /06z Saturday through Wednesday/...
VFR conditions will be found over the taf sites through most of
the period. At the tail end a nose of precipitation will affect
western sites after about 3 or 4z which will lower visibilities and ceilings
to MVFR range. At this time...rain may mix with snow at cvg/luk before the
warmer air on southerly winds push the mix north and mix out any
lower ceilings in the 6-12z time frame. Kday and Kiln stand a
better chance of seeing plain snow as a start to this winter
Kcmh/lck will likely not see any precipitation until after 6z.
Outlook...significant snow accumulations...IFR ceilings and
visibilities likely through Sunday night with MVFR conditions
possibly continuing into Monday.
Ohio...Winter Storm Watch from late tonight through Monday morning
In...Winter Storm Watch from late tonight through Monday morning