Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 120516
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
116 AM EDT Wed Mar 12 2014
...Updated Aviation Discussion...
Issued at 952 PM EDT Tue Mar 11 2014
Did go ahead and make some minor changes to the precipitation
forecast for the overnight period. Currently, light rain showers
have blossomed mainly across southern IN and north central KY along
and just south of the warm front. Expect these showers to continue
to lift off to the ENE on the nose of the the increasing LLJ and
where the best isentropic ascent is. This will keep the majority of
the activity along and north of I-64 for much of the evening, with a
relative lull across central and south central KY until the pre-dawn
hours when numerous showers and scattered t-storms arrive just ahead
of the cold front. Have reduced pops across south central KY to
isolated until this time. However, measurable pops are still likely
Did also want to quickly mention that there are numerous reports of
40 mph wind gusts just behind the front upstream. Additionally, a
few of the storms are rotating just north of St. Louis at the triple
point. These storms should remain elevated when they move through our
area, although lower levels will begin to try and destabilize toward
dawn which could allow for a few stronger wind gusts. Will need to
monitor forecast overnight, and be prepared for a few stronger cells
that might warrant Special Weather Statements for stronger wind
gusts and small hail. Stay tuned.
Issued at 838 PM EDT Tue Mar 11 2014
Made a few tweaks to the ongoing forecast to account for
temperatures running a bit milder than expected at this time, and
very weak showers that have popped up. Continue to think lows will
stay quite mild overnight under WAA, cloud cover, and precip. No
real changes to the temp forecast. The showers are associated with
and uptick in the LLJ over the past couple of hours, and the
associated isentropic lift over top of a warm front now positioned
across south central IL/IN/OH. These showers are very small in
diameter and will likely only produce a brief period of spinkles or
very light rain as they pass. Nevertheless, have started small
chances for measurable rain a couple of hours earlier to account for
them. Still expect focus for best coverage and intensity of showers
(and a few rumbles of thunder) to set up along and north of the Ohio
River as we move toward Midnight and beyond. Then, a broken line of
semi-organized storms are expected to accompany the front more
toward dawn. Small hail and gusty winds to 40 mph may accompany the
.SHORT TERM (Now through Wednesday Night)...
Issued at 258 PM EDT Tue Mar 11 2014
Deepening low pressure advancing from the Ozarks to the middle Ohio
Valley tonight will bring very warm air and increased moisture
northward on brisk SSW winds. As the system approaches showers will
break out and will become widespread, especially after midnight and
with the greatest coverage across southern Indiana and northern
Kentucky. Scattered thunderstorms can also be expected with some
elevated instability found on sounding progs. Wet bulb zero heights
indicate that a few of the storms could produce small hail,
especially north and east of Louisville towards morning.
Temperatures will not fall much tonight given the strong WAA in the
warm sector ahead of the low.
On Wednesday the low will exit to the ENE, reaching West Virginia by
midday. There could be some lingering thunderstorms for a few
hours early in the morning in the Blue Grass ahead of the surface
low, with small hail in the strongest cells again possible. Cold air
will then pour in behind the low on strong and gusty northwest
winds. The warmest readings of the day will occur early in the
morning, with the mercury dropping into the 30s in Kentucky and the
upper 20s in southern Indiana by late afternoon...a drop of 20 to 25
degrees over the course of the day. Those northwest winds will be
in the 20 to 30 mph range with gusts to at least 40mph...resulting
in a Wind Advisory for the entire area for Wednesday. The very
strongest winds look to be over the Blue Grass (Lexington) area.
Snowflakes will gradually mix in with the rain from northwest to
southeast in the afternoon...ending as scattered snow showers east
of Interstate 65 in the evening. Any accumulations would be very
The winds will die down Wednesday night as Canadian high pressure
invades from the northwest. Low temperatures will be in the middle
and upper teens across much of the area...lower 20s around Bowling
.LONG TERM (Thursday through Tuesday)...
Issued at 245 PM EDT Tue Mar 11 2014
The synoptic pattern at the start of the long term period will
feature an amplified trough across the eastern seaboard, with a
ridge across the central CONUS, and another trough over the western
United States. The subtropical jet will become more active by this
weekend into early next week, allowing for more of a split-flow
regime to develop. This expected pattern will be quite progressive,
bringing daily temperature swings and perhaps a few chances for
precipitation this weekend.
Conditions will start out dry on Thursday, as surface high pressure
slides through the Ohio Valley. By late Thursday afternoon, this
area of high pressure will push just far enough east that SW surface
flow will develop along the backside across the western CWA.
Therefore, expect a decent gradient in high temperatures on
Thursday, with upper 40s across southern KY and mid 30s across the
Northern Bluegrass. Lows Thursday night will remain warmer than
Wednesday night, due to southwesterly surface flow continuing.
Overnight lows will bottom out in the upper 20s and lower 30s.
Southwesterly winds will really ramp up during the day on Friday,
setting the stage for a quick warmup. As we have seen the past
couple of days, the mid-March sun angle is really allowing things to
warm up quite nicely in the afternoons. With southwesterly flow
aiding in deep mixing, partly cloudy skies, and dewpoints only in
the low to mid 30s, think Friday will end up being quite warm.
Therefore, have bumped up highs a few degrees from the previous
forecast, which puts them in the upper 50s to lower 60s.
Confidence in the forecast begins to decrease by the weekend, as
guidance quickly diverges. As the subtropical jet becomes more
active, guidance is struggling with just how much moisture will be
able to return north ahead of northern stream impulses. Overall
pattern recognition tends to favor the southern CWA in this type of
regime due to their proximity to the more moisture-laden systems of
the southern stream, thus will focus the best precipitation chances
there Friday night through Sunday. Regardless, what does fall
appears as if it will be generally be some light rain, with no
high-impact systems expected through the long term period.
Temperatures this weekend will be in the upper 50s on Saturday,
falling into the upper 40s/lower 50s on Sunday. Highs will be in
the upper 40s and 50s for early next week.
.AVIATION (06Z TAF Update)...
Updated at 110 AM EDT Wed Mar 12 2014
Conditions should start deteriorating more rapidly next few hours as
a deepening low pressure system, now just south of KSTL, moves up
the Ohio River through daybreak. A low level jet ahead of this low
is beginning to ramp up now, causing some low-level wind shear until
the associated surface cold front moves through the region mid
morning. In addition, showers and thunderstorms will develop as this
low-level wind picks up. The pressure gradient on the back side of
this low is very tight, and will contribute to gusty 25-35 knot
winds the rest of the day. Expect low clouds to hang in, at least
low-end MVFR through the morning. Rain showers should transition to
snow in the afternoon as northwest winds drive in much colder air.
Precipitation should cutoff by the end of the day.
KY...WIND ADVISORY from 8 AM EDT /7 AM CDT/ this morning to 8 PM EDT
/7 PM CDT/ this evening FOR KYZ023>043-045>049-053>057-
IN...WIND ADVISORY from 8 AM EDT /7 AM CDT/ this morning to 8 PM EDT
/7 PM CDT/ this evening FOR INZ076>079-083-084-089>092.