Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 100225

Area Forecast Discussion
National Weather Service Louisville KY
925 PM EST Fri Dec 9 2016

...Forecast Update...
Issued at 926 PM EST Fri Dec 9 2016

Made a few adjustments to sky cover given recent satellite trends.
Also, dropped MinT 1 degree north of I-64 and 1-3 degrees south of I-
64 given current T/Td and the fact that the center of the incoming
Arctic high will be directly overhead at 12Z.

Issued at 548 PM EST Fri Dec 9 2016

Reflectivities, while still weak, have increased quite a bit north
of I-64 so have gone ahead and thrown isolated flurries into the
forecast for southern Indiana east of Patoka Lake and central
Kentucky north of 64. Also increased cloud cover to 100% where it is

.Short Term (Now through Saturday Night)...
Issued at 239 PM EST Fri Dec 9 2016

As of mid afternoon, high pressure over Arkansas and low pressure
over the Great Lakes was continuing northwesterly flow over the
lower Ohio Valley. Upstream moisture and cold temperatures aloft in
the cyclonic flow resulted in an extensive strato-cu deck across
southern Indiana and north-central Kentucky. A recent RAP sounding
showed these clouds remained in the snow growth region around -12C,
and regional radar and surface observations confirm light snow
flurries across parts of the area. It`s been a cold day with
readings in the mid/upper 20s under the clouds while closer to the
TN border temperatures have risen to around the freezing mark.

The main focus in the short term is cloud trends and temperatures.
Latest visible satellite shows the strato-cu deck extending upstream
through Illinois and Indiana. Plan on a mostly cloudy to cloudy
night for far northern Kentucky and southern Indiana, and this is
where there might be a few flurries around through the night as
well. Otherwise, lows tonight will fall into the teens to low 20s.

The aforementioned high pressure moves nearly overhead during the
day tomorrow and should provide the area with more sunshine and
slightly warmer, but still below normal, high temperatures. Readings
are expected to top out in the low 30s across southern Indiana to
mid/upper 30s across central Kentucky. The high quickly moves east
and southerly return flow sets up Sunday night. The tighter pressure
gradient should keep the boundary layer mixed enough to hold lows in
the mid/upper 20s.

.Long Term (Sunday through Friday)...
Issued at 241 PM EST Fri Dec 9 2016

A few items of interest in the long term with the focus on the storm
system for Sunday and Monday, then another surge of Arctic air for
mid/late week.

Low pressure is forecast to move from the central Plains toward the
Upper Midwest Sunday and Sunday night. Overall, the 09.12z models
continued the trend of slowing down the frontal passage Sunday. As a
result, collaborated with PAH/OHX/IND to reduce chances early Sunday
morning, but still bring in higher chances during the afternoon and
evening, west to east. This further reduces the threat of a wintry
mix locally. Ahead of it, a push of Gulf moisture will bring higher
PWATs between 0.75 and 1.0 inches and combined with stronger forcing
for ascent, rain showers should break out across the area,
especially Sunday evening and night. Rain will taper off and move
east of the area Monday morning. Overall, total rainfall amounts
between 0.5 and 0.75 inches are forecast.

Temps will be warmer for the first part of the week.  Highs look to
range through the 40s Sunday and 40s/lower 50s Monday.  Temps
shouldn`t drop off much Sunday night with lows in the mid 30s to
lower 40s.

Forecast confidence drops off mid-week as the global deterministic
and ensemble models aren`t exactly painting the same picture
regarding the synoptic pattern. It does look like a stronger upper
level trough will dive toward the region mid-week which will bring
another round of colder temperatures (perhaps colder than the
current cold snap) but whether any shortwave troughs or surface
systems interact with this cold air remains in question. Sided with
a model consensus with just slight chances of rain/snow mix Tuesday
through Wednesday night. This is a compromise between the dry, cold
ECMWF solution versus the wetter, still cold, GFS and GEM.
Temperatures will trend downward mid-week onward with highs Thursday
and Friday potentially staying in the 20s or low 30s, and morning
lows in the teens.


.Aviation (00Z TAF Update)...
Issued at 626 PM EST Fri Dec 9 2016

Relatively quiet weather, but still not an easy forecast as we deal
with a stubborn stratocu deck over SDF and LEX. Looking at satellite
and model data, will give a best stab at when those airports will
lose their ceilings this evening. Base heights will be right around
3,000 feet, so the airports will be either VFR or MVFR by just a
couple hundred feet at any given time. Interestingly, the RAP, which
did an admirable job forecasting this stratus at this time
yesterday, shows possible rebuilding of the low clouds late tonight.
Again, these would be right around the VFR/MVFR boundary. Will go
ahead and include a TEMPO for possible ceilings during the pre-dawn
hours, but this will need to be re-evaluated as the evening
progresses to see if the signal remains.

A weak upper wave crossing the Wabash Valley at this writing is
helping to spark a few flurries from the clouds, but those will be
of no consequence to aviation.

Saturday looks nice with just some mid/high clouds and very light
winds as high pressure moves right through Kentucky.


.LMK Watches/Warnings/Advisories...


Short Term.....ZT
Long Term......ZT
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