Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 170510
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1210 AM EST Wed Dec 17 2014
...Updated Aviation Discussion...
Issued at 906 PM EST Tue Dec 16 2014
The forecast is largely on track tonight, although a couple of minor
issues to address. Enough low level moisture remains trapped under
the 875mb inversion that patches of drizzle and even a few
measurable rain showers will be able to persist for several more
hours across our NE. This activity should stay mainly confined to SE
Indiana and our northern Bluegrass counties. Thermal profile should
remain mostly warm enough for liquid, however with the increasingly
cooler low levels advecting into the region, some frozen
precipitation in the form of ice pellets cannot be ruled out. A few
have been reported in southern Indiana recently. Moisture does not
appear to be deep enough (saturated to temps above -5C) to promote
ice crystals for snow, although the further north and east you get
the possibility cannot be ruled out. Have updated the grids to
linger slight chances of measurable rain and drizzle for a few more
hours, comibined with a small chance of light snow in our most
extreme NE counties. Will leave mention of any ice pellets out due
to the lack of impacts. Sub-freezing surface temps should lag a
couple hours behind the deepest moisture so not expecting any road
Also, increased sky cover for tomorrow. Most areas should stay
mostly cloudy except for our far SW where some breaks in the low
clouds are anticipated by midday.
.SHORT TERM (Now through Thursday Night)...
Issued at 610 PM EST Tue Dec 16 2014
Medium confidence in the short term. Although the main cold front
will exiting the east coast by tonight...there is a secondary or
reinforcing cold front expected to move this evening. This combined
with wrap around moisture from the low could result in drizzle or
even some light rain this evening. Nothing significant is expected
overnight. The next system worth mentioning could bring some wintry
precip to the area...mainly along and south of the West KY Parkway.
At this time we could see trace amounts across central KY averaging
around a half inch along the TN border. We could see brief mixes
with sleet or freezing rain or sleet. But should only see trace to a
hundredth of ice if any falls at all. In addition if the temps are
one to two degrees warmer than forecast we could see liquid precip
which would negate snow accumulations a great deal.
.LONG TERM (Friday through Wednesday)...
Issued at 610 PM EST Tue Dec 16 2014
Thursday night through Tuesday...
Medium confidence in the extended at best due to the migration of
the next storm migrating southward from model run to model run.
The ECMWF seems to have the most stability from run to run but the
12z Tue run was slow to come in today. The gulf will open up ahead
of the next system allowing adequate moisture to flow back into
the region ahead of an upper level disturbance make its way onto
the west coast now. This upper level system does have surface
reflection as a surface low which marches across the gulf states.
This is a little far south for the most favorable path to produce
snow for this area. However as previous discussion stated we will
be on the northern portion of the precipitation shield. This
system will Friday night into Saturday according to model and
office consensus. After that high pressure will take over until
the middle of next week when the next system arrives.
As for temps...they appear to be near normal through the period.
.AVIATION (06Z TAF Update)...
Issued at 1205 AM EST Wed Dec 17 2014
IFR/MVFR conditions are expected for a large portions of this TAF
period. LEX looks to see the worst flight conditions for the
longest period of time. Low level moisture trapped below an
inversion will result in low clouds for much of the morning hours
for all TAF sites. Light drizzle will continue on and off at
SDF/LEX through around 9-11Z. The low clouds will slowly erode from
southwest to northeast today with BWG/SDF likely returning to VFR
late in the TAF period. LEX will probably stay MVFR through this
TAF period. WNW winds will remain between 6-10 kts overnight
decreasing to 4-7 kts for the daylight hours today.