Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 080505
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1205 AM EST Thu Dec 8 2016

...Updated Aviation Discussion...

.Forecast Update...
Issued at 845 PM EST Wed Dec 7 2016

Radar returns across the Wabash Valley and western Kentucky are not
being backed up by any precip in surface observations, and mid-level
ceilings suggest those returns are mostly virga. Northernmost
enhanced cloud band is now roughly along the Ohio River, and all the
synoptic and hi-res models show the upper forcing dropping southeast
as the night progresses. Have collaborated with PAH and JKL, and
will be delaying the mention of flurries until after midnight, and
restricting it to areas along and south of the Western Kentucky and
Bluegrass Parkways. Updates already sent, impact remains essentially
nil.

&&

.Short Term (Now through Thursday Night)...
Issued at 200 PM EST Wed Dec 7 2016

...Strong Cold Front to Bring Sharply Colder Air Tonight...

High pressure building into the region today will get reinforced as
a broad upper trough axis swings through tonight and Thursday. Winds
will pick up from the northwest, ushering in much colder air.
Temperatures Thursday will not warm too much, with highs in the 30s
for most, if not, all locations. Those winds should stay up during
the night as well, keeping a more uniform low temperature field.
Lows Thursday night will be around 20, with wind chills in single
digits in some spots.

Tonight, some mid level moisture will move into the region, in the 7-
10 kft range. Forecast soundings still show a dry layer under this
that should force any ice crystals/supercooled liquid to dissipate.
Cannot rule out a few patches of flurries/sprinkles surviving, but
they will come through well before daybreak and shouldn`t cause
anything more than a trace.  Of note, did a quick check to see when
the average first date for measurable snow (>=0.1") is at Louisville,
and that date is today. The date is a little earlier for Lexington,
Nov. 29th.

One more thing, we had flurries in our northeast for late Thursday
night. Plume of moisture looks to be a little farther north, so
backed those flurry grids farther north as well, effectively keeping
them into IND/ILN`s areas, if at all.

.Long Term (Friday through Wednesday)...
Issued at 310 PM EST Thu Dec 7 2016

...Cold airmass, even some true Arctic Air dominates the medium
and long term periods...

Well....High confidence forecast in terms of temperature and overall
pattern with low meridional upper flow.  This pattern regime will
garner plenty of cold advection keeping mercury readings 10-18
degrees below normal for highs and 5 degrees below normal for lows.
Periods of cloud cover will keep temps from dropping dramatically
for low temperatures.

Friday...

Latest models keep the weak vort max primary energy to the N of CWA
so cut back the flurries early Fri morning to the just along the far
NE CWA. Soundings show a decreased llvl moisture plume and not
reaching -10C so not as much ice nuclei.

Depending on the amount of high clouds Fri night, which may inhibit
strong radiational cooling, temperatures will likely fall hard
Friday night.

Saturday - Monday...

Very cold once again Friday night with Sat sunrise temps in the
upper teens with 1035 mb high over Red River Gorge.  Some of the
eastern favorable cold drainage spots across the Bluegrass could be
13-16 degrees. BURR.

The next weather system will move into the area late Sat night into
Sun and continue through Monday morning.  The Canadian is gelid and
cold...the ECM is much warmer and the GFS is a healthy compromise
especially the GFS ensemble. Will keep very light snow overnight
transitioning to a RASN and and cold rain down south and light snow
across S IN through mid morning before transitioning back to a cold
rain everywhere Sun aftn.  Temps will be 28-31 at daybreak but sfc
sly waa will climb temps into the 38-43 range.

Sunday morning will be gloomy and cold but think travel problems
will be minimal, with temps climbing all morning.  The models are
lingering the moisture Sunday night and Monday and the Canadian and
ECM have a second wave, so that could cause some minor travel issues
with cold air coming back in on wet roadways.  Stay tuned.

Wednesday...

Next system coming out of the Bitterroots and Tetons Ranges will be
more moisture starved and could bring a light RASN mix with another
resurgence of cold air. This air looks much colder, very arctic in
nature.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1200 AM EST Thu Dec 8 2016

VFR conditions are expected through this TAF period. For the
remainder of tonight a mid deck will remain across the region as a
disturbance moves through. This mid deck will clear out during the
morning, with cirrus moving across the region through today. For
tonight, a disturbance to the north of the area will bring lower
clouds back into north central KY, affecting SDF and LEX.

Winds will be out of the northwest through the TAF period. They will
pick up through the morning with gusts of 17-20 knots expected
through much of the day. Gusts will diminish this evening.

&&

.LMK Watches/Warnings/Advisories...
IN...None.
KY...None.
&&

$$

Update...RAS
Short Term........RJS
Long Term.........JDG/BJS
Aviation...EER


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