Area Forecast Discussion
Issued by NWS Cleveland, OH

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272
FXUS61 KCLE 182234
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
634 PM EDT Wed Apr 18 2018

.SYNOPSIS...
Low pressure will move across Central Ohio tonight, then to the
New England coast on Thursday. This will bring rain to northern
Ohio and northwest Pennsylvania later today which will mix with
and change to snow showers tonight before tapering off
Thursday. A large area of high pressure will build southeast out
of Canada reaching the Great Lakes region to end the week.

&&

.NEAR TERM /THROUGH THURSDAY/...
No significant changes for 630 update. Low pressure centered
just SW of Cincinnati with ht falls centered NRN WV. Light rain
just now starting across the western portion of the forecast
area.

Original discussion...
A narrow wedge of surface high pressure remains over northeast
Ohio and western PA this afternoon. Satellite shows stubborn low
clouds lingering over Lake Erie, far northeast OH and northwest
PA. Elsewhere skies are mainly sunny. Weak southerly low level
winds will continue to eroding the stratus from the south with
Erie, PA perhaps seeing a narrow window of some sun late this
afternoon before clouds increase this evening ahead of low
pressure approaching from the mid- Mississippi River Valley.
Surface temps are in the mid 40s across northern OH with mid 30s
in Erie, PA beneath the stratus and closer to the cold lake
waters.

The leading edge of thicker clouds are shifting across northern
Indiana this afternoon. Expect sunshine to fade to overcast
skies across western OH late this afternoon. Dry low level air
will delay the onset of precip ahead of the low until early this
evening. Earlier we slowed down the arrival of rain a few hours
based on 12z meso models/ensembles. Rain will expand from west
to east across Ohio between 5 and 9 PM but may be delayed into
northwest PA until after 9pm.

Tonight, the center of low pressure will quickly shift across
Central Ohio and into Central PA during the overnight. This will
be forced by a compact upper level wave dropping south of the
Great Lakes. Precipitation type will be plain rain through the
evening before cold northwest flow wraps into the back side of
the low and allows for a mix with then transition to snow
overnight. There is even a chance for some sleet to mix in
during the change over with NAM sounding indicating a thin warm
nose aloft before the center of the surface low shifts east.

Expecting that the timing of the bulk of the snow mainly being
during the overnight will help allow for some light
accumulations. Snowfall totals range from less than an inch in
NW Ohio to around 2 inches in portions of the snowbelt with
locally higher amounts in NW PA. Counties closer to Central Ohio
may only receive trace amounts of snow. Any sleet that mixes in
would even further lower snow accumulations. Low temps tonight
should drop to within a few degrees either side of freezing.

Wrap around moisture pulls away quickly on Thursday but expect
snow showers to linger in the snowbelt through at least the
morning in northeast OH and chances lingering into the afternoon
for inland NW PA. Daytime accumulations should be limited by
the high April sun angle with an inch or less additional. Temps
Thursday will be cooler downwind of Lake Erie with NE Ohio and
NW PA in the 35-40 degree range while NW Ohio reaches the mid
40s with skies clearing in the afternoon. Seasonal norms are
near 60 degrees.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
Cyclonic flow will gradually give way to surface high pressure
in the short term period. This will allow for an end to snow
shower activity in NW flow over NW PA and a marked reduction in
cloud cover going into the weekend. A couple of day of largely
clear skies are expect other than some mid-level clouds sullying
the sky on Saturday. Even with high pressure becoming the
controller of the forecast, however, temperatures will have
difficulty jumping toward normal and remain largely below normal
through the period.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
The pattern that has been in control over the region with
largely northwesterly flow throughout the column will finally
yield to a bit more progressive pattern, at least for a time.
This will mean ridging aloft will translate through the area
early next week and finally yield a period of southwesterly flow
and warm advection for the start of the week. As such, better
mixing profiles with the warm advection will yield a nice bump
upward in temperatures toward normal to start the week. However,
as a nearly cut off upper low meanders toward the Appalachian
Chain beyond Tuesday, rain chances will start to increase from
the southwest as a better plume of precipitable water starts to
edge toward the region. Model concurrence on this idea for the
progression seems strong, however timing is a bit specious
amongst the different pieces of guidance. Thus, a general trend
toward higher pops by day 7 seems like a prudent approach for
the moment with only liquid precipitation realistically
possible given the pattern and warm profiles.

&&

.AVIATION /18Z Wednesday THROUGH Monday/...
The stratus shield is continuing to slowly erode from the south
as diurnal mixing along its periphery is entraining drier air
into the lower levels. This should allow for a few hours of VFR
conditions at all sites before the next system approaches from
the west.

MVFR skies will again overspread the area from W-E late this
afternoon/evening as the next system approaches. Most sites will
start as rain with easterly flow increasing as the precipitation
develops. The exception seems likely to be KERI as colder air
feeding from the NE may keep all things snow. That said, as
colder air moves into the area on flow that turns from NE to N
late this evening and overnight, all sites will rapidly
transition to snow with cigs dropping like a rock to IFR as
precipitation becomes more persistent.

Once the system pulls east on Thursday, gusts NNW will prevail
at all sites with lake effect snow showers common.

OUTLOOK...Non-VFR possible again late Wednesday night and
Thursday, lingering in NE Ohio and NW PA into Friday.

&&

.MARINE...
Low pressure tracking just north of the Ohio river valley tonight
with bring increasing northeast winds tonight, becoming
northerly in the 15-25 kt range by Thursday morning. Small
craft advisories have been issued for late tonight into Thursday
night. Winds will subside to 15 kts or less Friday as high
pressure begins to build across the lake with waves below
advisory levels. Winds will become light and variable Friday
night through the weekend with high pressure overhead, becoming
predominantly easterly Sunday night into Monday as the ridge
moves east of the Great Lakes.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...Small Craft Advisory from 5 AM Thursday to 5 AM EDT Friday for
     LEZ147-148.
     Small Craft Advisory from 9 AM Thursday to 5 AM EDT Friday for
     LEZ149.
     Small Craft Advisory until 2 AM EDT Friday for LEZ144>146.

&&

$$
SYNOPSIS...SMITH
NEAR TERM...SMITH/DJB
SHORT TERM...FRIES
LONG TERM...FRIES
AVIATION...FRIES
MARINE...SMITH



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