Area forecast discussion
National Weather Service Wilmington Ohio
847 am EDT Tuesday may 21 2013
Synopsis...
a warm and humid air mass will remain in place through Wednesday.
Occasional periods of showers and thunderstorms will be possible.
A cold front will move through the region on Thursday...before
cooler air settles in on Friday and into the weekend.
&&
Near term /until 6 PM this evening/...
second mesoscale convective system has been weakening as it moves into the western
counties. This is elevated as outflow from earlier mesoscale convective system raced
across most if not all of the forecast area. Expect weakening
trend to continue with echoes dissipating before making it to
central Ohio.
Redevelopment of convection later in the day will be largely
driven by mesoscale processes. Several of the convection allowing
models suggest that storms could develop in or near the eastern
counties closer to where the old outflow boundary stopped. This
should be an area of higher instability. But cannot completely
rule out enough recovery of instability further west for some
storms to occur there as well. Have adjusted precipitation timing
based on this thinking and have lower probability of precipitation for later in the day.
Forecast shear is not overly impressive. But there could be enough
instability for some unorganized strong to severe storms.
Forecast temperatures look reasonable at this point.
&&
Short term /6 PM this evening through Thursday night/...
convection will likely be ongoing for at least part of the
forecast area during the Tuesday evening hours...with a diurnal
min leading to more tranquil conditions overnight. However...by
Wednesday morning...this may begin to change again. A shortwave
moving out of the Southern Plains will eventually make its way
just east of the iln County Warning Area by morning...with model agreement on an
associated convective complex spreading into Indiana by then.
Meanwhile...surface low pressure will strengthen as it moves
through Illinois and into Michigan...with general surface
troughing and height falls aloft spreading into the iln County Warning Area. This
is a favorable environment for lift...and should support a likely pop
forecast through most of the day Wednesday. Although generally
unidirectional...the increasing pressure gradient and
juxtaposition with the right entrance region of the upper jet will
also support an increased bit of shear and forcing (respectively).
The limiting factor for severe potential will be
instability...which does not appear to be particularly strong (and
this is not surprising given the lack of expected surface
heating). Temperatures aloft will continue to drop...which should help
generate 500-1000 j/kg if some sun can be realized. An alternate
possibility would keep precipitation over the County Warning Area through the
morning and early afternoon...essentially limiting destabilization
to near-zero. The soundings look rather moist...leading to thin
cape and low LCLs.
It is an interesting contrast in severe potential from today
(tuesday)...with different elements of the mesoscale analysis
appearing favorable on either day.
The large northern plains upper low will finally be on the move by
late Wednesday...crossing the iln County Warning Area on Thursday. This will bring
another high chance of probability of precipitation on Thursday...mainly in the north and
generally with diurnal timing. Behind the axis of this
trough...rapid drying is expected.
Temperatures will begin a downward trend after the poorly-defined
cold front (associated with the Wednesday surface low) moves
through the region. A stronger change in near-surface air mass is
expected behind the trough on Thursday night...with northerly
winds advecting colder and drier air into the region.
&&
Long term /Friday through Monday/...
surface high pressure will build down from the north and into our
area Friday into Saturday...keeping a seasonably cool airmass in
place through the start of the weekend. Highs on Friday will be in
the middle to upper 60s and with the surface high overhead...lows
Saturday morning will dip into the low to middle 40s. The surface
high will begin to shift off to the east through the remainder of
the weekend as middle level ridging begins to establish itself aloft.
This will result in a gradual return to warmer temperatures
through the rest of the Holiday weekend. Models are still trying
to suggest the possibility of some energy dropping down from the
northwest late in the weekend. However...timing and placement are
highly variable so will maintain a dry forecast at this point.
&&
Aviation /13z Tuesday through Saturday/...
large scale upper level low centered over the northern plains will
make little eastward progression over the next 24 hours. Region
will be located in a warm...moist south/southwest flow at the surface
and aloft.
Showers and isolated storms will pass across the Cincinnati
terminals shortly and could possible hold together to reach kday
and Kiln but should dissipate well before reaching central Ohio
terminals. As our area is in a moist southwest flow aloft...
additional shower and thunderstorm activity will be dependent on
any linger outflow boundaries from early morning convection...
embedded disturbances aloft and how much sunshine the area
receives for instability. Models are not offering much in terms of
specific timing except to favor the diurnal cycle and have include
only thunderstorms in the vicinity/cumulonimbus at the taf sites as such. This may significantly
change depending on previous mentioned factors if thunderstorms
get going on any mesoscale feature.
For tonight...models suggest a lull in the convective activity in
terms of coverage. Coverage should increase on Wednesday as a more
significant disturbance rotates from southwest to northeast across
the region out ahead of a cold front. Showers and thunderstorms
look like a good bet for Wednesday into Wednesday evening.
Outlook...thunderstorms likely Wednesday into Wednesday evening.
MVFR conditions possible Thursday into Thursday night.
&&
Iln watches/warnings/advisories...
Ohio...none.
Kentucky...none.
In...none.
&&
$$
Synopsis...hatzos
near term...
short term...hatzos
long term...jgl
aviation...Hickman
