-- Discussion containing changed information from previous version are highlighted. --
186
FXUS61 KCLE 050417
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
1217 AM EDT Wed Jun 5 2024

.SYNOPSIS...
A warm front will move north tonight through Wednesday morning followed
by a cold front Wednesday evening. A surface trough will build
in on Thursday, lingering over the area through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
12:10 AM Update...
Reworked the PoPs timing through Thursday, and especially to
better time out thunderstorms Wednesday afternoon/evening. Seems
like most model guidance is coming to better agreement with
timing. Also added heavy rain mention has the high moisture
content should result in efficient and heavy rainfall with most
thunderstorms Wednesday afternoon/evening. The severe weather
threat also appears to have shifted westward with the primary
severe weather threat west of I-71 and especially in the
vicinity of the I-75 corridor. Will discuss the details more
with the 4 AM forecast package.

Previous discussion...
A negatively tilted upper level trough will continue to push
south towards the Great Lakes region tonight. The occluded
surface low, now associated with this trough will linger north
of the US/Canada border, but a triple point will develop over
the western Great Lakes region, extending a cold front south
across the Midwest and moving a warm front north across the area
tonight. This warm front will bring the chance of showers and
maybe a rumble of thunder across the area, although much of the
convection looks to be elevated based on model soundings. The
best isentropic lift and frontogenesis will be centered over the
eastern portion of the CWA where the confidence is highest of
overnight showers, but cannot rule out a few showers elsewhere.
Overnight lows will remain mild, only falling into the upper 60s
to low 70s.

This boundary will push north of the CWA by Wednesday morning,
allowing for a very moist and warm air mass to push north over the
area in the warm sector of the low. By Wednesday afternoon,
dewpoints will climb into the upper 60s to low 70s. With this and
daytime heating, instability values should climb, the biggest
question is how much any lingering morning clouds/showers limit the
warming. On average, models currently have near 1000 J/kg of MLCAPE
developing over the area in the afternoon. There will be upper level
support from the aforementioned trough over the area, however
enhance low level features do not kick in until closer to 00Z
Thursday as a LLJ moves over the area. Near this time, shear values
should climb around 30 knots which coupled with the other
environmental factors should lead to some organized convection late
Wednesday afternoon through the evening hours. There is a potential
for some storms to develop earlier than this as a prefrontal trough
moves across the area, but will need to continue to monitor this and
the potential interaction with the storms along the cold front. High
temperatures will climb into the upper 70s to low 80s.

In addition to the severe threat, deepening warm cloud layers and
PWATS of 1.5-1.8" will combine to create a threat for heavy rainfall
with the strongest storms having rainfall rates near 1-2" per hour.
These rainfall rates, combined with a non-zero potential of some
training storms in the evening, may result in localized flooding
especially in low lying areas or areas prone to flooding. To account
for this threat, WPC has issued a Day 2 Marginal Risk ERO for the
entire area.

This forecast is highly dependent on morning conditions and how
quickly we can destabilize, but with what models are conveying now,
SPC has maintained the Day 2 Marginal Risk for severe weather across
the entire CWA. The biggest update this afternoon is an area of 2%
tornado risk has been introduced for much of the Ohio counties, with
the exception of far NW OH. There was also a 5% hail threat added to
counties north of US-224. The primary concern remains gusty winds
with any convection, but the other hazards cannot be ruled out. Best
timing for severe weather will be between 4-10 PM EDT Wednesday.

