Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
301 am EDT Thursday Jul 31 2014
a persistent trough will remain across the region through the
weekend. Increasing moisture will bring chances for showers and
thunderstorms to the area over the weekend...mainly during the
Near term /through today/...
shortwave shifting east of the area this morning will result in a
end to shower activity. Weak high pressure and subsidence in the
wake of the departing shortwave is expected to keep our area free
of convection today. Temperatures will be a few degrees warmer
today than yesterday...with highs reaching the upper 70s to lower
Short term /tonight through Saturday/...
high pressure will reside to the east of our area with a trough
across our region becoming positively tilted with the trough axis
just to our west. This will leave our area with low level southerly
flow and southwesterly flow aloft tonight through Saturday. The
result will be an increase in moisture across the area. This
increase in moisture will allow for an uptick in shower and
thunderstorm activity both Friday and Saturday afternoon and
evening. At this time it appears the better coverage of convection
will be Saturday afternoon.
Temperatures are expected to continue to run a few degrees below
normal over the weekend due to our close proximity to the
Long term /Saturday night through Wednesday/...
at 12z Friday /01.12z/ -- deep eastern Continental U.S. Longwave trough remains
intact in a highly amplified northern hemisphere flow pattern
consisting of a strong Atlantic ridge...the eastern Continental U.S.
Trough...strong western Continental U.S. Ridge...and deep closed low over Pacific
waters south of Alaska. According to 30.12z GFS/European model (ecmwf)
deterministic runs...a trio of midlevel vorticity maximums
rotating down the west side of the deep closed low near Hudson Bay
and rising heights in the Atlantic Ocean will force the l/west trough
axis in the eastern Continental U.S. To retrograde/refocus back to the west over
the Ohio Valley Fri/Sat...with midlevel flow backing with time. In
fact by Saturday...a deeper southwesterly middle/upper flow field will
overspread the Ohio Valley as the trough axis reforms to the west.
These forcing mechanisms will act to recarve/sharpen the trough
during this time period...inducing subtle synoptic scale lift and
the organizing trough begins to shift east across the area on Sat
evening. While lower level wind fields will remain very weak /not
much surface reflection of these synoptic scale processes/ there
will be modest moisture and temperature rises that occur Friday/Sat
which will continue to Foster an unsettled/unstable
atmosphere...with best coverage of diurnally-enhanced
showers/storms on Saturday as a weak inverted trough tries to
develop across the area from weak low pressure in TN/KY.
Uncertainty on how fast the trough axis shifts east...seeing two
ideas in the data...one in which the axis lingers over Ohio/Kentucky
through Sunday and a more progressive solution /30.12z European model (ecmwf)/ which
shunts the axis east into PA on Sunday. The latter would yield a
drier Sunday - the former still some lingering diurnal
showers/storms. Playing continuity from previous forecast and input
from HPC will keep lower rain chances in on Sunday...mainly in cntl
Running with a dry Sun night/Mon/Mon night in wake of this feature
pushing east of the area and nondescript/weak flow pattern absent of
any waves. Tues/Wed...glancing blow from energy moving through southeastern
Canada may push weak frontal zone into Ohio/ind these days with
small chance of storms along the front Tuesday afternoon into Wednesday amidst
very weak height falls. Again...small rain chances but most areas
likely remaining dry...and warmer...as negative height/temperature
anomalies will finally have been pushed east/northeast on flattening
overall hemispheric flow.
Aviation /07z Thursday through Monday/...
a persistent low level convergent boundary has helped keep scattered
showers and a few embedded thunderstorms going from east central
Indiana into central Ohio early this morning. This convergent
boundary is forecast to sag slowly south and weaken through 12z so
expect to see a gradual weakening/dissipating trend through
daybreak. Otherwise...we could still see some areas of fog through
daybreak but this may be mitigated somewhat by some of the clouds
that are still lingering across the region. We should cumulus up once
again later this morning and on into this afternoon as weak
diurnal instability redevelops across the area. Suppose an
isolated shower or thunderstorm is not out of the question...but
there is not much left in the way of forcing so will keep the tafs
dry this afternoon.
Outlook...thunderstorms possible Friday through Sunday.