Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 301941
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
341 PM EDT Sat May 30 2020

.SYNOPSIS...
High pressure will bring dry weather to the region through
Monday. A warm front will lift north across the Ohio Valley
through mid week, bringing warmer temperatures and the next
chance for showers and thunderstorms.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
High pressure centered over the Northern Plains will drop
southeast into the western Great Lakes by sunrise tomorrow.
Diurnal cumulus shield currently over the region will dissipate
over the next few hours as daytime heating wanes. Skies should
be mostly clear overnight.

Some fog will be possible in the river valleys. Temperatures
will drop back to mid 40s in West Central Ohio to the lower 50s
in nrn KY.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
The high will continue its southeastward trek on Sunday.
Scattered cu should develop again on Sunday, but with less cold
advection, coverage should be less. Highs on Sunday will be from
the mid 60s to lower 70s.

Skies will clear again Sunday night as the high remains over the
region. This should be the coolest night will lows from the
lower 40s east of Columbus to the upper 40s in the Cinci
Tri-State.


&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Start of the long term period features surface high pressure
directly over the Ohio Valley as it continues its southeastward
journey toward the east coast. Mostly clear skies and variable light
winds allow temperatures to quickly warm into the 70s by early
afternoon on Monday. Throughout the afternoon, cloud cover increases
from the northwest as a weak perturbation in the 500 mb flow moves
through the Great Lakes. Surface and mid-level high pressure shifts
southeastward during the second half of the day, supplying a new
surge of moisture to the Ohio Valley. Forecast soundings gradually
saturate Monday evening, and with weak lift embedded within
northwest flow, a few scattered showers are possible across the far
north Monday evening and into the overnight. However, most areas
likely stay dry. Low temperatures are right around average for
Monday night, in the mid 50s to lower 60s, much warmer than the
previous nights.

On Tuesday, longwave ridge across the central US begins to break
down as a trough moving through the northern Great Plains enters the
Midwest, setting the stage for an active weather week. Cut-off low
over California persists through the week, shedding weak
disturbances over the ridge and through the northwest/west flow into
the Ohio Valley. Surface high pressure to the southeast which
brought dry weather and lower humidity over the weekend, now begins
to enhance warm air and moisture advection as southwest to west flow
amplifies. Surface dewpoints in the low 60s and ambient temperatures
rising into to mid 80s, help to support the return of summer-like
air back to the region. Isolated showers are possible primarily
across the northeast during the afternoon and evening on Tuesday,
however, similar to Monday, most locations are dry. Forecast
soundings indicate increasing instability, but a strong 800 mb cap
should inhibit convective development. This changes heading into
Wednesday...

Northern Plains trough moves into the Midwest on Wednesday, with a
parent low pressure located in the Northeast and an associated cold
front stretching west across the Great Lakes. Throughout the day on
Wednesday, temperatures south of the cold front warm well into the
80s with some locations possibly approaching 90 degrees. NBM
probability for Max T reaching 90 degrees is between 20-40% for CVG,
DAY, and CMH. Given some uncertainty with cloud cover, have kept
temperatures to generally the mid 80s, but these could be elevated
as Wednesday approaches. With regards to the rainfall/thunderstorm
potential, attention will first need to be directed toward
convective development Tuesday night across the upper Mississippi
Valley. Across that region, CAPE values of 4000-5000 J/kg will
certainly result in convective initiation Tuesday evening, with mean
flow directing the progression of the activity southeastward. Given
the weakly sheared environment, doubt thunderstorms reach the
forecast area Wednesday morning, however, outflow boundaries and
cloud debris may play a role in convective initiation across the
north Wednesday afternoon. Latest guidance remains in fairly good
agreement that showers and thunderstorms increase in coverage across
the area from north to south during the late afternoon and evening
hours. Severe threat is an increasing concern as effective bulk
shear between 20-30 knots within the unstable environment (2000-3000
J/kg) will certainly result in multi-cell clusters capable of
damaging winds and hail. Digging through CIPS analog threat guidance
reveals probabilities for 5+ SVR reports (mostly wind) is between 50-
60% and 10+ SVR, 30-40% throughout the day on Wednesday. Depending
on how quickly thunderstorms advance southward, shear vectors
parallel to the cold front coinciding with 1.6-1.8" PWATs, could
result in locally heavy rain. A few dry days leading up to Wednesday
should limit the overall flood threat.

Front stalls and weakens throughout the day on Thursday as
southwesterly flow provides another round of warm air and moisture
advection. Additional showers and new convective development is
expected on Thursday as another shortwave moves into the Ohio Valley
over the weakening front. The greatest coverage is expected across
southern Ohio, southeast Indiana and northern Kentucky before
becoming more isolated by Thursday evening. Temperatures on Thursday
are likely to be influenced by cloud debris and scattered
convection, but with the cold front dissipating, allowed
temperatures to warm into the low to mid 80s.

Rain chances remain in the forecast for Friday and Saturday,
however, confidence is much lower in this forecast as synoptic
variability with these weaker features becomes greater with time.
For instance, the 12Z GFS is showing a deepening trough in the
Northeast on Friday night, but the 00Z GFS had a longwave ridge over
the eastern US. Will keep low PoPs and slightly above normal
temperatures for days 6-7 given this extreme variability.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
VFR cumulus has developed in the cold air advection on the east
side of high pressure. Ceilings should remain VFR through the
afternoon and then the cu will start to scatter out with loss of
heating around 22Z. Some wind gusts in the upper teens will be
possible this afternoon.

High pressure will sink down over the region tonight. Skies will
be clear. There are signals that some river valley fog will be
possible. Added a tempo MVFR fog to LUK between 08-11Z.

VFR cumulus are forecast to develop again around 15Z, but they
should be more scattered.

OUTLOOK...Thunderstorms are possible on Wednesday and Thursday.

&&

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

&&

$$
SYNOPSIS...JGL/Sites
NEAR TERM...Sites
SHORT TERM...Sites
LONG TERM...McGinnis
AVIATION...Sites



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