Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
346 PM EST Tuesday Feb 9 2016
a large upper trough will slowly move east of the Ohio Valley over
the next few days. This will keep a chance of snow showers through
Wednesday...and below normal temperatures (with drier conditions)
through the rest of the week.
Near term /until 6 am Wednesday morning/...
Winter Weather Advisory headlines have been extended slightly into
Wednesday...primarily due to the prolonged and continued chance of
snow showers over the next 24 hours. Chances for snow on Wednesday
will be discussed in the short term section below.
Large-scale troughing continues to envelop the entire eastern half
of the country...with the axis of the trough still in place over
the Great Lakes and Ohio Valley. Originally a closed low...the
trough is gradually weakening as it moves to the east. Water vapor
imagery shows the complexities of the system...with an obvious
large-scale circulation across hundreds of miles...but several
individual gyres embedded within the broader flow.
At the surface...a closed low is currently located north of London
Ontario. This low has several troughs rotating around it...with
one trough entering the forecast area from the northwest as of
this writing. With a noted wind shift...and some enhanced
convergence...snow showers have developed across the iln forecast
area this afternoon. Additional snow shower development is
expected as this feature moves through the region...with the
potential for around a half inch of snowfall. Forcing becomes
weaker going through the rest of the evening and overnight...but
model soundings suggest that the boundary layer will remain well
mixed...with moisture extending a little bit into the dendritic
growth zone from the bottom of the inversion. Thus...some light
snow showers or flurries will remain likely through the night.
Temperatures will continue to fall in the cold advection
tonight...and temperatures will likely reach the middle to upper
teens across the forecast area. For the area where snow was
heaviest this morning (hamilton County to Hocking
county)...temperatures were dropped a few degrees below the
otherwise-expected forecast numbers for the rest of the County Warning Area.
Short term /6 am Wednesday morning through Thursday night/...
the primary upper trough axis will be moving away from the region
early Wednesday...but chances for snow will increase again on
Wednesday morning. A combination of forcing from a shortwave and
surface trough will pivot eastward through the region between 09z
and 18z. With colder temperatures than experienced today
(tuesday)...especially aloft in the 900mb-750mb layer...the
potential for weak convective instability through the dendritic
growth zone will be increased. The combination of forcing and
steel lapse rates will be greatest over the northeastern quadrant
of the forecast area (central ohio) during the 15z-18z time
frame...where some heavy snow showers may be possible.
It is always difficult to draw a uniform snow total forecast grid in
a snow shower situation...given the inherent geographic
uncertainties caused by the eventual developmental locations of
the heaviest showers. That being said...accumulations of around an
inch will not be a surprise at all...with the greatest potential
for up to two inches in the northeastern iln County Warning Area. Probability of precipitation range from
40-80 percent across the forecast area from southwest to
northeast...with these values kept lower than preferred due to the
aforementioned issues and for collaboration purposes. These
pop numbers will likely need to be raised in future forecasts...as
it seems quite certain that most locations will at least measure a
little bit of additional snow on Wednesday morning. As a final
note about the snow...a favorably-positioned stratocumulus deck
will likely keep the chance of flurries in place through Wednesday
night...possibly even into Thursday morning.
The Winter Weather Advisory essentially has two segments...though
coding purposes require it to be split into four groups. For the
southern and southwestern County Warning Area (cincinnati/Wilmington/maysville)
the advisory was extended through morning. For the eastern County Warning Area
(portsmouth/Chillicothe/columbus) the advisory was continued
through late afternoon.
Temperatures are expected to rise only very slightly on
Wednesday...as continued cold advection (and a lack of insolation)
limits the potential for diurnal heating. Wednesday night will
be quite cold...especially with snow in place...and temperatures
in the single digits are now in the forecast (dropped several
degrees from previous numbers). Little change is expected to the
temperatures on Thursday...with a generally neutral low-level
advection pattern. However...with temperatures slowly beginning to
warm aloft...the clouds are expected to eventually break by the
end of the day.
Long term /Friday through Monday/...
a weak system will move generally south of the area Friday
morning. Introduce only a slight chance of snow showers to
southern portions of the region during this time. An upper level
disturbance moves through Friday afternoon into Friday evening
bringing better chances for some light snow to the region. Winds
off of Lake Michigan will linger snow showers across portions of
the area Friday night into Saturday. Temperatures will struggle to
rise on Saturday with cold airmass in place.
Any remaining snow showers will taper off by Saturday evening and
cloud cover will decrease. The combination light winds...mostly
clear skies...and snow on the ground will lead to temperatures
dropping into the single digits to single digits below zero Saturday
Dry conditions will be in place most of the day on Sunday however
expect an increase in clouds through the day in advance of the next
system. Models are in some disagreement on how quickly
precipitation will overspread the area. Have precipitation chances
beginning to move into the region Sunday evening into Sunday night
with better chances during the day on Monday. Although there may be
a brief mix in precipitation across southern portions of the region
generally expect temperature profiles to be cold enough that
precipitation will be in the form of snow. Snow will taper off
Monday night with high pressure and dry conditions moving into the
region for Tuesday.&&
Aviation /20z Tuesday through Sunday/...
a large scale upper level trough will remain over the Great Lakes
and Ohio Valley through the taf period.
For this afternoon into early evening...a surface trough will
rotate east across the northern tat sites. This feature will bring
a period of MVFR ceilings and IFR visibilities to kday...kcmh...and
klck. Elsewhere...diurnal instability and cyclonic flow will
result in mainly light snow showers. MVFR ceilings/visibilities
with perhaps pockets of IFR visibilities are expected with this
For tonight...models suggest that an embedded disturbance will dig
southeast toward the region between 06z and 12z. Before
then...forecast area will have a relative lull in snow shower
activity. Thereafter...snow shower coverage should increase from
west to east. Have tried to time the higher probability of snow
showers at the taf sites. MVFR conditions will persist with an
occasional lower IFR visibility possible.
On Wednesday...embedded disturbance will move east. Snow showers
will taper to flurries west. MVFR conditions will persist.
Outlook...MVFR ceilings possible Wednesday night into Thursday.
MVFR ceilings and visibilities possible Friday afternoon into
Ohio...Winter Weather Advisory until 10 am EST Wednesday for ohz053-
Winter Weather Advisory until 6 PM EST Wednesday for ohz046-
Kentucky...Winter Weather Advisory until 10 am EST Wednesday for
In...Winter Weather Advisory until 10 am EST Wednesday for inz058-