CLE issues Area Forecast Discussion (AFD) at Aug 1, 10:00 AM EDT624
FXUS61 KCLE 011400
AFDCLE
Area Forecast Discussion
National Weather Service Cleveland OH
1000 AM EDT Thu Aug 1 2024
.SYNOPSIS...
A general surface trough across the region will consolidate into
a weak low pressure system by Friday morning. This low will move
east and extend a weak cold front across the area on Friday.
However, the main surface low will meander across the Ohio
Valley through Saturday. High pressure will enter the region for
Sunday.
&&
.NEAR TERM /THROUGH FRIDAY/...
930 AM Update...
Outside of minor adjustments to temperatures, dew points, and
sky cover through this afternoon, the forecast into this
afternoon remains on track.
Uncertainty continues late this afternoon into tonight. The
forecast for this evening into tonight will rely on how the MCS
mentioned in the previous discussion behaves as it likely moves
southeast along the instability gradient, but there could be a
surge of moisture and higher instability across far southern
zones (from roughly Hancock to Holmes counties) as a warm front
lifts into the area this evening. Although showers and
thunderstorms could develop along the lake breeze this
afternoon, the better chance of convection will occur along the
warm front late this afternoon and especially this evening.
Given the moisture and buoyancy, any showers/storms that develop
this afternoon and evening could result in gusty
winds/downbursts in addition to localized torrential rainfall
rates, best chance in southern zones where a Slight Risk for
severe weather has been introduced and along the lake breeze
boundary. While there's still a bit of spread in
timing/placement of storms amongst CAMs due to uncertainty in
the northward extent of the warm front at the time of convective
initiation, latest RAP/NAM soundings suggest that effective
bulk shear could approach 25-30 knots in southwestern zones
which could result in more organized storms and an elevated risk
of large hail and a low-end tornado threat in southwestern
zones this evening. Precipitation will likely enter the western
portion of the area at around 21Z/5 PM EDT (give or take an
hour or two) before lifting northeast into NE OH/NW PA sometime
later this evening or even at some point overnight.
Previous Discussion...
Much of the daytime hours should be dry across the forecast
area today. There is a distinct lack of forcing for widespread
convection across the region and debris clouds from overnight
convection in Illinois should spread over the area and limit how
warm temperatures may get. However, temperatures should still
get to around 90 degrees across the area and just like
Wednesday, some isolated activity could generate as temperatures
get close to convective temperatures to allow for some
isolated/widely scattered afternoon activity. The 90/70
temperature/dew point spread will allow for some heat index
values into the upper 90s and potentially hitting 100 degrees
briefly in some areas.
For tonight, the main question will be what happens upstream of
the local area. Like tonight, an MCS type of feature will
develop west of the area. However, the activity will be further
east in Illinois and Indiana and the trajectory will be closer
to the forecast area. The better shear parameters for late this
evening through the overnight hours are better in Illinois and
Indiana and the instability gradient will likely try to angle
the bulk of this complex southwest of the area. However, given
some feature moving east toward the area with some lingering
instability and low 70 dew points will have PoPs increasing
through the night. However, a very low confidence forecast for
any particular hour of the night at this time.
For Friday, a more solidified surface low will develop behind
tonight's storms and will be coincident with an upper trough
moving through the Great Lakes region. This surface low will
bring a weak cold front with it and believe that there will be
more widespread shower and storms on Friday, compared to
tonight. There could be a bit higher severe potential with
storms on Friday, as they would be occurring during peak heating
hours. However, shear across the region remains very limited, so
the main concern would be damaging winds with instability
driving stronger storms.
Between showers and storms tonight and Friday, there could be
several bouts of heavy rainfall as warm cloud depths are above
10 kft and precipitable water values across the region will be
1.6" or greater with several instances of 2+" values. Perhaps
most concerning is that flow across the region appears to stall
out on Friday and extremely slow storm motions could allow for
more favorable flooding conditions. Overall, the trends for the
next 36 hours are generally down on the severe threat,
especially today/tonight, but the factors for heavy rain and
flooding are trending up.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
The upper-level low/trough will gradually move east across northern
Ohio Friday night into Saturday, shifting the threat for more
widespread showers and thunderstorms further south and east. Current
thinking is the best potential for showers and thunderstorms on
Saturday afternoon and evening will be generally along and east of
the I-71 corridor. Not anticipating any strong to severe storms with
this convection, though the heavy rain threat will remain in play
with seasonably-high PWATs and tall, skinny CAPE profiles.
Rain chances will decrease Saturday night into Sunday from northwest
to southeast as the upper trough continues northeast into New
England. On Sunday, a cold front will approach Lake Erie from the
north, though uncertainty remains on if this front will sweep south
through the area or stall just to the north across southern
Ontario.
&&
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
Low confidence forecast for the long term period as an upper-level
troughing regime appears to develop across the Eastern Great
Lakes/Northeast with large upper-level ridging towards the west. A
series of mid-level shortwaves may traverse along the base of the
upper-level trough Monday through Wednesday, though confidence is
low on the location of the surface cold front and storm tracks. DESI
clusters do indicate the potential for favorable instability/shear
overlap across the Upper Midwest/Lower Great Lakes region during
this time period which would support organized convection.
Temperatures are expected to remain seasonable in the low to mid-80s
for the long term period.
&&
.AVIATION /12Z Thursday THROUGH Monday/...
Scattered low VFR clouds continue across the region this morning
with some showers just to the southwest of the local area and a
larger fizzling complex to the west in Illinois and Indiana.
Clouds will continue to stream into the area today but will have
a mix of high and low VFR clouds. Some showers and storms could
move into the region from the west after 00z tonight and will
have a VCTS mention for some TAF sites at this time.
Unfortunately, overall confidence in timing is low to have
better TS mentions, but there is some confidence that there will
be shower and storm activity in the region tonight, and have at
least some mention. This situation continues to be a nowcast
situation and TAFs will need to be refined for the TS window
with time. Have changed over to VCSH later in the night where TS
becomes less favored. Winds will be light through the period
starting southwest and becoming south.
Outlook...Non-VFR possible in scattered and periodic showers
and thunderstorms through Sunday.
&&
.MARINE...
Outside of thunderstorms, the marine period appears quiet through
the weekend and into early next week with flow generally 10 knots or
less and waves less than 2 feet. Confidence remains low on strong
thunderstorms impacting the lake. A few stronger thunderstorms will
be possible this evening and again on Friday afternoon and evening.
Looking at primarily a wind threat with any storms.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
NY...None.
MARINE...None.
&&
$$
SYNOPSIS...Sefcovic
NEAR TERM...Maines/Sefcovic
SHORT TERM...Kahn
LONG TERM...Kahn
AVIATION...Sefcovic
MARINE...Kahn
Source:
CLE issues Area Forecast Discussion (AFD) at Aug 1, 10:00 AM EDT---------------
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