190
FXUS61 KCLE 121700
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
100 PM EDT Fri Jul 12 2024

.SYNOPSIS...
A weak trough moves across the region today. High pressure takes
control of our weather tonight through Saturday night. A warm
front lifts north on Sunday before stalling across the southern
Great Lakes for Monday and Tuesday.

&&

.NEAR TERM /THROUGH SATURDAY/...
1230 PM Update...
Opted to maintain the potential of scattered showers and
thunderstorms through this afternoon, especially west of I71
where the highest moisture values and upper level support exist,
although cannot rule out a storm or two east of there. No
changes were needed with this update.

930 AM Update...
Slight adjustments were made to PoPs this afternoon with
scattered showers and thunderstorms possible a bit further east.
Still not expecting anything widespread, but gusty winds and
heavy rain will be the primary concerns with any storms that
develop. Aside from that, the remainder of the forecast is on
track.

Previous Discussion...
Early morning water vapor imagery reveals a shortwave trough
axis stretching from Michigan into Indiana. A subtle increase in
south-southwest flow aloft ahead of this trough is resulting in
a bit of warm air advection and moisture transport, supporting
a broken cloud deck and some showers from northern Indiana into
parts of northwestern Ohio. This shortwave will shift east-
northeast while beginning to shear out/weaken today, causing the
mid-level cloud deck and hit and miss shower activity to spread
east into northwest OH this morning and into north central OH
this afternoon. By this afternoon modest and uncapped
instability will develop which could allow for a few
thunderstorms as well. Mainly focused 20-40% POPs west of the
I-71 corridor today, but also included a slight chance (20%)
from inland portions of the Cleveland metro east-northeast
across parts of far northeast OH and northwest PA as there may
be a couple of isolated showers/storms along a lake breeze this
afternoon or early evening too. No concern for severe weather
today and expect more of the area to remain rain-free than not.
Highs will generally reach the mid 80s today, though a few spots
down towards Canton may get a bit warmer. Parts of northwest PA
may struggle to get much above 80.

Generally expect the hit/miss shower/storm activity to quickly
dissipate this evening, leaving us with a quiet night as surface
high pressure takes control. Some hi-res models suggest that
gradually increasing moisture from the west may cause weak
instability to linger and keep isolated activity going into the
overnight. Did linger some very low (~15%) POPs across parts of
northwest OH longer through about midnight to account for this
low-confidence potential. Lows tonight will be a couple degrees
warmer than this morning, generally ranging from the low to mid
60s in far northeast OH and northwest PA to the mid to upper
60s across the rest of northern OH.

A generally quiet start to the weather weekend is expected for
Saturday with temperatures gaining a few degrees from today.
Look for highs ranging from the mid to upper 80s in far
northeast OH and northwest PA to the upper 80s to near 90
across the rest of northern OH. There will not be much forcing
on Saturday but modest and only weakly-capped instability will
develop by the afternoon hours. Marginal amounts of low-level
moisture combined with convergence along the lake breeze (and
perhaps over some hilltops) could allow this instability to be
released in the form of a few pop-up showers/storms in the
afternoon. This justifies some low (20-30%) POPs across most of
the forecast area Saturday afternoon. This is just enough for a
mention in the forecast though in general the theme for Saturday
will be warm and dry with a fair amount of sunshine.

Nighttime microphysics satellite imagery shows patchy valley
fog ongoing across parts of interior northeast OH and northwest
PA early this morning. Expect it to quickly mix out after
sunrise. Some patchy radiation/valley fog is again possible late
tonight into early Saturday, quickly mixing out in the morning.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
High pressure becomes centered over southern Appalachia and
generally encompassing much of the southeast CONUS through the short
term period. Ensuing broad southwest flow will result in increasing
heat and humidity with dew points in the low 70s and peak afternoon
temperatures in the upper 80s to low 90s on both Sunday and Monday.
This could result in max heat indices near 100, especially Monday
when model guidance is hitting the heat and humidity the hardest.

High heat indices is of course contingent on precipitation, for which
there are thunderstorm chances Sunday through Monday night.
Northwest flow develops aloft and there isn`t really distinct
synoptic-scale forcing, so it`s difficult to discern timing and area
of thunderstorm chances. Thunderstorms will likely be more
influenced by mesoscale forcing, which will become more clear as we
get closer to these days. What is clear is that the environment will
be primed for severe weather as high surface dew points/mid-level
lapse rates contribute to building instability from the west, with
some models forecasting MUCAPE as high as 3000-4000 J/kg (which
suffice to say, is very high for our region). Mid-level flow isn`t
impressive but general idea is for 20-30 knots of deep layer shear,
which is marginally supportive for severe weather. Latest CSU-ML has
15% probabilities for damaging winds (equivalent to an SPC slight)
on both days, which increases confidence in the occurrence of severe
thunderstorms. Additionally, high moisture content will support
efficient rainfall and thus a chance for localized flooding (which
is supported by D3 & D4 marginal WPC ERO).

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
Heat and humidity along with active weather continues into Tuesday.
The main difference however is that an upper-level trough (and
associated cold front) approach from the northwest on Tuesday,
providing better synoptic-scale forcing and mid-level flow (i.e.
better deep-layer shear). Confidence in thunderstorm development is
higher on Tuesday due to the synoptic-scale forcing, and while there
probably will be slightly lower instability compared to
Sunday/Monday, the instability/shear combo will probably result in
Tuesday having the greatest chance of thunderstorms and severe
weather. Currently, PoPs peak in the 40-60% range on Tuesday but
could see this getting higher as model guidance converge on
timing/area with this approaching upper-level trough. Just like
Sunday/Monday, will likely see efficient heavy rainfall and the
chance for localized flooding.

Most model guidance has the cold front sweeping through either
Tuesday night or Wednesday, with a cooler and dryer airmass moving
in behind it. Peak afternoons temperatures drop to around 80 on
Wednesday/Thursday with dew points down to around 60. Low PoPs
linger in some of our southern counties but otherwise most of the
region should be precipitation-free on these two days.

&&

.AVIATION /18Z Friday THROUGH Tuesday/...
VFR conditions with an isolated chance of showers and
thunderstorms this afternoon, especially east of I-71 so opted
to handle this potential with VCTS as confidence in exact
development location remains low through this afternoon. At
terminals impacted by any showers/storms, visibilities may
briefly be reduced to MVFR, but should quickly rebound.
Elsewhere, VFR conditions will continue through this evening
and into the early overnight hours with light and variable winds
expected. By late tonight/early Saturday morning, a weak low
level inversion is forecast to become established over the area,
resulting in the potential of patchy fog. The best chance of fog
is across NW OH and far NE OH/NW PA (inland from Lake Erie) and
for any areas that receive precipitation this afternoon. Have
opted to decrease KTOL to IFR, KFDY to MVFR, and KYNG to IFR
conditions from near 8-13Z. Confidence is lower elsewhere and
thus did not include it with this update. By mid-Saturday
morning, conditions should all rebound to VFR and light and
variable winds will persist.

Outlook...Periodic rounds of showers and thunderstorms with
non-VFR may be possible this Sunday through Tuesday.

&&

.MARINE...
Quiet conditions are expected on Lake Erie as high pressure builds
in. A modest afternoon lake breeze and very weak overnight land
breeze are expected the next couple days. Southwest flow of 10-15
knots develops on Sunday as high pressure moves to the southeast.
This southwest flow persists through Tuesday.

&&

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

&&

$$

SYNOPSIS...Sullivan
NEAR TERM...Campbell/Sullivan
SHORT TERM...Saunders
LONG TERM...Saunders
AVIATION...Campbell
MARINE...Saunders