Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 311043
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
643 AM EDT Fri Oct 31 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Saturday)...
Issued at 300 AM EDT Fri Oct 31 2014
...Windy Conditions and Falling Temperatures Expected Today...
...Wintry Mix Likely This Evening Changing to Snow with Minor
Accumulations Possible East of I-65...
Short Term Synopsis
In the near term, first in a series of upper level waves is
transversing the region. This will bring mostly cloudy skies to the
region early this morning with scattered showers moving through the
area. Associated with this lead wave is a surface cold front off to
the northwest. This feature will swing through the region and allow
much colder air to filter into the region from the NW this morning
and through the afternoon hours.
Secondary/potent and unseasonably strong upper trough will drop
nearly southward out of the Great Lakes and into the eastern Ohio
Valley tonight. This feature, combined with strong cold air
advection aloft will result in quite a bit of lift in the atmosphere
to produce widespread shower activity. As the colder air aloft
descends further toward the surface this evening, the rain showers
will change to a wintry mix before ending a snow showers late
tonight and Saturday morning. Some of the snow showers this evening
may occur in bands and may be locally heavy...resulting in minor
snow accumulations in areas mainly east of I-65. The strong upper
trough will pull off to the south and east during the day on
Saturday resulting in drier conditions moving in from the W/NW...but
unseasonably cold temperatures are expected.
Model Preference & Confidence
Tonight`s model guidance continues to show relatively good
continuity from previous runs and are generally in good agreement.
The multi-model consensus suggests higher probabilities of
precipitation today with the two systems moving through the region.
Thus, will be increasing PoPs for this afternoon and evening. All
model data suggest the pressure gradient will increase and
northwesterly winds of 15-20 MPH with gusts up to 30-35 MPH will be
possible late this afternoon and evening. The higher resolution
models continue to show the strong potential for TROWAL formation on
the backside of the upper wave coming through the region tonight.
These TRAWL`s`s can set up banded heavy precipitation and with
thermal profiles crashing tonight from top to bottom, current
thinking is that some bands of moderate to heavy snow will be
possible across our eastern areas. Snow accumulations will continue
to be a challenge as the snow will be fighting relatively warm
ground temperatures and there is some uncertainty where any banded
Have generally favored the short term multi-model consensus for this
forecast. Have generally used a blend of the SuperBlend model
guidance for hourly T/Td which is fairly close to the raw 2m temps
from the NAM/GFS...but slightly cooler than the statistical MOS. We
expect precipitation to gradually diminish late tonight as upper
level forcing exits the region and a decent push of drier air works
in aloft from the NW/W. This drier air will infiltrate the entire
region during the day on Saturday.
Forecaster confidence on precipitation chances are higher than
average for Today and Tonight given the relative low spread in the
deterministic and ensemble guidance. Forecast confidence on
temperatures is also higher than average for Today and Tonight.
Medium confidence on temperatures for Saturday exists due to
lingering uncertainty in how much clearing will develop from west
to east during the afternoon hours.
Sensible Weather Impacts
For today, cloudy conditions with passing rain showers will be the
rule across the region. Daytime high temperatures will occur this
morning prior to the cold front pushing through the region. Highs
will range from the upper 40s in the northwest to the lower 50s in
the southeast. Once the front clears the area this afternoon,
northwesterly winds will pick up and sustained winds of 15-20 MPH
with gusts of 30-35 MPH will be possible this afternoon and evening.
Temperatures are expected to fall throughout the afternoon and
evening and will likely cool into the upper 30s to around 40 by
early evening. As the evening wears on, colder air aloft will work
its way downward and allow precipitation to mix with snow. It
appears that all precipitation will likely end as snow showers as
thermal profiles cool sufficiently. At this time, rain will be the
pre-dominant precipitation type through early evening with a
rain/snow mix beginning around 7-8 PM and then a complete change
over to snow occurring by 11PM to Midnight. Surface temperatures
this evening will likely remain above freezing. Thus any mixed
precipitation will not accumulate on roadways and hazardous road
conditions are not expected. The combination of falling
temperatures and gusty winds will lead to wind chill readings
falling into the upper teens to the lower 20s.
