Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
1259 am EST Thursday Dec 18 2014
weak high pressure will nose into the region tonight. However
abundant low level moisture will result in a continuation of mainly
cloudy skies. A weak upper level disturbance could lead to a few
flurries Thursday afternoon into Thursday night. High pressure will
build back in offering dry conditions and near seasonable
temperatures for the end of the week.
Near term /until 6 am this morning/...
an elongated area of high pressure is currently centered west of
the Ohio Valley. This high will nudge into the area by
morning...with cool west-northwest flow on its north side allowing for a
relative min in surface/925mb temperatures that will stretch from central
Ohio to Minnesota. Temperatures have been cooling off a little
faster than the previous forecast indicated...so a slight downward
adjustment was made to the min temperature grid.
As the pressure gradient weakens...winds will become lighter as
the overnight hours progress. However...the direction of flow will
not be favorable for the advection of the moisture currently over
the middle and upper Ohio Valley. The 00z Kiln sounding indicated
saturation between 925mb and 875mb...captured well on the nam12
and rap13...but very poorly on the GFS and European model (ecmwf). The erosion of
the southern/western edge of these clouds has slowed or
stopped...and the forecast for the overnight will remain very
cloudy. However...some slight warming is expected to begin at
900mb after 06z...which may be enough to lead to some breaks in
the clouds closer to morning.
Previous forecast >
elongated middle level low over the Great Lakes to shift off into New
England. A few isolated lingering flurries in the low level cold air advection will
come to an end early. Middle level flow becomes briefly northwest ahead of an
upstream short wave ridge. Surface high pressure to nose into the Ohio Valley
overnight in region of 500 mb confluence. 12z iln sounding shows low
level moisture trapped below an inversion around 850 mb. GFS is
aggressive with clearing low level moisture. NAM and rap solutions keep
clouds overnight. Will allow a few breaks over the south/southwest
but lean toward the NAM/rap solution. Temperatures will be close to
normal with lows from the middle 20s north to the upper 20s south.
Short term /6 am this morning through Friday night/...
middle level short wave to ripple quickly east from the Central Plains
through the Ohio Valley Thursday. This weak shortwave is dampening
and crossing over the surface ridge. Forcing is very weak and in the
middle levels. A flurry or sprinkle is not out of the question from a
middle deck. Flurries/sprinkles already in the forecast...so will
continue. Temperatures will be below normal with highs from the
lower 30s north to the middle/upper 30s south.
In westerly middle level flow regime...surface high pressure to build
across the Great Lakes/Ohio Valley Thursday night/Friday. A few
flurries will remain possible Thursday evening but will come to an
end with the passage of the short wave. As the high build noses in
expect some partial clearing Thursday night. Lows expected to
range from the middle 20s north to the upper 20s south.
Expect to see more sunshine Friday with an increase in high level
moisture late in the day. Fridays highs from the middle 30s north to
near 40 south.
Clouds will thicken and increase Friday night as system approaches
from the southwest. Will keep forecast dry Friday night as consensus
does not bring moisture in until Saturday. Lows Friday night to
range from the upper 20s north to the lower 30s far south.
Long term /Saturday through Wednesday/...
for Saturday...looks like we could see snow changing to rain as low
pressure travels near the Gulf Coast. The low has trended farther to
the south so cut back on probability of precipitation and precipitation amounts. High pressure and
a cool airmass should allow dry weather on Sunday. Light precipitation will
be possible Monday extending from a trough along the East Coast.
We may begin to feel the effects of a powerful low pressure system
on Tuesday. Have less than average amount of confidence due to model
differences from run to run. At this point it appears the low will
develop over the Southern Plains on Tuesday...before lifting through
Ohio to the Great Lakes on Wednesday. The low may feature a very
tight pressure gradient surrounding its deep center...producing
strong winds. Copious moisture feeding from the tropics and from the
Atlantic Ocean could advect around the low. Current temperature
forecast allows rain Tuesday into Wednesday...changing to snow later
Wednesday as colder air wraps in behind the low.
Temperatures will be relatively close to normal for the most part.
Highs are forecast to be in the middle and upper 30s Saturday...then a
couple degrees warmer for Sunday and Monday under neutral to weak
warm advection. Readings on Tuesday and Wednesday will be dependent
on the position of the anticipated strong low. Warm advection ahead
of the low could bring highs up into the middle 40s on Tuesday...or
even higher if the warmer mex guidance verifies. Highs could slip to
around 40 on Wednesday in cold advection behind the low.
Aviation /06z Thursday through Monday/...
a persistent MVFR cloud deck is likely to remain in place across
the taf sites into the afternoon. At that time the deck should
break as a weak upper level system approaches the area. However
the reprieve will be short live as the MVFR ceilings should return
during the evening. During this break in the MVFR ceilings there will
be multiple layers of clouds at or below fl050 in association with the
next system. While moisture with this next system will be lacking
in terms of precipitation...flurries are expected this afternoon and
evening. Since no visibility restrictions are expected and the timing
during this period will be variable have not included this mention
in the forecast.
West winds of under 10 knots are expected through the forecast period.
Outlook...MVFR ceilings may continue into Friday. MVFR ceilings
and visibilities are possible on Saturday.