Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
719 PM EST Friday Dec 6 2013
a winter storm will impact the region through this evening before
coming to an end after midnight. High pressure will then build
into the region for Saturday. The high will move off to the east
Saturday night. Another weather system will bring more wintry
precipitation beginning Sunday and will linger into Monday across
much of the area.
Near term /until 6 am Saturday morning/...
update this evening was to allow precipitation to become all snow over the
entire forecast area. Snow is mainly light to moderate now with
isolated pockets of brief heavy snow. The remainder of the previous
forecast still holds.
Previous discussion ----->
Winter storm is reaching its height across our region in terms of
strength. Upper level shortwave combined with a strong jet has resulted in
strong frontogenetic forcing. Colder air has been slowly seeping
south and am expecting lingering mixed precipitation in our southeast to turn to
snow by this evening. Heaviest snow will fall where warnings have
been hoisted which is along the I-71 corridor. Winter weather
advisories will continue across our far northwest where snow will be the
lightest. Winter weather advisories will continue for the southeast County warning forecast area due
to mixed precipitation changing to snow. 4 to 7 inches still look plausible
in the warning area with 1 to 3 inches far northwest and 2 to 4 inches in
the southeast County warning forecast area. Once the shortwave ripples by this evening into early
morning...snow will taper off quickly from west to east. Models
suggest all precipitation should be just about over with in our eastern zones
by 1 am EST. Headlines will likely be adjusted and let go as precipitation
moves out of the region. Overnight lows will drop into the middle
teens to the lower 20s.
Short term /6 am Saturday morning through 6 PM Saturday/...
high pressure of Arctic origin will build into the region on
Saturday. This will allow skies to become mostly sunny.
Temperatures are forecast to rise into the middle and upper 20s...but
they could be a little colder given fresh snow cover.
Long term /Saturday night through Friday/...
the reprieve from winter precipitation over the iln County Warning Area will be
brief...as another system moves into the area from Sunday morning
The overall weather pattern continues to be modeled with consistency
and stability through the middle of the week...providing confidence
in the large scale forecast features. The Sunday-to-Monday system
will be discussed in detail below. Beyond Monday...quasi-zonal flow
will set up over the Ohio Valley...with surface high pressure
building into the region. Although a shortwave will pass through the
Great Lakes Tuesday night...the iln County Warning Area should be too far south to
be impacted (flurries in the northern County Warning Area may not be an
impossibility). It would not be until very late in the week that
moisture flow (in advance of broad troughing in the western and
central states) would increase enough to bring a chance of
precipitation back into the area.
The focus remains on the system that will move into the iln County Warning Area
early Sunday morning...bringing with it a challenging precipitation
type forecast. Weak high pressure over the Ohio Valley and southern
Great Lakes is forecast to move northeast of the region Saturday
night...as northern stream troughing over the plains amplifies as it
heads into the Great Lakes region. Broad ambient surface low
pressure over the southeastern states will eventually make its way
northward as a trough...with pressures lowering through Sunday and
into Sunday night. A surface low is also forecast to develop ahead
of the middle-level trough...moving into lower Michigan by Monday
A significant quantitative precipitation forecast response is generated on the models ahead of the
trough...in a regime favorable for large-scale lift. However...this
will pass well north of the iln County Warning Area. Instead...much of the quantitative precipitation forecast
response over the iln County Warning Area seems tied to a feed of moisture from the
south...with the deepest moisture stretching from Louisiana to the
mid-Atlantic. Most of the iln County Warning Area ends up caught between the two
streams...in a void of more significant forcing. The heaviest storm
total quantitative precipitation forecast amounts (about an inch by model consensus) will occur in
the southeastern County Warning Area...tapering off very quickly with northwestward
extent. Confidence remains high enough to allow for the use of
100-probability of precipitation for much of the iln County Warning Area...dropping to likely in the far
northwest. However...actual precipitation amounts over the
northwestern half of the County Warning Area may not be overly significant. A couple
of adjustments were made to the pop grids from the forecast
yesterday. First...onset appears to be closer to 12z Sunday morning
in the southern County Warning Area...which is a slight slowing from the model runs
yesterday. Second...models are hinting at a second wave of enhanced
moisture for Sunday night...just ahead of the surface trough axis
connecting the Great Lakes surface low to the low pressure in the
southeastern states. There appears to be a lighter period of
precipitation between the two waves.
