Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
639 PM EST Wednesday Jan 28 2015
a cold front will approach tonight and move through the region on
Thursday. This system will bring a threat of wintry precipitation at
least at the onset in some locations. As the low pressure system
departs...any lingering showers should turn to snow showers from
late Thursday afternoon into Thursday evening. High pressure will begin
to build back into the area on Friday and remain in control of the
weather into the start of the weekend.
Near term /until 6 am Thursday morning/...
dry conditions are expected initially due to high pressure that
will begin to depart the region. Satellite imagery and model data
continue to suggest an increase in high clouds through the evening
ahead of an approaching low pressure system.
It still appears that temperatures will generally be steady
during the evening hours with guidance suggesting min temperatures
around midnight in many locations outside of any decoupled valleys
in eastern and southeast part of the County Warning Area. Southerly flow will
increase tonight. As southerly flow increases temperatures will
begin to slowly rise through the overnight hours.
Precipitation will hold off for most of the overnight hours. There
is enough concern for some of this to reaching the ground toward
dawn that a Freezing Rain Advisory is planned for the northern
tier or two of counties...though most of this should hold off
until the short term period.
Short term /6 am Thursday morning through Friday night/...
in the SW part of the area...expect temperatures to already be
near or above freezing to start the period and the precipitation
will likely just begin as rain. However...there is some
uncertainty with the time of arrival of precipitation as the GFS
saturates this area a bit quicker and the top down approach would
suggest the possibility of a mix at onset there as well.
The chances for a mix at onset are better further to the north
and east as the initially dry airmass will be able to wet bulb and
freezing rain or sleet would be possible for a longer period of
time...but this precipitation would be very light. In this
area...there will be a brief window for a couple of hours where
temperatures could be at or just below freezing as precipitation
moves into the area. Due to this...a brief period of freezing rain
will be possible considering the cold and initially frozen or snow
covered ground in place particularly across the north and
northeastern part of the area due to the recent colder weather. Any
precipitation that reaches the ground before middle morning in the far
north and east could lead to some impacts of slick or icy spots on
untreated or secondary roads...bridges...overpasses and walkways
during the morning...so a Freezing Rain Advisory has been issued for
the northern tier or two of counties to include the Columbus metropolitan
area. Any freezing rain is expected to be light...but still a
potential threat. As for the severe weather potential statement...we plan to continue to mention
freezing rain or mix at onset for the southwest three quarters of
Warmer air will continue to surge into the area by middle to late
Thursday morning and as it does temperatures will rise above
freezing across the entire forecast area ahead of the cold front. This cold
front move through the forecast area during the afternoon and early evening
hours on Thursday bringing additional precipitation chances to the
area. As the colder air begins to work into the region later in
the afternoon and evening...precipitation will changeover to snow
showers from north or northeast to southeast. The chances for
light snow showers will continue Thursday night and possibly into
early on Friday due to a combination of a weak disturbance passing
through and winds off of Lake Michigan. Snowfall accumulation from
this is still expected to light and an inch or less.
High pressure will begin to work into the forecast area later Friday
afternoon into Friday night. Cloud cover will decrease through the
night Friday night and winds will be light. With this combination
expect temperatures to drop down into the single digits to the
teens across the forecast area.
Long term /Saturday through Wednesday/...
surface high pressure passing northwest to southeast over the region at the start
of the period will provide clear to partly cloudy skies and cold
temperatures Friday night and Saturday. After this...the forecast
troubles begin. An upper level trough about to move onshore on the
West Coast will close off a low over the SW Continental U.S. Late in the week.
An upper level impulse should then drop southeast out of Canada across the
Great Plains this weekend. The degree to which this phases with the
upper low/residual trough over the SW Continental U.S. Is still uncertain. The
eventual track and strength of the upper level system will affect
subsequent surface low development in the eastern Continental U.S.. a wide
range of tracks and strengths of surface systems has been observed
in the models in recent days...with the GFS and European model (ecmwf) showing both
run to run and model to model inconsistencies...and no consensus
yet. The latest 12z runs have generally trended weaker with the
system. Bottom line...there is still a large degree of uncertainty
regarding the forecast during this period. At this point the
forecast is still one of low confidence...and is based on a blend of
recent model runs. The precipitation threat will be from Saturday night
into Sunday night...and mainly in the form of snow. Have allowed for
a potential mix with rain in southern Ohio and northern Kentucky.
In the wake of the weekend system...high pressure with another
Arctic air mass is expected to move in from the northwest and dominate
through Tuesday. On Wednesday...another large scale upper trough
begins to deepen as it moves in from the northwest...and low level warm air
advection begins in advance of it. Timing of weak upper level
impulses in that time frame would be a guess at this point...but
some model runs have shown a potential for a bit of snow...and have
used a 20 percent pop on Wednesday.
Aviation /00z Thursday through Monday/...
conditions are VFR to start with high pressure moving east. Precipitation
associated with low pressure and a cold front will impact taf
sites starting around 09z at day. -Ra will be the primary form of
precipitation...with a period of -fzra at cmh and lck expected between
12z and 14z. MVFR is forecast to occur once the boundary layer nears
saturation beginning around 15z. Southeast winds under 10 knots
will shift to south and increase in speed with gusts to around 20
knots...then to west with gusts close to 30 knots Thursday
afternoon as steady precipitation ends. Scattered showers will follow for
the latter part of the forecast period as MVFR ceilings persist.
Outlook...MVFR ceilings possible through Friday. Snow likely
to impact taf sites Sunday with IFR possible.