Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
147 am EDT Sat Apr 25 2015
an area of low pressure will track across the Ohio Valley on
Saturday into Saturday night...bringing rain showers. There will be a
a chance of thunderstorms across northern Kentucky and extreme
southern Ohio. Another area of high pressure will move in for
Sunday and Monday...with dry weather expected to start the week.
Near term /until 6 am this morning/...
isentropic lift will increase across the area tonight. This will
allow for some spotty shower activity early tonight. Not all of
the returns on radar are reaching the ground as precipitation is
falling out of a middle deck. Precipitation will begin to increase in
coverage across SW portions of the forecast area late in the overnight hours.
Instability is pretty limited and therefore did not include any
thunder mention in the forecast for the overnight hours. Made
minor adjustments to temperatures overnight however not expecting
a big decrease in temperatures overnight tonight.
Short term /6 am this morning through Sunday night/...
during the day on Saturday the ejecting 500 mb short wave weakens as its
gets absorbed into the overall westerly flow. Models are still
consistent with in tracking the surface low just to the south of the
forecast area on Saturday into Saturday night. This should limit the ability
of the system to pull unstable air into the region for
Saturday...keeping the better threat of severe weather south of
the region. There is some surface based and elevated instability
across southern sections of the forecast area...so will keep a mention of chance
thunderstorms there for Saturday. Went ahead and went with categorical
probability of precipitation for the entire forecast area...as it looks like almost all locations
will southeast some sort of precipitation on Saturday.
With the latest model runs now passing the surface low south of the
region until Saturday night...they have continued to show
lingering precipitation Saturday night as upper level energy remains from
the filling short wave. Kept the highest probability of precipitation in the south for early
Saturday night...with lesser probability of precipitation in west central Ohio. Precipitation
should diminish from the north to south Saturday night. It still
looks like there could be some lingering showers in the southeast early
500 mb short wave trough rotating around a broad upper low Sunday will combine
with 800 mb cold air advection and northerly winds to develop clouds across the region
Sunday. Have these lingering into Sunday night. This will help
mitigate the chance of frost for late Sunday night.
Rain and cloud cover will limit solar insolation keeping
temperatures down. Highs will struggle to get into the lower 50s
for much of the region. Around the Ohio River they should make it
into the middle 50s...with parts of Owen County making it to near
60s. Temperatures will cool off Saturday night behind the low
ranging from the upper 30s in the north to the upper 40s in northern
Kentucky. On Sunday...highs will make it back into the middle 50s to the
lower 60s. As hinted at above...temperatures Sunday night will
drop back into the upper 30s across much of the region...with the
lower 40s in northern Kentucky.
Long term /Monday through Friday/...
west-east oriented 500 mb trough axis will dive south through Ohio Valley on
Monday and provide cloud cover and the weak possibility of a
sprinkle. Left sprinkle mention out being day 4 of the forecast with
the thought that there may not be enough of a moist layer beneath
the middle level forcing to wring out any more than a thicker cloud.
This leaves Monday high temperatures as the coolest in the
forecast...starting out around 60 or in the low 60s for Kentucky and areas
along Ohio River.
High builds northwest of the region but gets caught up in the
muddled surface pattern and only a weak ridge is expected to nose
into the Ohio Valley for Tuesday.
Northeast flow at the surface will be found as the 500 mb pattern really
gets knocked around with weak ridges in between various troughs and
cutoff lows downstream of an entrenched ridge in the western U.S.
The mean longwave trough in the east will prevail and hamper any
significant warmup which would normally be expected with the higher
sun angles of this time in the season.
Interspersed periods of clouds during the daytime periods are
expected with a general warming trend as temperatures reach and slightly
exceed climatology normals by day 7 by tipping into the 70s.
A southern low pressure center in the mean 500 mb ridge may result in a
heightened threat of some light showers for the tail end of the
Aviation /06z Saturday through Wednesday/...
conditions are VFR to start. That will change as showers develop
and expand in coverage along a stationary front over Kentucky.
Greatest effects will be at cvg and luk where prevailing showers
with MVFR are forecast around 14z. Thunderstorms could occur in
the vicinity there late in the afternoon...followed by IFR
ceilings as low pressure moves along the front.
Farther north at day and iln...showers with MVFR are expected
from 14z through the evening hours...while cmh and lck may see
MVFR for a briefer period this afternoon to early evening.
Winds will be out of the east at about 12 knots by this
afternoon...shifting to northeast late in the forecast
period...with some gusts over 20 knots.
Outlook...MVFR ceilings possible Monday.