Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 142313
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
713 PM EDT Fri Mar 14 2014
...Updated Aviation Discussion...
Issued at 710 PM EDT Fri Mar 14 2014
The Wind Advisory was allowed to expire at 7 PM EDT. Still seeing a
few gusts up around 30 mph at this hour, however these will continue
to slacken early this evening and will remain below criteria. The
rest of the forecast is on track this evening as a cold front is
poised to pass through overnight. This frontal passage will be dry,
other than a few localized areas seeing some sprinkles.
.SHORT TERM (Now through Saturday Night)...
Issued at 255 PM EDT Fri Mar 14 2014
...Gusty Southwest Winds This Afternoon and Evening...
A cold front approaching from the west has tightened the surface
pressure gradient as it bumps up against the west side of high
pressure off the Carolina coast. As a result we`ve had some wind
gusts over 40 mph and have issued a Wind Advisory to cover those
winds for the remainder of the afternoon.
Tonight that front will cross the region, bringing clouds and
perhaps a few sprinkles with it. Winds won`t be as gusty this
evening but will still be brisk out of the southwest. The front
will cause winds to switch to the west and further decrease in
speed. Low temperatures tonight will range from the mid 30s to
lower 40s north to south.
Saturday should be a nice day as we sit between systems. Expect
mostly sunny skies, light winds, and afternoon temperatures peaking
in the 60 to 65 degree range.
Saturday evening clouds will thicken and lower as low pressure
deepens and advances from the Red River Valley to the Ozarks. A
warm front will set up, reaching eastward into the Tennessee
Valley. Light rain will spread from southwest to northeast,
bringing most people precipitation by the overnight hours. Right
now will have low temperatures ranging from the middle 30s in the
north to the middle 40s in the south. There is a slight chance of
some very brief, very light wintry mix well north of the Ohio River
after midnight, but chances are small enough right now that
we`ll just go with rain in the forecast.
.LONG TERM (Sunday through Friday)...
Issued at 300 PM EDT Fri Mar 14 2014
...A chance of a rain-snow mix late Sunday into Monday...
Upper air pattern early Sunday will feature a strong ridge across
the western CONUS and a split flow across the eastern CONUS depicted
by a northern jet across the upper Great Lakes and a southern jet
across the Gulf Coast States. A positively tilted trough will
stretch from Texas to the Great Lakes. A strong jet rounding the
western CONUS ridge will dive southward into the southern jet
stream. This will strengthen the positively tilted trough as it
pushes east and crosses the lower Mississippi Valley late Sunday.
Just how strong the system becomes remains the key question, as
models do differ on strength. There is better consensus that the
mid-level trough will remain an open wave, as opposed to the NAM
solution, which really strengthens the system and closes the
mid-level low. Either way, the trough axis eases across western
Kentucky early Monday and exits our eastern CWA by mid morning, with
a surface low traversing the Tennessee Valley.
With our area being on the northern side of the surface low, gusty
northeasterly winds are expected Sunday and will usher in some
cooler air through the day Sunday. We should have a cold rain
ongoing across much of the forecast area Sunday morning,
overspreading from the southwest. Do not expect much warming at all
Sunday. Temperatures ranging from middle 30s north to upper 40s
south will likely hold steady through the morning before cooling in
the afternoon. Combining these temps with gusty gradient winds and
rain will make for quite a raw day Sunday.
By late Sunday, a dry slot will begin to develop across the
Tennessee Valley, as the 850 hPa low tracks directly over our
forecast area. At the same time, a deformation precip band is
expected to become established along the Ohio River. Surface and
boundary layer temperatures should cool enough for rain to change to
snow across southern Indiana and northern Kentucky during the late
afternoon and evening hours. This type of system is one that could
bring 2-4 inches (perhaps locally more) of accumulating snow within
the heart of the deformation band. However, the exact placement of
that band remains uncertain. A stronger system (i.e., the NAM) would
push this snow farther north and provide more sleet and possibly
freezing rain just south of the snow. Going with a model consensus,
however, places the band generally across southern Indiana and
northern Kentucky, with some sleet and maybe light freezing rain
just south of the snow line.
Three items that may limit snow totals are a warmer layer aloft,
perhaps a loss of deeper moisture aloft, and warm ground conditions.
If the system is a bit stronger and more warm air aloft is pulled
northward, we might be talking about more sleet and perhaps some
freezing rain. Also, the ECMWF/NAM/GFS now indicate moisture begins
to diminish above 600 or 700 hPa Sunday evening. This would greatly
limit ice crystals, leaving a lot of supercooled droplets for
possibly a mix of sleet and freezing rain. Additionally, the recent
warm temperatures have really warmed the ground temps, which should
reduce the snow/frozen precip totals a bit, at least at onset. Still
too early to nail down precip types and accumulations, particularly
since model sounding profiles differ, but have started adding more
mixed precip into the forecast. Precipitation should taper off from
northwest to southeast late Sunday night through early Monday.
Temperatures Monday will depend highly on what precip falls Sunday
night. With some clearing late, highs in the upper 30s to middle 40s
are possible Monday afternoon. Dry conditions will continue Monday
night and Tuesday. Southerly winds will increase Tuesday ahead of
our next weather system, which should help boost temps into at least
the 50s, perhaps a little warmer across the south.
A shortwave trough approaches our area late Tuesday or Wednesday,
with a cold front passing through the area Wednesday afternoon or
evening. There are model timing and strength differences with this
system. This will continue the warmer temperatures into Wednesday
and provide a chance of showers. Thunder with this system still
appears limited, but will continue to monitor trends. Highs
Wednesday are expected to be in the 50s, perhaps a little warmer
depending on the strength of the system. Temperatures may be a
couple degrees cooler Thursday under northwest flow, with similar
temperatures expected Friday. We should remain dry Thursday through
.AVIATION (00Z TAF Update)...
Updated at 708 PM EDT Fri Mar 14 2014
Expect VFR conditions through this forecast cycle. Southwest winds
are still gusty early this evening, however will continue to slacken
over the next couple of hours with the loss of daytime heating.
Meanwhile, a relatively dry cold front will pass through overnight,
with only some mid and upper level clouds associated with it. A few
sprinkles are possible, however terminals are not likely to see any
negative impacts. Will continue to mention a brief LLWS threat at
the terminals before the front passes as a 40 knot LLJ will ramp up
and combine with a sharp inversion below 1800 feet AGL.
Expect winds to be light out of the west toward dawn, before
becoming light and variable on Saturday as surface high pressure