Scientific Forecaster Discussion
fxus61 kcle 210554
Area forecast discussion
National Weather Service Cleveland Ohio
154 am EDT Sat Jul 21 2018
slow moving low pressure will track from Southern Lake Michigan
tonight into the Ohio Valley by Sunday. The low will weaken and
dissipate as it drifts into the Tennessee Valley Monday. A cold
front will slowly move across the area during the middle of the
Near term /through tonight/...
convection has pretty much died down so went with scattered
showers and isolated tsra for the overnight period. Also removed
mention of potential for severe tsra from severe weather potential statement. Rest of forecast
looks reasonable for the 930 update.
not many changes to the forecast tonight through Saturday
night, with the focus of the forecast on convection/severe
potential this evening and precip chances Saturday. A slow
moving, vertically stacked low will track from near Lake
Michigan this evening southward into the Ohio Valley late
Saturday night into Sunday morning. Several waves of
precipitation will rotate east-northeast across the region, with
a focus on diurnal development during the afternoon on
Saturday. In the immediate, ongoing showers/storms across far
northeast Ohio and northwest PA will continue to work northward
late this afternoon, while and area of rain with embedded
thunderstorms pushes east across the southern part of the area,
south of US-30, over the next couple of hours, generally in a
Focus turns to line of convection currently across northern Indiana.
Modest/narrow corridor of 1000-1500 j/kg SBCAPE exists ahead of this
line, with fairly weak/marginal effective bulk shear values of 30
kts or so. Biggest challenge is the intensity trend of this line,
and whether or not it will remain organized and severe into the I-75
corridor a couple hours from now. Hi-res guidance has been
consistent in weakening any convection as it tracks into the local
area around/after 00z, however the latest runs of the hrrr are not
handling the speed/intensity of the current line. The line may
weaken if the instability corridor gets pinched off between the
advancing severe line and the more stable boundary layer near the I-
75 corridor from ongoing or recently ended rainfall. Still have high
likely pops working into the I-75 corridor from 22z to 00z, and
think there is some potential for a few organized/strong storms to
sustain into the area. Convection should diminish from 03z Onward
through the night.
Kept pops generally in the chance range overnight with a brief
period of likely pops across the southern part of the area towards
morning, as an area of lift associated with the low level jet moves
into the southeast part of the forecast area, with a consistent
signal of precip development in recent model runs. A lull in
convection is possible through the morning hours tomorrow, however
have ramped pops up to likely across the area in the afternoon as
modest destabilization of 500-1500 j/kg occurs across the area. Have
again trended pops downward through the evening/overnight with a
loss of instability. Kept temps near previous forecast tonight and
Saturday night, and maybe a degree or two lower for highs on
Saturday given expected cloud cover and scattered precip.
Short term /Sunday through Monday night/...
the upper level low will weaken on Sunday as it drifts southward.
However with the cooler air aloft within the upper level trough we
will have to maintain chances of showers and thunderstorms. Another
piece of energy will approach Monday night into Tuesday with chances
of thunderstorms increasing by Tuesday afternoon.
Sunday looks to be the cool day of the short term with highs in the
middle 70s. Seasonal temperatures Monday into Tuesday with highs in
the lower to mid 80s.
Long term /Tuesday through Friday/...
the long term begins Tuesday night with models showing weak forcing
across the area however at the surface there should be a cold
front/trough bisecting the area. Best chance of precip should be
east with lower level flow bringing Atlantic moisture into the area
from the southeast. Will have chance pops east to start the night
and go up to likely pops after midnight as moisture increases. For
Wednesday will continue with the likely pops far east, chance
through the central Lakeshore and Highlands to nothing northwest.
Wednesday night and Thursday models try to bring drier air in slowly
from the northwest, shifting the best moisture east. The cold front
will also shift east and dissipate as another cold front moves into
the region from the northwest. With the drier air in place however
believe rain chances still drop through the 24 hour period. For
Thursday night and Friday high pressure begins building in from the
northwest so will go with a dry forecast. Highs Wednesday should get
into the low and mid 80s with a few upper 80s west. Thursday and
Friday look for highs 80 to 83.
Aviation /06z Saturday through Wednesday/...
low pressure over Southern Lake Michigan will continue drifting
southeast today. This low will generate scattered showers and
isolated thunderstorms this morning before many of these fizzle.
MVFR ceilings are creeping into the area with several spots
toggling back and forth between sct/bkn at 2500. Later today,
convection redevelopment is possible but trend in rain coverage
is down with more isolated/scattered convection expected this
afternoon and evening, so with this round of tafs, opted for
prob30s over a vicinity mention. With the low moving in, the
increasing pressure gradient will allow for stronger southeast
winds and gusts to 20 kts are possible inland with higher gusts
in favored downslope areas, especially Keri and kcle.
Outlook...non-VFR possible on Sunday with showers and
stacked low pressure will drift from Lake Michigan to southwest Ohio
by Sunday morning. This will keep south to southeast wind going on
the lake through Saturday afternoon. Winds will then shift a bit
more to the east as the low weakens as it drifts further south.
Current thinking is that he southeast to south winds will be low
enough to avoid the issuance of a Small Craft Advisory. However
stronger gusts may occur with any thunderstorms. Low level lapse
rates steepen enough on Saturday to be concerned about waterspouts.
While it does look marginal the proximity of the upper level low
makes US think that the spouts could occur across the western half
of the lake from Toledo to Avon.
By Sunday easterly winds will increase with a good chance that we
will need a Small Craft Advisory. We will take a closer look at this
tomorrow. The winds will only slowly decrease Sunday night into
Monday becoming light Monday night and remaining that way into