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Area forecast discussion 
National Weather Service Wilmington Ohio
1249 am EST sun Feb 14 2016

Synopsis...
an Arctic high pressure will build into the area tonight. A warm
front will start to move through the region on Sunday...bringing
snow to the area through Sunday night. Low pressure will move
southeast of the area on Monday...with additional precipitation.
Another area of low pressure will move into the area on
Tuesday...with warmer temperatures expected for the end of the
week.

&&

Near term /until 6 am this morning/...
diurnal cold air advection cumulus has eroded out of the forecast area...but is being replaced by
some cirrus clouds associated with the next weather system. The cirrus
will be on the increase during the second half of the night.

Winds at the surface will be light and variable overnight as high
pressure works across the region.

Lows will be in the single digits tonight.

&&

Short term /6 am this morning through Monday night/...
during the short term forecast period...two shortwaves will be
moving through the Ohio Valley...presenting an array of
forecasting concerns. Impacts from the first shortwave (snow on
Sunday / Sunday night) are coming into view with respectable
clarity...with decent agreement between models in the overall
setup. Confidence is also growing that impacts from the second
shortwave (largely a rain event for monday) will be minor...even
though the details of the actual meteorological factors remain
remarkably discombobulated.

On Sunday morning...surface high pressure will be moving to the
east of the iln County Warning Area. The shortwave in question will be moving
eastward through Iowa at around 12z. Ahead of the wave...surface
to 700mb flow will take on a southerly component...and elevated
warm frontal processes will begin (with notable convergence and
ascent at 850mb). A swath of snow (with the front edge oriented
northwest-to-se) is expected to develop and move into the iln forecast
area during the late morning to early afternoon. It may take some
time for the column to saturate...with quite a bit of dry air
(especially in the 5kft-10kft layer) to work through. Once it
occurs...the forcing type and overall setup favor a widespread
light snow for the entire forecast area...with some slightly
heavier rates in the southern third of the County Warning Area. Temperatures
through the lowest 10kft appear likely to warm up just enough to
not really support any significant dendrite development...so snow
ratios may not end up being as high as the initially frigid
temperatures might otherwise suggest. Nonetheless...the prolonged
nature of the snow (perhaps up to 6-8 hours of steady light snow)
will allow for a gradual accumulation...especially in the southern
County Warning Area where deep-layer moisture will remain in place for a longer
period of time. Total accumulations of 2-3 inches can be expected
for the far southern counties...with around 2 inches near the
cutoff of the Winter Weather Advisory...and lesser amounts further
to the north. The advisory GOES into effect in two segments
tomorrow based on timing. However...the entire advisory will
remain active until Monday morning...allowing time for surface
temperatures to rise above freezing. Though not specifically
mentioned in the west-southwest product...there does appear to be some
potential for light precipitation to continue after the wave has
moved through...but moisture becomes extremely shallow during this
time frame (early Monday morning). Thus...freezing drizzle could
be a possibility...with ground conditions that will be very
susceptive for icing if that scenario were to occur.

The forecast for the second system on Monday remains notably
convoluted...with major differences between models in the
evolution of the next shortwave...and the surface low it helps to
develop. This wave (or at least its genesis) can be traced all the
way back to the southern British Columbia coast this evening...an
indication that it has a long way to travel before reaching the
Ohio Valley on Monday. The vast majority of 12z operational
guidance allows for a surface low to develop...remain somewhat
weak...and head east-northeast into the Middle-Atlantic States. The
European model (ecmwf) has remained the furthest west with regards to the low
track...and the strongest with regards to the low strength.
Looking at ensembles (gfs/sref)...even through an array of
perturbations...there appears to be little support for the European model (ecmwf)
solution. The expected weaker low track does still allow for
another increase in precipitation chances for the southeastern iln
County Warning Area...and perhaps a significant increase for Monday afternoon and
evening...with good forcing to the north of the low and plenty of
moisture to work with. However...there is a huge caveat to all of
the above...and that is the continued trend toward a warmer
solution across all available models Sans the NAM. This means
that much of the precipitation on Monday...and in particular any
potential for heavier precipitation...will fall as a cold rain.
So...despite the continued befuddling model differences in the
setup...a somewhat-reasonable level of confidence in the
temperature situation does provide for a slightly better idea that
this second system will produce little additional hazardous winter
weather impact. There remains a possibility that cooling
temperatures Monday evening could allow for some light snow on the
back side of the system...but given all the other uncertainties
mentioned...it would be foolish to try to make an accumulation
forecast (if any snow occurs at all) at this point in the forecast
process.

