Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wilmington Ohio
637 am EST Wed Dec 7 2016

as upper level low pressure moves east across Ontario and Quebec,
cooler and drier air will continue to move into the Ohio Valley
today, with temperatures continuing to get colder through the end
of the week. A few flurries are possible on Friday, but a more
significant chance of rain and snow will move into the region on
Saturday night and Sunday.


Near term /until 6 PM this evening/...
as a large area of upper low pressure gradually moves east across
the northern Great Lakes region, surface high pressure is entering
the Ohio Valley, signifying the beginnings of the cold and
generally dry air mass that will be in place over the region for
the next several days. Stratocumulus clouds have almost completely
shifted east of the iln forecast area early this morning, but high
clouds (and a few mid clouds) are already streaming in from the
WSW, ahead of a very weak 700mb shortwave. Ultimately, there are
no notable features to discuss for the weather through the daytime
hours. The dry low levels and very-weak-to-neutral surface
advection will allow for a little bit of warming this afternoon
(highs in the mid 30s to lower 40s). However, stronger cold
advection just off the surface will be an indicator for what is
yet to come later this week (as discussed below).


Short term /6 PM this evening through Saturday/...
by Thursday morning, the lumbering/sprawling area of low pressure
north of the region will be moving eastward through Quebec, with
deep-layer flow over the Ohio Valley shifting to more of a
northwesterly direction. As this occurs, and the aforementioned
weak trough axis passes the area, the advection pattern will
switch to one that is definitively cold. As this occurs, low-level
moisture will remain sparse, but some mid-level moisture will pass
through the area. The weak and transient upper jet forcing no
longer appears likely to combine with this moisture in a favorable
manner, and with the dry air mass through the lowest 5kft-10kft,
precipitation is no longer expected for early Thursday morning.
All mention of snow / flurries has been removed from the forecast.

The cold advection will continue unabated through the rest of the
short term period of the forecast. 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
on Thursday night and Friday night, even in conditions that are
advective and completely unfavorable for Standard radiational
cooling. In fact, the continued cooling aloft will result in a
steep (but shallow) mixed layer near the surface, resulting in
occasional stratocumulus through this period of the forecast, with
winds will stay in the 10-15 knot range (with higher gusts). Given
the positioning of the top of the mixed layer through the first
half of Friday, some flurries or light snow showers appear
possible, with no apparent potential for accumulation for now.
This has been focused mainly in the north/NE sections of the cwa, but
a chance of flurries will extend to most of the area.

Though conditions are not expected to warm up too much for
Saturday, 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 conditions are expected on Saturday, with an
overall diminishing in low-level clouds.


Long term /Saturday night through Tuesday/...
a cold front and wave of low pressure will approach from the west
Sunday before crossing the area Sunday night. Rain will be the
primary type of precip with the front, with snow mixing in at the
start and end of the event. Light precip may linger Monday in the
cyclonic flow off the Great Lakes. A few snow showers will be
possible Tuesday in northern locations, ahead of an Arctic cold

Look for below normal temperatures through the period. Highs Friday
are forecast to be in the upper 20s, then up to around 30 Saturday.
Modestly warmer readings near 40 are expected for Sunday through


Aviation /12z Wednesday through Sunday/...
mid/high level clouds will be streaming across the region in a
broad southwest/west flow aloft today.

Large upper level low centered just north of the upper Mississippi
River valley will slow rotate east and elongate today into
tonight. Some embedded energy in the southwest to west flow around
the low will bring another round of mid clouds to the region
overnight. Any precipitation looks unlikely with this energy/mid
clouds as low levels will be quite dry.

Outlook...MVFR ceilings possible Thursday afternoon into Friday.
MVFR/IFR ceilings and visibilities possible Sunday.


Iln watches/warnings/advisories...


near term...hatzos
short term...hatzos
long term...coniglio

National Weather Service Glossary of Abbreviations