Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 270817

317 AM EST Tue Jan 27 2015

.SHORT TERM (Now through Wednesday)...
Issued at 302 AM EST Tue Jan 27 2015

Light snow and patchy freezing drizzle will push through the region
early this morning, with little more than a few flurries and a few
patches of very light freezing drizzle left over after the sun
rises.  Clouds will persist through much of the morning, but should
begin to break up this afternoon as drier air moves in.  Though
temperatures will be in the upper 20s early this morning, helping to
foster slick spots on untreated roadways, we should make it into the
middle and upper 30s most at most locations this afternoon (maybe
only lower 30s in the northern Blue Grass).  Winds will be light
from the north.

High pressure advancing from Chicago to Pittsburgh will provide us
with mostly clear/partly cloudy skies and light winds tonight and
Wednesday.  It will be quite chilly when the sun comes up Wednesday
morning, with readings ranging from 11 to 16 in the Blue Grass to 17
to 22 west of I-65.

.LONG TERM (Wednesday Night through Monday)...
Issued at 310 AM EST Tue Jan 27 2015

The start of the long term period is expected to feature weak upper
level ridging Wed night across the Ohio and Tennessee Valleys while
the east coast trough begins to move offshore. Upstream, we`ll be
watching a quick moving shortwave trough coming out of the Upper
Midwest. At the surface, high pressure likely will be centered along
the spine of the Appalachians.

The 27.00z guidance is in reasonable agreement taking the
aforementioned Upper Midwest shortwave through the lower Great Lakes
Thursday, keeping the local area with southerly flow Wednesday
night. Eventually, saturation and lift will begin to win out and
combined with the dry and sub freezing low levels may allow
precipitation to initially fall as a light wintry mix across
northeast KY before the low level temperatures warm into the upper
30s to low 40s. Overall, the best moisture/lift reside in the
low/mid levels and much of the precipitation should be on the
lighter side. The best timing for rain showers looks to be Thursday
morning to early/mid afternoon. The cold front pushes through the
area Thursday afternoon/evening and colder air begins to filter in
in its wake. We`ll have to watch for a brief changeover to wintry
precipitation on the back edge but this may end up being more of a
drizzle situation as there`s a lack of saturation above 850 mb /-5C/.

Northerly to northeasterly flow will then prevail Thursday night
into Friday as Canadian high pressure builds in from the northwest.
Lingering moisture could be trapped within the low level inversion,
keeping clouds in place Thursday night and into parts of Friday.
Otherwise, plan on lows in the upper 20s to lower 30s and highs
Friday to range from the mid to upper 30s. For Saturday, there`s
good consensus we`ll have weak zonal flow aloft with cool Canadian
high pressure at the surface. Likely to see increasing high clouds
from the west associated with the next storm system. Highs are
forecast to top out in the upper 30s to mid 40s.

Potential Wintry Weekend Storm System:

An active upper level flow late in the weekend could bring wintry
precipitation to the Ohio and TN Valleys. Split southern/northern
stream pieces of energy will traverse the central Plains while a
surface low takes shape somewhere along the Gulf coast.

The 27.00z GFS came in much warmer than its previous run thanks to a
stronger and more northwesterly surface low track /through
north-central KY/. This scenario would support an all-liquid event.
Meanwhile, the GEM remained the southern outlier, keeping the
surface low across AL/GA. This solution would result in snow for
most, with rain/snow line closer to the TN border. Finally, the
ECMWF lies in the middle, bringing the surface low through middle TN
and a rain/snow line somewhere across central/northern KY. For now,
leaned toward the ECMWF for a compromise, which blends well with the
previous forecast and neighboring offices.

However, a time trend analysis shows that the deterministic models
are struggling with this system, placing synoptic features all
across the OH/TN Valleys. Precipitation type/timing/intensity
confidence is well below average at this point. Given the
uncertainties, will still advertise the rain/snow mix possibilities
late Saturday through early Monday. Despite the lower confidence,
this system still has the potential to bring winter weather to the
region, so keep updated to the latest forecasts.


.AVIATION (06Z TAF Update)...
Issued at 1220 AM EST Tue Jan 27 2015

A small disturbance diving to the SSE will bring a brief period of
light snow to the region during the pre-dawn hours.  BWG will be the
most affected by the snow, with SDF on the eastern edge and LEX east
of the main axis.  IFR conditions are most likely at BWG, with
transient IFR ceilings possible at SDF for a couple of hours.

The system should be just south of the airports by the time the sun
comes up.  Low clouds will gradually lift today and clear out
tonight as high pressure enters the region from the north.




Short Term........13
Long Term.........ZBT
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