Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 060303

Area Forecast Discussion
National Weather Service Wilmington OH
1003 PM EST Mon Dec 5 2016

Surface high pressure was centered over the region this afternoon
allowing for a few hints of sunshine. The high will quickly move
off to the northeast tonight and Tuesday as low pressure moves
into the Ohio Valley. A cold front will follow on the heels of the
low Tuesday night, bringing drier and cooler weather behind it for
mid week. Much colder weather is expected by the end of the week
as another cold front pushes across the region.


Southern stream upper low over eastern TX to open up and lift
northeast into the lower MS VLY by morning and further deamplify
as it tracks into the Ohio valley Tuesday. Associated surface
wave to track northeast into the region ahead of the upper s/w.

Rain over the TN valley ahead of this system to spread north to
near or just north of the Ohio river by 09z and then overspread
ILN/s FA, early on Tuesday. Have slowed down precipitation based
on observation and model trends. Temperatures to have non-diurnal
trace, falling off and then steadying out or slowly rising late.

Previous Discussion...
Surface high pressure will pull east of the area this evening into
Tuesday morning as an upper level low over south Texas gets
picked up in the main flow and ejects northeast. Currently over
the area there are some breaks in the low clouds with the sun
making a rare appearance. Already cirrus blow off just to the
south is starting to encroach on the area. Both NAM and GFS
forecast soundings show this trend of low clouds thinning only to
be replaced by cirrus. This evening high clouds will slowly lower
to mid clouds with soundings full saturating in northern Kentucky
around 8z. High res models are in pretty good agreement across the
board showing precipitation starting across the southern zones
between 2 and 4 am Tuesday morning and then spreading north across
the CWA by 8 am.


Looking at GFS/ NAM omega fields reveals a broad swath of low
level moisture and lift moving across the area Tuesday morning.
Upper level support also remains favorable as speed divergence
moves over the ILN forecast area. PWATs on both the NAM and GFS
also rise to around 1.10" (~ 1 to 2 SD above normal for this time
of year). The surface low with this feature will track across our
far southeastern zones bringing a swath of gulf moisture with it.
Tuesday afternoon rain looks to continue across the area with
global models indicating a potential band of higher rainfall
totals across the center of the CWA (esp. on the GFS) thanks to
strong low level convergence. This band of higher precip is also
shown on the NSSL- WRF and WRFDART. Overall event totals of 0.5"
to 1.00" are likely with some isolated totals above 1" possible (6
hr FFG is above 2.00" in most places).

The surface low will then pull northeast of the area with rain
coming to an end across the CWA by 7pm Tuesday evening. Also
Tuesday evening an upper level low near northern Minnesota will
pull east and push a surface cold front through the area. The cold
front looks to be near I-71 around 1 AM Wednesday morning. During
the day Wednesday colder air will start to filter into the region
with 850 mb temperatures falling to around 3 degrees below zero.
Looking at forecast soundings from the GFS and NAM there looks to
be some partial clearing Wednesday but will be transient.


Thursday will start with a surface ridge building south of the area
from the west and an upper level trough passing through the region.
West to northwest flow at the surface will combine with northwest
flow aloft to bring in significantly cooler air to the region with
highs on Friday only reaching the mid to upper 20s, sandwiched with
teens in the overnight hours on both Thursday and Friday night.
Friday night lows may be a bit cooler with lighter winds and less
cloud cover as the high pressure center settles in eastern Kentucky.

The westerly flow over the region during this time will likely
preclude any snow from occurring in the region, though a passing
flurry is possible along and north of the I-70 corridor Friday

With the upcoming weekend, a warm front will cross northeast through
the Ohio Valley and increase the threat for rain on Sunday, possibly
a rain/snow mix as the warm air overspreads the cooler air in place.
Models continue to disagree in how this system evolves with the
ECMWF notably drier and further west than the more progressive and
much wetter GFS. Modelers from WPC also seem to have split the
difference here noting the warm frontal passage similar to the GFS
solution on Sunday, then bows to the ECMWF on Monday morning with
the surface low east of Lake Superior. GFS occludes the front off
of the east coast on Monday morning and pushes in drier air.
Meanwhile the ECMWF continues to keep a strong baroclinic zone in
the midwest with continued threat for precipitation over the Ohio
Valley during this same time frame.

Tried to trend lower on the threat for precipitation on day 6 and
7 and culminated the pops on the high end category Sunday
afternoon, in line with the GFS. Against better judgment and
nodding towards ECMWF the pops have been lingered into Monday and
Monday night to account for lower confidence and natural
variability of the models on day 7.


Weak surface high pressure will slid off to the east as
low pressure tracks northeast thru the TN VlY into the Ohio
valley Tuesday.

Conditions will start out VFR with an increase in mid and high
level clouds thru the evening. Rain will overspread TAF sites from
south to north early Tuesday. IFR ceilings are expected to
develop, once the boundary layer saturates with steady rain over
all TAF sites. As the low tracks off to the east a cold front will
sweep through the TAF sites. Rain will end late in the afternoon
with CIGS improving to MVFR.

East winds around 10 kts will shift to the west Tuesday afternoon
at 10 to 15 kts.

OUTLOOK...MVFR ceilings will persist into Wednesday morning. MVFR
ceilings are possible again on Friday.




LONG TERM...Franks
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