Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
1037 PM EDT Sat Aug 1 2015
high pressure over the area this afternoon will move towards the
east this evening allowing for another pleasant night. A very
weak upper level disturbance will also skirt across Northern Ohio
overnight but no rain is expected at this time. On Sunday... as
the high continues to move away from our region...a cold front
will approach from the northwest. This front will slowly move into
the Ohio Valley on Monday.
Near term /until 6 am Sunday morning/...
northwest flow aloft with surface high pressure building across the
Ohio Valley. Middle/upper level disturbance dropping southeast across the region
was resulting in an axis of middle/hi level clouds. Airmass is
dry...so have continued dry forecast. Lows on the cool side in dry
airmass with readings from the upper 50s far NE to the lower 60s
a broad and weak area of surface high pressure will slowly push
east overnight bringing another night of near normal temperatures.
An upper level disturbance currently just west of Chicago is also
forecasted to push southeast and move over the northern parts of
our County Warning Area just after midnight tonight. Some high res models are
showing some light returns with this along with the NAM (on Omega
and quantitative precipitation forecast fields). Precipitable waters overnight remain low though. Both the GFS
and NAM are forecasting values only around 1.00". Soundings also
don't show much. Given the above have kept the chance of rain out
of the forecast.
Short term /6 am Sunday morning through Monday night/...
on Sunday surface high pressure will be pulling east as the next
upper level system approaches from the northwest. At 250 mb
current convergent flow will end as the next shortwave dives south
During the day Sunday precipitable waters are forecasted to slowly rise near
1.25" during the afternoon with very little instability
forecasted. A weak shortwave will approach from the west and move
overhead during the afternoon but given weak lift (via Omega
fields) and low moisture values have left the mention of rain out
for Sunday during the day. 850 temperatures are also on the rise
Sunday and approach 17 degrees c. This will translate into high
temperatures a couple of degrees warmer than Saturday.
Early Monday morning a cold front will push southeast as the main
shortwave gets wrapped up into an upper level low. Have gone ahead
and trended probability of precipitation higher Monday morning into afternoon as diffluent
flow from a splitting jet moves into the area. The main chance of
rain will come from the front but surface convergence looks weak.
Omega values also look weak not surprisingly given weak vorticity
advection and warm air advection. Moisture values are forecasted
to be near normal Monday for this time of year (pwats ~ 1.4" -
1.5"). Winds could also be gusty during the day Monday as both the
GFS and NAM are showing the low level jet in the 30 to 40 kts. The front
then looks to clear the area Monday evening into Tuesday morning.
Long term /Tuesday through Saturday/...
a closed upper low over eastern Canada will keep a broad upper
trough over the Great Lakes region through the first part of the
extended period. Northwesterly flow aloft will carry several
disturbances through the Ohio Valley...bringing multiple
chances for showers and thunderstorms Tuesday through Thursday.
Meanwhile an upstream upper level ridge will flatten out as it
interacts with a developing shortwave over the northern rockies. Energy
associated with this shortwave will support Lee cyclogenesis over the
Oklahoma Panhandle Wednesday into Thursday...a system which will impact
the Ohio Valley by the end of the week. The 01.12z GFS run shifted this
system and its associated quantitative precipitation forecast quite a bit further south than the
06z run...taking it right through the iln County Warning Area on Friday. Based on
this large shift and the fact that its quantitative precipitation forecast and upper level energy still
look overdone...have used a blend more heavily weighted towards the
European model (ecmwf) /which has shown a little better run to run consistency/ to
handle this system.
With the 500 mb trough overhead and a quasi-stationary front staying to our
south for several days...a cooler and slightly less humid airmass looks
to establish itself over the region for much of the extended period.
Highs will generally range from the middle 70s to middle 80s with the warmest
temperatures staying near and south of the Ohio River. Lows will range
from around 60 to the middle 60s.
Aviation /03z Sunday through Thursday/...
VFR is expected through the taf period with surface high pressure
building across the Ohio Valley. Expect mainly high level clouds
overnight. On Sunday few to scattered cumulus clouds will develop along
with some high level moisture.
Winds will back from northwest to southwest...with speeds less
than 10 kts overnight and then around 10 kts on Sunday as
the pressure gradient tightens between departing high pressure
and an approaching cold front.
Outlook...MVFR ceilings and visibilities are possible late Sunday
night with thunderstorms. Scattered thunderstorms are also
possible Monday and Tuesday.