Until the event gets a little closer and mesoscale models can pick
up on some of the specifics of the forcing (such as frontogenesis or
deformation placement)...it appears (in general) that the
liquid-equivalent precipitation output may not be enough to turn
this event into one with significant widespread impacts. That will
end up being a crucial factor...because confidence is high that
thermal profiles for much of the day Sunday will support a mix of
snow...sleet...and especially freezing rain. Coming out of a snow
event and a very cold period on Saturday...ambient temperatures
(ground and air) will be quite low. At the time of precipitation
onset early Sunday morning...snow will be the favored precipitation
type. As an elevated warm front moves north into the region through
Sunday morning and into the afternoon...conditions will eventually
support precipitation types changing from snow to a mix of freezing
rain and sleet. As conditions continue to warm...the surface
temperatures will walk a very fine line on Sunday and Sunday
night...making the eventual forecast between rain and freezing rain
challenging and pivotal. As the system moves away early on
Monday...a brief period of mixed precipitation will be possible as
colder air moves in again...before dry conditions take over late
Monday into Monday night.
The heaviest quantitative precipitation forecast amounts (with both waves of precipitation) will be
in the southeastern County Warning Area. The first wave may fall mostly as
snow...producing up to a couple inches in that area. Snow at the
onset elsewhere will be tempered by the lack of moisture...resulting
in most locations receiving an inch or less. Freezing rain appears
likely to occur as the warm layer aloft moves in...but gfe-produced
forecast grids and BUFKIT precipitation output agree on this being
limited to several hundredths of an inch. Of greatest concern will
be the speed of which the warm layer aloft moves in...which could
lead to more ice than currently forecast. By and large...the second
wave of precipitation appears likely to fall as rain...especially in
the southeastern County Warning Area where amounts will be the highest. This
scenario has the appearance of a multi-faceted advisory-level event
for the mix of wintry precipitation types...perhaps excepting the
far northwestern County Warning Area corner...which may only receive light snow from
the event. Mesoscale forcing features would have to be pinpointed to
see if any enhanced precipitation areas can develop anywhere in the
County Warning Area...and certainly no headline decisions will be made this early
on...as there is certainly still the potential for change in the
In summary...while confidence is high in a mix of winter
precipitation types...marginal forcing and moisture over most of the
County Warning Area will limit amounts...providing moderate to good confidence that
a significant (warning criteria) event will not occur.
Beyond Monday...behind another cold front...most of next week
appears dry but frigid. Raw model temperatures are certainly
influenced by an expected snow pack...thus the resulting forecast
numbers will probably be able to be improved more significantly
after the current storm is finished and the snow pack is laid out.
Sorting through the usual assortment of raw min temperature bullseyes (well
into negative numbers)...the overall temperature forecast has held
mostly steady since yesterday...giving confidence in a cold week
(with single-digit lows across The Heart of the cwa). While
temperatures should eventually get (barely) above freezing for most
of the iln County Warning Area early on Monday...sub-freezing temperatures are forecast for
the next four days straight...even for maxes. A slight moderating
trend will begin on Friday...perhaps lasting into the weekend.
Non-diurnal temperatures were drawn in for the entire period
from Saturday night through Monday.
Aviation /00z Saturday through Wednesday/...
winter storm will continue to impact the area through the early
overnight hours. LIFR conditions will improve to MVFR in a few
hours as the system moves east and snow ends. MVFR conditions will
persist in lingering low level moisture through about 14z...when
high pressure will bring VFR. Skies will become mainly clear
during Saturday afternoon...and winds will stay out of the north
at under 10 knots. After 00z Saturday...cvg will see increasing
clouds ahead of the next system.
Outlook...MVFR to IFR ceilings and visibilities likely Sunday into Monday.
Ohio...Winter Storm Warning until 1 am EST Saturday for ohz042>046-
Winter Weather Advisory until 1 am EST Saturday for ohz026-034-
Kentucky...Winter Storm Warning until 1 am EST Saturday for kyz089>097.
Winter Weather Advisory until 1 am EST Saturday for kyz098>100.
In...Winter Storm Warning until 1 am EST Saturday for inz050-058-