Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 182010

Area Forecast Discussion
National Weather Service Louisville KY
410 PM EDT Tue Apr 18 2017

.Short Term...(This evening through Wednesday night)
Issued at 315 PM EDT Tue Apr 18 2017

A cloudy, warm, and damp - though not wet - short term forecast
today. A relatively weak short wave in zonal flow has finally
triggered convection from parts of central and south central KY
southward.  Temperatures aloft are warm, though, so there is little
support for longevity or intensification, and only sporadic showers
are expected - mainly this evening, and mainly south of the
Cumberland Parkway. Most will see no rain, or sprinkles, while a few
could see between 0.10 and 0.20 inch.

With southerly low level winds pushing gulf moisture into the Ohio
Valley, mostly cloudy skies will prevail through the period,
preventing radiational cooling tonight, so low temperatures will
will only bottom out around 60 - some 15 degrees above normal for
the date.

The clouds will eventually drift east of the region Wednesday as the
weak zonal flow aloft continues.  With a little more sunshine,
temperatures could reach the lower 80s west of I-65, while the
slower cloud exit in the east should hold temperatures into the 70s.
Even so, these will still be above average for the day.  A few
showers or garden-variety thunderstorms can`t be ruled out for the I-
75 corridor and south of the Cumberland Parkway Wednesday, but POPs
for these will only be in the 20s.


.Long Term...(Thursday through Tuesday)
Issued at 400 PM EDT Tue Apr 18 2017

...Unsettled weather to continue through the weekend...

Relatively wet weather will linger through the extended period as
two upper level lows make their presence felt in the Ohio Valley.

The first system will move through as a cold front trailing from a
surface low that moves through the Great Lakes Thursday. The front
will serve as the focus for convection as it moves through the Ohio
Valley Thursday night, then stalls over the Tennessee Valley Friday.

A second surface low is then expected to develop over the southern
plains and move to the lower Mississippi Valley by Saturday morning,
and attempt to push the Tennessee boundary back north as a warm
front. There has been less consistency across model runs and times
with this system, so confidence on timing and location of any rain
with this one remains low.  There has been a general tendency
southward in the last 24 hours, which should keep the bulk of any
showers and thunderstorms associated with it mainly over the
southern half of the forecast area.  With limited sunshine,
instability will remain relatively low, so despite the potential for
extended periods of rain potentially totaling up to 3 inches over
southern Kentucky, the threat of very strong thunderstorms should
remain low.

Ahead of the cold front arrival on Thursday, temperatures will warm
into the 80s across the area.  After its passing, highs on Friday
will drop into the mid 60s to lower 70s, then fall another 5 degrees
for Saturday.  High temperatures remain mostly in the 60s for
remainder of the period weekend, with lows dropping to seasonal
readings in the mid 40s to lower 50s.


.Aviation...(18Z TAF Issuance)
Issued at 140 PM EDT Tue Apr 18 2017

Isolated-sct showers and storms are expected this afternoon,
therefore, will continue the mention of VCTS at all TAF sites
through 0-2Z.  Flight restrictions to MVFR/IFR and gusty winds will
be possible in any convection.  The chance for rain showers will
continue into the late evening and overnight hours, however, with
weakening instability t-storms won`t be as likely.  Low level
moisture is expected to increase late tonight increasing the chances
for MVFR below 2 kft agl.  Some models indicate IFR cigs as well,
but will hold off on that since there is some spread in the model
data at the moment.  Cigs should lift/sct tomorrow late morning
or early afternoon with VFR conditions returning.




Short Term...JBS
Long Term...JBS
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