Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 260507
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
107 AM EDT Sun Oct 26 2014
...Updated Aviation Discussion...
Issued at 1005 PM EDT Sat Oct 25 2014
Current forecast is well on track as a weak surface boundary remains
hung up just north of the Ohio River. Main challenge is fog and
thinking really hasn`t changed much. The main limiting factor in fog
formation will be the low-level wind field that cranks up behind the
boundary, with a 20 kt northerly jet developing at 950mb. Latest
NAM12 pushes this jet farther south, catching all but a few counties
near the Tennessee border by 09Z. Therefore, still not enough
confidence to issue a Dense Fog Advisory at this time.
However, this jetting will weaken around sunrise or shortly before,
and may weaken enough to allow some locations to fog in quickly.
Best chance of this happening is near Lake Cumberland, but again,
confidence in dense fog is lacking. Special Weather Statement
highlighting the potential for locally dense fog will be allowed to
ride as is.
.SHORT TERM (Now through Sunday Night)...
Issued at 314 PM EDT Sat Oct 25 2014
...Areas of Fog, Patchy Dense Across South Central KY Tonight...
A weakly defined surface boundary will move through the area over
the next few hours, with little more than a wind shift for sensible
weather. Otherwise, skies will rapidly clear across our east,
yielding a pleasant evening. Highs have made their way into the
upper 60s and low 70s, however still expect to see mostly low and
mid 70s through the late afternoon and under mostly full sun.
Surface high pressure will gradually settle over the area tonight,
with the center settling over the lower Wabash River Valley by dawn.
The clear skies, calm winds, and relatively high dew points
(compared to last night) across south central Kentucky are expected
to lead to areas o fog formation, patchy dense. Will issue a Special
Weather Statement to highlight south of a line from just north of
Bowling Green to just south of Madison, KY toward dawn. Stay up to
date for possible upgrades to a Dense Fog Advisory.
Sunny skies and light and variable winds will continue into Sunday,
with the surface high pressure shifting over region. Still expecting
warm temperatures, however have backed of a few degrees for Max Ts
as data supports readings more in the low and mid 70s.
Shortwave ridging will remain in place Sunday night, with surface
high pressure shunted to the east. This will give us some light
return southerly flow, keeping things mixed and mild across our
western counties. Low should only drop into the mid and upper 50s.
Further east, cooler temps will be possible under the more decoupled
and drier regime. Look for mostly low 50s, with a few upper 40s
possible in the coolest spots.
.LONG TERM (Monday through Saturday)...
Issued at 305 PM EDT Sat Oct 25 2014
The synoptic pattern at the start of the long term period will
feature an amplified ridge over the east-central CONUS, including
the Ohio Valley, with an upstream trough across the Central Plains.
This trough will build into the Ohio Valley through the long term
period, bringing much cooler temperatures for the end of next week.
Monday is shaping up to be a gorgeous late October day, especially
for those who like warmth. 850mb temperatures will climb to near
16-17C. Breezy southwest winds in response to a deepening cyclone
out west will aid in mechanical mixing, which coupled with abundant
sunshine, should yield near record highs. For now will keep the
forecast just below record highs, but SDF especially has the
potential to tie or even exceed their record high. Monday night will
also be quite warm given increasing cloud cover associated with an
incoming cold front/upper trough and southwest winds staying up.
Lows will only fall into the low and mid 60s. Below are the records
for Monday and Monday night that may be in jeopardy.
Record Max for Oct 27 Record Warm Low for Oct 28
Louisville 84 (1940) 64 (1991 and 1984)
Lexington 87 (1940) 64 (1984)
Bowling Green 87 (1919) 65 (1984)
Frankfort 89 (1940) 61 (1899)
The 25/12Z suite of guidance has continued to come in a bit quicker
with the fropa on Tuesday. Will only slightly trend the forecast
quicker, as still think this is a scenario where guidance tends to
bring in a front too quickly. A deepening low, amplified
upper-level flow, and the trailing end of the cold front typically
mean they are slow to pass through. With that in mind, looks like
the bulk of the precipitation will fall Tuesday afternoon into
Tuesday evening. With the quicker timing, it does appear that some
modest SBCAPE (around 500-1000 J/kg) will develop within a thin
moisture axis ahead of the front. Given shear of 40-50 knots,
cannot rule out a stronger cell or two on the leading edge of the
line capable of some gusty winds. But with the better dynamics
passing well north, the front will not be deeply forced which should
help to limit overall updraft intensity. Precipitation amounts will
range from a quarter to a half of an inch.
Cool weather will move in behind the front for the remainder of the
week. Temperatures on Wednesday and Thursday will fall into the 60s
and upper 50s for highs.
Guidance continues to suggest a pretty good blast of cold air slated
for Friday into next weekend. A reinforcing PV anomaly will dive
through the trough aloft, driving another cold front through the
region on Friday. There could be a few showers with this front, but
the main story will be the cold air behind it. Despite being just
outside the scope of this official forecast, highs next weekend may
not get out of the 40s, with overnight lows in the 30s or even upper
20s. Certainly a pattern change to watch over the coming days.
.AVIATION (06Z TAF Update)...
Updated at 105 AM EDT Sun Oct 26 2014
Main aviation concern is fog development in the very near term at
BWG and to some degree at LEX. Higher low-level moisture pool ahead
of a boundary that lies across southern Indiana combined with
light/variable surface winds has resulted in MVFR fog at BWG and
surrounding sites. Although latest forecast guidance does not
suggest a long period of IFR conditions to develop at BWG, soundings
show favorable light surface winds and near surface saturation to
linger through the early morning hours. However, just off the
surface /950 mb/ winds remain elevated overnight and this may limit
dense fog formation. For now, will continue tempo period of IFR for
early this morning at BWG but confidence is not very high. At LEX,
patchy MVFR fog remains a possibility while VFR conditions will
prevail at SDF.
Otherwise, once morning fog burns off, weak high pressure and drier
air will work into the region so plan on sunny skies and
light/variable winds for the TAF sites. By late in the period, winds
will begin to take on a southerly flow but remain less than 5 kts.