Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 221912
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
312 PM EDT Wed Oct 22 2014
.SHORT TERM (Now through Thursday Night)...
Issued at 310 AM EDT Wed Oct 22 2014
...Frost Advisory in Effect for Late Tonight into Thursday Morning...
Upper level ridging aloft and sfc high pressure will move into the
Ohio Valley late tonight providing for good subsidence across the
region. Clear skies and light winds are expected overnight and
combined with the subsidence, this should provide an ideal rad
cooling night causing sfc temps to fall into the 33-39 degree range
with perhaps valley/sheltered locations dipping closer to the
freezing mark. These temps combined with low level moisture should
result in frost formation. However, the extent of frost formation
is unknown since current dewpts are running in the 35-40 degree
range and overnight dewpts are not expected to drop below freezing.
This may result in a heavy dew and perhaps some light fog and
prevent frost formation. Will go ahead and issue a frost advy from
9z-13z late tonight into tomorrow morning though assuming at least
areas of frost will form in rural locations. Those with sensitive
outdoor plants should take precautions to protect them from frost.
After a chilly start Thursday, expect temps to warm into the upper
50s and lower 60s Thurs afternoon. Upper level clouds will increase
throughout the day.
Thursday night a dry front will approach the area bringing increased
cloudiness. Low temps will range from the mid 40s west of I-65 to
upper 30s/lower 40s east of I-65.
.LONG TERM (Friday through Wednesday)...
Issued at 245 PM EDT Wed Oct 22 2014
Main forecast concerns in the long term are a shortwave trough
passing through Friday then the next chance for rain during the
middle of next week.
A shortwave trough that currently resides across the northern
Rockies will advance eastward across the Great Lakes region
Thursday, then dip southeast toward the Ohio River valley on Friday.
22.12z guidance continues to show a spread in regard to its
strength, with the ECMWF the stronger outlier. However, its solution
has trended weaker and flatter compared to the 00z run. Despite the
upper level forcing, high pressure at the surface and the drier
mid-levels are expected to keep sensible weather limited to just
passing mid/high level clouds Friday. Given this trend and
environment, continued a dry forecast Friday for the area.
In the wake of this system, northwest flow aloft will remain in
place through Sunday with the 500 mb ridge axis extending along the
mid-Mississippi River valley. At the surface, a weak front
approaches the region on Saturday and again with very little
moisture in place, it is expected to pass through dry.
Upper level pattern transitions from zonal to southwesterly late in
the weekend through the first part of next week as a deeper
shortwave trough advances through the central Plains. This system
looks to have more moisture return, as it pushes a front through the
region Tuesday afternoon into Wednesday. Still some timing and
placement differences between the 22.12z guidance but a model
consensus of 30 to 50 percent chances spreading west to east Tuesday
through Wednesday, highest on Tuesday night, looks appropriate at
this time. Soundings show little to no instability, so have kept
thunder mention out of the forecast at this point.
Temperature wise, plan on a steady warm up Friday through early next
week, with the exception Sunday as cooler air slides in the wake of
the Saturday frontal passage. Readings will rise above normal with
the warmest day expected Monday with middle 70s common.
.AVIATION (18Z TAF Update)...
Updated at 125 PM EDT Wed Oct 22 2014
The most immediate TAF concern is at LEX this afternoon as low
clouds continue to remain over the TAF site. They will likely
bounce between SCT and BKN this afternoon just under 2 kft. These
low clouds look mostly diurnally driven so do expect them to burn
off around or after sunset with conditions returning to VFR at LEX.
All TAF sites stand a chance at MVFR fog tomorrow morning around
sunrise. Crossover temps and NAM soundings look favorable, however,
believe the light NE wind overnight will allow slight dry air
advection which should limit fog intensity. Thus, will continue
MVFR vsbys and monitor environmental conditions closely this evening.