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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 160829

Area Forecast Discussion
National Weather Service Wilmington OH
429 AM EDT Thu Aug 16 2018

Multiple disturbances moving through the region will keep
unsettled weather across the area through the rest of the week.
High pressure will briefly build in on Sunday. But approaching 
low pressure and cold front will cause rain to return early next


Showers and embedded thunderstorms are moving northeast across
the area early this morning. Expect this to weaken heading into
the daylight hours as low level jet temporarily weakens. But 
high resolution guidance suggests that another surge of 
precipitation will move across the area later this morning and
continuing into the early afternoon. Once this clears, it
appears that some instability will develop despite what is
expected to be a considerable amount of clouds. So as a weak
short wave passes, scattered storms are possible late in the
day. If there are sufficient breaks in the clouds to allow more
destabilization, then some strong to severe storms are not out
of the question. Showers and thunderstorms will remain efficient
precipitation producers with high precipitable water and deep
warm cloud depths in place. Did give some consideration to a
flash flood watch in the Tri-State. But rain early this morning
should just be a priming event. And there is enough uncertainty
with where more robust activity will be later today to just
continue to monitor. Temperatures will be slow to climb through
early afternoon, but they should be able to rally late. A
blended guidance approach seemed best for highs. 


Any convection that develops late in the day will likely push
east in the evening although weaken with the loss of heating.
However, axis of better moisture transport will still be slowly
translating east across the forecast area through the night. So
continued development of showers and possibly some thunderstorms
may persist through the overnight hours, especially in southeast
counties. It does appear that there may be a lull in activity 
late tonight into Friday morning. But more showers and 
thunderstorms will develop during the day as another short wave 
moves into the area. Lows will be near persistence and highs 
will be below normal again. 


Confidence is still quite high that this period will be absent of 
summertime heat - in fact - the middle of next week looks quite 
refreshing by late August standards.  That being said, plenty of 
muggy air will be hanging around for the first part of the weekend 
and again early next week along with plenty of rain chances.  

Rain chances will continue to be high Friday night into Saturday 
/especially the southeast half of the ILN forecast area/. Mid/upper 
level trough axis will be positively oriented and nearly bisecting 
the forecast area Friday evening. The weak surface boundary that had 
been working ever so slowly southeast will still be plaguing the 
area as focus for low level moisture convergence in an anomalously 
moist airmass while the cyclonic flow and subtle jet support 
continue to encourage large scale ascent. Continue to expect one or 
more thunderstorm clusters to be migrating through the south/east 
half of the forecast area especially Friday evening, and then 
showers and a few storms again redeveloping on Saturday in the 
south/east half of the forecast area as a gradual deepening/lowering 
of the heights due to more energy rippling through aloft will slow 
the pesky low level boundary even further. 

By Saturday night, finally enough push south/east of the low level 
forcing to bring a period of dry weather into the area. High 
pressure will build southeast out of the Great Lakes and place the 
area in east/northeast low level flow - which means a maintenance of 
below normal high temperatures and perhaps a slight reduction in 
muggy air.  

Height rises will begin on Sunday as shortwave ridging develops 
downstream of a vigorous shortwave trough which will help re-carve 
out a very large/deep longwave trough across the central/eastern 
CONUS. This shortwave will progress quickly from the Central Plains 
into the Ohio Valley on Monday. Backing low/mid level flow will 
induce warm frontal development and another significant surge of 
deep moisture into the Ohio Valley on Monday, and with large scale 
forcing becoming very supportive, expect showers and storms to begin 
to develop Monday afternoon on the nose of the returning deeper 
moisture, and especially Monday night into Tuesday morning as deep 
surface low pressure develops in the Great Lakes and rides a strong 
advancing cold front through the Ohio Valley.

There is still a lot of detail uncertainty amidst a pretty 
stable/strong large scale picture of the development and passage of 
this weather system. It will most certainly rain at some point 
Monday afternoon into Tuesday, but specific timing will be refined 
in later forecasts, as will the potential hazards with this system 
owing to strong large scale forcing, plenty of moisture, and 
seemingly a setup to support organized storms either in the open 
warm sector ahead of the system, or along its advancing frontal 
zone. But there is wide variation in the strength of the surface 
cyclone and low/mid level wind fields depending on where/when the 
frontal wave develops. So despite a pretty strong signal of high 
rain chances in the Monday night/Tuesday timeframe, other details 
will need more time to resolve. 

Behind the strong cold front attendant to this system, several days 
with highs in the mid 70s are in store are strong high pressure 
builds in from the north, and should usher in a rather decent period 
of dry and pleasant weather. 


Periods of showers will affect the terminals through the first
half of the TAF period. Initially, this should only result in
temporary visibility reductions. Also, cannot rule out wind
gusts over 20 kt at KCVG/KLUK. Later, likely after 12Z, VFR
ceilings will develop which may lower to MVFR in some places,
especially with precipitation. Precipitation is expected to 
move off to the east of the region towards 18Z. However, it 
appears that thunderstorms may then develop after 21Z. Expect 
storms to be more scattered and have continue with just VCTS for
this time period. Any convection that develops late in the day 
should diminish around 00Z. 

OUTLOOK...MFVR to IFR ceilings and visibilities likely late
Thursday night into Friday morning. Thunderstorms possible
Friday afternoon and evening and then again on Sunday.