Area Forecast Discussion
Issued by NWS Louisville, KY

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185
FXUS63 KLMK 250000
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
800 PM EDT Tue Apr 24 2018

...Updated Aviation Discussion...

.Short Term...(This evening through Wednesday night)
Issued at 340 pM EDT Tue Apr 24 2018

The upper low that has persisted the last couple of days across
central Kentucky is becoming more disorganized this afternoon
(less vertically stacked in nature). There is a diffuse middle and
upper level circulation centered between Bowling Green and Glasgow
Kentucky with the main surface low displaced over South Carolina
with an inverted trough extending northward into eastern Kentucky
and West Virginia.

There has been some entrainment of drier air from the south and
southeast around this circulation that may help overturn some
lower level higher theta-e air. Given the sharp vorticity
gradients and potential for some insolation, will keep the
small mention of thunderstorms across the southeast part of the
WFO LMK forecast area. There has been intermittent moderate rain
showers over parts of Monroe and Cumberland counties near the
Kentucky-Tennessee border, but updrafts have not been organized
enough to support charge separation for thunderstorm development
at this time. The potential will still be there through this
afternoon.

Anticipate a diurnal downturn in convective activity late this
afternoon and this evening. Persistent cloud cover and light winds
tonight will limit any significant drop in temperatures
overnight and mitigate any fog development.

Going into Wednesday, the upper low will be slow to move along the
mid-Atlantic coast. With high pressure slowly building in,
steering currents will be too weak to completely scour out the
deeper layer moisture. Will keep skies mostly cloudy for tomorrow
and tomorrow night. The diurnal amplification around the upper low
should support some isolated showers along the eastern edge of the
WFO LMK forecast area.

No real significant changes made in the short term from the
previous package. The NAM-WRF and RAP guidance seem to have a good
fit on the convective trends associated with the upper low this
afternoon and this evening.

.Long Term...(Thursday through Tuesday)
Issued at 340 PM EDT Tue Apr 24 2018

An upper level shortwave diving through the Central Plains/Middle
and Lower Mississippi Valley on Wednesday will skirt through the
Tennessee Valley on Thursday. As this shortwave moves southeast,
it will amplify across the southeast U.S., bringing some moisture
and enough instability northward to generate some showers for
mainly the southern 1/2 of central Kentucky mainly Thursday and
Thursday evening.

Another progressive, but weaker shortwave will follow on the heels
of the aforementioned shortwave (that is forecast to produce
showers on Thursday) leading to a small chance for rain on Friday
afternoon. Any shower development will likely occur during the
peak heating/greatest potential for instability associated with
the shortwave.

Beyond Friday, and through the remainder of the forecast period,
large scale high pressure is expected to dominate the region. This
will finally allow the region to dry out and bring temperatures
closer to seasonal normals expected in late April and early May.

In addition to the regionally blended model guidance
initialization, the ECMWF and Canadian numerical guidance was
preferred for the longer range forecast solution with respect to
temperatures and weather.

&&

.Aviation...(00Z TAF Issuance)
Issued at 758 PM EDT Tue Apr 24 2018

Upper level low pressure will slowly make its way eastward, with
plenty of low clouds plaguing the airports into Wednesday morning.
Ceiling heights should mostly start out in the low MVFR ranges below
fuel-alternate, then find their way down to IFR in the pre-dawn
hours. The exception is LEX which will find it`s way down to IFR
shortly after sunset, and possibly down toward minimums through the
overnight.

Also wanted to mention the fog potential at BWG/HNB toward dawn.
Cloud cover could be thinner in these areas and could promote enough
radiational cooling to promote some fog. Didn`t go as pessimistic as
some of the guidance suggests, but did take conditions a bit in the
pre-dawn hours.

Otherwise, conditions slowly improve through the day tomorrow with a
return to VFR possible by late afternoon/early evening. Winds should
be steady out of the NW through this cycle.

&&

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

$$

Short Term...WFO PAH
Long Term...WFO PAH
Aviation...BJS



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