Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 231037

Area Forecast Discussion
National Weather Service Louisville KY
637 AM EDT Tue Apr 23 2019

...Updated Aviation Discussion...

.Short Term...(Today and tonight)
Issued at 314 AM EDT Tue Apr 23 2019

Early This Morning Through Mid Afternoon...

A few light returns are showing up on radar well to the north of the
CWA at this hour, and are associated with warm advection/isentropic
lift to the SE of a Great Lakes surface low. That activity doesn`t
impact us, and we`ll stay dry here overnight through a good portion
of Tuesday. Other than some variable upper level cloudiness, look
for partly sunny skies and steady WSW winds mostly between 10 and 20
mph. A few gusts up around 25 mph will be possible, especially over
toward the Bluegrass. Despite the increasing clouds through the
afternoon, highs should still reach up into the upper 70s to around
80 along and south of the Ohio River. North of the river, temps will
be a bit lower because a cold front will impinge on that area
quicker. Look for mid 70s for highs.

Late Afternoon Through The Evening...

The aforementioned Great Lakes low pressure system will move east
into Canada by later this afternoon and evening, with the trailing
cold front sliding down into our area. Given upper 50s to near 60
dew points pooling ahead of the front, and at least some heating for
destabilization, we should see somewhere around 750-1500 J/KG of ML
CAPE by afternoon/evening. Scattered showers and storms are expected
to develop along and just ahead of the front mostly along and south
of the Ohio River as a result. Given modest instability and marginal
deep layer shear (~25-30 knots) most of the storms will be of the
garden variety. Suppose a few stronger/organized updrafts could
produce an isolated strong wind gust or some smaller hail, however
not overall impressed with severe potential. SPC took our area out
of the Marginal Risk as the better deep layer shear will be
displaced to our NE a bit.

One other thing work noting is that the 0-6 km bulk shear vectors
are going to be oriented roughly parallel to the cold frontal
boundary, so there is some potential for training of showers and
storms from W to E. Since updrafts may not survive all that long in
the marginal shear profile, some backbuilding could occur as cells
collapse and new updrafts quickly form to the W. Repeated brief heavy
rainfall could cause a few nuisance flood trouble spots as grounds
are still quite moist from recent rains. Overall, not too worried as
the front will also be slowly progressing south which should
mitigate the threat to train over one area for too long, but
something to keep an eye on.

Late Tonight...

Otherwise, convection should steadily diminish after sunset with the
frontal boundary likely stalling over our southern CWA overnight.
Lows should sink to the upper 40s and low 50s north, with lows only
falling to the upper 50s across southern KY.

.Long Term...(Wednesday through Monday)
Issued at 305 AM EDT Tue Apr 23 2019

Wednesday through Thursday Night...

A quasi-stationary boundary is forecast to be draped across the
region early on Wednesday.  This front looks to become more diffuse
during the day with at least isolated to scattered showers and
thunderstorms during the afternoon.  Overall coverage looks to be
greatest in our southwestern areas from western KY into the western
half of TN.  Some mid-level height rises look likely Wednesday night
which would allow the remaining boundary to drift northward with
scattered thunderstorms pushing back across the region.

By Thursday, upper trough to our west, combined with a closed upper
low over Texas will surge eastward. These features will bring
widespread clouds and more widespread showers and thunderstorms to
the region.  This unsettled weather looks to linger into Thursday
night before ending from west to east by late in the period as a
cold front slices through the region.

Highs on Wednesday will likely have a gradient of temperature across
the region.  Highs will likely top out in the upper 60s to the lower
70s across southern IN and northern KY.  Mid-upper 70s are likely
south of the boundary across southern KY.  Lows Wednesday night will
be mild with readings in the upper 50s to around 60.  Highs Thursday
should solidly be in the upper 60s to the lower 70s across the
region.  With the upper trough and surface front moving through
Thursday night, we`ll see temperatures drop back into the low-mid
50s for lows.

Friday through Monday...

Friday will be a transition day across the region as the cold front
from Thursday night pushes off into eastern KY during the day. We`ll
probably start off the day cloudy with clouds decreasing from west
to east during the afternoon hours. Highs look to top out in the
upper 60s to the lower 70s.  Lows Friday night will be a bit cooler
with readings in the low-mid 40s.

A brisk zonal flow aloft will be seen across the Ohio Valley by the
start of the weekend as surface high pressure slides off the
southeastern US coast.  The day should start off sunny, but a fast
moving weather system will approach from the west bringing
increasing clouds to the area.  Highs will range from the upper 60s
over southern IN and northern KY with lower 70s mainly confined to
areas south of the Cumberland Parkway.

A quick hitting system will push through the region Saturday night
and into Sunday.  As it moves through, it looks to fall apart and/or
shear out.  Enough lift should be present to pose a threat of some
isolated-scattered showers in the Saturday night and early Sunday
time frame.  Highs on Sunday will be slightly warmer with lower 70s
over southern IN and northern KY with mid 70s down across the
southern half of the state.

By early next week, the global models show the southeast ridge
building back northward from the Gulf coast states into the TN
Valley.  A mainly zonal flow regime looks to take grip once again
forcing the storm track a bit more to the north.  This should result
in warmer high temperatures with upper 70s and lower 80s common in
the afternoon and overnight lows in the 50s/60s. However, this mid-
level ridging probably will not hold with showers and storms a
likely bet as we head toward the middle of the week.


.Aviation...(12Z TAF Issuance)
Updated at 637 AM EDT Tue Apr 23 2019

VFR prevails early this morning, and for much of the day as surface
high pressure to our SE holds for a bit longer. During this time,
expect few-sct mid to upper level clouds with a more steady WSW wind
as we progress toward midday. A few gusts in the 20 to 25 mph range
will be possible, along with few-sct cumulus around 4 k feet. As we
move deeper into the day, a weak cold front trailing from a low
pressure system passing through the Great Lakes will sink down
around HNB/SDF/LEX. This feature will be enough to trigger scattered
showers and storms in the evening hours, which will slowly die off
after sunset. Continued mention of Prob30 -TSRA or -SHRA for those
sites, but will keep BWG dry. Surface winds go NW and then NE behind
the front outside of any thunderstorm outflow boundaries which could
create variable surface winds for a while.




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