Area Forecast Discussion
Issued by NWS Wilmington, OH
FXUS61 KILN 260609
Area Forecast Discussion
National Weather Service Wilmington OH
209 AM EDT THU MAY 26 2016
Persistent southwesterly flow will keep temperatures above normal
through the weekend. The combination of the warm temperatures and
occasional upper level disturbances moving through the region will
lead to chances for showers and thunderstorms through at least the
end of the week.
.NEAR TERM /THROUGH TODAY/...
Weak upper level disturbance was helping to provide a few showers
across portions of central and south central Ohio this afternoon.
Disturbance will shift to the east through late afternoon, and
scattered showers will follow suit.
Behind this disturbance, there is not a whole lot activity going
on underneath plenty of mid/high level clouds within the immediate
CWA. As such...there is not a lot instability to work with
through late afternoon. We can`t rule out a stray shower or
thunderstorm mainly across the west/southwest portion of the CWA
where there are a few breaks, but the balance of the late
afternoon should be dry.
This evening into the overnight hours, guidance suggests another
upper level disturbance moving into/through the Ohio Valley and
lifting to the northeast. Expect at least scattered showers to
make their way into the western CWA and therefore pops have been
bumped to high chance in this area, with lower pops remaining
further east as there is question as to how far east showers make
it before they may dissipate late at night. Can`t rule out thunder
particularly across the Tri-State area/western CWA this evening
either but overall trend will be for activity that develops to
weaken after dark and would primarily be in the form of showers.
.SHORT TERM /TONIGHT THROUGH 6 PM FRIDAY/...
We remain in a similar pattern Thursday/Thursday night, being on
the western edge of a ridge and south/southwest flow maintaining a
warm and also somewhat moist air mass throughout the Ohio Valley.
We may begin Thursday with plenty of clouds before the
aforementioned upper level disturbance moves outside of the CWA.
With some breaks in the afternoon, there should be enough
instability for a few mainly diurnally driven showers and
thunderstorms but overall forcing looks weak and therefore kept
pops in the slight chance to low chance range.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The certainties of this period revolve around warmer and more humid
conditions than normal for late May and early June /high confidence/
and a rather unsettled sensible weather period /moderate confidence/.
In the details...at 12Z Friday there is strong clustering/agreement
among NCEP/non-NCEP deterministic and ensemble data showing a rather
amplified/blocky flow structure across the CONUS. Features of
interest will be an evolving/cutoff/closed upper trough off the
southeast US coast...and negative height anomalies in the nations
mid-section in association with continued longwave troughing
underneath ridging across the US/Canadian border north in cntl
Canada. Of particular interest...as the deep layered trough
continues to develop off the southeast US coast...will be ridging
developing on the north/west side of this feature...and downstream
of the negative height anomalies in the cntl US. This has direct
implications on Ohio Valley temp/precip trends.
Unfortunately...once we remove the certainties that Friday-Wed will
be warm/seasonably moist in the boundary layer with daily highs in
the 80s and nighttime lows in the 60s with dew points in the lower-
mid 60s...there/s not much to hang our hats on in terms of sensible
weather predictability. The presence of the continued
troughing/negative anomalies in the cntl US will keep a weak swly
mid layer flow directed into the Great Lakes...thus convectively
produced/enhanced perturbations will be a constant threat to evolve
east out of plains convective systems. These will inherently run
into a height/flow pattern on the nwrn side of the developing sern
CONUS trough that will not be conducive to organized/strong
lift...and ridging over the Appalachians/Great Lakes will be
reinforced. End result - there/s a lack of surface boundaries and/or
appreciable stronger s/w troughs moving through the flow to produce
more enhanced/higher predictability periods of vertical motion.
Thus...precipitation chances will be driven in a very weakly forced
manner under marginal flows and instabilities. Thus...there is no
choice but to run 20-40% chances of showers/storms each day with the
notion that many hours will be dry...and many locations could go
several days without seeing rain. A true summertime pattern. It
would seem that weak height falls centered later Sunday into Monday
with the passage of a very subtle low-level boundary may afford the
opportunity to introduce higher rain chances in coming
forecasts...but forcing is so weak and soundings unimpressive enough
from a shear/instby perspective that it gets tough to justify it.
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Main forecast concern for the TAF period will be the potential
for MVFR cigs developing before daybreak as a weak mid-level
disturbance interacts with a moist airmass. Low level moisture
has increased substantially over the past 24 hours, and models
(although slightly overdoing the moisture) all indicate an MVFR
deck developing over western Indiana and expanding eastward into
Ohio and northern KY early this morning. Current upstream
observations along IL/IN border confirm this is plausible, but the
main question will be how expansive this deck will become. Can`t
rule out some brief BR at KLUK by daybreak and perhaps a few
spotty showers developing.
Models are slow to mix out the low levels during the day on
Thursday, suggesting the MVFR deck may linger into early
afternoon before scattering out and lifting. Instability will
increase Thursday afternoon, but with very little forcing to be
found did not include any showers/storms in the TAFs. Winds will
remain out of the SSW around 10 knots or less through the TAF
OUTLOOK...Thunderstorms possible Saturday through Monday.