Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 240212

Area Forecast Discussion
National Weather Service Louisville KY
1012 PM EDT Fri Mar 23 2018

.Forecast Update...
Issued at 1010 PM EDT Fri Mar 23 2018

No big changes to the winter headlines this evening. Did issue a
Special Weather Statement for the possibility for minor slushy
accumulations in four counties bordering the Winter Weather
Advisory. We`re still looking at a tight thermal gradient from
southeast Indiana into the Bluegrass region of KY. For instance, in
the Winter Weather Advisory, we could easily see snowfall totals
range from 1 to 4 inches across one county. Most likely area for
heavy snow is still the five counties in the Winter Storm Warning,
where 3 to 6 inches is possible.

Late this evening, a warm advection band of showers extended from
Iowa down through Illinois and the western half of the Bluegrass
State. Enhanced convergence has resulted in a narrow, intense
band of showers from southern IL through western KY. Precip
coverage will continue to expand east overnight. Precip intensity
will also ramp up quite a bit between 06-12z as isentropic lift
increases. Snow is likely to begin mixing in after 06-07z from
southeastern Indiana down through the Bluegrass region. Snow could
persist in the Winter Storm Warning counties until 16-17z. Strong
easterly flow and moderate precip will really put a lid on any
warming potential at the surface during the daytime. However, max
wetbulb temp in the warm nose aloft should finally rise above 0 C
in the afternoon.


.Short Term...(This evening through Saturday night)
Issued at 310 PM EDT Fri Mar 23 2018

...Another Round of Wintry Weather Expected Late Tonight and

Satellite imagery this afternoon has a distinct line across the
region going from mostly clear skies to mostly cloudy. Clouds cover
will continue to increase into the evening hours as the next weather
system moves in.

For tonight a warm front will approach southwestern portions of
central KY. Isentropic lift will result in widespread precipitation
overspreading the region overnight. Rain will begin in the southwest
portions of central KY this evening and spread into the Bluegrass
region of KY overnight late tonight into early tomorrow morning.
Temperatures will drop into the lower to mid 30s across southern IN
and north central KY overnight with the lowest temps across the far
northeastern portion of this area. The easterly flow tomorrow will
keep the low level cold air in place.

Soundings are still showing a deep isothermal layer just at or below
freezing setting up late tonight across the northern Bluegrass and
southeastern IN. As we go into the morning hours, warmer air will
edge northward through the day. Aloft the soundings show some warmer
air working in as well, at least for a brief time. The result of all
of this is an area of snow developing early tomorrow morning which
will eventually change over to all rain during the day. We could
then see a brief transition back to snow tomorrow evening,
especially across the far northern Bluegrass region, before
precipitation ends. The highest confidence in accumulating snow
reaching 4+ inches is across the counties where the Winter Storm
Watch was, so will go ahead and upgrade them to a Winter Storm
Warning. Jefferson county, IN and Scott and Bourbon counties in KY
may only see these higher amounts in the northern portion of their
counties, however. Will also issue a Winter Weather Advisory for one
tier of counties just to the south of the Warning. The Winter
Weather Advisory will expire earlier than the Winter Storm Warning
as snow is expected to change over to rain through the morning hours
in these counties. Travel difficulties are expected in the Warning
areas tomorrow morning. In addition, some power outages will be
possible as this will be a heavy, wet snow.

In the areas that are getting just rain across southern IN and
central KY, rainfall totals will be in the 1-1.75" range from
tonight through tomorrow night. This is not expected to cause
widespread flooding issues, but some ponding of water in low lying
areas will be possible. Also, the latest forecasts for Woodbury and
Rochester on the Green River have rises above action stage and
approaching flood stage early next week.

.Long Term...(Sunday through Friday)
Issued at 300 PM EDT Fri Mar 23 2018

On Sunday, the Saturday system will have moved off to our east.
Clearing should occur over south-central IN into north-central and
east-central KY during the day, but low clouds may linger over
southern KY. Highs will be in the 40s north to lower 50s south.

For next week, the mid-level flow pattern changes as a ridge aloft
moves east through the OH Valley Monday resulting in a southwest
flow aloft thereafter. This will result in increasing and more
persistent moisture transport from the lower MS Valley into the OH
Valley. As this change occurs, a shield of rain showers associated
with warm air advection/isentropic lift will spread northeast into
the OH Valley Monday afternoon and night.

Models then diverge a bit thereafter with placement/movement of the
deep moisture/precip axis Tuesday-Wednesday along and ahead of a
slow moving frontal boundary. The ECMWF and GEM models are a little
slower/farther north with this axis, suggesting our northern
forecast area will have a better chance of locally heavy rain, while
the operational GFS tends to slide the axis quicker across our area
to the south. However, the GFS ensembles tend to favor the slightly
slower solution. Our probability of precip forecast tends to follow
the slower trend for now. Either way, the frontal boundary should
sag south into or through the forecast area Wednesday-Thursday.
Models actually all do then show another surface low pressure wave
riding northeast along this boundary bringing more potential
rainfall to the area Thursday or Friday. Conditions are finally
expected to dry out by next weekend as the flow aloft turns more
westerly, shifting the moisture plume well to our east.

Total precip amounts during the period could vary significantly
across the area, depending on how stationary or variable the
movement of the main precip axis. While deep convection does not
appear likely during much of the period, moderate to locally heavy
rain could occur at times, with some embedded thunder possible at
times. A general 1-2 inches of rain across the region looks likely,
with some 2-3+ amounts possible. Given wet grounds already and the
rain expected tomorrow (Saturday), this could lead to some flood
concerns, which we will monitor as weather conditions evolve over
the next several days.


.Aviation...(00Z TAF Issuance)
Issued at 736 PM EDT Fri Mar 23 2018

During this TAF period low pressure will advance along a warm front
from Kansas to the KY/TN border. Moisture will ride up and over the
boundary, resulting in widespread precipitation by the late night
hours tonight and continuing through Saturday. HNB and BWG will see
all rain. As a matter of fact, BWG could even hear a rumble or two
of thunder Saturday afternoon. SDF will see mostly rain, but a few
wet snowflakes mixing in isn`t entirely out of the question during
the pre-dawn hours. There could be times where SDF is experiencing
-RA while LOU is seeing -SN or -RASN. LEX stands the best chance
among the TAF sites of seeing -SN, especially during the late night
into the early and mid morning hours before temperatures warm just
enough in the afternoon to change everything to rain.

Winds will come in from the east and will increase in speed Saturday
in the 10-20kt range with a few higher gusts possible at the I-64
TAF sites as the low pressure center approaches and tightens the


IN...Winter Storm Warning from 2 AM Saturday to 2 AM EDT Sunday for

KY...Winter Storm Warning from 2 AM Saturday to 2 AM EDT Sunday for

     Winter Weather Advisory from 2 AM to 2 PM EDT Saturday for



Short Term...EER
Long Term...TWF
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