Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
647 am EDT Thursday Oct 30 2014
high pressure will control the weather over the Ohio Valley
today...with dry and cool conditions expected. A trough of low
pressure and a cold front will move southeast into the region on
Friday...bringing occasional rain...which may mix with light snow
early Saturday morning. Much colder conditions are expected behind
the cold front for the weekend...with a warming trend beginning
early next week.
Near term /until 6 PM this evening/...
the cloud forecast has been the challenge early this
morning...with some fairly solid patches and bands of
stratocumulus drifting southeast across the iln forecast area. The
clouds have made it far enough south to stunt the falling
temperatures...in an area that was well on its way to some very
cool and potentially frosty conditions. The general expectation is
that these clouds will start more of a dissipating trend through
the day...especially in the southern portions of the forecast area
(closer to the Ohio river).
As surface high pressure becomes centered over the region...winds
will become light...with an advection pattern that is slightly
cool just off the surface. The temperature arrangement today will
feature much less of a gradient than yesterday...with the slightly
cooler conditions in the north...where a little more in the way of
cloud cover may persist.
Short term /6 PM this evening through Saturday night/...
the short term forecast period will be dominated by a complex
weather system that will affect much of the eastern part of the
country. A sharp middle-level trough is expected to develop
into a compact closed low as it moves south-southeast out of the Canadian
plains...crossing the western Great Lakes on Friday...and reaching
the southeastern states on Saturday morning. The strength of this
system (as noted by height anomalies) is very much out of the
Ordinary...and as admitted by National Weather Service wpc...this leads to some
confidence concerns in the overall forecast for the next few days.
Overall...the impacts for the iln forecast area will be most
notable in terms of the cold temperatures moving into the
area...with a few interesting notes in terms of winds and light
snow behind the surface cold front.
A brief period of southwesterly flow will help keep temperatures
steady headed into Friday morning...in advance of a surface cold
front. This front is forecast to move southeast through the iln
County Warning Area during the day on Friday. This required a non-diurnal
temperature curve...with a gradient in maximum temperatures from
northwest to southeast. The front is not expected to be a
significant focus for precipitation on its own...but a large area
favorable for ascent will be located ahead (east) of the middle-level
low...especially as a region of upper divergence moves through
late Friday afternoon into the evening. Additional precipitation
from a weak shortwave crossing the lower Ohio Valley will
eventually wrap into the main deepening trough by Friday
afternoon. Focusing on the afternoon to early evening
period...likely probability of precipitation have been included for the entire forecast
area...with the greatest chances (where there was serious
consideration for categorical pops) in the eastern half of the
County Warning Area. A very small amount of instability may allow for a few
convective showers in southern Ohio and northeast Kentucky on
Friday afternoon...but BUFKIT soundings suggest equilibrium levels
of only around -5c...not tall enough for thunder.
Though model agreement in the general setup is fairly
strong...the speed of the departure of precipitation early
Saturday morning is an important question that remains somewhat
uncertain. Seeing no strong reason to make a big change...this
forecast will stick mainly to continuity...with similar timing to
the previous forecast. This will allow for dry conditions in the
western County Warning Area by 12z Saturday...and clearing out of the Scioto
valley after 18z.
The temperature forecast for early Saturday morning is going to be
very closely tied with the potential for snow. As temperatures
continue to cool behind the surface front on Friday night...model
soundings suggest that sub-freezing air will eventually work its
way close enough to the surface to allow for snow to mix with
rain. However...this currently seems most likely to occur over the
western half of the County Warning Area...where drying conditions and a loss of
ascent will be limiting precipitation potential as temperatures
cool. In the eastern County Warning Area (especially central ohio)...wrap-around
warm advection on the north side of the low center is now expected
to keep temperatures too warm for snow. This change has been
reflected in the grids...with all rain expected through the
Columbus metropolitan and eastward. Even where temperatures become cold
enough for snow (while precipitation continues to occur)...the wet
nature of the setup will keep the chance of accumulation very low.
This adjustment to temperatures Saturday morning also means that
sub-freezing conditions will only be likely to occur west of
The northerly flow behind the cold front on Friday night and early
Saturday will increase significantly...becoming quite gusty. Wind
gusts of 25 knots (southern cwa) to 30 knots (northern cwa) will
remain in the forecast.
Models have continued to suggest that low-level relative humidity will be
extremely slow to scour out on Saturday and into Saturday
night...and sky grids have been increased through this period of
the forecast. Conditions on Saturday are now expected to remain
rather cloudy...doing no favors to a maximum temperature forecast in
the lower to middle 40s...about 15 degrees below normal.
The change to the cloud forecast is also resulting in a slight
change in thinking for Saturday night / Sunday morning. What once
looked like an easy hard freeze for the entire County Warning Area is now slightly
in doubt for northeast Kentucky and the Scioto valley. The new
hazardous weather outlook will reflect this thinking (and the
level of confidence) in multiple segments.
Long term /Sunday through Wednesday/...
skies should clear and as the high shifts east return flow will
set up starting Tuesday with a warming trend that will put
readings more towards normal values...slightly warmer on overnight
Another cold front will cross the Ohio Valley on Tuesday. Models
diverge in the evolution of the system. Initial forecast had the
front cross early Tuesday and have dry weather over the Northern
Ohio valley. Latest European model comes through with an elongated
NE-SW trough with a middle level strong shortwave riding northeast
along it on Wednesday. The forecast blended the two with an initial
nod to the GFS. Feel that this may need to lean towards the wetter
and more dynamic Euro model solution in future forecasts.
Aviation /12z Thursday through Monday/...
surface high pressure will settle over the Ohio Valley today.
Scattered-broken VFR stratocumulus will continue to linger across the
region. Middle and high level clouds will spread east into the area
between 18z and 00z.
For tonight...an embedded disturbance aloft will increase clouds.
This feature is forecast to pass just to the southwest with
perhaps a small chance of a light shower encroaching near the
On Friday...a potent upper level low will dig southward into the
Great Lakes and Ohio Valley. This system will bring an increase
for showers along and behind a strengthening cold front that will
push through during the day. Aviators can expect MVFR conditions
with the showers. Gusty northwest winds to 25 knots will develop
behind the front.
Outlook...MVFR/IFR ceilings likely Friday night into Saturday
morning...with MVFR/IFR visibilities possible. MVFR ceilings
likely Saturday afternoon into Saturday evening. Gusty north winds
to 30 knots expected Friday night into Saturday