Area Forecast Discussion
Issued by NWS Cleveland, OH

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051
FXUS61 KCLE 272338
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
738 PM EDT TUE SEP 27 2016

.SYNOPSIS...
An area of low pressure will move from the Upper Lakes overnight
into the Ohio Valley by Wednesday. This feature will meander over
the region for several days providing cloudy skies, rain, and
isolated thunderstorms.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
The dry slot over the region will push east overnight. Energy
moving in advance of an upper low dropping south from the Lake
Superior this evening will help develop some clouds over the area.
The clouds will progressively fill in overnight as a strong vort
max moves in. This feature along with height drops will begin to
support shower activity mainly in our western counties. Believe
the showers should hold off until daybreak given how much dry air
needs to be overcome to support measurable rain. Winds will come
down overnight as the mixing is reduced. Temperatures will drop
down into the lower 50s. Some area will touch the upper 40s, but
given more wind and encroaching clouds than last night most areas
should remain in the 50s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As stated above the rain chances will start Wednesday morning
mainly in the west and gradually spread east through late morning.
The height falls associated with the upper low are impressive,
which will help steepen the lapse rate over the area. Temperatures
will struggle to reach the upper 60s given cloud cover and
showers, but this will be sufficient to support thunder. Best
timing will be early afternoon when the vort max moves in.

The upper low will become cut off right over the Ohio Valley
through late week. Generally speaking conditions under this set up
are cloudy skies with on and off showers with isolated
thunderstorms during peak heating (or timing of best divergence
aloft and/or convergence along the moisture axis). The exact
placement and evolution of this feature and the surface low could
have big impacts on the rainfall forecast. The location of the mid
level moisture advection from the Atlantic combined with the
placement of the left exit region of the upper level jet,
deformation zone, and vorticity max will help develop large bands
of rain that could extend into southern PA. On the flip side a dry
slot could move in and bring a break to the rain for portions of
the CWA. The favored location at this time looking at the
impressive forcing aloft is the north and eastern counties
Thursday into Friday. These areas could see hours of moderate to
heavy rainfall. Overall most areas should see an inch of rain
through the end of the week with the potential for notably more.
The slow movement of the low could lead to excessive rainfall
problems should banding develop over the area. Will have to see
how the models come in-line over the next 24hrs.

Temperatures will be challenging as well. There will be warm
advection moving in Thursday and Friday as we develop a strong
moisture feed from the mid Atlantic. However the upper level low
will support notably cooler temperatures. Believe we could see a
bigger temperature gradient from West to East as the exact
placement of the low and surface features come into line. For now
have temperatures generally in the 60s.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Fall is upon us and the overall pattern is shaping up to remind us
this season is here.  Vertically stacked low right on top of the
local forecast area will slowly meander around the eastern Great
Lakes through the forecast period.  The upper level low sort of gets
cut off and begins the slow shift east as amplification of the broad
upper level ridge encompassing three fourths of the United States
and Canada begins to shift east. The stacked low will keep a
relatively cool pool of air over the forecast area along with
pumping a conveyor belt of moisture in from the Atlantic Ocean. This
flow of moist air could bring quite a bit of rainfall to the eastern
portions of the forecast area early in the extended periods.
However, one caution is how extensive the dry slot interacts with
the conveyor belt and pushes the moisture further north and out of
our area. So, this all remains to be seen in how the storm system
winds down by the weekend.

As mentioned, with the cool pool over the area and potential for
showers, we will not see temperatures climbing much out of the 60s
through the first half of the extended periods.  Eventually, as the
upper level low pulls out, some warm air advection will take place
and restore temperatures back into the 70s. Otherwise, overnight lows
will be consistently in the 50s.

&&

.AVIATION /00Z Wednesday THROUGH Sunday/...
Low across Lake Superior will spiral southward to the Ohio Valley
where it will linger for days. VFR conditions on the
fringes...but as we get some of the deeper moisture into the area
late morning/midday...Non-VFR conditions will take over...from
vsby issues in RA and/or from lowering ceilings. Western terminals
will likely be the focus for the steadier showers on Wednesday.
IFR possible in the heavier rain. Thunderstorms possible in the
afternoon. Winds will shift counter- clockwise around the dial
over the next 24 hours. Low confidence in the exact timing of the
impactful changes though.

OUTLOOK...Periods of non-VFR through Sunday.

&&

.MARINE...
Massive upper level and surface low will slowly work their way
southeast across the lake over the next 24 hours. The low will
continue to cause winds to gradually diminish overnight from west to
east. Will continue the small craft advisory in the west into the
evening and the east late tonight.  We will likely need to reissue
the small craft advisory once again Thursday and continue it until
Friday when the winds finally start to diminish again. Otherwise,
lake will be quiet for the duration of the weekend.

As the upper level low settles in over the area, there will be a
chance for waterspouts through the rest of the week. This should
begin during the day tomorrow as the showers move into the local
area.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...Small Craft Advisory until 3 AM EDT Wednesday for LEZ146>149.
     Small Craft Advisory until 10 PM EDT this evening for
     LEZ142>145.

&&

$$
SYNOPSIS...Jamison
NEAR TERM...Jamison
SHORT TERM...Jamison
LONG TERM...Lombardy
AVIATION...Oudeman
MARINE...DJB/Lombardy



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