Scientific Forecaster Discussion
fxus61 Kiln 171505
Area forecast discussion
National Weather Service Wilmington Ohio
1005 am EST sun Dec 17 2017
weak weather disturbances crossing the Ohio Valley today and
tomorrow will bring clouds and a little rain or drizzle to much
of the area as temperatures remain mild in the 40s. While clouds
will likely hang on into Tuesday, temperatures will warm into
the 50s ahead of the next weak cold front which will slip
through the area rather quietly on Tuesday evening. This front
will bring cooler temperatures and a little sunshine for
Near term /until 6 PM this evening/...
water vapor satellite imagery shows shortwave over mid MS Vly
this morning. This S/W will eject northeast and run into the
mean ridge position over the region and deamplify and shear out.
Forcing will be weak and airmass is starting out rather dry.
Expect to see a good deal of virga on the radar with a light
rain event developing this afternoon. Will continue to have pops
ramp up to likely where band of light rain is expected to
develop generally along and south of the I-70, once the column
saturates later this afternoon. Have used a blended approach for
temperatures with mav guidance appearing too high given light
rain and clouds. Generally expect highs of 40 to 45 degrees
Short term /6 PM this evening through Wednesday night/...
wave departs this evening with scattered light rain quickly
ending but clouds continuing to thicken/lower as weak warm
advection on swly boundary layer flow continues in the wake of
the wave. In fact, forecast soundings suggest low level moisture
will continue to deepen past 2km this evening as next subtle
ripple in midlevel height field approaches. Combination of weak
vertical motion in/above this deeper low level moisture field
will induce patches/areas of drizzle and fog, particularly later
tonight into much of Monday. Introduced a pop for measurable
drizzle or even very fine/light rain given maintenance of low
level moisture field in excess of 1.5km into Monday evening.
With saturated surface temp/dewpoint traces, think the temp
curves will be muted on both Monday afternoon and Monday night,
so tightened those up considerably. Monday night may not see any
fall, and despite current forecast indicating steady temps
overnight or perhaps dropping a degree, would not be at all
surprised if temps Monday night actually went up a degree or two
given most recent data trends. Bottom line - the Monday and
Monday night periods will see plenty of stratus, light fog, and
patches/areas of drizzle - most of which will diminish with time
through Monday night.
On Tuesday, height falls dropping through the northern Great
Lakes will allow a weak cold front to slip toward the area.
Continued southwesterly low level flow will allow temperatures
to respond into the 50s, particularly with a few breaks of
sunshine possible on Tuesday afternoon, though still expect
mostly cloudy skies with any breaks confined to the later part
of the afternoon. Front slips through quietly /dry/ on Tuesday
evening with modest low-level cold advection signal and temps
back below freezing Tuesday night.
Wednesday will feature high pressure moving directly over the
area with good subsidence/drying which should allow for more
sunshine although it will be cooler, with highs back in the
Will need to watch southern stream shortwave trough/surface low
coming out of the southern branch of the western Continental U.S. Split
flow regime. Bulk of deterministic/ensemble data has taken this
system and its rain shield south of the area, though enough
members grazing nrn Kentucky with a bit of light rain to keep an eye
on this system into mid-week.
Long term /Thursday through Saturday/...
while Thursday is a relatively high confidence dry forecast as
high pressure pulls away into New England and a large upper
trough advances eastward from the Central Plains, confidence in
this portion of the forecast degrades very quickly. Gefs/eps
plumes continue to indicate a tremendous amount of spread in the
details despite a slowly increasing signal of a cold front/low
pressure shifting through the Great Lakes Friday afternoon
through Saturday morning.
There's a great deal of variety in the timing of the front,
orientation of the boundary, and whether a frontal wave will
form on the boundary or a dominant surface low will deepen
through the Great Lakes and swing the cold front through with
much more brute force. There's solutions ranging from a very
potent surface low developing through WI/Michigan which allows highs
on Friday well into the 50s with nearly similar dewpoints, and
then a strong frontal surge with hints of cape and need for
thunder consideration. Other solutions continue to be seen of a
much slower/strung out frontal passing that takes far longer and
entrains very deep moisture from the Gulf of Mexico, and hints
at a heavy rain/flooding threat Friday night into Saturday.
Still further, there have been members/runs showing a rain-to-
wet snow scenario for Friday night/Saturday morning, or a band
of rain passing quietly through and then the front clearing for
a quiet/dry Saturday. Just not seeing any ensemble movement to
a preferred solution, so will hit rain chances highest on Friday
night, with a trend to cooler temperatures for Saturday and
perhaps some rain/snow mix or brief wet snow. Given ensemble
spread that exceeds the natural variability, continue to expect
a very low confidence forecast in this time period for a few
Aviation /15z Sunday through Thursday/...
warm frontal processes north of the area will help usher in
more moist air on southerly winds today. A mid level shortwave
will enter this afternoon and flatten out the weak h5 ridge that
is currently in place over the Ohio Valley. As it shears out
crossing Ohio, a few showers or area of light rain is expected
to affect the region. Models continue to indicate a WSW-ENE
orientation of the band of rain, which would hit Dayton and then
Columbus areas with a higher potential for rain for a few hours
this afternoon. Hrrr and nam12 are showing another southern
maxima to the rain today, so have included some showers with
MVFR cigs and VFR vsbys at just about everywhere with a slightly
pessimistic forecast with lower vsbys from day to cmh
This h5 shortwave moves east of the region tonight and with it
the threat for rain is removed. Increasing moisture in the lower
levels will be found in the region overnight, and an area of
enhanced upward motion may initiate some patchy drizzle or a few
sprinkles late overnight or early Monday morning. The sprinkles
and/or drizzle does not have a feature to key off of, and the
h7 upward motion fields are as splotchy in coverage as the quantitative precipitation forecast
fields being generated by the nam12. The better threat of any
drizzle or sprinkles will occur towards 12z Monday.
Models continue to show saturation of the low levels overnight
so ceilings should lower overnight and trend toward IFR category.
Have kept vsbys VFR for the overnight hours given the latest
guidance is holding the onset of any precip until after 12z.
Outlook...IFR/LIFR ceilings and MVFR/IFR visibilities continuing
into Monday. MVFR/IFR ceilings and MVFR visibilities possible
Monday night into Tuesday morning.