Area Forecast Discussion
Issued by NWS Cleveland, OH

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FXUS61 KCLE 271359
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
959 AM EDT Thu Apr 27 2017

.SYNOPSIS...
Low pressure across Illinois will deepen and track north through the
Great Lakes today, bringing a cold front through the area. High
pressure will build across the area tonight into Friday. A warm
front will lift north into the area and linger Friday night through
Saturday night as a series of low pressure systems track
northeast along the front.

&&

.NEAR TERM /THROUGH TONIGHT/...
Update...Showers are expanding across western Ohio this morning
ahead of the approaching cold front. The first batch should just
scrape the western borders of the cwa but then expect showers
and a few thunderstorms to move into the area. will also likely
see further development to our south that will move north into
the area towards noon/2pm. Have made a few adjustments to ops
and wx but no big changes.

Original discussion...
Low pressure across southern Illinois will track northward across
Lake Michigan this morning and over Lake Superior this afternoon, in
response to negatively tilted upper trough and associated upper jet
swinging northeastward into the Great Lakes. This will force a cold
front across the area today with increasing chances for showers and
thunderstorms. Biggest factors for coverage of precipitation will be
the timing of the front and the role of ongoing upstream convection
across the local area.

Convection has increased somewhat in intensity across southern IN
south of KIND, likely on the nose of increasing LLJ. Hi-res guidance
has struggle to capture evolution of ongoing precipitation. Recent
runs of the HRRR starting to latch on a bit to current convection,
and trends have shown decaying showers racing northeastward into the
SW part of the CWA shortly around/after 12Z. As the cold front
pushes into the area, renewed convective activity is expected, with
the best chances along/east of a Mansfield to Cleveland line from
16Z-18Z onward. Have kept pops in the slight chance/chance range
west of this line through the morning hours, then introduce high
likely pops east of the line through the afternoon/early evening
hours.

Severe threat remains somewhat conditional for this afternoon.
Severity likely hinges almost solely on degree of pre frontal
destabilization across northeast Ohio. Surface temperatures
approaching 80F with dewpoints at/just above 60F should allow for
SBCAPE values to approach 1500 j/kg. If this is realized, more
organized convection is likely, mainly in the form of multicellular
clusters, especially with ample deep layer shear values of 45-50
kts. Steep low level lapse rates, inverted V shaped soundings, with
decent dry air aloft would pose a damaging wind risk, with isolated
large hail a secondary risk. However, many factors working against
severe convection. Still questioning whether or not we will realize
enough CAPE for severe updrafts, especially if upstream convection
stabilizes the boundary layer and limits destabilization. Also,
marginal mid level lapse rates and decent mid level warm layer could
limit sufficient UVM for severe convection. SPC marginal risk looks
like a fair call at this point, but mesoscale environment will need
to be monitored throughout the morning/early afternoon to understand
the extent of severe potential for this afternoon.

Front should clear the forecast area to the east by 00Z, with mainly
dry conditions tonight/overnight as high pressure builds into the
area. Temperature forecast for today is trick. Kept highs near
previous forecast, but refined hourly temperatures to reflect non-
diurnal post frontal temp curve. High temps for the day may be
realized late morning/early afternoon before dropping west of the I-
71 corridor. Lows tonight near previous forecast.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
Ridge axis will shift east of the area on Friday, with warm
southerly flow into the region. Low pressure will track from the
southern Plains towards the southern Great Lakes during the day.
This may bring a few showers to the western part of the forecast
area, but the best forcing will be northwest and southwest of the
area through the afternoon and evening, but will keep a slight
change/low chance for western areas. The low will track through the
area along a quasi stationary warm front Friday night. Kept
likely/chance pops similar to previous forecast. The stationary
boundary will linger across the area through Saturday, with
continued likely pops Saturday and Saturday night as piece of energy
eject along the boundary. The boundary will lift north of the area
as a deepening upper trough across the central CONUS amplifies the
pattern. Currently thinking there will be a dry period Sunday across
the area so have backed off to low chance to low likely pops from
south to north on Sunday. Kept temperatures through the period
similar to previous forecast with boundary lingering across the
area.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
Large area of low pressure will be moving into the central Great
Lakes on Monday. Still some uncertainty on how fast it will really
lift out of the southwestern US. Still think the models are bringing
northeastward a little on the fast side. Would not be surprised to
see another 12 hours slower with the timing of the cold front which
would shift the thunderstorms chances into Monday evening. We will
continue to monitor this and adjust as needed over the next few
days.

The unsettled weather will continue into Tuesday and Wednesday as
the upper level trough persists across the central Great Lakes and
brings temperatures back to reality.

Monday will be the warmest day of the long term. However with
uncertainty with the timing of the front it will be difficult to
forecast. At this point will keep highs ranging from the mid 60s to
lower 70s. Cooler Tuesday into Wednesday with highs ranging from the
mid 50s to lower 60s.

&&

.AVIATION /12Z Thursday THROUGH Monday/...
Cold front is moving into the central Indiana with a few showers
along it. These will likely struggle to development much more
through the morning. However we will continue to monitor.

VFR conditions are expected to continue well into the afternoon
as a cold front moves across northern Ohio. The weakening cold
front should reach NW PA by early evening. Expect to see cloud
cover thicken and lower through the day with increasing chances
of showers and thunderstorms. It appears that NW OH may miss out
on the showers/thunder as outflow boundaries and better
convergence set up further to the east. The better low level
convergence and instability will be located over the eastern
half of northern Ohio into western PA. Have placed a couple hour
tempo group in the TAF`s from KCLE to KMFD and points eastward.
Expect to see all of the shower/thunder activity that can
develop to be east of the region by sunset.

Winds will be southeast to south this morning. KERI area may see
winds a bit more gusty with the downsloping conditions. All
locations will become gusty this afternoon from the south and
southwest. Current thinking is that wind gusts should be around
25 knots but could be slightly higher. Will have to watch for
stronger gusts near the stronger thunderstorms that can
develop.

OUTLOOK...Non-VFR at times in showers and thunderstorms Saturday
through Monday.

&&

.MARINE...
Winds become south to southwest today and will increase this evening
as a weak cold front passes. There is a small window where winds and
waves could increase enough from Willowick to Ripley for a small
craft advisory. Since it appears that it will be very short lived we
will hold off for now and let later shifts watch it closely.

This weakening cold front will stall over southern Ohio tonight and
then begin to work its way back northward toward Lake Erie. Before
the front can move back northward the lake will experience a period
of high pressure and lighter winds. So this should allow a lake
breeze to develop on Friday.  There are several pieces of low
pressure that will track along the front. The strongest piece will
move into the central Great Lakes Sunday night. Northeasterly winds
will develop ahead of this area of low pressure will small craft
conditions expected from Cleveland to the Western Basin.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...None.

&&

$$
SYNOPSIS...Greenawalt
NEAR TERM...Greenawalt/TK
SHORT TERM...Greenawalt
LONG TERM...Mullen
AVIATION...Mullen
MARINE...Mullen



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