Temperatures were hand-edited non-diurnally through the entire
forecast period. Although conditions at the surface on Sunday will
only warm a little from Saturday (despite the start to a warm
advection pattern)...a more significant boundary layer warming
will begin on Sunday night. Temperatures will likely be rising
going into Monday morning...and will then go above freezing for
the entire County Warning Area by early Monday afternoon.

&&

Long term /Tuesday through Saturday/...
a fast moving shortwave in a northwest flow aloft will be right on the
heels of departing system Monday night. This disturbance will be
associated with an area of surface low pressure. Models have the energy
in different spots with the NAM the farthest north and the European model (ecmwf) the
farthest south. Have gone with the middle of the Road GFS.
Regardless...all solutions suggest that warm air advection ahead of this system
should keep precipitation in the form of rain as it moves in on Tuesday. Have
used likely probability of precipitation. Temperatures will warm into the upper 30s to the
lower 40s.

For Tuesday night into Wednesday...as the system quickly moves
east...colder air will filter into the region on the back side...so
some mix with or a brief change over to snow is expected before
tapering off toward Wednesday morning. Any snow accumulations should
be across the far north and minor in nature...less than an inch. On
Wednesday...will go with a dry forecast...although considerable cold air advection
stratocumulus is expected.

For Wednesday night into Thursday...high pressure will build south
into the Ohio Valley. Skies are expected to become partly cloudy.
Models different on the extent of cold air filtering in the
region...so have sided with a wpc blended approach.

As the high moves east Thursday night...a warm front is forecast to
approach from the west. We should see an increase in warm air advection induced
clouds. As of now...any precipitation generated with the warm front is
expected to stay northwest of the area. Overnight lows will be early
followed by slowly rising temperatures as winds increase from the
south.

For Friday into Friday night...low pressure will traverse the Great
Lakes as a cold front pushes in from the northwest. Models vary on
how much moisture will be pulled northward along and ahead of the
front system...along with the timing...so have gone with a chance of
rain. Friday certainly looks to be the warmest day of the extended
with temperatures rising into the 50s area wide.

On Saturday...front exits to the east...but cold air advection stratocumulus moves
into the region. Precipitation will move east as well. Temperatures will cool
into the middle 40s to lower 50s for highs.

&&

Aviation /06z Sunday through Thursday/...
VFR and dry conditions will start out the taf period. Snow will
move into the taf sites Sunday afternoon into the evening hours
and remain in place through the end of the taf period. Ceilings will
gradually lower on Sunday and visibilities will be reduced with the snow.
There is some concern that towards the end of the taf period ice
may not be introduced into the clouds and therefore there is the
potential for some freezing drizzle. Have precipitation as snow at this
time however will have to monitor this with future tafs to see if
confidence in freezing drizzle increases.

Outlook...MVFR/IFR conditions are possible with precipitation
from Sunday night through Tuesday.

&&

Iln watches/warnings/advisories...
Ohio...Winter Weather Advisory from noon today to 10 am EST Monday
for ohz077-078.
Winter Weather Advisory from 5 PM this afternoon to 10 am EST
Monday for ohz079>082-088.
Kentucky...Winter Weather Advisory from noon today to 10 am EST Monday
for kyz089>098.
Winter Weather Advisory from 5 PM this afternoon to 10 am EST
Monday for kyz099-100.
In...Winter Weather Advisory from noon today to 10 am EST Monday
for inz073>075-080.

&&

$$
Synopsis...hatzos
near term...sites
short term...hatzos
long term...Hickman
aviation...Novak

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