Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
644 am EDT Tuesday Apr 21 2015
a strong low pressure system over the Great Lakes will bring very
windy conditions today...along with a chance of showers at times
through Wednesday morning. Drier conditions are expected from
Wednesday afternoon through the rest of the week...with breezy
afternoons and cool temperatures. Another chance of rain will arrive
Near term /until 6 PM this evening/...
scattered to broken clouds in the 6kft-10kft layer are crossing
the iln County Warning Area from west to east...delineated very nicely on infrared
satellite. Within these patches of clouds are some
convective-looking showers...and although no lightning has been
observed...pea size hail was observed with one of the showers
(thanks to the freezing levels of around 4kft).
The primary concern today remains the threat for strong
winds...and an analysis of 00z model data supported maintaining
the current orientation for the Wind Advisory (with a Special
Weather Statement for the rest of the forecast area). Strong
unidirectional flow (at about 250 degrees) extends through the
entire depth of the troposphere...with values steadily increasing
off the surface. Using a recent rap run at kday on BUFKIT as an
example (at 18z)...winds increase to 40 knots at 825mb...then 50
knots at 700mb...and 60 knots at 600mb. Today will be an exercise
in mixing...as the eventual depth of the mixed layer will likely
determine just how strong the winds get. Gusts in this forecast
were generally gleaned from BUFKIT momentum Transfer via rap/GFS
forecasts...with values in the lower 40 knot range in the northern
County Warning Area...and lower 30 knot range in the southern County Warning Area.
Although clear skies will be in place at the beginning of the
day...weak elevated forcing and a slight increase in moisture at
the top of the (rather high) mixed layer will result in some cloud
development...and eventually showers in the southeastern half of
the forecast area. These showers may be very high-based (perhaps
8000 feet)...with scattered coverage at most.
Short term /6 PM this evening through Friday/...
precipitation is expected to move into the region (or perhaps
develop over the forecast area) on Tuesday night into Wednesday
morning. Although there are some model differences with regards to
the intensity and layout of the precipitation...the overall timing
appears to favor the 06z-15z time frame for the iln forecast
area...ahead of a shortwave and a surface cold front. Although
this front shows up nicely on mslp plots...the wind shift and
change in air mass are not especially notable. Instability (even
elevated) will be hard to come by...so though thunder is not an
impossibility with this setup...the chance seems very low.
Once this front passes...very similar conditions are expected for
the rest of the week...with northwest flow and cool weather. Ohio
is likely to remain in between areas of enhanced moisture from the
northern and southern streams...leading to generally sunny
conditions until Friday night.
Temperatures on Thursday and Friday morning may be cool enough for
frost...but moisture and wind forecasts are not as favorable.
Thus...frost will not be included in the grids or severe weather potential statement.
Long term /Friday night through Monday/...
some deeper moisture will be pulled up toward our area on
Saturday ahead of short wave energy moving out of The Rockies.
While the best forcing/moisture associated with this will remain
to our south...some precipitation could sneak up into at least southern
portions of our forecast area early in the weekend. This may also allow for a
slight modification in temperatures with highs pushing into the
upper 50s to lower 60s by the end of the long term period.
Aviation /12z Tuesday through Saturday/...
large scale upper level low centered over the western Great Lakes
this morning will move slowly east through the taf period. Embedded
disturbances rotating around the low will affect our region from
time to time.
For today...strong surface low pressure will remain north of the
Great Lakes. Meanwhile...a cold front will approach the region
from the west. The increasing surface pressure gradient combined
with deep mixing will result in windy conditions from middle morning
into early evening. Winds will veer from a southwest to a
west/southwest direction with wind gusts in the 30 to 40 knot
range. Models continue to indicate that some moisture in the low
to middle level will develop/advect northeast into the region by this
afternoon. This cloud layer could become convective enough to
produce a few sprinkles or light showers...mainly along and south
of the Ohio River.
For tonight...one of those embedded disturbances mentioned will
dig southeast into our area. This feature will team up with
frontal convergence from the advancing cold front to bring a
threat of showers to the taf sites between 06z and 12z. There
could be some pockets of MVFR visibilities associated with the
more robust showers.
Outlook...gusty west to northwest winds up to 30 knots expected
Wednesday afternoon into early evening.
Ohio...Wind Advisory from 11 am this morning to 8 PM EDT this evening
In...Wind Advisory from 11 am this morning to 8 PM EDT this evening