Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 230748

Area Forecast Discussion
National Weather Service Louisville KY
348 AM EDT Fri Mar 23 2018

.Short Term...(Today through Saturday)
Issued at 315 AM EDT Fri Mar 23 2018

...Another Round of Wintry Weather Expected Late Tonight and
Saturday for the Northern Bluegrass Region...

Early morning satellite imagery shows mid-high level cloudiness
streaming into western KY.  The clouds are very thin east of the I-
65 corridor, but really thicken as you head west of I-65.
Temperatures ranged from the upper 20s to the lower 30s over the
eastern sections of the forecast area where clear skies were noted.
Further west, underneath the high clouds, temperatures were in the
upper 30s to the lower 40s. For the remainder of the overnight
period, we`ll see the high clouds expand eastward slightly.  Morning
lows will drip into the mid-upper 20s in the east with mid-upper 30s
in our far western areas.

For today, we expect cloud cover to increase throughout the day with
all locations going mostly cloudy by mid-late afternoon.  The day
will be mostly dry as the models have slowed down the eastward
progression of the next weather system coming into the region.  A
few light showers are possible out west of the Natcher Parkway.
Afternoon highs look to warm into the upper 40s to the very low 50s.

As we move into tonight, a warm front will advance into the region
from the west.  Associated with the front, warm air advection scheme
will kick into high gear and we should see strong isentropic lift
that will result in widespread precipitation developing. This
precipitation looks to increase in intensity as we head into the
overnight hours.  Low-level easterly flow just to the north of the
advancing warm front looks to re-enforce a low-level cold airmass
across far SE IN and into the northern Bluegrass region.

Suite of 00Z guidance has trended a little further south with the
heaviest precipitation band which is forecast to stretch from
northern IL through central IN and into southern OH and NE KY. Model
proximity soundings are slightly colder across SE IN and the
Bluegrass region of KY.  While surface temps remain near freezing,
low-level thermal advection courtesy of an increasing low level jet
will allow a deep isothermal layer to develop.  The warm nose may be
strong enough to result in mixed precipitation across SE IN and into
the Bluegrass region.  Though, overall 00Z soundings side closer to
mostly snow, with perhaps some sleet/freezing rain mixed in,
especially if the aforementioned warm nose kicks in.  As surface
temperatures warm by mid-late morning Saturday, precipitation type
transitions over to all rain across SE IN and into NE KY.

In terms of forecast confidence, our confidence is high that we`ll
see precipitation overnight and into Saturday morning.  However, the
confidence of the low-level thermal field remains uncertain.  A
chance of 1-2 degrees in the forecast in the lower atmosphere would
have large changes to precipitation types and wintry precipitation
amounts.  Given the latest suite of a data, an accumulating snow
appears likely for the extreme northeast portions of our forecast
area, mainly along and northeast of a line from Madison, IN to
Paris, Kentucky.  In areas north and east of these towns, a 4-6 inch
snowfall is possible with locally higher amounts.  For this reason
and given forecast confidence, we will hoist a Winter Storm Watch
for Jefferson (IN), and for Scott, Harrison, Bourbon, and Nicholas
Counties of east-central KY with this issuance.

For areas just west of the Winter Storm Watch, a tight gradient of
snowfall accumulation will also be possible.  The transition line
between plain rain and snow looks to be along a line from
Scottsburg, IN SE through the Lexington metro area to near Richmond.
Accumulations in these area could range from a dusting to near 4
inches in areas that border the watch area.  Given the continued
shifting in the models and the lower confidence in this area, we
will maintain the ongoing Special Weather Statement at this time.
However, if further data supports the snow accumulations, these
areas will likely need a Winter Weather Advisory in later forecasts.

For the remainder of our area, a plain cold rain is expected tonight
and into Saturday. Lows tonight will range from the lower 30s in SE
IN and in the Bluegrass region with upper 30s to the lower 40s
across the Heritage corridor (I-65) and points south and west.  A
very strong temperature gradient will be seen on Saturday as the
warm front bisects the region.  Highs will range from the mid 30s in
SE IN and the northern Bluegrass with upper 50s to the lower 60s
being seen in areas along the KY/TN border region.


.Long Term...(Saturday night through Thursday)
Issued at 340 AM EDT Fri Mar 23 2018

Rainfall is expected to linger across the region into Saturday night
before ending late.  A general 1-2 inches of rainfall is expected to
fall across the region.  Some locally higher amounts of QPF will be
possible across south-central IN and into portions of north-central
KY.  This may result in some localized hydro issues on Saturday and
into Saturday night.  As the weather system pulls east, we`ll see
colder weather return Saturday night as lows drop back into the
lower-mid 30s in the north and upper 30s across the south.  We
should see a period of drier weather on Sunday and Sunday night.
Highs on Sunday look to warm into the upper 40s to the lower 50s
with overnight lows in the upper 30s.

For much of next week, a deep southwest flow regime looks to set up
as troughing develops over the desert southwest and ridging develops
over the northern Gulf.  This will result in a moderating
temperature pattern with along with episodic bouts of showers and
thunderstorms.  The overall set up is concerning as it usually
results in excessive rainfall.  Model forecasts have been suggesting
an additional 1-2 inches of rainfall for next week.  The cumulative
effects of this weekends rainfall plus next week`s suggests a
heighten threat of flooding in the Ohio Valley...depending on where
the axis of heavy precipitation sets up.  Highs next week will
seasonal with readings in the upper 50s to the lower-mid 60s and
overnight lows in the upper 40s.


.Aviation...(06Z TAF Issuance)
Issued at 100 AM EDT Fri Mar 23 2018

High to mid level clouds are beginning to move in from the west, and
regional radars show some light returns across western Kentucky.
Very dry air in the low levels of the atmosphere should keep the
precipitation from reaching the ground, and expect dry conditions at
all TAF sites through the rest of the this morning and afternoon.
Additional clouds and moisture will move in from the west this
evening ahead of a strong area of low pressure, resulting in lower
ceilings toward the end of the TAF period and reduced visibilities
from rainfall.


IN...Winter Storm Watch from late tonight through late Saturday night
     for INZ079.

KY...Winter Storm Watch from late tonight through late Saturday night
     for KYZ036-037-042-043.



Short Term...MJ
Long Term....MJ
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