Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 151900
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
300 PM EDT Mon Sep 15 2014
.SHORT TERM (Now through Tuesday Night)...
Issued at 255 PM EDT Mon Sep 15 2014
The synoptic pattern this afternoon features a broad trough across
the eastern 2/3rds of the CONUS. This trough will amplify slightly
through the short term period as a strong shortwave slides through
the southern Great Lakes region tonight.
Latest water vapor imagery depicts the aforementioned shortwave
sliding through western IL as of this writing. In response, a
low-level jet of around 30 knots has helped to maintain elevated
convection across portions of IL and IN early this afternoon. The
near-term forecast challenge will be whether or not this activity
makes it into our Indiana counties. Given its current orientation,
the WSW LLJ should continue to foster development on it`s southwest
flank which should keep it going over the next couple of hours.
However, as we get towards 21Z and after, the 850mb flow will veer
enough that favorable inflow into this activity will be lost, thus
likely causing it to weaken. Have introduced thunder wording into
southern IN counties for a bit early this evening, but think this
convection will likely be in a weakening state as it approaches the
region given the loss of favorable elevated inflow.
The cold front associated with this system remains well back across
portions of MO and NW IL. It will push through the region Tuesday
morning. Out ahead of it, guidance continues to suggest some light
showers will be possible tonight. Given the main upper-level
forcing is passing well north of the region, this front will only
have low-level ascent to produce any QPF. In addition, moisture
within this region of ascent is very shallow (around 200mb deep).
Therefore, really don`t think many will see measurable precip. The
most likely scenario will be some patchy drizzle, with perhaps a few
locations reporting a hundredth or two in some light shower
Any precip will come to an end by mid-morning Tuesday, but cloud
cover will likely linger into the late morning north and afternoon
across the south. Have trended temps down a bit for Tuesday to
account for this expected cloud cover through at least the first
part of the day, which puts highs in the upper 60s and lower 70s.
A surface ridge will build into the region Tuesday night as skies go
mainly clear. This will make for good radiational cooling
conditions, which will allow temps to dip into the mid 40s across
southern IN, and upper 40s/lower 50s across KY.
.LONG TERM (Wednesday through Monday)...
Issued at 300 PM EDT Mon Sep 15 2014
High pressure will be centered over northern IN/OH Wednesday
morning. An upper disturbance will cross within the northwest flow
aloft during the day, but with no surface reflection. Thus just
expect some mid/high clouds to keep afternoon highs below normal.
Another disturbance passing by to our north Thursday will allow a
reinforcing high pressure centered over SE Canada to ridge over the
east central U.S., keeping our temperatures below normal and weather
dry to Friday.
The next shot for rain looks to come as a more organized surface low
crosses the northern Great Lakes Sunday and drags a cold front
through here. Timing of this system is fairly uniform among the
GFS/00Z Euro/Navy NOGAPS ensemble. Also looks like we may get an
influx of tropical moisture ahead of the front, so will keep
highlighting the best chance for rain on Sunday/Sunday night. Then
will go dry for Monday for all but our southeast forecast area, as
another cool shot of air builds in from Canada.
Temperatures will warm up ahead of this front, likely into at least
the low 80s Saturday and perhaps even around 80 over southern KY
.AVIATION (18Z TAF Update)...
Issued at 110 PM EDT Mon Sep 15 2014
The main focus of the TAF period will be a cold frontal passage
tonight, which may bring a period of MVFR cigs to all sites along
with some light showers. For the remainder of the afternoon hours
today, expect VFR conditions with increasing mid/high cloud cover.
Winds will be out of the WSW at 4-7 knots.
Later this evening into tonight, a cold front will approach the
region. There will be a few showers along this front that may drop
some light amounts here and there, but coverage and associated
aviation impacts will remain limited. The more impactful aspect of
this system will come after the fropa, as it looks like a period of
at least MVFR stratus will affect all sites Tuesday morning.
Guidance suggests even IFR cigs will be possible, but given the
limited moisture this system has to work with, will go more
optimistic and advertise fuel-alternate MVFR cigs for now.
Ceilings will slowly rise Tuesday morning, but likely won`t go VFR
until the late morning or early afternoon. Winds will be out of the
north at 5-10 knots.