Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 281751
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
1251 PM EST Tue Feb 28 2017

.SYNOPSIS...
A warm front will lift northward across the area today.
For tonight, an upper level disturbance will move over the
region providing another chance of showers and thunderstorms.
Some thunderstorms could be severe with locally heavy rain.
During the afternoon Wednesday a cold front will sweep across
the region with gusty winds possible behind the front. Colder
conditions will be in store for the region through Saturday
morning with a chance of snow early Friday morning.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Quick update late this morning to include a flash flood watch
for the southern almost-half of the ILN forecast area. Rainfall
this morning has primed this area and flash flood guidance
values are very low. There is solid model agreement on deep
convection occurring tonight and through Wednesday morning, with
intense moisture transport and very high precipitable water
values. Thus, it is believed that any persistent storms through
the next 24 hours will be able to create a flash flood threat on
the already-saturated grounds. The watch will run until 21Z
Wednesday, which may be generous but ensures the timing is
covered.

Previous discussion >
Showers and embedded thunderstorms will continue across much of
the southern two thirds of the CWFA through early afternoon as
warm, most ascent in the form of a low level jet occurs. Warm
front will lift northeast into the region later this afternoon.
Precipitation will begin to shift east this afternoon as the low
level focus shifts east, with western/northern zones seeing a
decrease in the threat. Highs will range from the upper 50s to
the lower 60s by days end.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tuesday evening will likely see a brief decrease in coverage as
the weak disturbance from this afternoon exits. Coverage will
remain light until the upper level disturbance that was over AZ/
NM rounds the base of the upper level trough axis and heads
northeast. As this occurs vorticity will spill northeast towards
the CWA with the upper level jet streak rotating northeast. A
split in the upper level jet will occur across northern KY and
southern OH with a surface low tracking northeast towards
Chicago. As this happens many high res models show a complex of
showers and thunderstorms pushing northeast towards the region.
The ARW, NMM, WRF DART, and NCEP WRF all show this feature
moving into southern OH around 6z.

During this time forecast soundings destabilize across the
region with PWATs approaching 1.30" on the NAM and GFS. SFC to 3
km shear is forecasted to between 40 and 50 kts with SFC - 3km
SRH exceeding 300 m2/s2. Mean flow is also from the southwest at
around 60 kts. Lapse rates will be around 7 degrees C/ km which
coupled with ML CAPE values of 300 to 600 J/kg will support the
possibility of some severe hail. Given the parameters above all
threats appear to be in play. SPC has also highlighted the area
in an enhanced possibility of severe weather for day 1. Day 2
enhanced also clips of southeastern zones. High res models show
this complex of storms then moving east of the area between 9
and 12z. Towards our northwest though (northern IN/ IL) a
squall line will likely form as precipitation from the upper
level disturbance moves over our area. The main question will
then be whether the squall line hold together as it dives
southeast. High res models are mostly split on this. Given the
strong upper level forcing think the squall line will hold
together. The primary severe threat timing will be starting
around 4z and continuing though Wednesday morning until the
squall line clears the area. It should also be noted that heavy
rain will also be possible with these storms. In particular
where the first round of showers and thunderstorms moves over
Wednesday morning. 6 hr FFG is generally greater than 1.80"
across the area which is right on the border of expected
rainfall totals. Overall guidance suggests that heaviest
rainfall amounts will be across our southeastern zones which
makes sense given the placement of the upper level lift. WPC
also has the entire area in a marginal for excessive rainfall
with the central and southern zones in a slight.

Wednesday morning into afternoon the main upper level trough
axis will push east with the best upper level lift heading east
as well. A cold front will approach the western zones late
Wednesday morning. Timing with the front appears to be in good
general agreement with the GFS only being slightly faster. Some
high res models have the squall line from earlier aligning more
with the cold front while other models have the squall line
racing ahead of the front. Given the placement of the upper
level lift have trended forecast to show the squall line moving
ahead of the front. As the cold front passes through the area
Wednesday afternoon strong low level CAA will follow. PWATs will
also plunge to around 0.30". As this happens lapse rates will
steepen allowing strong low level winds to mix down to the
surface. NAM forecast soundings are showing gusts around 35 mph
possible with the GFS showing wind gusts of 40 to 45 mph
possible. Overall have kept forecast trended towards the NAM.
Given the above a wind advisory might be required for Wednesday
afternoon.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A clipper like system will drop out of southern Canada Wednesday
night and into the upper Ohio Valley Thursday into Thursday night.
This will be accompanied by an associated low level trough axis and
a secondary shot of CAA. This will lead to an increasing chance of
showers later Thursday afternoon into Thursday evening before
tapering off later Thursday night as the system pushes off to the
east. Initially, low level thermal fields are supporting mainly
rain, but as we start to cool down, we should see a transition over
to snow as we head into Thursday evening. The models are trying to
latch on to some very weak short wave energy dropping quickly
southeast across our area Friday night into Saturday. This could
lead to a few snow showers, especially across northern portions of
our area. We will then transition to more of a zonal pattern as we
head through the weekend. Short wave energy will move across the
Great Lakes region Sunday night into Monday, bringing the next
chance of rain showers toward the end of the long term period.

Highs on Thursday will be in the 40s, cooling into the mid 30s to
lower 40s for Friday. Unseasonably warm temperatures will then
return through the end of the period with highs by Sunday and
Monday back up into the upper 50s to lower 60s.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Active TAF cycle expected the next 24 hours with MVFR/IFR
threats via thunderstorms, as well as strong winds in/around
storms as and behind the strong cold front which plows through
the area this morning. Most of current activity on radar will
only impact CVG/LUK...with lighter rains over ILN/DAY/LCK/CMH
for a few hours this afternoon.

Should be a lull from late afternoon through much of the
evening...but increasing low level flow and destabilization will
promote increased thunderstorm growth/development along the Ohio
River near/after midnight. Some of these storms may be robust
with strong winds and very low visibility in heavy downpours.
However...timing/confidence on the main band of storms that will
develop is hard to pin down this far out...so have gone with a
prevailing MVFR shower and VCTS for the bulk of the overnight
period.

Increasing/gusty surface winds will be problematic later tonight
and especially during the day Wednesday as the low level flow
starts to veer/increase after frontal passage. May need to
introduce low level shear into TAFs with the 00Z cycle...right
now it is a marginal signal that peaks in the 06Z to 12Z
timeframe. Surface wind gusts >30kts will be likely Wednesday
both immediately ahead of the cold front...and also behind the
front through much of the afternoon.

OUTLOOK...MVFR ceilings may linger Wednesday afternoon and
night. In addition, wind gusts to 35 kt will be possible during
that time. MVFR ceilings and visibilities will be possible
again Thursday night into Friday morning.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Flash Flood Watch through Wednesday afternoon for OHZ073-074-
     077>082-088.
KY...Flash Flood Watch through Wednesday afternoon for KYZ089>100.
IN...Flash Flood Watch through Wednesday afternoon for INZ073>075-
     080.

&&

$$
SYNOPSIS...Haines
NEAR TERM...Haines/Hatzos/Hickman
SHORT TERM...Haines
LONG TERM...JGL
AVIATION...Binau



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