Late tonight, temperatures will approach the freezing mark...most
likely after 3 AM or so. Light snow will likely be ongoing in areas
east of I-65 and if banded precipitation sets up, the snow may be
moderate to occasionally heavy at times. The snow will be fighting
off relatively warm ground temperatures, so accumulations will be
difficult unless moderate/heavy precipitation occurs. With this
thinking in mind, we feel some minor accumulations will be possible
in the eastern third of our forecast area...east of I-65. The
highest chances of accumulation looks to be generally in areas east
of US 27/127. Accumulations of a dusting to a light slushy
accumulation mainly on grassy and elevated surfaces will be possible
in this area.
Out west of I-65, some clearing will take place as this area will be
further west and in the more drier air. If clearing takes place,
temperatures will have the potential to drop to around 30 degrees.
The pressure gradient will likely remain elevated enough to preclude
frost formation. With temperatures expected to be close to
freezing, will leave the current freeze watch in place to preserve
continuity. However, it appears that Saturday night will be much
more favorable for a season ending, killing freeze.
For Saturday, the upper trough will pull away from the region.
However, low clouds and some light precipitation may still be
ongoing out across our far eastern sections. Slow clearing will
work across the central parts of the region. It will be a
cool/crisp day with high temperatures only warming to around 40 in
areas east of US 27/127 with lower to middle 40s possible out in the
I-65 corridor and points west.
.LONG TERM (Saturday Night through Thursday)...
Issued at 244 AM EDT Fri Oct 31 2014
...Sub-Freezing Temperatures Expected Sunday Morning...
Cold high pressure will move directly over the region Saturday night
into Sunday morning. Any lingering clouds Saturday evening across
the Bluegrass should clear out overnight. This will lead to a decent
setup for radiational cooling with the lowest temperatures of the
season expected. Lows on Sunday morning are expected to drop into
the mid to upper 20s in most locations, though the Louisville metro
may stay right around 30. These temperatures should put an end to
the growing season.
High pressure will shift east through the beginning of next week and
heights will build aloft. Temperatures will gradually warm through
Tuesday. While highs on Sunday will reach only into the upper 40s to
lower 50s, highs on Tuesday will be back into the mid 60s. Morning
lows will correspondingly increase to the lower 50s by Wednesday
The next system will affect the area midweek as a low pressure
system across Canada swings a cold front through. A few showers may
be possible Tuesday afternoon ahead of this front. However, the bulk
of the precipitation should move through Tuesday night and Wednesday
with showers likely across much of the area. Showers will move out
Wednesday night with just a few lingering in the east Thursday
morning. This front will bring cooler temperatures for the end of
next week, though they are not expected to be nearly as cold as
temperatures this weekend.
.AVIATION (12Z TAF Update)...
Updated at 642 AM EDT Fri Oct 31 2014
First in a series of mid-level disturbances is moving through the
region this morning. This has brought widespread clouds and light
precipitation. Expect ceilings to hover around the MVFR/VFR
threshold this morning with precipitation moving east of KBWG/KSDF
by 31/14Z and then exiting the KLEX terminal by 31/15Z time frame or
so. As we see a brief lull in the precipitation, winds will shift
to the northwest and start to pick up.
For this afternoon/eve, widespread shower activity should pick up
once again as a stronger and more potent upper level wave dives out
of Wisconsin and toward eastern KY. This will bring an increase in
winds from the NW with sustained speeds of 12-16kts and gusts up to
25-30kts. Rain showers and MVFR ceilings are expected at the
terminals. Colder air will push into the region this evening
resulting in the rain showers changing over to snow showers. Snow
will likely bring the most impact over at KLEX where MVFR cigs/vsbys
will be possible after 01/03Z.
KY...FREEZE WATCH from late tonight through Saturday morning FOR
FREEZE WATCH from Saturday evening through Sunday morning FOR
IN...FREEZE WATCH from late tonight through Saturday morning FOR
FREEZE WATCH from Saturday evening through Sunday morning FOR