Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
1249 am EST Sat Nov 22 2014
a weak upper level disturbance will push east across the area late
tonight into Saturday morning...bringing the chance for some light
rain and freezing rain. A developing low pressure system over the
Southern Plains will lift into the Great Lakes region Saturday night
into Sunday night. Increasing southerly winds ahead of this will
lead to a warming trend for the Ohio Valley through the weekend
along with an increasing chance of showers.
Near term /through today/...
clear skies this evening have allowed for temperatures to drop
off fairly quickly after sunset. Have adjusted temperatures down but
expect warm advection to start after midnight. Low level
southerly flow will be on the increase later tonight as the high
pressure continues to push off to the east. This will lead to
developing isentropic lift across our western areas late
tonight...shifting up across our northern areas through Saturday
morning. Low levels are fairly dry so it may take a little while
to saturate the air column. However...think we will eventually
see at least some scattered shower activity develop across the
west late tonight and then transition more up across our northern
areas through Saturday morning. Surface temperatures will be an
issue as they should slowly rise overnight with the increasing
clouds and warm advection...but will likely still be near or
below freezing at precipitation onset. The warming temperatures may also be
offset a bit by some evaporational cooling early on with the precipitation.
As a result...a period of freezing rain will be possible late
tonight into Saturday morning across about the northwest half or so
of our forecast area. Since there is still some uncertainty to the coverage
and quantitative precipitation forecast amounts should be rather light...will hold off on an
advisory at this point but issue an Special Weather Statement and continue to mention a
freezing rain threat in the severe weather potential statement. Temperatures should warm above
freezing across the north through late morning with any lingering
freezing rain transitioning to light rain. Expect highs on
Saturday ranging from the middle 40s north to lower 50s south.
Short term /tonight through Sunday night/...
weak middle level ridging will develop across our area Saturday night
into early Sunday ahead of short wave energy moving into the
lower Mississippi Valley. This short wave will then pivot up into
the Ohio Valley through Sunday with an impressive 70 knot 850 jet
rotating up into our area through Sunday evening. This will allow
for showers to overspread our area from the southwest through the
afternoon and then continue into Sunday evening. The 12z
GFS is trying to pull some very weak elevated instabilities up
to about our southern border Sunday afternoon into Sunday evening.
Suppose an isolated thunderstorms is not out of the question across
our south given the strong forcing. Will then hang on to likely
probability of precipitation through the rest of the night as the cold front approaches
from the west. In the good warm air advection pattern...highs by Sunday will be
well into the 50s. Good southerly flow ahead of the front will
lead to steady or even rising temperatures Sunday night.
Long term /Monday through Friday/...
latest European model (ecmwf) appears too slow with the cold front on Monday. Have
gone with the NAM/GFS/wpc solution which pushes the cold front
through our region during the morning/early afternoon. With decent
frontal convergence and moisture...a band of showers is expected
to accompany the front. Given tightening pressure gradient and
winds 40 to 50 knots between 925 mb and 850 mb...some of the
showers may contain gusty winds. By afternoon...models suggest we
get into a dry slot while the cold front moves east and low
pressure over Ontario deepens. Models indicate that we should mix
fairly well in the dry slot. With cold air advection and mixing...winds could
gust in the 30 to 40 miles per hour range from middle morning into middle
For Monday night into Tuesday...upper level trough will traverse the
region. Best moisture and lake effect influence should remain to our
north and have kept it dry. There will be some Post frontal cold air advection
induced stratocumulus...most numerous across the northern zones.
For Tuesday night...surface high pressure is expected to briefly
build into the region.
For the upcoming travel day Wednesday and into Thanksgiving...European model (ecmwf)
and GFS are similar in pushing a cold front and weak surface low
pressure through the region. European model (ecmwf) is a little slower while the GFS
is slightly faster. In either case...there will be a chance of snow
with this feature as temperatures become colder once again in the
wake of the front.
On Friday...surface high pressure will build back into the region
behind departing system on Thursday.
Monday will be the warmest day with temperatures near or a little
above normal. The remainder of the extended will feature
temperatures below normal once again due to the northwest flow
Aviation /06z Saturday through Wednesday/...
showers will be widely scattered as they cross the Ohio Valley
towards daybreak...with a higher occurrence noted north and
northwest of kday. Ceilings 5-7kft will lower in the showers that do
occur to approach the threshold MVFR 3kft. Do not expect any visibility
restrictions with the showers that occur...but temperatures may mean that
they are freezing rain when they do fall. Freezing rain is not expected at
kcvg/kluk as the warm air that gets pulled into the area with the
showers will hit them first...and they have an even lower
probability of occurrence than other sites. Kcmh/klck could go
either way and I was leaning towards not freezing but included a 2
hour period of freezing rain to be cautiously pessimistic here.
Removed gusts that were in previous forecast for today in favor of
a 12-13kt sustained wind that will probably continue into the
evening hours at kday. Daytime ceilings will be 6-8kft and persist
into the evening.
Outlook...MVFR ceilings possible Sunday and Monday.