Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
415 am EDT Thursday may 28 2015
a weak cold front will continue to move through the region
today...settling near the Ohio River by evening. Warmer and more
humid air will return on Friday and Saturday...with increasing
chances for showers and thunderstorms. Another cold front will
move into the area on Sunday and Monday...continuing the chances
for storms into early next week.
Near term /until 6 PM this evening/...
a cold front is currently moving very slowly southeast through the
iln forecast area. Near-surface convergence along this front is
rather negligible at the moment...with weak wind flow on either
side of the boundary. Showers that had developed earlier have
dissipated...and a dry forecast will be maintained for the first
half of the day.
By afternoon...there will be a notable change in air mass from the
northern sections of the forecast area to the south. Dry and
stable air will lead to zero or near-zero instability in the far
north...where even clouds will be hard to come by. South of the
boundary (along the Ohio River tiers of counties)...instability
will build to 1000-1500 j/kg of MLCAPE...in the presence of weak
convergence near the front. However...with a lack of large-scale
forcing...there will be nothing to help develop any organized
thunderstorm development. Probability of precipitation will be kept on the low-end...with
an expectation of isolated pop-up / pulse / single-cell storm
Mode. A 19z kcvg nam12 sounding has winds of under 10 knots
through the entire lowest 20kft of the atmosphere...a remarkably
shear-free profile that will keep storm motions slow and storm
organization very poor. Nonetheless...if instability reaches the
higher end of expectations (possibly up to 2000 j/kg
sbcape)...some heavy rain or gusty winds may occur.
With a slightly drier air mass in place...cloud cover (especially
in the northern half of the forecast area) will be less than in
the past few days. Despite 850mb temperatures dropping by a degree or
two...surface temperatures should thus still make it into the lower 80s
across the forecast area.
Short term /6 PM this evening through Saturday night/...
high pressure will be moving into the northeastern states on
Thursday night...with a return to southwesterly flow beginning
over the middle Ohio Valley by Friday morning. Some of the models
seem a little too aggressive in bringing precipitation back into
the region on Friday...but with increasing moisture amid weak
isentropic ascent...it does appear that shower/storm chances will
be necessary by Friday afternoon...especially in the west /
southwest portions of the forecast area. Given the nebulous
forcing...timing/location for this activity is not going to be an
exact forecast. With shear on the weak end of the scale and
instability only marginally more impressive...strong storms appear
As the pressure gradient begins to tighten on Saturday...the
southwesterly flow will become a little more pronounced...helping
to increase instability ahead of an approaching cold front. With
high confidence in fairly widespread precipitation from Saturday
afternoon into Sunday...probability of precipitation have been increased to the likely
category County Warning Area-wide (with some categorical probability of precipitation at peak diurnal
timing in the far north on saturday). Wind support is going to be
fairly weak through the period...but persistent moisture
transport and near-surface convergence definitely support the
higher precipitation chances (even if the threat for any strong
storms is uncertain).
Temperatures on Saturday will moderate slightly from
Friday...though the vast majority of the day will still be solidly
south of the frontal boundary (something that will certainly
change by sunday). Highs should still reach the 80s for most
locations...though where precipitation chances are higher...there
should be more of a temperature gradient north of Interstate 70.
Long term /Sunday through Wednesday/...
appears as though front will be slow to make progress and thus at
least scattered rain showers and thunder will continue into Sunday mainly
south parts of County Warning Area. Some better drying across the north. The front
will linger into Monday with scattered rain showers and thunder again
mainly near the Ohio River. Some discrepancy about extent of
drying for Tuesday and Wednesday. Will opt for token small pop for
now. Temperatures cooling down Sunday and Monday but went at or just
above guidance with clouds at night. Near guidance for Tuesday and
Aviation /07z Thursday through Monday/...
a weak cold will continue to push slowly southeast toward the Ohio
River valley by 12z. The boundary will remain poorly defined near
the Ohio River for later today. Meanwhile...surface high pressure
will pass across the southern Great Lakes.
A mix of clouds along and ahead of the front may keep fog
potential in check at southern sites that remain in a more humid
airmass. Have continued with MVFR visibilities at kcvg...kluk and
Kiln with some IFR visibilities possible at kluk due to river fog.
Mist/fog should dissipate between 12z and 13z.
For later today...diurnal heating will result in cumulus
development. With the weak boundary in place near the Ohio
River...enough instability may allow for isolated showers or
thunderstorms. The coverage is too small to mention in the tafs.
For tonight...surface high pressure moves off to the east.
Meanwhile...an upper level ridge becomes established along the
eastern Seaboard. Deeper moisture will be drawn northward around
the return southerly flow. Right now...it looks like ceilings will
remain VFR with any diurnal shower/storm diminishing during the
evening hours as instability wanes overnight.
Outlook...thunderstorms will be possible Friday through Monday.