Scientific Forecaster Discussion
fxus61 Kiln 081437
Area forecast discussion
National Weather Service Wilmington Ohio
937 am EST Thu Dec 8 2016
cold air will continue to get colder over the next day or two, and
temperatures will remain well below normal. Some flurries are
expected on Friday morning, before an area of high pressure moves
into the region late Friday into Saturday. On Sunday and Monday, a
complex low pressure system will through the Ohio Valley, bringing a
mix of rain and snow to the region.
Near term /until 6 PM this evening/...
low clouds across the northern half of the area should be
persistent through the day with only a few breaks at the most.
Clouds across the south look to be more transient. However, a
second surge of clouds now seen back across Indiana and Illinois
will eventually spread back into southern counties later in the
day. Radar shows some light echoes across the north and there have
been a few reports of flurries. So added scattered flurries in the
northern half of the area today. Expect little variation in
temperature with perhaps a couple of degree rise from mid morning
readings. West winds will remain brisk resulting in wind chills
remaining in the teens to lower 20s.
Short term /6 PM this evening through Sunday/...
the cold advection will continue unabated through Friday and into
early Saturday. Aloft, the coldest air is expected to be in place
on Friday morning. GFS/gefs/NAM anomalies indicate that 700mb /
850mb temperatures will be about 2.0-2.5 / 1.5-2.0 Standard
deviations below normal, respectively. This will easily allow min
temps to drop into the upper teens to lower 20s tonight and Friday
night, even in conditions that are advective and completely
unfavorable for Standard radiational cooling. With the continued
cooling aloft, a steep (but shallow) mixed layer will continue to
exist near the surface, resulting in occasional stratocumulus
through this period of the forecast. Given the thermal
positioning of the top of the mixed layer through the first half
of Friday, some light snow showers appear possible. This has been
focused mainly in the northern sections of the cwa, but a chance
of flurries will continue to be used for the majority of the
forecast area. Though most locations will not receive any
accumulation, a quick tenth or two could occur in a snow shower on
Friday morning / early afternoon, likely limited to areas north of
Outside of the Great Lakes, most of the eastern half of the US
will be dry to start things out on Saturday. This will only be a
brief interlude before a shift in the pattern. Though conditions
are not expected to warm up too much for Saturday in the Ohio
Valley, the signs of the change in pattern are evident, as the
surface high and 850mb/700mb ridge axis move east through the
Tennessee Valley -- bringing a deep-layer change in wind
direction. Dry weather is expected, with an overall diminishing
trend in low-level moisture.
By Saturday night, attention will focus on developing
precipitation, which will affect the Ohio Valley from early Sunday
morning through Monday afternoon. Although there is high
confidence in precipitation occurring, and high confidence that
some accumulating snow will occur, the specifics are not yet
possible to predict -- given continued run-to-run / model-to-
model changes in the modeling of the thermal fields, surface low
track, and overall mid-level flow pattern. As an example, the
spread among gfse members increases significantly between 12z
Saturday and 12z Sunday, first showing notable inconsistency with
the initial low- amplitude / high-speed wave moving into the
southern Great Lakes. Combined with some right entrance jet
dynamics, this will spark the first wave of precipitation over the
area on Sunday. Hard to ignore the operational 00z European model (ecmwf)/GFS runs,
which both keep precipitation focused mainly north of the Ohio
River through early Sunday, before additional precipitation
develops everywhere later on Sunday and Sunday night. Will keep
changes minimal given the uncertainty, but pops were adjusted
based on these trends, and weather grids continue to indicate an
expectation for rain and snow to mix during diurnal heating on
Sunday. There was enough confidence to start off an severe weather potential statement mention of
accumulating snow for the northern half of the cwa, but no reason
to get into details as of yet.
Long term /Sunday night through Wednesday/...
this low is forecast to move northeast into/through the Great
Lakes, eventually allowing a cold front to pass through Sunday
night or Monday morning. Until then, confidence has increased in a
period of precipitation Saturday night into Sunday and therefore
have likely pops across the County Warning Area. Precipitation type will likely be
snow at the onset, but with some warmer air moving in from the
south on Sunday, expect snow to mix with/change to rain
particularly south of Interstate 70. GFS is colder than the ECMWF,
and therefore used a blended approach for p-type transition
Sunday. Eventually, any lingering precipitation would change back
to snow Sunday night/Monday morning as colder air moves back in
behind the cold front.
High pressure briefly builds in for Tuesday, but a fast-moving, weak
system may bring a chance of light precipitation by Wednesday,
although timing this far out is in question.
Below normal temperatures are expected for the long term forecast
Aviation /15z Thursday through Monday/...
the center of a large scale upper level trough was located just
southeast of James Bay Canada this morning. This feature will
rotate east/northeast through the day.
For today, cold air advection in conjunction with stratocumulus clouds will
advect/develop through the day as they move southeast. Northern
terminals will experience MVFR ceilings with southern terminals
fluctuating between MVFR/VFR from time to time. An increasing
pressure gradient along with some diurnal mixing will bring wind
gusts into the 20-25 knot range.
For tonight, low level flow will shift to a northwest direction,
allowing cold air to move across the Great Lakes. This will allow
stratocumulus to thicken and lower overnight. There could be some
scattered flurries, with a few snow showers possible near the
northern terminals. Ceilings will be in the MVFR category, with
below 2000 foot readings likely after 06z. Winds will remain a
little gusty through 06z.
Outlook...MVFR ceilings expected on Friday, which may linger into
Friday night. MVFR/IFR ceilings and visibilities possible Sunday