Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 270014
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
714 PM EST Wed Feb 26 2020

...Updated Aviation Discussion...

.Short Term...(This evening through Thursday)
Issued at 242 PM EST Wed Feb 26 2020

Low pressure over the central Appalachians will lift to the
Adirondacks tonight. Light rain mixing with and changing to light
snow early this evening will gradually taper off. Road temperatures
are expected to stay above freezing before midnight, with little if
any precipitation after midnight, so road impact should be minimal
if any. Cold air sweeping in behind the departing system will take
temperatures down into the middle 20s and wind chills in the teens
by morning.

Thursday weak ridging from Texas to the Ohio Valley will give us a
dry day and we should even see at least partial sunshine! A west
breeze will add a bit of chill to the air but the mercury should
rise to around 40.

.Long Term...(Thursday night through Wednesday)
Issued at 225 PM EST Wed Feb 26 2020

...Some snow Thu Night...
...Looks quite wet and warmer next week...

Synoptically...

Well...the forecast period begins with a large upper low (507 m)
over the St Lawrence River Valley. There is so much cold air and it
is so expansive that it has set up a strong meridional flow thru Sat
morning. On the very back side of this trough in the nw-se flow
aloft are 2 small vort maxes swinging down from Saskatchewan and
diving down toward the MO Ozarks. This Saskatchewan Screamer will
bring potential for snow early Friday morning.

As the deep low pressure pulls out of Maine/New Brunswick a broad
West Coast trough will be the most significant weather maker for the
medium and long range. The northern stream moves from the Cascades
to Alberta province with the upper jet diving down to deepen out the
trough over Redwoods NP to Channel Islands NO by late Sunday. As
this trough deepens...upper heights will respond and temps will
respond accordingly to above normal...but also pump a lot of
moisture towards the Ohio Valley.

Thu Night - Fri AM...

Quick moving disturbance will bring in a chance for some light snows
that could impact the Friday morning commute. By 06z column is
saturated and way too cold in the column for much more than a few
flurries. LLVL lapse rates really steepen which will bring some
quick bursts of snow with -8 - -10 C in the DGZ from 08-13z.
Forecast totals for this clipper system should stay under an inch
for most part. Feel fairly confident for light snow accumulations
but the exact track of the vort max will really be the crux on what
areas receive the most snow.

Winds will freshen Thu night from SW and shift to the west at 10 to
20 mph and gusty as the feature pushes through. Lows 28-32 F, plus
road temperatures likely below freezing and any untreated roads
should get a coating of snow. This portends to be problematic for
Fri am commute in some localities.

Fri night...

Then a second vort max rotating in a broader trough over the Great
Lakes could bring another round of light snows for Friday night.
Coverage doesn`t look quite as widespread, but another few tenths of
an inch of snow could fall.

Weekend...

Giant trough pulls out Saturday morning with 1028 mb sfc high over
Pelican State to take over. Extensive cloud shield will push out by
late Sat morning and bringing abundant sunshine and with a modicum
of warmth on Saturday rising into the mid 40s and then sfc high
moves to SAV/Tybee Island...southerly winds will warm things up big
time on Sunday to around 60. Not out of the question to see mid 60s
near BNA/PAH/LMK border. Temps will be 5-10 above climatological
normal.

Mon-Wed...

A 590 m high over Cuba will help sling srn stream trough coming out
of S AZ/Mexico and bring a bunch of Pacific moisture and W GLFMEX
moisture and set stage for several waves of rain...most notably
Monday night and another one Tuesday afternoon and night. The
GFS/GEFS/ECM/CMC all show this slow-moving high PWAT airmass
bringing heavier rains in the vicinity of the Ohio Valley. WPC is
hitting this fairly hard too.

This is nothing like the March 1, 1997 rain event when Louisville
measured 10.48".  However...March is going to start off quite wet
after another very wet February in the Ohio Valley.

&&

.Aviation...(00Z TAF Issuance)
Issued at 710 PM EST Wed Feb 26 2020

Low pressure now located over western PA will continue to move off
to the northeast, and scattered light snow showers on the backside
of this system will continue through about 06z. Low stratus will
also slowly lift through the morning hours of Thursday. Through 06z
tonight, snow could briefly reduce vsbys into the MVFR range. Winds
will remain breezy out of the northwest. Gusts in the 20-25 kt range
should be common, with a few peak gusts up to 30 kts possible.

&&

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

$$

Short Term...13
Long Term...JDG
Aviation...EBW



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