Showers will taper from west to east on Wednesday night as the cold
front moves east. In addition, cooler air will move east behind the
boundary, allowing overnight lows to fall into the low to mid
60s.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Cyclonic SW`erly to NW`erly flow aloft and embedded shortwave
disturbances affect the eastern Great Lakes and Upper OH Valley on
Thursday through Friday night as a mid/upper-level low wobbles
SE`ward from northwestern ON province to near Georgian Bay. At the
surface, troughing lingers over/near our CWA and trough axes
accompany the aforementioned shortwave disturbances. This pattern
will support net low-level CAA across our region. Periods of
isolated to scattered rain showers are expected due to moist
isentropic ascent preceding shortwave trough axes, low-level
convergence/moist ascent along attendant surface trough axes, and
the presence of potential instability in the surface to roughly 850
mb layer. Daytime heating of the relatively-moist boundary layer
coinciding with considerably colder air farther aloft should yield
weak, yet sufficient mixed layer CAPE for isolated thunderstorm
development each afternoon through early evening. The greatest
potential and coverage of convection are expected each afternoon
through early evening because a typical diurnal cycle in boundary
layer temperatures and instability is expected. In addition, a
sufficiently-cold/moist low/mid-level atmospheric column and the
seeder-feeder process should support periods of lake-enhanced rain
over/generally east or southeast of ~18C Lake Erie during the late
evening through morning hours of Thursday into Friday and Friday
into Saturday. Late afternoon highs should reach the 70`s to 80F on
Thursday and the mid 60`s to lower 70`s on Friday as colder air
overspreads northern OH and NW PA. Overnight lows should reach the
50`s around daybreak Friday and mainly the upper 40`s to mid 50`s
around daybreak Saturday.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Cyclonic and primarily W`erly to NW`erly flow aloft, and embedded
shortwave disturbances are expected to affect our CWA during this
period, but evolution of the aforementioned mid/upper-level low is
uncertain. At the surface, troughing persists over/near the eastern
Great Lakes and Upper OH Valley, and multiple trough axes will
accompany the shortwave disturbances. This pattern at the surface
and aloft will allow an unusually-cool air mass to remain entrenched
across our CWA. Periods of isolated to scattered showers and
thunderstorms are expected for the same reasons noted in the short-
term discussion. The greatest potential and coverage of convection
are expected each afternoon through early evening due to a continued
typical diurnal cycle in boundary layer temperatures and
instability, and self-destructive sunshine. Late evening/early
morning periods of lake-enhanced rain remain possible over and
generally east or southeast of Lake Erie for the same reasons noted
in the short-term discussion. Daily afternoon highs should range
from mainly the mid 60`s to mid 70`s. Overnight lows should range
from mainly the upper 40`s to upper 50`s.

&&

.AVIATION /06Z Wednesday THROUGH Sunday/...
VFR conditions are expected to continue through the first half
of TAF period. There will be 2 periods that may see scattered
diminished conditions to MVFR. Visibility values will lower to
MVFR overnight 08-12Z along and VCSH is possible, especially
KCLE/KCAK line eastward. In the warm sector, prevailing VFR
conditions expected Wednesday morning before the approach of
the cold front Wednesday evening. Added SH and VCTS for western
TAF sites 21z to 00z Thursday. Visibility values could be
reduced at times in heavy rainfall Wednesday afternoon and
evening.

Winds will slowly veer from east to south 5 to 9 knots
overnight, finally southwest 9 to 14 knots late Wednesday
morning through the afternoon, and decrease to 5 to 10 knots
Wednesday evening outside of SH and TS.

Outlook...Non-VFR will be possible with scattered rain showers
and isolated afternoon thunderstorms Thursday through Saturday.

&&

.MARINE...
The western flank of a ridge lingers over Lake Erie before a warm
front drifts N`ward across the lake tonight through Wednesday.
Variable winds around 5 to 15 knots become E`erly to SE`erly this
evening and then veer to S`erly to SW`erly following the passage of
the warm front. A cold front is then poised to sweep E`ward across
Lake Erie Wednesday evening through Thursday morning. The cold front
passage will cause S`erly to SW`erly winds around 10 to 20 knots to
veer to W`erly. Behind the cold front, a trough is expected to
linger over the Lake Erie region through Sunday and be accompanied
by SW`erly to NW`erly winds around 10 to 20 knots. Waves are
expected to be mainly 3 feet or less, but occasional 4 footers are
expected, especially east of The Islands, on Thursday through this
weekend. At this point, Friday and Saturday have the best potential
for Small Craft Advisory conditions to develop.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
OH...None.
PA...None.
NY...None.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...Saunders
NEAR TERM...Campbell/FZ/Saunders
SHORT TERM...Jaszka
LONG TERM...Jaszka
AVIATION...FZ
MARINE...Jaszka