Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 280456
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1156 PM EST Tue Jan 27 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 933 PM EST Tue Jan 27 2015

Nashville radar shows the light wintry precipitation has moved south
of the TN/KY border. Dry conditions are expected the rest of the
night. Just did a quick update to bring the forecast in line with
current conditions. Otherwise, it is in good shape.

Issued at 743 PM EST Tue Jan 27 2015

Have has some reports of some very light mixed wintry precip across
the far southwestern portion of the forecast area this evening.
Radar mosaic shows some light returns that continue to shift off to
the southeast. Did issue a short SPS for this activity as there have
been one or two reports of some very light accumulations on
secondary roads. This activity is expected to move out of the area
over the next couple of hours with dry conditions for the remainder
of the night. Updated the forecast to add in a few hours of the
mixed precip this evening.

.SHORT TERM (Now through Sunday)...
Issued at 255 PM EST Tue Jan 27 2015

Current satellite and observations show dry air advecting in from
the northeast.  Clearing line is working southwestward across the
forecast area.  Despite the clearing over in the Bluegrass,
temperatures have not really spiked up all that much with readings
generally in the lower 30s.  Further west, clearing is working in
and temperatures were in the lower to middle 30s.

In the near term, we expect the clearing line to work slowly to the
south and west through the evening hours.  Temperatures will fall
from the lower-middle 30s down into the mid-upper 20s this evening.
For the overnight period, the forecast challenge will be how far
southwest the clearing line will get.  Clouds are likely to hold
tough across our far southwestern CWA...but eventually clear out
toward dawn.  Winds are expected to be light and with the lower
dewpoints advecting in from the west, fog does not look to be a
concern at this time.  Overnight lows will be the coldest in the
Bluegrass region with readings dropping into the 10-15 degree
range.  Middle teens look likely across the I-65 corridor with the
warmest readings down across the west/southwest with lower 20s.

High pressure will drift across the region during the day on
Wednesday resulting in mostly sunny conditions.   Temperatures will
be slightly below seasonal normals with highs in the upper 30s in
the northeast to the mid 40s in the southwest.  Generally stuck
close to the bias-corrected Canadian GEM raw numbers here which have
verified well in the last few days.

High pressure will drift eastward into southern New England
Wednesday night.  A stronger southwesterly flow will pick up during
the evening and overnight hours.  Some weak isentropic lift will
push in late which will result in an increase in cloudiness early
on.  Some light precipitation will likely develop late tomorrow
night.  Temperatures will likely hit their lows around midnight and
then slowly rise through the overnight hours on the increasing warm
air advection.  Some precipitation that develops early enough may be
a wintry mix...especially across the Bluegrass region.  Overnight
lows look to cool into the lower 30s in the NE with mid-upper 30s
across the central and western areas.

.LONG TERM (Sunday night through Friday)...
Issued at 315 PM EST Tue Jan 27 2015

Thursday - Thursday Night...

A PV anomaly and it associated surface low will slide across the
lower Great Lakes on Thursday, swinging light precipitation and a
cold front through the area through late Thursday evening. Light
precipitation is expected to be ongoing in the morning and expect
that we might see a race against time in our NE between temperatures
rising above freezing and overrunning precipitation arrival. At this
time, its still looks like there could be potential for a brief and
light wintry mix in that region. Elsewhere, temp profiles look more
favorable for plain rain, although web-bulbs will be close to the
freezing mark so will still have to monitor over the coming forecast
cycles.

Any mix in our NE should change to all rain quickly on Thursday,
with measurable precipitation likely less than a tenth of an inch.
Cold air will move in behind the departing cold front Thursday
evening and try to change some of the lingering precipitation back
over to snow. As the previous forecast mentioned, p-type will be in
question as saturation will struggle to be above -5C. Will continue
to mention a mix changing over from west to east through
evening/overnight.

Expect Thursday to briefly get mild ahead of the front with highs
topping out mostly in the mid and upper 40s. Temps crash Thursday
night with lows finding their way to the 25-30 range.

Friday - Saturday...

Dry conditions return Friday through Saturday as surface high
pressure slides into the area underneath benign NW flow aloft. Highs
on Friday aren`t expected to make it out of the 30s, with some
improvement on Saturday into the upper 30s and low 40s. Lows Friday
night should be quite cool in the 20-25 range. Perhaps a few teens
could appear in our far east.

Saturday Night - Monday Morning...

...Continue to Monitor Potential for Wintry Weather...

Split stream flow will begin to converge over the eastern Plains
Saturday night, with a weakly coupled jet structure somewhere near
our just of the region. This should allow for cyclogenesis somewhere
near our CWA as the jet streams phase and organize deep moisture
over the area. Much like Thursday, will have a situation Saturday
night into Sunday morning where surface temperatures will be close
to freezing with overrunning precipitation winning the saturation
battle. Will start off with a wintry mix over a good portion of the
area Saturday night, however expect a warm sector to develop ahead
of the strengthening surface low, given the recent north trends. At
some point, expect mostly rain to take over, with our north possibly
holding onto a mix. The surface low then passes late Sunday
afternoon into the evening with cold air then wrapping back into our
area. This scenario would bring a change over back to all snow
through Sunday night, where much more robust moisture is likely to
be present.

The above scenario would play out, give a solution similar to the
27/12Z ECMWF. There are still plenty of available solutions that
could end up resulting in mostly snow or mostly rain. Likely won`t
be able to gain much more confidence on this potential wintery
precipitation until after our Thursday system. In other words,
confidence is low in saying anything more than there is a healthy
storm coming and all p-types are on the table at this point.

We would likely dry out through Monday with colder temps and some
sort of dry northwest flow taking over.

&&

.AVIATION (00Z TAF Update)...
Issued at 1156 PM EST Tue Jan 27 2015

Low clouds are slowly eroding at BWG and will be gone before flights
resume in the morning.  Otherwise, high pressure moving from the
Ohio Valley to the Appalachians will keep our weather quiet with
mostly clear skies and generally light winds.  A storm system
approaching from the west will increase winds and clouds at SDF
towards the tail end of this TAF period.

&&

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

$$

Update.........EER
Short Term.....MJ
Long Term......BJS
Aviation.......13





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