Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 270527
Area Forecast Discussion
National Weather Service Louisville KY
1227 AM EST FRI NOV 27 2015
...Updated Aviation Discussion...
Issued at 915 PM EST Thu Nov 26 2015
Weak southerly flow across the Ohio Valley this evening, but thicker
clouds remain well to our north and west. Temps have dropped well
into the 40s in some of our eastern valleys, while readings are
still near 60 along and west of I-65. As the clouds thicken
overnight, and knowing typical model biases in pre-frontal southerly
flow, expect we will have a hard time dropping more than a few
degrees. Thus have bumped mins up a couple degrees overnight, except
where temps have already bottomed out.
.SHORT TERM (Now through Friday Night)...
Issued at 255 PM EST Thu Nov 26 2015
In the near term, skies have remained partly to mostly sunny across
the region. This has led to a mild Thanksgiving day with highs the
mid-upper 60s. There have been a few 70 degree readings out to our
west and we could top 70 here at SDF in the next 1-2 hours. Dry and
mild conditions will continue into the evening hours with
temperatures falling into the mid-upper 50s.
For tonight, another dry night is expected as the latest suite of
guidance has continued to slow down the eastward movement of the
approaching weather system. For this reason, have backed off PoPs
in the west and have lowered cloud cover amounts in most
areas...especially the east. We`ll likely see a gradient of
overnight low temperatures with upper 40s to lower 50s in the east
and lower 50s from I-65 and points west.
On Friday, the slower movement of the frontal boundary to the east
will result in some changes to the ongoing forecast. It is likely
that areas east of I-65 will remain pretty much dry throughout the
day on Friday. A strong gradient of precipitation looks to develop
out to our west, with generally slight chance to chance PoPs in
areas west of I-65. In fact, the highest PoPs on Friday would
likely be contained to the Pennyrile region of KY and points west.
Therefore we have backed off PoPs a bit in this forecast issuance.
We also backed off the cloud cover as well. This has a net result
in warmer temperatures because of the lesser amounts of clouds and
precipitation expected. Highs on Friday look to warm into the lower
60s across our far NW with mid-upper 60s elsewhere. The warmest
areas will probably be along and east of a line from Lexington to
By Friday night, the frontal boundary looks to nose a little more
toward the east. Current thinking is that expansive precipitation
shield to the west will march eastward overnight. Highest chances
of precipitation look to be in areas generally west of I-65 with
lesser chances as one heads eastward. We have slowed the
precipitation expansion to the east a bit more than in the previous
forecast, while increasing our PoPs across the far west and
northwest sections. A southwesterly surface flow will keep
temperatures mild with lows only cooling into the upper 40s to the
.LONG TERM (Saturday through Thursday)...
Issued at 307 PM EST Thu Nov 26 2015
As we head into the middle of the holiday weekend, aforementioned
frontal boundary will sink southward into the Ohio Valley and then
stall out across the region through Sunday. As this occurs, a deep
moisture plume, courtesy of the subtropical jet will feed a steady
stream of moisture into the region. Instability and forcing are
expected to remain marginal for thunderstorm development. Main
forcing here is isentropic in nature. That combined with well above
normal for late November PWATs (1-1.5 inches) will result in
moderate to occasionally heavy rainfall. With this said, we plan
to go with higher PoPs in this forecast for Saturday through Sunday
Highs Saturday will likely top out int he low-mid 50s in the north
with upper 50s to around 60 in the south. Sunday`s highs will be
cooler with the frontal boundary pushing a bit further south. We
could end up with a bit of a gradient on Sunday depending on the
frontal position. For now, have gone closer to the SuperBlend
guidance here which results in lower 50s across the north and mid-
upper 50s across the south. Overnight lows through the period will
be mainly in the 40s.
As we head into next week, the upper flow will flatten out a bit
across the Ohio Valley as faster flow pushes into the desert
southwest and begins to kick out the upper low in the intermountain
west. As the upper low rolls eastward, we`ll see another surface
wave of low pressure develop to our southwest and move northeastward
through the area. This feature will bring more clouds and continued
precipitation chances through Tuesday. Instability and forcing with
this secondary system still looks marginal and thunderstorm risks
look very low at the moment. For now, plan on continuing at least
likely PoPs going through Monday night with diminishing PoPs from
west to east during the day on Tuesday. Temperatures are not really
going to show much diurnal variation through the period with highs
generally in lower 50s with overnight lows in the upper 40s.
As for total QPF with this system, there is not much change in the
QPF fields through Tuesday with this forecast. Current forecasts
suggest 1.5 to 3 inches of total rainfall through Tuesday. This
rainfall, falling over a rather extended period should preclude any
water issues. However, rises on area lakes and streams looks likely
early to the middle part of next week.
By midweek, closed low pressure system aloft will likely roll
eastward and to the south of a mid-level positive height anomaly
over Canada. This would generally result in a track from the
Midwest into the interior Northeast and we should see temperatures
come back down to seasonal early December levels for Wednesday and
A secondary mid-level wave over the central Plains looks to close
off and head eastward by late week. This may result in a secondary
system developing to our south and east as suggested by the last few
Euro runs. The GFS is showing its typical bias of over powering the
northern stream and resulting in more zonal/progressive flow over
the eastern US. We`ll have to watch this secondary system for
additional development. Colder than normal temperatures do not look
likely during this period as the EPO is expected to go positive
again and the zonal flow across the western US allows mild/modified
Pacific air to flow across much of the CONUS.
.AVIATION (06Z TAF Update)...
Updated at 1226 AM EST Fri Nov 27 2015
A cold front will slowly edge toward the TAF sites during this
forecast period, reaching the Ohio River tonight. High ceilings
early this morning will slowly lower over the course of the day but
will stay well VFR. (There is also a chance of some VFR lower clouds
forming this morning, especially at BWG and SDF.) Scattered showers
should hold off until tonight.
Winds will come in from the south throughout the TAF period, and may
get a little gusty during the daylight hours today.