Area Forecast Discussion
Issued by NWS Wilmington, OH-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KILN 270744
Area Forecast Discussion
National Weather Service Wilmington OH
344 AM EDT Thu Apr 27 2017
A cold front will push east across the region today. High
pressure will briefly build in behind the front tonight. A
frontal boundary will develop and then linger across the area
through the first half of the weekend. This will result in
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Mosaic radar early this morning continues to show a decreasing
trend in echo coverage and lightning activity to our west.
Precipitation to our west is within a prefrontal convergence
area. High resolution/convection allowing models indicate that
by the time the precipitation reaches our western zones toward
sunrise, coverage should be scattered with little in the way of
For today, as low pressure moves north toward eastern Lake
Superior, a cold front will advance east across the forecast
area. There should be enough forcing and some diurnal
instability for a chance of showers and thunderstorms for
roughly the eastern half of the CWFA. There is a low chance for
an isolated strong/severe storm (wind) as the front pushes
east. It will be breezy given fairly decent pressure gradient
and winds mixing down from aloft. Wind gusts will be the highest
in the climatologically favored Whitewater/Miami Valleys and
west central Ohio where wind gusts maybe as high as 35 mph. High
temperatures will be somewhat muted in terms of a normal
diurnal trend due to clouds and some CAA behind frontal passage.
Will forecast highs from the mid 60s far west to the mid 70s
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
The cold front will have cleared our area by this evening,
allowing weak high pressure to build into the middle Ohio Valley
overnight. Post frontal stratocumulus clouds should scatter,
eventually being replaced by some mid/high clouds streaming in
from the southwest aloft. Winds will diminish fairly quickly
near or after sunset. Lows will fall into the mid and upper 40s
toward sunrise Friday morning.
On Friday, weak high pressure will move off to the east. In a
southwest flow aloft, a weak disturbance and developing
isentropic lift will increase clouds from west to east through
the day. A few showers may develop across the western CWFA late
in the day. There will be a decent temperature gradient from
northwest to southeast due to differences in the thickness of
cloud cover and the overall low level thermal fields. Highs
will range from the upper 60s northwest to near 80 along and
south of the Ohio River.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --On Friday evening, ridging off the southeast coast will set up a
pattern of deep-layer warm and moist flow across and north of the
southeastern states. Height rises over the Ohio Valley will also be
occurring, as a frontal zone begins to develop from the middle
Mississippi Valley into the southern Great Lakes, well in advance of
a big upper wave developing in the central plains. As moisture
advects into the region from the Gulf, models are also consistent in
depicting a plume of steep mid-level lapse rates moving northeast
into the lower and middle Ohio Valley on Friday night. As these
factors combine, nocturnal elevated convection is expected to
develop, in a regime with moderate to strong shear. The threat for
severe weather will be contingent on how much instability develops,
though confidence is a little higher than it was yesterday, at least
in terms of elevated instability. Surface-based convection is
appearing somewhat unlikely, but elevated cells capable of large
hail and heavy rain appear to be an increasing threat, especially in
the southwestern ILN CWA between 02Z-10Z. While a more significant
heavy rain threat is developing west of the region, current
indications are that while storms in the ILN CWA Friday night (and
into Saturday) may produce heavy rain, a prolonged / widespread
event is less likely. Thus, the chance for flooding (like the chance
for severe) will probably be somewhat localized.
As frontogenesis continues to occur into Saturday, the surface
boundary appears likely to set up directly over the ILN CWA. This
will result in a significant gradient in both temperatures and
weather, with continued chances for showers and thunderstorms
gradually shifting north, but a very warm and likely capped air mass
further south. Additional precipitation thus looks like more of a
concern in the northern half of the ILN CWA on Saturday, then perhaps
only with disorganized activity in the northwestern CWA by Saturday
night and into Sunday. Temperatures are expected to range by as much
as 20 degrees across the ILN CWA on Saturday, with mid 80s in the
southeast and mid 60s in the northwest. The very sharp temperature
gradient currently forecast here results in lower-than-normal
confidence in the exact numbers, however.
There remains strong agreement in the general pattern for Sunday
into Sunday night, with deepening low pressure at the surface and
aloft ejecting from the plains into the Great Lakes, driving a
strong cold front through the Ohio Valley. GEFS clustering of the
mid-level low has improved, suggesting that timing confidence is
becoming a little more certain, but the 00Z ECMWF came in
significantly slower than its previous run, functionally negating
the preceding statement. One other item of note is that the 00Z
models suggest a slight change to the pattern, which appears a
little more occluded than depicted before.
It looks mostly certain that the ILN CWA will end up completely in
the warm sector within a regime of deep and strengthening southerly
flow on Sunday, before precipitation becomes more likely on Sunday
evening from west to east. With a slight bit of increased confidence
in later timing and drier conditions in the warm sector, the
temperature forecast has been increased slightly, allowing for mid
to possibly upper 80s in the far southeast. The gradient will not be
as strong as Saturday, so the northwest ILN CWA should still get at
least into the mid 70s, unless pre-frontal precipitation has greater
coverage than expected.
The front on Sunday night will be strong and moving fast, ushering
in a pretty significant change in air mass. Thus, low-level forcing
is not expected to be an issue, and convective development along the
front should be solid. That will combine with a fairly strong
magnitude of shear to allow for some level of severe threat to
exist. Waning instability, unfavorable timing, and mostly-meridional
flow (questionable directional shear favorability) will serve as
limiting factors to the severe threat. As this is still several days
away, for an event with several question marks, it is probably too
early to make a specific forecast for hazards. With that said, some
threat for heavy rain and severe weather could occur.
Behind this front, there will be a notable change in air mass -- and
strong cold advection that will lead to strong wind gusts, into the
35-40 MPH range. There will also be a significant drop in
temperatures -- a difference of around 20 degrees from Sunday.
This forecast will continue to undercut the general model blend,
coming closer to raw GFS/ECMWF numbers for Monday.
No signs of significant weather on Tuesday, with a slight bit of
warming in pseudo-zonal flow. By Wednesday, another developing
frontal zone will combine with an approaching wave to allow for
increases in precipitation chances through the middle of the
-- End Changed Discussion --
.AVIATION /08Z THURSDAY THROUGH MONDAY/...
As low pressure lifts north toward eastern Lake Superior today,
a cold front will advance east across the region. Before any
precipitation arrives toward the western terminals by sunrise,
we first must deal with winds increasing along with a strong low
level jet aloft. The strong low level jet requires at least a
period of non-convective LLWS at the terminals roughly between
06Z and 12Z.
For today, high resolution models/convection allowing models are
really backing off on precipitation coverage ahead of the front
across our western forecast area. Also, instability is expected
to be fairly low this morning. As a result, just have a chance
of showers for western terminals this morning. It is unclear if
ceilings will lower into the MVFR category west due to lack of
widespread rain. Have kept ceilings VFR. As the front moves east
this afternoon, there may be enough diurnal instability for a
chance of thunderstorms toward the KCMH/KLCK. Winds will be
gusty with a subtle shift in wind direction from south to
southwest behind frontal passage. Expect wind gusts in the 25 to
30 knot range.
For tonight, front will be east of the area. Weak surface high
pressure will build briefly into the middle Ohio Valley. Post
frontal stratocumulus clouds should scatter through the evening
with some mid and high level clouds arriving from the southwest
aloft. Gusty winds should diminish fairly quick after sunset.
OUTLOOK...MVFR ceilings and visibilities with a chance of
thunderstorms are possible Friday night into Monday. Wind gusts
to 30 kt possible Sunday through Monday.