Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 290709
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
309 AM EDT Mon Sep 29 2014

.SHORT TERM (Now through Tuesday)...
Issued at 305 AM EDT Mon Sep 29 2014

Low-amplitude upper pattern continues to be a slow-moving one as it
remains disconnected from the stronger westerly flow well to the
north. Weak trof axis will push east of the lower Ohio Valley today,
giving way to shortwave ridging that will persist into the middle of
the week. Warm and dry conditions will be the rule, leaving us with
mainly a temp and fog forecast.

Daytime temps both today and Tuesday will run several degrees above
normal. Will favor the slightly warmer GFS MOS given how max temps
have overachieved lately. Favorable radiational cooling conditions
tonight will allow temps to drop very close to seasonal normals.
Given the very weak low-level flow, and forecast mins several
degrees below this afternoon`s forecast dewpoints, fog seems to be a
good bet toward daybreak Tuesday. The ability of NW winds this
afternoon to mix down dry air will make all the difference in fog
potential. Will go with areas of fog in the grids and zones, but
will let the day crew evaluate whether dense fog will need to be
mentioned.

.LONG TERM (Tuesday Night through Sunday)...
Issued at 245 AM EDT Mon Sep 29 2014

The synoptic pattern at the start of the long term period will
feature a weak ridge over the Ohio Valley, with a strong upstream
trough located over the western CONUS.  This trough will build into
the region through the long term period, marking a pattern shift
from the warm and dry weather to a cooler/wetter regime by the end
of the work week.

Tuesday night through at least Wednesday night will continue to
feature benign weather as the upper-ridge remains in place.  This
regime will make for temperatures continuing to run above normal, as
highs top out in the low to mid 80s on Wednesday, with lows in the
50s and lower 60s.

Clouds will begin to increase on Thursday as the system approaches
from the west.  Warm-air advection associated with the warm conveyor
belt (30-40 kt low-level jet) of this system will spark a few
showers/storms a early as Thursday afternoon across portions of
southern IN, spreading into portions of Kentucky late Thursday
afternoon/evening.  Mid-level lapse rates look quite poor during
this timeframe which will limit overall instability and deep-layer
shear will be on the order of about 30 knots.  Therefore, do not
expect any significant severe weather out of these storms Thursday.

The cold front and associated upper-level kinematics will sweep
through the region overnight Thursday into Friday.  Dprog/dt shows
the trend has been to speed this system up, now pushing the bulk of
the precip through overnight Friday.  Given the timing, guidance
suggests instability along the front will be waning as it pushes
in.  Given surface moisture/temperature advection will not be that
strong ahead of the front, it appears we should decouple enough to
limit the potential for surface-based storms.  Therefore, while a
few bouts of gusty winds may be possible, think these storms will be
on the decline and becoming elevated as they push in, carrying just
a locally heavy rainfall threat.

Precipitation will push out by early Friday afternoon.  Will have to
continue to monitor the timing of fropa, as the slower GFS suggests
the atmosphere could destabilize early Friday afternoon over far
eastern portions of the FA before the front clears the area.  Given
the overall quicker trend in guidance, will lean away from this
solution for now.

In the wake of the front, much cooler air will push into the
region.  Highs Saturday will struggle to get out of the middle 60s.
Overnight lows Saturday night will be dependent on clouds/location
of the surface ridge.  However, if ideal radiational conditions can
be realized, lows in the upper 30s will certainly be possible in
some locations.

&&

.AVIATION (06Z TAF Update)...
Issued at 115 AM EDT Mon Sep 29 2014

Main challenge overnight will be fog potential at BWG, where cirrus
shield has cleared within the last hour or two. Temps are progged to
just touch the crossover temperature, but latest MOS guidance is not
hitting the fog as hard as previous runs. High-resolution models
don`t seem to have a very good handle either. Will go with
prevailing MVFR and a TEMPO for IFR visibilities around daybreak.
SDF and LEX will not have as much time to radiate out due to the
lingering mid-level deck, and will have a harder time reaching
crossover temps. Will keep thos sites VFR.

Light W-NW winds expected late in the morning, along with scattered
diurnal cu as mixing picks up. Even better radiational cooling
conditions Monday night will open the door for significant
restrictions to visibility on Tuesday morning, especially in BWG.
Can`t rule out IFR Tuesday morning in LEX either, but that remains
beyond the scope of this TAF issuance.

&&

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

$$

Short Term........RAS
Long Term.........KJD
Aviation..........RAS




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