Scientific Forecaster Discussion
fxus61 kcle 210130
Area forecast discussion
National Weather Service Cleveland Ohio
930 PM EDT Tue Aug 20 2019
a cold front will move southeast across the local area Wednesday
evening. A ridge of high pressure will build southeast across
the area Thursday. High pressure will be centered over the local
area Friday night. Below average temperatures are expected for
the end of the week and weekend.
Near term /through Wednesday night/...
a line of showers and thunderstorms stretches from Mentor to
Warren to Salem, moving east-northeast at about 25-30 mph. These
storms will only last for about the next four hours or so and
most of the area should be dry for tonight after being worked
over by convection over the last several hours. Some showers may
try to creep along the Lakeshore overnight following a subtle
boundary across Southern Lower Michigan, but precipitation
chances appear isolated at best. Winds are light and variable
behind the convection but will likely settle into a westerly
direction at some point overnight. Temperatures will remain warm
overnight with lows in the upper 60s to near 70.
focus of the near term forecast is thunderstorm potential this
afternoon evening, as thunderstorms begin to develop in west
central Ohio ahead of a long lived but somewhat decaying mesoscale convective system
tracking through Indiana. Surface destabilization has continued
through the afternoon across the local area, with 2-3k j/kg
MLCAPE centered across western Ohio. Mid level lapse rates
steepen ahead of the MCS, which will influence the area in the
next several hours. Shear remains marginal, with effective bulk
shear values of 20-25 kts across the area through early evening,
which should limit overall organization of storm activity.
However, dry air above 700mb and resultant dcape values of
1000-1300 j/kg across the area, coupled with steep low level
lapse rates, will enhance the risk for damaging winds with the
stronger thunderstorms across the area. Storm Prediction Center has expanded the day
1 slight risk northward into the southwest part of the forecast
area, with a marginal risk for the rest of the area. The best
severe thunderstorm potential will be from 4 PM through 10 PM
across the area.
The associated mesoscale convective vortex will slowly shear out/weaken across the area
this evening and push east of the area by Wednesday morning.
Precip chances will be on the downtrend after midnight, but held
onto chance pops east/slight chance pops elsewhere with the
disturbance across the area and ample boundary layer moisture
and perhaps residual outflow boundaries as a focus of surface
forcing. A synoptic cold front will slowly sink south towards
the area Wednesday and into the area Wednesday night. Surface
forcing is marginal with the boundary, and weak destabilization
may limit widespread precipitation development across the area
during the day, especially with the better mid level forcing
displaced north and southwest of the area. Have kept pops in the
chance range on Wednesday, with MLCAPE values up to 1000 j/kg as
much drier air in the 850-700mb layer moves into the area from
the north. High temperatures rise into the mid/upper 80s across
the area. Forecast pops diminish to slight chance range
Wednesday night as the front slides south across the area, with
the loss of daytime heating inhibiting much fuel for precip
development. Pops may linger across the south and southwest
parts of the forecast area after midnight into early Thursday
morning as upstream convectively induced disturbances propagate
eastward along the front, although much of the guidance favors
precip placement just south of the area.
Short term /Thursday through Friday night/...
weak cold front will start off across our southern counties on
Thursday. A deepening upper level trough will push south across Lake
Michigan on Thursday, maintaining a southwest flow aloft. This may
delay the southward movement of the front and will hold onto a low
chance of showers and possibly a thunderstorm across the south on
Thursday. A noticeable change in airmass will be felt with
highs dropping below normal into the 70s where they will remain
heading into the weekend. High pressure will strengthen across
the Great Lakes Thursday night into Friday, finally pushing the
front south of the area.
Long term /Saturday through Tuesday/...
upper level trough shifts east across New England allowing a ridge
to build overhead. Some weak troughing will also be in place across
the southeastern states with moisture focused across the Tennessee
Valley and mid-Atlantic. The 12z GFS is the fastest in trying to
pull moisture back north into the area on Sunday but given the
strength of the surface high will continue with a dry forecast.
Finally by Monday the next upper trough will approach from the
northwest with low pops returning to our western counties
Monday, increasing and expanding Monday night into Tuesday.
Aviation /00z Wednesday through Sunday/...
showers and thunderstorms are moving across the area this
evening. Have a ts mention at kcak, kyng, and Keri, as
convection remains over or will approach those terminals over
the next several hours. IFR is likely with any ts this evening.
Clouds will remain over the area overnight and should abate any
fog development. Ceilings may settle down to non-VFR by morning
and lift back to VFR by Wednesday afternoon. Winds will be light
and variable to start and then begin out of the west to
southwest for much of the overnight into Wednesday.
Outlook...intervals of non-VFR possible primarily with
thunderstorms on Wednesday.
southerly flow of 10-15 knots will develop on Lake Erie tonight and
increase into the 10-20 knot range on Wednesday ahead of an
approaching cold front. Winds will shift to the north with the
passage of the front Wednesday night and a Small Craft Advisory will
likely be needed east of the Lake Erie islands. Winds will drop off
fairly quickly on Thursday as high pressure expands south over the
Great Lakes region. Northeast to east winds of 5-15 knots will
maintain a little bit of a chop on Lake Erie on Friday and Saturday
with flow becoming more east/southeast on Sunday.