Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 230551

Area Forecast Discussion
National Weather Service Wilmington OH
151 AM EDT Tue May 23 2017

A ridge of high pressure will remain across the region tonight
and Tuesday. Rain chances will increase as low pressure
approaches the region from the southwest late Tuesday night,
and then moves north through the area Wednesday. Rain showers
may linger on Thursday, as the low begins to move east and
cooler conditions return to the area.


Center of surface ridge over the upper Ohio Valley this evening
will move to southern New England by Tuesday morning. Its ridge
axis will continue to extend into our region into Tuesday.
Satellite imagery shows enhanced cirrus shield moving up from
the southwest should encompass the region tonight. As a result,
have increased sky percentage to allow for mostly cloudy
conditions. Overnight lows will dip into the lower 50s.


Jet energy will dig south across the northern plains sharpening up a
trof Tuesday and eventually carving out an upper level low over the
mid MS Vly Tuesday night. Expect to see an increase in high and
some mid level clouds during the daylight hours Tuesday. The digging
system will delay the eastward push of deep moisture and precipitation.
Expect Tuesdays highs to be close to normal, ranging from the lower
70s northwest to the mid 70s southeast.

Have opted for a slower onset of precipitation with low level
easterly flow. Have limited rain shower pops to chance category
spreading in from the southwest Tuesday night. Expect Tuesday
nights lows to be in the lower and middle 50s.


On Wednesday morning, a deepening upper-level trough will be
gradually moving southeast into the middle Mississippi Valley
region, as southwesterly flow aloft becomes more established over
the southeastern states.  As this trough closes into a low, surface
cyclogenesis is expected to occur in the lower Ohio Valley, with all
models now depicting a deepening surface low rotating north through
somewhere near the IN/OH/KY corner during the first half of
Wednesday. Ahead of the surface low, widespread precipitation now
appears likely, so PoPs have been increased to 70 percent and will
likely have to go higher at some point in future forecasts. As
colder air moves in aloft near the upper low, steepening mid-level
lapse rates should allow for at least some instability to develop,
especially on the back edge of the main precipitation area. This
will allow for a chance of thunder, in a regime with forcing and
cyclonic turning associated with the surface low. This may allow for
a few organized storms, though marginal shear and instability values
make any level of severe threat very uncertain, and differences with
regards to the track of the surface low also preclude defining an
area for any potential risk. The forecast is always worth a second
look when assessing a deepening surface low moving through the area
in the spring. Will keep the HWO blank for now, but continue to
watch as additional model runs lock in the pressure patterns a
little closer.

A dry slot is expected to move into the area (particularly the
southeastern CWA) on Wednesday evening, as additional precipitation
becomes more focused in the higher theta-e air on the back side of
the upper low. This will bring another area of precipitation through
the ILN CWA on Thursday, as the upper low passes overhead, perhaps
again providing some weak instability due to the cooler air aloft.
However, there is a wider range of solutions regarding the placement
of enhanced vorticity around the low on Thursday, so PoPs will be
kept on the lower end until agreement improves.

Both Wednesday and Thursday will see relatively cooler temperatures,
with highs in the 60s both days -- below normal for late May.

12Z GFS/ECMWF runs have, interestingly, continued to trend faster
going into the weekend -- not just with the departure of the upper
low on Friday, but with additional precipitation chances beginning
early Saturday. Beyond that, model spread remains somewhat high for
the weekend forecast, as a series of shortwaves is expected to move
eastward across the region in the pseudo-zonal flow. At least
initially, it is likely that some sort of surface boundary will
exist across the region, with greater theta-e just to the south.
Though this may eventually shift northward, this pattern is one that
would support multiple rounds of showers and storms within an
increasingly moist air mass. Thus, there will be at least some
potential for both stronger storms as well as heavy / repeated
rainfall for Saturday and Sunday. Within the GEFS suite and from run-
to-run of the operational ECMWF/GFS, there are still big differences
in wave amplitude/timing, negating the ability to forecast the
specifics. For now, lower-end PoPs will be maintained through the
entire weekend (though this has been increased from the previous
forecast), with slightly above normal temperatures. This may come to
an end with a cold frontal passage late Sunday into Monday, leading
to drier conditions to start next week.


Surface ridge centered to the northeast will continue to
extend down across the tafs today. This will keep the low
levels dry. Stubborn cirrus will provide broken to overcast
ceilings into afternoon when it is expected to thin.

After 00Z, the low levels start to moisten as vort max swings
around the closed H5 low in the Mississippi Valley. Pcpn started
to work into the the sw tafs, so added a VCSH to CVG at the end
of the period.

OUTLOOK...MVFR ceilings and visibilities possible Wednesday
into Thursday, and again Saturday.




NEAR TERM...Hickman
LONG TERM...Hatzos
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