Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 300454
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1254 AM EDT Thu Mar 30 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 815 PM EDT Wed Mar 29 2017

Latest short term and high-res models show isolated to scattered
shower activity after midnight for western parts of the CWA before a
decaying line of convection reaches the area near sunrise. Forecast
soundings show some dry air aloft in the low to mid levels of the
atmosphere, but believe some of the precipitation could overcome the
dry air and reach the ground. Have added sprinkles into western
portions of the CWA starting after midnight. Otherwise, rest of
forecast is on track.

&&

.Short Term...(This evening through Thursday night)
Issued at 308 PM EDT Wed Mar 29 2017

...SEVERE WEATHER POSSIBLE THURSDAY AFTERNOON AND EVENING...

In the short term, low-level stratus deck from southern IN southeast
through much of central KY has been slowly eroding.  This trend is
expected to continue this afternoon and into the evening hours.
Under the cloud cover, temperatures have remained quite cool with
reading in the upper 50s in the Bluegrass to readings in the lower
70s down across the karst region of south-central Kentucky.
Temperatures across southern KY should remain in the upper 60s to
lower 70s this afternoon before cooling into the 60s this evening.
Further north, we should see some temperature recovery late in the
day as the clouds mix out.  Still think highs in the lower-middle
60s will be attainable in areas north of the Parkways.

For tonight, we`ll see a bit of clearing early in the evening hours,
but convective debris from activity out west will move into the
region late.  Overnight lows look to cool into the lower 50s in the
Bluegrass region and into the upper 50s to around 60 across southern
Kentucky.  As surface warm front moves northward toward the region
late tonight, we could see some scattered showers erupt.  Best
chances look to be west of I-65.  Additional convection from MO/AR
will move eastward and likely reach the MS River by dawn and remain
west of our area for the tonight period.

For Thursday and Thursday night...

The forecast for Thursday and Thursday night is quite complex and
there remains much uncertainty in the overall convective evolution
with this storm system.  Some of the high resolution convective
allowing models continue to show very good kinematic and
thermodynamic profiles for the development of very strong/severe
thunderstorms with damaging winds, large hail, and a few tornadoes.
These convective models would be the 3KM NAM, high res WRF ARW runs,
and the NSSL ARW WRF runs.  Those models do show a convective line
approaching from the west and weakening during the morning hours.
Model soundings suggest that skies would generally clear out and we
would destabilize through the afternoon.  Overall convective
parameters look decent for an early warm season convective event
(CAPES 800-1500 J/Kg, >40 kts of bulk shear, and a bit of
directional and speed shear in the low levels).

On the other hand, the more coarse horizontal models (GFS/Euro)
continue to insist on a large arching convective band pushing to the
MS/OH River confluence around dawn Thursday and then rolling
eastward across the OH/TN Valleys throughout the day.  Plenty of low
level cloudiness would remain in place limiting instability and
resulting generally poor lapse rates.  Some redevelopment is seen as
the convective band pushes eastward into eastern KY and TN during
the evening hours.

Given the spread in the model agreement here and the uncertainty
associated with the overall convective development, we`re hesitant
to make significant changes to the forecast.  In an ensemble
approach of things, the likely overall convective evolution could be
a mix of both solutions outlined above.  Typically, we have seen
some decent forecasts from the high resolution convective models,
but also there have been busts as well.  In this forecast, we have
leaned a little closer to the convective allowing model solutions
featuring the possibility of strong to severe thunderstorms across
our region Thursday afternoon and evening.  This maintains good
consistency from our previous forecast.

Having said that, strong to severe thunderstorms will be possible in
the afternoon and early evening hours mainly in areas west of I-65.
Damaging winds, large hail, and isolated tornadoes will be possible
with this activity.  The better combination of
shear/kinematic/thermodynamic parameters still look to be centered
to our southwest.  The band of storms will likely cross the I-65
corridor by mid-evening and then blast through east-central Kentucky
during the mid-late evening hours.

Highs Thursday will be largely dependent on cloud cover.  Giving
more weight to the convective allowing modeling solutions, we have
gone a little more on the warmer side of guidance with highs in the
lower-mid 70s in the west with mid-upper 70s in the east.  However,
more cloudiness could really bust these temp forecasts.  Lows
Thursday night look to cool into the lower 50s.

.Long Term...(Friday through Wednesday)
Issued at 308 PM EDT Wed Mar 29 20127

The overall pattern during the long term period will remain quite
active with several strong disturbances moving through the region.

Upper wave responsible for the impactful weather on Thursday will
lift northeastward into the eastern Great Lakes by Friday afternoon.
Plenty of low-level cloud cover will likely remain in the region on
Friday keeping highs in the upper 50s to around 60.  Lows Friday
night look to cool into the lower 40s.

Mid level ridging will build into the region for Saturday and Sunday
resulting in quiet and tranquil weather.  Highs Saturday look to
warm into the lower to middle 60s and then warm into the upper 60s
to near 70 by Sunday.  Overnight lows in the 40s are expected which
is normal for early April.

By Monday morning, the next closed upper low will move from the Red
River Valley into the TN Valley by Monday night.  This is a little
south of the previous model consensus which would likely confine
 thunderstorms to our south.  However, the model bias has
been a little south and systems have come more poleward with time.
So we will continue to monitor this system.  Nonetheless, another
round of rainfall looks likely for Monday and into Tuesday.

A brief break in the weather looks possible from Tuesday night into
Wednesday before the next weather system arrives late Wednesday into
Thursday.  This system could bring another round of showers and
thunderstorms to the region.

Highs during the week look to warm into the upper 60s to around 70
with overnight lows mainly in the lower 50s.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1252 AM EDT Thu Mar 30 2017

Expect easterly flow to prevail through sunrise as broken high
clouds continue to move over central Kentucky. Winds will become
southerly after 12z and begin to increase into the 12-18 kt range
through the morning hours. A strong low pressure system near Kansas
City currently will track eastward during the day. Strong wind gusts
up to 30 kts are likely at all TAF sites from late morning into the
afternoon, ahead of any showers or thunderstorms.

Thunderstorm chances will increase by mid-afternoon at SDF and BWG
and mid-late afternoon at LEX. Some uncertainty in how the event
will evolve with the potential for storms to develop as soon as mid-
afternoon, or hold off until early-mid evening. As this point, the
best consensus puts the greatest chance of seeing stronger storms
from 23z to 03z across central Kentucky.

As storms end west to east toward the end of the current TAF period,
winds will shift to the southwest then eventually west while
ceilings lift back to 5kft or higher.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...DM
Short Term...MJ
Long Term....MJ
Aviation...ZT



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