Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 180525

Area Forecast Discussion
National Weather Service Louisville KY
125 AM EDT Thu May 18 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 740 PM EDT Wed May 17 2017

Warm southerly flow continues across the area, but deep moisture
remains largely lacking. Scattered showers lifting out of the
Mississippi Valley into SW Indiana are weakening as they make a run
at Dubois County, but believe we could see a few spritzes sooner
than later, especially in the western sections of the county. As the
night goes on, slight or low-end chance POPs will spread across most
of southern Indiana as some weak isentropic lift develops. This
aspect is fairly well handled in the previous forecast, with only
small adjustments needed to the timing.

Net result is minor tweaks to the hourly grids, so updates on the
way shortly to refresh the hi-res forecast products. Legacy
forecasts such as ZFP remain on track.


.Short Term (Now through Thursday Night)...
Issued at 305 PM EDT Wed May 17 2017

Plenty of mid-high level cloudiness moving through the region this
afternoon.  Despite the filtered sunshine, temperatures have warmed
into the lower to middle 80s with the warmest locations down in the
Lake Cumberland region of south-central Kentucky.  Gusty southwest
winds were also noted across the region, though most gusts so far
have been under 30 MPH. In the near term, we expect quiet weather to
continue with temperatures this evening dropping back into the upper
70s.  Surface winds will remain a bit elevated given the decent
pressure gradient across the region.

For tonight, an upper level trough axis will move into the Great
Lakes region and will drag a surface cold front toward the region.
Models still show a narrow corridor of moisture and some lift
pushing into the western forecast area late tonight.  This will
likely result in some isolated to scattered showers/storms mainly
west of the I-65 corridor.  Lows tonight will remain warm with lows
in the upper 60s to around 70 in many places.

As we move into Thursday, the surface front will be in close
proximity but will likely have some trouble moving eastward as
strong ridge to our east remain in place.  The atmosphere does look
to destabilize in the afternoon but overall bulk shear is rather
marginal for severe weather.  Though model soundings do show some
drier air working in aloft and any storm that develops tomorrow
could produce locally heavy rainfall (PWATs running around 1.5 in),
along with some gusty winds and some hail being possible.  Best
convective coverage looks to remain generally along and north of the
WK/BG Parkways.  Highs on Thursday will warm into the lower 80s
across southern IN and northern KY.  Some mid 80s look possible down
across far southern KY.

By Thursday night, surface cold front will likely sink into the
region while weakening as the flow aloft become parallel to the
front.  Scattered showers and storms will be possible out along the
frontal boundary with the best coverage across southern IN and into
far northern KY (again mainly north of the Parkways).  However, did
increase Pops slightly across southern KY for late tomorrow night as
the front stalls across the region.  Lows look to cool into the mid-
upper 60s.

.Long Term (Friday through Wednesday)...
Issued at 328 PM EDT Thu May 17 2017

At the beginning of the period, surface cold front will stall out
across Kentucky on Friday.  With the front stalled out, a mid-level
perturbation will move eastward across the region during the day
setting the stage for a round of showers and storms across the
region.  By Friday night and Saturday, surface cyclogenesis will
take place in the Plains with the low racing off toward the Great
Lakes.  As this occurs, the stalled out boundary across our region
will lift northward as a warm front.  We should get firmly into the
warm sector on Saturday.  It`s possible that we could see a lull in
the action during the afternoon/eve as the warm front will be
located well to our north.  However, can`t really rule out any
isolated convection within the warm sector.  Highs on Friday look to
warm into the lower 80s with highs on Saturday warming into the mid
to upper 80s.  Overnight lows will be in the mid-upper 60s.

Surface cold front to the west will slide eastward into the region
late Saturday night and into the day on Sunday.  The model solutions
are a little faster on the frontal passage.  Nonetheless, Sunday
looks to be quite rainy/stormy as the front pushes through.  We`ll
see a break in the action on Monday and Tuesday as weak surface and
upper level ridging hold sway across the region.  However, stormy
weather will return by Tuesday as a progressive aloft will allow
another mid-level trough axis to swing into the region.  This will
likely bring another round of showers and storms to the region. This
trough axis looks to cut off over the Ohio Valley on Wednesday
before slowly migrating off to the east by Thursday.

Highs on Sunday should be cooler with plenty of cloud cover and
precipitation around.  Highs look to warm into the mid-upper 70s
with overnight lows dropping back into the 50s by Monday morning.
Noticeably cooler weather will be seen on Monday and Tuesday with
highs in the 70s.  Major differences exists for highs by midweek
depending on the placement of the surface low.  While most models
yield temps in the upper 60s to lower 70s, it is entirely possible
to see highs some 10-15 degrees cooler than that if the upper low is
right over top of us.  I suspect that we may see the model blend
shift colder in the next few runs.


.Aviation...(06Z TAF Issuance)
Issued at 120 AM EDT Thu May 18 2017

The main TAF concerns will be wind related under a strong southerly
flow.  Early this morning a good LLJ from the SW between 37-40 kts
at 2 kft was occurring and expect that to continue through 9-11Z.
Thus will continue LLWS during the pre-dawn hours.  Around or just
after sunrise, showers with potentially a rumble of thunder may
develop near SDF.  SDF will remain in a favorable area (less capping
with subtle shortwaves possible) for convective development
throughout the day so will keep VCSH in through 3Z.  Left VCTS out
of SDF for now since coverage of convection will be isld-sct and t-
storm chances too slim to mention.  BWG/LEX look to remain more
capped further under the ridge so will continue to keep these TAFs
convection free for now.  SSW winds will gust to 17-20 kts
throughout the daylight hours and then decline after sunset.




Short Term.....MJ
Long Term......MJ
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