Absolute Vorticity

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AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
343 PM EDT Fri Jul 1 2022

.SYNOPSIS...
Periods of showers and storms expected through Friday night as a
cold front slides through the region. The front stalls south of
the Ohio River and has trended further south, lowering
precipitation chances over the weekend. Front begins to lift
back northward Monday, increasing chances for precipitation by
Monday night, with chances for showers and storms continuing
into the next work week as the front stalls across the Ohio 
Valley.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Radar imagery at 3:30 PM shows isolated to scattered showers and
storms continuing to move across portions of northern KY and 
the Scioto Valley along a theta-e plume. Isolated to scattered
convection remains possible ahead of the cold front, primarily
along/SE of I-71.  

The SPC has the ILN fa in a Marginal Risk for severe weather, 
which covers the majority of Ohio, as well as our eastern IN 
counties. Instability levels continue to increase throughout the
afternoon - MLCAPE values are currently around 1000-1500 J/kg, 
with some pockets nearing 2000 J/kg. The highest CAPE values 
remain along/southeast of I-71. Steep low-level lapse rates of 
8-9 C/km have also developed, aiding in the potential for hail 
development in thunderstorms. With DCAPE values also exceeding 
1000 J/kg, any storms that develop during the daytime hours have
the potential for producing strong, damaging winds from 
downbursts. Overall, coverage in storms this afternoon should
remain isolated to scattered, but may increase by the early
evening. 

There are a couple of limiting factors with the severe potential
today however. The first is wind shear - with bulk shear values
generally peaking around 25 kts (and sfc-3km shear only around 20
kts), storms will have a hard time remaining organized. The 
second (and arguably more substantial) limiting factor is the 
timing of storms along the cold front in our fa. It appears from
latest hi-res models that the cold front is slower in its 
southeastward progression tonight. Storms along the actual cold
front don't seem to enter our CWA until closer to midnight, 
although once again, a few isolated storms may still initiate 
ahead of the main line of storms. Hi-res models suggest that the
line of storms will be lower in their intensity as they 
progress southward tonight. This is mainly driven by weakening 
instability values, as well as a low-level inversion that forms 
and forces the storms to become more elevated. While models do 
suggest modest bulk wind shear improvement (increasing 5-10 
kts), the threat for a severe thunderstorms still seems limited 
given the waning instability and non-surface based storms. 

One final note...Hi-res models do suggest that there could be a
pre-frontal line of storms that develops this evening 
along/near I-71. This could impact the metro areas of Columbus 
and Cincinnati starting around 8PM and continuing into the late 
evening hours (it appears to remain just SSE of Dayton). With
the environment still maintaining most of its instability and
storms generally remaining more surface-based, this timeframe
will be something to monitor closely. 

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Coverage in showers expected to be greatest along/south of the
Ohio River Saturday morning before pushing even further south
into KY. Models seem to favor a more southward progression of 
the cold front down into south-central KY on Saturday. If this 
holds, majority of our counties should end up remaining dry now 
on Saturday. Best chances for isolated storms to develop would 
be along/south of the Ohio River. 

Locations along/NW of I-71 expected to have a more pleasant day
with dewpoints dipping below 60 degrees in the afternoon, 
lowering the humidity levels. High temperatures across the CWA 
will generally peak in the mid-80s. 

Forecast continues to trend dry Saturday night for majority of 
the fa, but cloud coverage is expected to increase and provide 
mild overnight lows in the mid-60s. 

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Old frontal boundary will extend from central Indiana into eastern 
Kentucky at the beginning of the period. Some convection may develop 
along and north of this on Sunday. So have kept some diurnal low 
chance PoPs near and south of the Ohio River. 

Boundary will likely dissipate by Monday and air mass will be in the 
process of moistening. Cannot completely rule out a few storms, but 
with weak forcing the chance is rather low.

Northwest flow aloft will become established along with a wavy front 
extending from the upper Mississippi Valley into the Great Lakes. 
This will be a favorable pattern for MCSs to roll into the region. 
Obviously details are not clear, but it looks like a convectively 
active period with chances of showers and thunderstorms from Monday 
night onwards.

Temperatures will be above normal through the period.