Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 071736
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1236 PM EST Fri Mar 7 2014
...Updated Aviation Discussion...
Issued at 1055 AM EST Fri Mar 7 2014
Made only minor tweaks to the forecast this morning. Should be a
sunny day with temperatures warming into the mid 50s to around 60.
Issued at 510 AM EST Fri Mar 7 2014
Fog is really failing to materialize, as the models did not have a
good handle on low-level wind fields. Winds at 975-950mb had been
progged to diminish to around 5 kt, but VAD Wind Profiles from LVX,
HPX, OHX, and VWX remain at 15-20 kt out of the S-SE.
Grids and products have been updated to remove any and all mention
of freezing fog, as significant impacts to visibilities are no
.SHORT TERM (Now through Saturday)...
Issued at 240 AM EST Fri Mar 7 2014
Weak surface gradient is in place over the Ohio Valley, and the main
forecast challenge is the potential for fog formation over the next
few hours. On a typical fog night, we would expect to see
visibilities already dropping by now, at least more so than the 5-6
miles that is showing up in observations from BWG and over western
Kentucky. VAD Wind Profiles from local 88-D radars show SSE winds at
15-20kt not even 2000 feet off the deck. While GFS and NAM low-level
wind fields show that winds will really slacken around 09Z,
confidence is limited because these models are advertising ENE winds
currently, a full 90 degrees off reality.
Given that fog/freezing fog has yet to materialize, and would likely
dissipate by 14Z even if it does so, will allow the main suite of
forecast products to go out without it. However, will keep it in the
pre-1st period grids for now, and use Special Weather Statements
and/or Graphical Nowcasts to convey anything that does develop.
Otherwise a benign weather pattern is expected through Saturday as
shortwave ridging aloft keeps us mild and mostly dry. A series of
northern stream disturbances will push a weak cold front SE into the
Ohio Valley by late Saturday. The boundary should be very near the
Ohio River by 00Z Sunday, and with most of the precip looking
post-frontal, will only carry a slight chance POP across southern
Indiana on Saturday afternoon, while keeping Kentucky dry.
.LONG TERM (Saturday Night through Thursday)...
Issued at 245 AM EST Fri Mar 7 2014
Models remain in fairly good agreement on the large-scale pattern
for our area through about the end of next week. A cold front moves
through the area Saturday night, cooling us down just a bit Sunday.
Then we warm up Monday and Tuesday ahead of our next weather system.
This next system will spread precip across the Ohio and Tennessee
Valleys late Tuesday through Wednesday, with temperatures dropping
below normal for the latter half of next week.
As mentioned above, a cold frontal passage is expected Saturday
evening and overnight. Total PW values of around 0.7-0.8 inches are
expected, which is around the 75th percentile for this time of year.
Nothing to write home about, but adequate when combined with modest
forcing. Soundings still favor rain, with our warm air ahead of the
front, then becoming drizzle as 900-500 hPa moisture dissipates with
the system pushing east. It could be a very light freezing drizzle,
but that highly depends on how fast the temperatures drop. Without a
strong arctic airmass pushing in behind this system, do not really
favor temperatures dropping all that fast, but worth keeping an eye
on. Temperatures are expected to drop into the upper 20s far north
to upper 30s far south by daybreak Sunday. So, a few slick spots
cannot be ruled out Sunday morning where surfaces remain wet,
particularly elevated surfaces across portions of southern Indiana
and northern Kentucky.
Any lingering light precip across our southeast Sunday morning will
quickly depart, with dry conditions then expected until late
Tuesday. Temperatures will warm from highs in the upper 40s to
middle 50s Sunday to 60s by Tuesday. By late Tuesday, a strong upper
trough will swing through the central CONUS. The trough and
associated surface low will traverse the Ohio Valley Tuesday night
through Wednesday. There remain some differences on strength,
timing, and exact track of the surface low, but certainly an
unsettled period for our area. Warm-air advection ahead of this
system signals rain, perhaps some thunderstorms if the surface low
tracks further north. On the back side, there is a chance of a
rain/snow mix, as temperatures begin descending to below normal
.AVIATION (18Z TAF Update)...
Updated at 1230 PM EST Fri Mar 7 2014
VFR conditions are expected for this TAF period as sfc high pressure
and upper level ridging dominate the region. We will see upper
level clouds gradually increase tonight and tomorrow morning ahead
of an approaching cold front progged to cross the area Sat night.
Winds will be primarily from the WSW through the TAF period under 7
kts today and tonight. Tomorrow afternoon they could be stronger
ahead of the fropa. Debated adding a tempo group for fog at BWG,
but decided to hold off for now due to increasing cloud cover