Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 230249

Area Forecast Discussion
National Weather Service Wilmington OH
1049 PM EDT Sun Oct 22 2017

An upper level disturbance will bring an increasing chance of
rain late tonight and through the day on Monday. This will also
usher in a much cooler airmass that will then remain in place
across the region through the rest of the week.


Thickening cirrus pushing into the area with widespread
precipitation band slowly approaching and along western Indiana
border, but will take nearly all night to push into western
forecast area. Have adjusted overnight temperatures slightly, as
temperatures had dropped a little more quickly prior to the
spread of high clouds into the region so some potential for
slightly cooler lows in espcially the east before the increase
in southerly low level winds with approaching moisture. Have
also tightened up the precipitation onset chances as high res
models are capturing the sharp precipitation edge pretty well,
coinciding with the leading edge of the 09-12z low level
convergence ramping up in SE Indiana and portions of KY on the
front edge of a 55+ kt low level jet. This means slowing down
precipitation chances in central and eastern forecast area.


An upper level low will move out of the mid Mississippi Valley
late tonight and pivot up across our area as it gets absorbed
into the broader trough settling in across the central CONUS.
As it does, an associated surface low will lift northeast across
the region through the day. This will all lead to increasing
dynamics across the region with an impressive low level
convergence/upper level divergence couplet working northeast
across our area in the 12Z-18Z time frame. This will result in
widespread shower activity overspreading our area through the
morning hours with the more widespread pcpn then tapering off
from the southwest later through the afternoon as we start to
get on the back side of the surface low. Instability looks to be
very limited although there are some hints of possibly some
very weak instability developing through early afternoon,
especially across our southeast. Given the low level winds
fields, this could lead to a very low end severe threat across
our southeast if we are able to get a bit more instability.
However, this chance appears low enough that will keep any
mention of thunder out of the forecast at this point.

The low level wind fields will allow for some fairly impressive
moisture advection through the morning with PWs pushing up in
excess of 1.5 inches. This will lead to the possibility of some
locally heavy rainfall with some of the embedded convective
elements. With 1 hour FFG values in the 2.0 inch range and the
fact that any convective cells should be moving fast given the
strong mean flow, think the overall flash flood threat will
remain low through the day on Monday. We will likely see some
non diurnal temperatures through the day on Monday with the
pcpn moving in through the morning hours and then some CAA
developing through the afternoon. Will generally range highs
from the mid 60s in the west to the upper 60s in the east.

We could see a lull in the more widespread shower activity
early Monday evening. However, additional mid level energy will
drop down toward the area Monday night as a secondary low level
trough axis approaches. This will lead to a continued chance of
showers through Monday night.


Most of the long term will be characterized by below normal
temperatures with only a brief period of near normal
temperatures. The long term will open up on Tuesday with an
upper level low located near Lake Michigan and much cooler 850
mb temperatures pushing in from the west. Most of the day looks
to be cloudy and breezy with temperatures only reaching into the
mid to upper 50s. Have continued to lower highs Tuesday as 850
mb temperatures and 1000/ 850 mb thicknesses look to drop
through the afternoon (near freezing and 1325 m respectively).
Have kept the chance of precipitation in the forecast given the
falling 850 mb temperatures and steep lapse rates, but am a
little concerned that the NVA on the backside of the trough axis
might limit development.

Wednesday the piece of energy from Tuesday will eject northeast only
to have another shortwave dive southeast out of Canada towards the
Great Lakes. Thanks to this 850 mb temperatures will remain slightly
below zero (supported on both the GFS and ECMWF) helping to keep
high temperatures only around 50 degrees.

Wednesday night into Thursday a widespread frost looks likely as the
shortwave energy will pull north east and the main longwave trough
axis modulates. This will allow the best ageostrophic convergence to
move overhead, along with a brief clearing to occur.

Thursday the surface high pressure will slide east with high
temperatures warming into the mid 50s as heights recover. Friday
another more potent shortwave will dive southeast out of Canada
towards Wisconsin. A surface cold front in association with the
shortwave will then cross the area Friday afternoon. The CMC and GFS
are in pretty good agreement with the latest ECMWF changing its
tune to more in alignment with the 12z GFS/ CMC. Have gone ahead and
matched the highest chance of precip with the front.

For the remainder of the weekend precipitation will be slow to exit
as the shortwave again is forecast to wrap up into an upper level
low with heights quickly rising across the west coast. Either way,
highs only look to reach the mid 50s (at best) with lows in the 30s.


Thickening cirrus and mid clouds working into the area, with
mid clouds to western TAF locations by 09-10z and MVFR ceilings
by 12z with showers spreading into KLUK/KCVG in that timeframe.
Fairly slow progression across the area with KCMH/KLCK after
15z. Could occasionally see MVFR visibilities as there is
potential for moderate rainfall rates as well. As the surface
low lifts toward the NE, widespread rain will come to an end,
but more spotty showers and ceilings will linger the potential
for MVFR cigs.

OUTLOOK...MVFR ceilings and visibilities possible through




LONG TERM...Haines
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