Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 190504
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
104 AM EDT Sun Oct 19 2014
...Updated Aviation Discussion...
Issued at 937 PM EDT Sat Oct 18 2014
Forecast remains largely on track this evening. Earlier showers over
the Bluegrass region have pushed southeast. Mostly cloudy skies
were noted across the region. Some breaks in the overcast have
developed across portions of northern KY...just south of the Ohio
River. Current thinking is that this is just some temporary breaks
as upstream clear pockets have clouded back up. Still believe that
skies will eventually clear late tonight from west to east.
However, the clearing trends are going to likely be a little later
than the models say.
We have updated the forecast to remove the earlier rain chances that
were in the forecast. Also adjusted the sky cover grids to better
match radar trends. Overnight lows still look to cool into the
upper 30s to the lower 40s...depending on the erosion of cloud
cover. If clearing takes place earlier, then overnight mins will be
cooler than forecast. Some patchy fog will be possible late tonight
in the river valleys. In those areas that get cold enough, some
patchy frost will also be possible. The expected cloud cover and
limited radiational cooling suggest that frost will be patchy at
Update issued at 632 PM EDT Sat Oct 18 2014
Did a quick update to push PoPs a bit higher out across the
Bluegrass region as a band of showers passes southeastward
through that part of KY. Expect the rain showers to continue for
the next 2-3 hours and then diminish.
A rather large amount of low-level cloudiness remains to our
northwest and the cloud shield is advecting SE. The latest model
data still suggest that much of this will mix out this evening and
into the overnight hours. We believe that the models are probably
too fast with this...and it will be a little later before things
clear out. This current thinking supports the current
forecast...albeit that cloud grids may have to be increased this
evening and into overnight accounting for the slower clearing
trend. Wind forecasts still show winds staying up tonight as
well...thus radiational cooling effects look to be very minimized
at this point. Current overnight low temps still look good with
upper 30s...though these could be lower if the clouds clear out
faster than expected. Frost production looks to be quite limited at
this time and we will continue to look at the early evening data and
evaluate that threat with the next update.
.SHORT TERM (Now through Sunday Night)...
Issued at 301 PM EDT Sat Oct 18 2014
...Some Patchy Frost Possible Tonight...
Clouds have spread across the region this afternoon and though there
may be a few peeks of sunshine from time to time, they are expected
to remain in place for the remainder of the afternoon. A shortwave
diving southeast through the upper level flow has generated a batch
of showers across central Indiana. These showers will continue to
move southeast as the shortwave does. It still looks like the best
chance for some light showers this afternoon into early evening will
be across southern Indiana and north central KY. These should move
out by 03Z tonight with dry conditions expected for the remainder of
the short term period.
High pressure will begin to build in from the west tonight. With
this, clouds are expected to begin to clear from the west this
evening and continue overnight. How fast these clouds will clear out
is certainly a question and will have an impact on low temperatures.
For now we have most of the clouds clearing out by early tomorrow
morning, but they potentially may hang on longer than that.
Temperatures tonight will drop into the upper 40s by around midnight
and into the upper 30s to around 40 by sunrise. Winds will become
light overnight, though do not think they will go completely calm in
many locations. Given temperatures will stay in the upper 30s and
questions remain about clouds, areas of frost are not expected to
develop. There could be some very patchy frost in sheltered
locations with the best chance across southern Indiana. If clouds
linger longer, however, temps may be a few degrees warmer and
prevent frost development.
High pressure move right across the area tomorrow with mostly clear
skies and light winds expected. Highs will be in the upper 50s to
lower 60s. Clouds will be on the increase tomorrow as another
disturbance approaches. Lows will be a few degrees warmer tomorrow
night in the lower to middle 40s.
.LONG TERM (Monday through Saturday)...
Issued at 300 PM EDT Sat Oct 18 2014
The upper air pattern over the CONUS will amplify Monday, with
somewhat of a ragged Omega Block setting up centered over the
Continental Divide. A trough at 500mb will dive southeast across the
western Great Lakes early Monday, become vertically stacked with its
associated surface low near the mid-Atlantic States, and eventually
form a closed low near New Jersey by late Wednesday. A sharp ridge
over the eastern Rockies will move little, and will lie over the
Missouri Valley by Wednesday as well.
Temperatures will rebound just a bit Monday under light
southwesterly winds ahead of an approaching surface trough
associated with this Great Lakes shortwave. Cloud cover will
increase and some scattered sprinkles or light showers may develop
by afternoon or evening due to weak convergence along this surface
front. With negligible moisture return and stronger forcing well to
our northeast, any rainfall amounts Monday will likely stay less
than one tenth of an inch. Expect highs Monday to rise into the
lower to mid 60s.
Surface high pressure building across Wisconsin will bring northerly winds
and cooler temperatures Tuesday. With the blocky nature of this
upper air pattern, this high won`t move much. Even by Thursday,
expect a continuation of light northeasterly winds. Skies may become
partly cloudy by early Tuesday, but clearing may be slow on Tuesday,
with the potential for strato-cu on the west side of the
mid-Atlantic`s closed low possibly extending as far west as the
Clearing should arrive late Tuesday and basically clear skies should
continue through Friday as subsidence develops across the eastern
edge of the slowly approaching 500mb ridge.
Aside from Monday`s potential for some light rain, this whole
upcoming work week looks dry, with a very good potential for nice
weather for this upcoming weekend as well. Temperatures Tuesday
through Thursday will remain cool, with highs not exceeding 60 by
much. Thursday and Friday will warm into the mid to upper 60s.
.AVIATION (06Z TAF Update)...
Updated at 101 AM EDT Sun Oct 19 2014
The main question for the early morning hours continues to be a
stubborn stratocu deck plaguing the TAF sites. Will continue with
the pessimistic forecast as higher resolution models indicate that
low clouds will survive at SDF/LEX past sunrise. Also, forecast
models usually show a bias toward clearing low clouds out too
quickly. Ceilings are currently just above the MVFR/VFR threshold,
however do expect them to drop around or after 4 AM EDT, likely
lasting through mid to late morning. The deck is then expect to
rise and scatter as we head into the afternoon hours. Surface
winds will be light and variable during this time as surface high
pressure settles over the area.
Will keep a more optimistic forecast for the BWG area, where only
some light fog/mist and a few/sct low clouds should impact the
terminal until just after sunrise. Thereafter, expect few/sct clouds
with light and variable winds.