Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
422 am EDT Tuesday Jun 30 2015
showers and thunderstorms will be possible today...as a trough of
upper level low pressure moves through the Ohio Valley.
Temperatures will remain slightly below normal through the rest of
the week...with additional chances for showers and storms
returning on Thursday and into the weekend.
Near term /until 6 PM this evening/...
an area of surface low pressure is currently centered somewhere
near Sandusky Ohio...but general nebulous low pressure is in place
across most of the southern Great Lakes and Northern Ohio valley
region. An upper level trough is also in place over the same
region...and this feature will be slow to move east.
The fog forecast early this morning has been problematic.
Temperatures have dropped into the middle 60s to upper 50s...with
near-saturated conditions recorded at virtually all observation
sites in the iln forecast area (sans a notably clear spot near
Cincinnati and to the southwest). Several observation sites have
reported dense fog for brief periods of time...but not with much
persistence. In general...the dense fog observations have been
shifting northward with time...following behind the slow movement
of the surface low. With this in mind...fog has been placed in the
grids through early morning...though mainly for the northern half
of the forecast area. The brief nature of the truly dense fog may
preclude the issuance of an advisory...but this will continue to
be monitored...especially for parts of the Columbus metropolitan area.
The forecast focus going into the afternoon will be on the
potential for thunderstorm development. Probability of precipitation were largely based on
Storm Prediction Center-WRF and ncar ensemble simulated reflectivity
projections...spreading likely probability of precipitation across the County Warning Area from northwest
to southeast between 18z and 00z. This region will be ahead of the
upper trough axis...in a favorable area of lift. Although the
surface pressure pattern is kind of a mess...there does seem to be
a weak boundary moving southeast into the iln forecast area...with
convergent flow also helping to provide forcing for storm
development. With cooler air moving in aloft...thanks to the upper
trough...mid-level lapse rates will be steeping slightly. Even
though near-surface conditions will not be especially moist or
warm...instability should be able to build fairly well...up to
around 1500 j/kg of SBCAPE. Looking upstream early this
morning...some thunderstorm cells moving into Indiana are an
indication of elevated instability...which further suggests that
diurnal heating will be able to generate some energy out of this
airmass. Wind shear is forecast to be marginal...primarily
unidirectional from the west...and perhaps around 15-25 knots
through a 6km layer. Thus...the ingredients are expected to be in
place for a low-end severe event across the forecast area. Timing
should be mainly diurnal...with a threat for wind and hail.
However...the expected instability and shear are simply not
expected to be appreciable enough for a significant or widespread
event. Since the overall focus is not particularly
well-defined...and environmental conditions will be similar across
the region...chances for strong storms do not appear significantly
different from one section of the County Warning Area to another. However...if
recent hrrr runs are correct (and storms move through a little
faster than currently forecast)...the chances for stronger storms
may shift slightly south and east.
Clouds should break enough to allow some insolation for most
locations in the County Warning Area today...though central Ohio may stay in the
clouds a little longer than elsewhere. Thus...a north-northeast-to-SSW
temperature gradient was employed in the grids...with middle to upper
70s in the northern/northeastern County Warning Area...and lower 80s in the far
Short term /6 PM this evening through Friday/...
with the axis of the upper level trough crossing the middle Ohio
Valley on Friday evening...favorable conditions for ascent will
quickly come to an end...and precipitation should diminish from
northwest to southeast across the forecast area. Upper flow will
remain generally northwesterly over the region through the rest of
the week...and though there is general agreement in the
arrangement of the surface pattern through Friday...the exact
latitudinal alignment will have a big role in thunderstorm
chances (especially on thursday).
Dry conditions are expected tonight and through the day on
Wednesday...as surface high pressure begins to build in over the
Great Lakes region. 925mb/850mb temperatures will cool by one or
two degrees celsius from Tuesday to Wednesday...but with cloud
cover expected to be fairly limited...temperatures should still
rise to similar values as on Tuesday. With forecast highs in the
middle 70s to around 80...conditions will remain about five
degrees below climatological normals.
As the Great Lakes surface high grows in size headed into
Thursday...its eventual movement will determine how far south a
frontal boundary and convergent zone will set up from Wednesday
night through Friday. This will be an important question...as
models have consistently shown that convection will be likely
along this boundary...perhaps with one or more convective systems
moving in the quick westerly flow aloft. In general...the last 12
hours of model runs have favored a slight shift to a southward
solution...settling storms across the southern half of the Ohio
Valley. Some changes were necessary to the pop grids through this
time frame...significantly limiting convective chances in the
northern half of the County Warning Area...while still allowing a chance for
convection (especially in the southern half) on Thursday.
With this boundary setting up south of the County Warning Area...temperatures
should remain slightly below normal through the forecast period.
Long term /Friday night through Monday/...
middle/upper level trough will persist across the eastern United
States into early next week as the West Coast ridge axis shifts
very slowly eastward. There are some model discrepancies with the
northward extent of the short wave energy moving through the
trough on Thursday. As a result...have stuck close to the model
blend/current forecast with this...ranging probability of precipitation from low chance
north to likely in the far south. On the back side of this short
wave...we should get into a precipitation minimum for Thursday night into
Heading into the weekend and early next week...it becomes more
difficult to time/place short wave energy in the troughy pattern.
Will therefore maintain some lower chance probability of precipitation through the remainder
of the long term period. With the trough in place across the
region...temperatures will remain at or slightly below seasonable
normals. Expect afternoon highs in the upper 70s to lower 80s.
Aviation /07z Tuesday through Saturday/...
an area of weak low pressure centered over north central Ohio
early this morning will drift slowly to the northeast through
sunrise. The combination of recent rainfall...light to calm winds
and nearly saturated low levels have resulted in varying amounts of
ceiling and visibility reductions across the taf forecast area. It
appears the worst conditions will occur near the kcmh/klck
terminals where IFR ceilings and MVFR visibilities are forecast into middle
morning. At the other terminals...a little bit more wind and
stratocumulus clouds should keep ceilings and visibilities in the
MVFR category for the most part.
For later today...region will remain under a northwest flow
pattern aloft. Another in a series of embedded disturbances is
expected to work its way east across the region by the afternoon
hours. This feature will team up with a low level convergent
boundary...along with a quickly destabilizing airmass...to
produce scattered to numerous showers and thunderstorms.
At this time...believe all terminals warrant a tempo thunderstorm group
with MVFR conditions during the 18z and 22z time frame...or peak
heating. As typical...local visibilities can drop below into the
IFR or lower category where the more robust cells occur. Winds by
afternoon will be generally from a 240 to 250 direction with
synoptic scale gusts in the lower 20 knots.
By this evening...disturbance pivots away as well as the
convergent boundary. With the loss of daytime heating...convection
should wane fairly quickly during the evening. A weak cold front
will approach the region from the northwest overnight. With the
lack of forcing...not much is expected with this boundary at this time.
Skies should become partly cloudy with perhaps some MVFR
Outlook...thunderstorms possible Wednesday night into Thursday and
again Friday night into Saturday.