Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 062302

Area Forecast Discussion
National Weather Service Louisville KY
602 PM EST SAT FEB 6 2016

...Updated Aviation Discussion...

.SHORT TERM (Now through Sunday Night)...
Issued at 310 PM EST Sat Feb 6 2016

Afternoon satellite imagery and surface observations reveal partly
cloudy skies across the region.  Temperatures were generally in the
upper 40s where clouds were located while areas that had more
sunshine were in the lower 50s.  We expect temperatures to hit their
daily maximums in the next 1-2 hours and then see temperatures fall
back into the lower-mid 40s during the evening hours.  High pressure
will drift off to the east overnight, but the area will see mostly
clear skies.  With high pressure to our east and an approaching
system to the west, we`ll see a light southwesterly flow overnight
which will keep temperatures up a bit.  Overnight lows look to cool
into the mid-upper 20s in the east with mainly upper 20s in the
central (I-65 corridor) and western sections.

We`ll see mid-high level cloudiness spread back into the region late
Sunday afternoon. However, Sunday will be a dry day across the
region.  Surface pressure gradient should also increase as well so
conditions will be breezy.  Afternoon high temperatures should warm
into the upper 40s to lower 50s in the east with mainly lower-mid
50s in the central and southwest sections.

A surface cold front will approach the region from the northwest
Sunday night.  Skies will cloud up quickly during the evening and
some light precipitation should start to break out from NW to SE
during the overnight hours.  Lower boundary layer temperature
structure continues to look warm enough for mostly liquid
precipitation to fall, though can not rule out some light snow
mixing in at times across our far northern southern IN counties.
Overnight lows will likely cool into the lower 30s in most

.LONG TERM (Monday through Saturday)...
Issued at 318 PM EST Sat Feb 6 2016

...Winter Returns To The Ohio Valley Next Week...

Monday through Wednesday Night...

Global teleconnection pattern of -AO/-NAO/+PNA/-EPO will result in a
colder pattern over the eastern half of North America early next
week.  Driving the amplification is the high latitude ridging over
the western CONUS (+PNA) which will result in an anomalously deep
trough developing over the eastern US.  The global models have been
advertising this for well over a week, though finer details are
starting to become more apparent.  In terms of model trends, the
models continue to have good agreement aloft with the trough
developing and the eventual closing off of the upper low.  The trend
over the last few days however, has the closed low more to our
north/northeast along with the slug of coldest air passing through
the Great Lakes and into the interior northeastern US.

As the upper trough digs in and closes off, we`ll see plenty of low
level moisture and very cold air pouring into the region from the
northwest.  Several perturbations aloft will rotate around the
closed low bringing multiple rounds of precipitation to the region
from Monday through late Tuesday night.  Initial precipitation on
Monday will likely be in the form of rain and snow due to a lack of
sufficient cold air depth near the surface.  This will be a temporary
situation as colder air will mixdown and additional cold air will be
pulled in from the northwest throughout the day.  Precipitation will
likely be in the form of light snow by afternoon and will continue
into Monday night.  With near surface temperatures remaining near
freezing, snowfall accumulations will likely be quite limited during
the day on Monday.  Temperatures will start off the day in the lower
30s and may see a small diurnal rise in the morning hours into the
lower-mid 30s before crashing back into the upper 20s to lower 30s
by evening.

By Monday night and Tuesday, combination of very cold air aloft and
plenty of low-level moisture will result in snow showers across the
region.  Model proximity soundings do show some periods of increase
instability so periods of moderate to occasionally heavy snow
showers will be possible.  In addition to the snow, gusty
northwesterly winds are likely resulting in reduced visibilities at
times along with some blowing snow.  Snow showers will continue into
the day on Tuesday and then start to diminish from west to east
Tuesday night as the upper level low moves off to the east and the
upper trough axis also shifts to the east.

In terms of snowfall potential, there remains a bit of spread in the
deterministic runs on QPF amounts.  In addition, we`re likely to see
a very sharp gradient in precipitation from our western sections to
our eastern sections.  Out across the west (west of I-65), we`re
likely to see a few hundredths of QPF to maybe a tenth, while two to
three tenths of liquid QPF will be possible out in the east.
Combining this with snow ratios starting off at 11-12:1 and then
increasing to 19-20:1 by the end of the period would result in a
gradient of snowfall across the region.

The SREF ensembles are generally lighter in the QPF department as
well with the ARW core members showing higher QPF amounts than the
NMM counterparts.  The ARW cores are likely picking up on the
potential for convective snows. Though, we should note in the last
major snow event that the NMM cores performed much better than the
ARW cores.

Utilizing the above QPF and snow ratios, it appears that a total of
1-2 inches of snowfall will be possible in areas along and west of I-
65...with amounts of 2-3 inches possible east of I-65 out toward the
I-75 corridor.  Given that we`ll be on the SW side of the cyclonic
flow, we expect slightly higher amounts just to our east and
southeast given the orographical lift component.  These anticipated
accumulations are very close to the existing forecast, so forecast
continuity has been preserved.

As for temperatures, the trend in the blended guidance has been
slightly cooler in the most recent runs.  Lows Monday night look to
cool into the lower 20s with highs on Tuesday warming into the mid-
upper 20s.  Lows Wednesday morning will depend on snowpack and if we
see any clearing.  Current model blends suggest lows in the lower-
middle teens at this time.  Highs on Wednesday look to warm into the
lower-mid 20s in the north with mid-upper 20s across the far south
and southwest.

Thursday - Saturday...

Overall, not much change in the forecast thinking through this
portion of the forecast period.  We`ll remain in a broad northwest
flow during the period as a mean trough axis will be parked across
the eastern third of the US.  The core of the cold will be shunted
off to our east, so a moderation in temperatures is expected.  Will
continue to watch for the potential for another fast moving clipper
that may move through the region Thu/Fri.  The GFS is a bit more
aggressive through the period with these systems while the Euro is a
bit weaker.  These systems could bring another period of light snow
along with some additional accumulations.  For now, have trended
temperature forecasts close to the ensemble means to resolve the
differences in the deterministic runs.  Highs Thu-Sat will likely
warm into the 30s in the north with some low 40s in the south,
overnight lows will range from the teens to the lower 20s.


.AVIATION (00Z TAF Update)...
Updated at 545 PM EST Sat Feb 6 2016

VFR conditions and generally SW flow expected through the valid TAF
period. Mid/high clouds are already dissipating and skies should
clear early this evening. Light winds overnight will pick up out of
the SW late Sunday morning, with sustained speeds just over 10 kt
and gusts falling just short of 20 kt during the afternoon. Mid-
level clouds will develop in the warm advection regime, but will
keep ceilings out until at least 00Z Mon.

For the planning period at SDF, look for a ceiling to develop and
gradually lower as mid-level winds back and increase, but it will
remain solidly VFR. Will hold off any precip until beyond the end of
the TAF given the lack of low-level saturation.


.LMK Watches/Warnings/Advisories...


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