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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

                            
000
FXUS61 KILN 201645
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
1245 PM EDT Fri Sep 20 2019

.SYNOPSIS...
Southerly flow over the Ohio Valley will persist through the
weekend, increasing on Sunday ahead of a cold front that will 
cross the region early Monday. Storms will fire along and ahead 
of the front, primarily overnight Sunday with a decrease in 
activity during the day Monday as high pressure builds over 
Illinois. This high will cross the Ohio Valley Tuesday and 
southerly flow will return for the latter part of next week. 

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Earlier update was generally cosmetic but did add low chance
pops for a lot of the CWA at some point today. Used CAPE values
over 800 J/Kg as the inclusion point for any showers to
potentially have thunder, but the general trend for today is for
scattered to isolated shower activity in KY to generally
dissipate and have the source region move northward towards
central Ohio later in the afternoon. 

Morning and early afternoon showers were sparked by a lljet that
provided a good moisture transport that was wrung out along a
weak trough noted above the surface. This trough will translate
northward and the moisture transport looks to wane fairly early
today. However, the sunshine will add to instability in the
northern 2/3 of the CWA and necessitate inclusion of at least
low chance pops and possible Tstorms for today. Temperatures
should be on track to reach the mid 80s for yet another day with
a few outlying upper 80s. 

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Mid level ridge axis will continue to be centered over the 
southeast Conus. With weak forcing and loss of heating any
widely scattered showers or thunderstorms that develop across
the north are expected to dissipate this evening. A southerly
flow will persist in the low level along with some clouds. These
factors will work to keep temperatures mild. Expect tonights lows
to generally range from the lower to the middle 60s.

Mid level ridge builds slightly into the Ohio Valley Saturday. 
As the H8 flow backs across the Great Lakes low level jet and 
favorable instability look to stay to the north during the 
daylight hours Saturday. There is some uncertainty due to model 
solution spread and can not totally rule out a few showers or a 
thunderstorm across the far north-northeast counties Saturday 
afternoon but will keep the forecast dry due to lack of
favorable forcing and instby. Again expect temperatures a good
10 degrees above normal with highs Saturday in the mid and upper
80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Period starts with an upper ridge positioned across the Eastern 
CONUS, allowing the persistence of above normal geopotential heights 
over the Ohio Valley. Heights will drop closer to normal later in 
the long term following the passage of a rather potent upper trough. 

Large surface high pressure located on the eastern flank of the 
upper ridge will probably provide dry weather Saturday night through 
Sunday morning. A couple showers and thunderstorms may creep into 
western counties Sunday afternoon as the upper ridge starts to break 
down in advance of the upper trough, while the surface high slides 
gradually east. Thunderstorms will become likely Sunday night when 
the upper trough is forecast to push a cold front through from west 
to east. Lingering showers and thunderstorms for Monday behind the 
front will be followed by high pressure and dry air on Tuesday. A 
weak disturbance crossing the Great Lakes may produce a few 
thunderstorms on Wednesday, before high pressure and a dry airmass 
return Thursday.

Well above normal temperatures should continue to be observed on 
Sunday, with highs mainly in the middle 80s. Highs are then forecast 
to retreat to the close to normal middle and upper 70s for the rest 
of the period under cold advection, cloud cover, and limited 
precipitation.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Strong mid level ridge ridge centered over the Southeast
placing the Ohio Valley on its northern periphery. In a moist 
southerly flow a very weak jet will offer some VFR clouds and a 
few showers mainly southeast of I-71 this morning. A axis of 
very marginal elevated instability advects into the far
southwest, so an isold thunderstorm is is not out of the
question over the far southwest early but should stay south of 
the TAF sites. 
 
Expect this precip to remain southeast of the TAF sites and 
track to the northeast. WAA clouds that have moved into the 
area have mitigated the development of widespread fog.

The Ohio Valley will remain in a weak southwest flow through 
the day. A relatively dry airmass in place, and instby is 
limited and model soundings show an initial cap in place. 
These factors are all working against widespread pcpn, so have 
limited any mention to a slight chance across the far north 
later this aftn. Coverage and probability are too low to mention
in the TAF fcst at this time. 
 
Have some scattered to perhaps bkn cu with the best coverage 
across the northern TAF sites. Dependent on how much clearing 
takes place across south tonight, some fog develop will be
possible late. Have a mention of MVFR vsby restrictions at 
KLUK and KILN. 


OUTLOOK...Thunderstorms possible on Sunday night into Monday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...Franks
NEAR TERM...Franks
SHORT TERM...AR
LONG TERM...Coniglio
AVIATION...AR