Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
755 PM EDT Tuesday Sep 1 2015
an upper level low will drift southeast across the area tonight
into Wednesday. An upper level ridge will then build across the
region through the remainder of the week with continued warm and
Near term /until 6 am Wednesday morning/...
a closed upper level low evident over Indiana on water vapor
imagery this afternoon continues to slowly drift northeastward.
Coupled with a warm and muggy airmass...energy associated with
this system has triggered isolated to scattered convection across
mainly our northwestern County Warning Area this afternoon. With rather weak flow
from about 0-6 km...individual cells will continue to be slow
moving and not well organized. Thus...main issue with stronger
cells through early evening will likely just be locally heavy
rainfall. Expect this activity and much of the cumulus field to
diminish with the loss of daytime heating this evening.
Kept slight chance probability of precipitation across mainly our northwest overnight as
the upper low moves over western Ohio. Overall forcing from this
feature will remain weak but cannot rule out some isolated
lingering convection in its vicinity. Various model quantitative precipitation forecast fields
seem overdone behind the low along the in/Ohio border...which is
probably tied instead to a weak low level jet and convergence over
that area. Cloud cover overnight is somewhat uncertain given the
upper low overhead but also some drier air moving in aloft. Have
gone partly cloudy for now with lows in the middle to upper 60s.
Short term /6 am Wednesday morning through Thursday night/...
models are in agreement with the upper low opening up into a
weakening shortwave early Wednesday morning...becoming absorbed
into middle level flow and pushing southeast of the County Warning Area by afternoon.
Have discounted the the GFS which was quite a bit slower than the
NAM...European model (ecmwf) and Canadian in clearing the low out of our area. A
weak surface trough will push through Northern Ohio during the
day...resulting in a chance of showers and storms given the
continued warm and humid airmass with temperatures rising into the
middle to upper 80s. Precipitation chances will diminish with the loss of
daytime heating Wednesday evening.
A building upper level ridge will then gradually take hold of the
region beginning late Wednesday...resulting in dry conditions for
Wednesday night. A weak ridge of high pressure at the surface
will develop just west of our area on Thursday causing winds to
become northerly. Despite this change in surface flow...temperatures
will still remain up there with highs flirting with 90 in many
spots and dewpoints around 70. A weak disturbance aloft may allow
for isolated convection in conjunction with daytime heating on
Thursday with dry conditions expected for Thursday night.
Long term /Friday through Tuesday/...
while some of the specifics regarding the extended forecast remain
uncertain...the large scale pattern supporting above-normal
temperatures shows no signs of change through the weekend...with
only a slight trend toward the middle-level ridge breaking down going
into the first half of next week.
On Friday morning...the axis of a fairly strong ridge will extend
from the Texas coast north-northeast through the northern Great Lakes. At the
surface..the pressure pattern will be fairly nebulous...with weak
high pressure over the northeastern states. This will keep the Ohio
Valley in a regime of weak and moist low-level easterly flow through
the weekend. This is certainly a pattern that supports warm
conditions...and maximum temperatures in the upper 80s to around 90 are
expected. Gefs 850mb/700mb temperature and 500mb height anomalies
are not extreme...ranging from around 0.5 to 1.5 Standard deviations
above normal through the forecast period. This lends support to a
forecast for above normal temperatures...but not at the high end of
the climatological record.
With very little appreciable forcing...any chances for precipitation
will be limited. Between the GFS and European model (ecmwf)...the GFS has been a
little more willing to convect...but quantitative precipitation forecast output is not significant
in either case. A dry forecast will be maintained for most of the
forecast period...though slight chance probability of precipitation were kept in for Friday.
On Monday and Tuesday...there are signs that the ridge will begin to
flatten...though the extent and quickness that this occurs is not in
good agreement. As a shortwave moves across the north-central Continental U.S.
Going into Tuesday...eventually a cold front will develop and move
toward the Ohio Valley. How far this process gets is much too early
to forecast...but there is enough confidence to show a slight
decrease in temperatures and as light increase in probability of precipitation for
Aviation /00z Wednesday through Sunday/...
a weak upper level low currently moving into Ohio will slowly
drift east/southeast through the region between now and 18z
A moist and unstable airmass interacting with this feature had
resulted in isolated to scattered convection this afternoon and
evening. With the lack of low level forcing and a decrease in
diurnal instability...any convection with this feature should be
isolated overnight into Wednesday morning. Looking behind this
feature...high resolution models indicate that a trough axis
associated with an impinging west/northwest low level jet may
develop some convection to our northwest late tonight...drifting
it east/southeast toward the kday/kcmh/klck taf sites toward
Wednesday morning. Confidence is not high on what coverage the
convection may manifest itself so have only placed a vcsh at the
kday terminal at this time. Cloud cover will vary between mostly
clear to partly cloudy. With light winds...some MVFR fog will
develop. But given the in and out cloud cover...confidence is
lacking on how low to go with the fog at the typically fog prone
locations of kluk...Kiln...and klck...so have only lowered
visibilities to IFR at klck and kluk. Fog should burn off by 14z.
Later in the day on Wednesday...best threat for convection should
be across the north (20 to 30 percent) with a diurnal drop off
after 00z as middle level ridging builds into the area.
Outlook...no significant weather expected.