Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 280924
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
424 AM EST Tue Feb 28 2017

.SYNOPSIS...
A warm front will lift northward across the area this morning
providing a chance of showers and possibly a thunderstorm.
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/...
Showers and isolated rumbles of thunder have started to move
into Indiana this morning as strong low level WAA moves over
the area. Looking at GFS isentropic surfaces also reveals the
best lift and saturation further towards the north. GFS and NAM
forecast soundings show a surface inversion across our area
with weak elevated instability. The GFS is more restrained with
the elevated instability while the NAM is slightly more robust.
Overall thinking is in a slight decrease in lightning activity
as storms move this way towards sunrise.

Later this morning into afternoon showers and isolated
thunderstorms from earlier will weaken across the central and
northern zones with a warm front clearing the northern zones of
the CWA before noon. As this occurs the surface inversion from
this morning will slowly erode. Latest RAP, GFS, HRRR then show
an upper level disturbance pushing northeast and clipping our
southeastern zones. Also at the time an upper level jet streak
will rotate north and east and approach the area. This is thanks
to an upper level disturbance pushing east across AZ/ NM. The
jet streak pulling north will likely translate into widespread
showers and thunderstorms across KY/ TN this afternoon with the
northern extent being around Interstate 71. Moisture wise PWATs
around 1.20" (90th - 97.5th percentile for this time of year via
NAEFS) will be easily found across the CWA with higher values
preferred towards the south and east. Given the best lift, track
of the upper level disturbance, and moisture values mentioned
above have kept highest PoPs towards the southeastern zones this
afternoon. Any storms that form this afternoon do have the
potential to become severe as sfc- 3 km shear values will be
mostly greater than 40 kts. The main inhibiting factor will be
the lack of surface based instability. This means that the
effective shear will still be impressive but less than
mentioned above.

&&

.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 /10Z TUESDAY THROUGH SATURDAY/...
Most TAF sites are VFR this morning with high pressure off to
our east and low pressure off to our west. High and mid clouds
are starting to move into the area but not before KLUK had a
chance to fall to VLIFR. As the high and mid clouds have moved
in from the west though visibilities have tried to recover a bit
which isn`t surprising. Have gone ahead and shown this on the
TAFs.

This morning a warm front will lift north across the area with
models showing a good swath of precip ahead of the warm front
(mostly north of the TAF sites initially). Precipitation will
likely then fill in south as the latest run of the RAP has a
shortwave pushing through the area just after sunrise. Forecast
soundings at this time show a surface inversion which will limit
surface based instability but some of the high res and global
models have enough elevated instability that thunder will be
possible. Overall thinking for morning precipitation is that
most of it will be shower based with some embedded thunder.

During the afternoon hours as the warm front moves north of the
area the surface inversion will erode. As this happens the
chance of thunder will grow. The main inhibiting factor to
development of precipitation in the afternoon will be the likely
cirrus shield overhead from morning precipitation. Still though,
the RAP is showing another shortwave moving across the
southeastern zones Tuesday afternoon. The RAP, HRRR, ARW, NMM
all hint at precipitation developing thanks to this lift.

Tuesday evening as the shortwave exits the region there should
be a brief break in the precipitation before the next round of
showers and thunderstorms moves into the area from the
southwest. This next batch of precipitation will likely move
into the area around midnight Wednesday morning. The latest NMM,
ARW, NCEP WRF all show this third round of precipitation moving
in just with slightly different timing. Timing will likely have
to be adjusted for future TAF packages.

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...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...Haines
NEAR TERM...Haines
SHORT TERM...Haines
LONG TERM...JGL
AVIATION...Haines



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