Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
400 am EDT Tuesday may 5 2015
a frontal boundary has now stalled across Northern Ohio and will
slowly start to wash out and pull northwards through Wednesday. At
the same time... weak upper level ridging will take shape over the
Ohio Valley Wednesday into Thursday. The next cold front is
forecasted to cross the region next Tuesday.
Near term /until 6 PM this evening/...
showers and thunderstorms have continued to develop this morning
while the line continues to pull back towards the northeast.
Expect this line to continue to move northeast towards dawn along
with the best low level convergence zone. The best area of low
level convergence looks to be in Northern Ohio but soundings still
support rain across northeast and central parts of the County Warning Area. NAM
forecast soundings for cmh show cape values ~600 with precipitable waters up
around 1.24". GFS forecast soundings are slightly less favorable.
High res ncar ensemble suite also showing redevelopment possible
across central Ohio this afternoon. For these reasons have gone
ahead and introduced probability of precipitation across the central areas of the County Warning Area.
Rain chances towards Cincinnati still look low for Tuesday.
Short term /6 PM this evening through Wednesday night/...
on Wednesday a shortwave over The Rockies will begin to eject
towards the northeast allowing surface cyclogenesis to occur on
the Lee side of The Rockies. This will allow weak ridging to take
shape over the area. Not completely convinced that the area will
be rain free Wednesday as ridging remains relatively weak and
precipitable waters don't completely drop off. Forecast soundings from both the
NAM and GFS do show some instability with also a hint of upper
level subsidence from the ridge. Either way rain chances will be
low Tuesday night into Wednesday night and any rain that does form
will be mostly diurnally driven.
Long term /Thursday through Tuesday/...
in the extended models continue to struggle with the progression
of an upper level system and its associated surface cold front. On
Thursday the area of vorticity that was over The Rockies Wednesday
will move up and over the ridge as an area of low pressure off the
coast of South Carolina begins to retrograde. The low will then
retrograde underneath the weak ridge forming a temporary Rex
block which will help to block the flow. Another shortwave will
also dive south Thursday off the West Coast of the United States
quickly wrapping up into a low. This means a return of southwest
flow at 500 for the area opening the way for pockets of positive vorticity advection to
traverse the area starting Saturday. Precipitable water values are also
forecasted to rise Saturday into Sunday and approach 1.70" Sunday
evening (1 - 2 South Dakota above normal for this time of year). Have
increased probability of precipitation slightly earlier due to the lift and moisture.
On Sunday models begin to diverge significantly. The Euro brings
another upper level disturbance southwards Sunday over the Canadian rockies
picking up the low over northern Arizona. The low then pushes east
across Ohio Tuesday pulling a surface cold front along with it.
The GFS on the other hand has the energy from the Canadian rockies
never making it far enough south to dislodge the low over southern
Arizona. The low eventually opens up and shears out. This solution
keeps the area warm and humid. The latest Canadian appears to
resemble the European model (ecmwf). Have kept grids trending towards the CMC and
European model (ecmwf) solutions for now.
Aviation /07z Tuesday through Saturday/...
showers with embedded thunderstorms are continuing to push east
along the I-70 corridor early this morning. The precipitation is associated
with a boundary currently draped across the area that is forecast
to lift slowly north through the day. As a result...expect current
precipitation to slowly shift off to the north and thus only affect the
northern taf sites through the pre dawn hours. Ceilings/visibilities are
primarily VFR...but some MVFR/isolated IFR conditions will be
possible with some of the stronger storms. Some patchy MVFR br
will be possible toward daybreak in the southern river valleys so
will allow for some brief visibility restrictions at kluk.
Otherwise...VFR conditions are expected through the remainder of
the taf period.
Outlook...no significant weather is expected at this time.