Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 110532
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
132 AM EDT Tue Mar 11 2014
...Updated Aviation Discussion...
Issued at 935 PM EDT Mon Mar 10 2014
Forecast is on track this evening, although have made a few tweaks
to hourly temp/dewpoint grids. Current obs show most spots sitting
in the mid and upper 50s, with a few locations lingering around 60.
However, a few of the cool southeastern valleys have already dipped
into the mid 40s. This is only occurring where the winds are very
light and valleys are able to decouple. In these spots near Lake
Cumberland, a few lows around 40 are possible. Elsewhere, winds will
stay up enough to keep lows mostly in the mid 40s by dawn on
Tuesday. Otherwise, expect mostly clear skies tonight as the few
upper level clouds streaming across the north continue push out.
.SHORT TERM (Now through Tuesday Night)...
Issued at 305 PM EDT Mon Mar 10 2014
...Well above normal temperatures through Tuesday night...then
abruptly back to winter by Wednesday afternoon...
Dry mild weather prevails this afternoon across southern IN and
central KY with a mostly sunny sky except for a band of high clouds
over southern IN into parts of east-central KY. These clouds will
filter south a little farther late this afternoon and evening before
they retreat or reform farther north later tonight. Therefore,
expect a mostly clear sky or one that becomes mostly clear tonight.
Lows will range in the lower and mid 40s in many areas. Expect some
haze or areas of light fog around daybreak Tuesday morning.
On Tuesday, sunny skies will give way to some clouds as moisture
begins to advect in from the southwest ahead of a significant
mid-level shortwave that will approach the Ohio Valley Tuesday
night. A very mild southwest surface flow will send high
temperatures to at or above 70 Tuesday afternoon. Lower and mid 70s
are expected, higher than our previous forecast and higher than MOS
guidance which has been generally too cool in brief warm up
situations this winter. These temperatures will represent about
15-20 degrees above average for the date.
Changes start Tuesday night as a deepening surface low moves up the
Ohio Valley accompanied by a decent increase in low-level winds and
the approach of the exit region of an upper-level jet streak. The
synoptic pattern resembles one that severe weather could occur in.
However, the necessary instability is not there for such an event to
occur. Nevertheless, model soundings show steeper lapse rates above
a nocturnal cooling boundary layer. Combined with moderate to strong
forcing, this should be plenty for at least scattered elevated
thunderstorms along with showers Tuesday night. With a deepening
surface low, not out of the question that some stronger winds aloft
still could mix down in isolated areas. Timing and evolution of the
precip is a bit tenuous, and a continuous soaking rain is not
expected. Instead, a couple/few periods of showers and a few storms
are expected, with greatest coverage generally along and downwind of
the surface low track over southern Indiana and the northern third
of central KY.
Temperatures Tuesday night will not fall too much likely staying up
in the 60s before probably easing back into the 50s by daybreak
Wednesday. The exception will be where the trailing cold front is
located by 12z Wednesday, which will be entering south-central IN.
This front will mark a very substantial thermal gradient, so 12z
readings over Dubois to Jefferson County in Indiana may fall to near
40 by that time as the front then plows southeast into KY thereafter.
.LONG TERM (Wednesday through Monday)...
Issued at 300 AM EDT Tue Mar 11 2014
A coupled upper jet structure will lead to a rapidly deepening
cyclone across the Appalachians and eventually coastal New England
by Wednesday evening. Both the NAM and the GFS in fact both forecast
a surface pressure near 980mb just west of New York City at 00Z
Unseasonably cold air will continue to pour into the Lower Ohio
Valley Wednesday evening and overnight as arctic high pressure
builds southwards into Texas. Gusty northwest winds will continue
through the evening hours but diminish after midnight as surface
ridging approaches western Tennessee. Scattered snow showers, during
the afternoon Wednesday will diminish Wednesday evening as moisture
associated with the back edge of the cyclone moves to the east.
Expect cold temperatures well down into the teens early Thursday
Although skies will become mostly sunny Thursday, unseasonably cold
temperatures will continue with highs expected only in the mid 30s
to the lower 40s. At least winds will become light by afternoon, and
will back to the southwest late as surface high pressure becomes
established over the central Gulf States.
A split jet will develop across the CONUS by late Thursday. A
shortwave associated with the northern branch will move across Lake
Superior early Friday. A surface trough trailing from this feature
will move south towards Chicago and tighten the pressure gradient
along and north of the Ohio River for Friday afternoon. This will
allow temperatures to moderate substantially from Thursday highs.
Under partly cloudy skies, highs Friday will range from the lower to
upper 50s under breezy southwest winds.
For the weekend, a deep 500mb trough will develop, centered over St
James` Bay. Wintry air will spill south across Illinois and the
Great Lakes by early Sunday. However, the southern extend of this
chill is in question. It is likely that the Commonwealth will not
feel the brunt of this chill, although highs will likely fall into
the 40s for Saturday and Sunday.
The long term will start off with a robust center of low pressure
centered near Louisville with a cold front dropping to the SSW.
This system will move quickly to the east, with the deepening low
over West Virginia by mid day. Precipitation will be widespread
Wednesday morning, become lighter in the afternoon and begin to
taper off in the northwest, then end in the east Wednesday evening.
As for precipitation type, we`ll see mostly rain with maybe a few
rumbles of thunder in the morning, a gradual mix with and changeover
to light snow in the afternoon from northwest to southeast, and
mostly light snow in the east during the evening. Snow
accumulation? Maybe a dusting in the Blue Grass in the evening.
Strong northwest winds Wednesday will bring in very cold air,
resulting in falling temperatures through the day. Wind gusts of
30-35 mph continue to look possible. By evening wind chills will
generally be in the 20s.
Cold air will continue to pour in Wednesday night as a ridge of
Canadian high pressure enters the region. Lows by Thursday morning
will range from the middle and upper teens in southern Indiana and
the northern Blue Grass to the lower 20s in southern Kentucky.
That`s about 15 degrees colder than normal, 10-15 degrees warmer
than record lows.
That ridge will keep us dry Thursday and Thursday night as it moves
through. High temperatures Thursday will vary from the mid 30s to
lower 40s, with lows Thursday night mostly in the 25-30 degree range.
An upper wave and associated surface cold front will sweep in from
the west Friday night. There won`t be much moisture associated with
this feature so will continue with a dry forecast for now, but
changes may be necessary to this in later updates. Precipitation
type would be light rain.
The forecast becomes quite murky for the weekend into St Patrick`s
Day, with little model consistency. The most likely time for
precipitation seems to be Sunday/Sunday night as waves move along an
east-west surface boundary and upper troffing digs in. However
confidence is not high enough for any PoPs above slight chance at
After the chilly mid-week weather we`ll be back into the 50s for at
least Thursday through Sunday. Monday is still iffy...will go for
40s at this time.
.AVIATION (06Z TAF Update)...
Updated at 130 AM EDT Tue Mar 11 2014
AMDAR soundings indeed show the presence of some low-level wind
shear early this morning, so will maintain in the TAFs this package
through mid morning. At that points winds will pick up from the
southwest, ahead of a cold front forecast to move into the region
tonight. Expect ceilings to lower with showers and possibly some
thunder late in the period.