Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 170726

Area Forecast Discussion
National Weather Service Louisville KY
326 AM EDT Sat Mar 17 2018

.Short Term...(Today through Sunday)
Issued at 315 AM EDT Sat Mar 17 2018

Currently, mid-level low is located near the MO-IA border with a
surface low over central MO and a west-to-east oriented jet streak
from southern MO to western KY within a large dry slot aloft.
Forcing within the exit region of this jet streak along with a broad
area of modest elevated instability is resulting in a line of
showers and some thunderstorms over parts of south-central IN and
along our western county warning area. NAM and HRRR show this
activity should maintain itself as it pushes across our forecast
area, with a few robust cells still possible over far south-central
KY near a surface a warm front which extends west-to-east just south
of BWG at this time. The strongest storms could produce small hail
and brief heavy rain.

This area of rain will move east during the morning and out of our
area. In its wake, it should be dry for several hours over central
KY and much of south-central IN. The mid-level low is forecast to
slowly propagate ESE into IN this afternoon and slowly weaken as it
does. The surface low will do the same pushing into central KY this
afternoon. The warm front will drift northward to some degree today
but should stall as the surface low moves ESE along it. Where the
front stalls will have a major effect on high temps this afternoon.
For now, it appears the front may reach a rough line from just south
of Louisville to south of Lexington. North of the front, low clouds
and cooler temps will occur while south of it, low clouds should mix
out at least somewhat with a warm SW wind. Afternoon readings should
top out in the lower and mid 70s over south-central KY but only the
mid 40s from about Jefferson County IN to the northern Bluegrass,
north of Lexington. There is potential for this max temp forecast to
bust higher or lower near this front depending on where it ends up
later today.

As for precip potential, models especially the HRRR destabilize the
atmosphere south of the warm front this afternoon, but overall
forcing weakens and moisture depth becomes limited. Nevertheless,
scattered convection is expected along and east of the surface low
track along and near the warm front, mainly over the eastern half of
central KY this afternoon before before moving east of the area this
evening. Scattered showers are possible north of the front.

For tonight, skies should remain mostly cloudy with low clouds,
although clearing should commence by Sunday morning from the N and
NE over our northern and northeastern counties. Expect lows in the
30s north and around 40 south.

On Sunday, brief ridging aloft moves into the OH Valley as surface
high pressure drifts east to our north. Expect more sunshine north
and a mix of clouds and sun south across central KY and southern IN.
Afternoon highs should be in the 50s over much of the area.


.Long Term...(Sunday night through Friday)
Issued at 315 AM EDT Sat Mar 17 2018

A rather active extended forecast is in store for much of the OH and
TN Valleys for next week as several systems traverse from west-to-
east from the central U.S. In such a pattern, model variability is
inherent with some timing, location, and intensity differences
expected. Nevertheless, several rounds of precip are expected, with
everything from thunderstorms and heavy rain to some wet snow
possible during the period.

Models in reasonable agreement on Monday as the next system
approaches from the west. This system looks similar to the current
one, except a little farther south. A mid-level closed low will push
east from MO into the lower OH Valley while a surface low tracks out
of AR into TN or southern KY. Models show that at least some
elevated instability will be present within the left exit region of
a strong jet streak aloft. Thus showers and thunderstorms are likely
Monday afternoon and evening. If the system ends up being a little
farther north, then surface-based instability will develop over at
least south-central KY with strong storms possible.

The most uncertainty occurs Tuesday night and Wednesday morning as
another complex but broad shortwave is expected to dig southeast
over the region right on the heals of the departing system Monday.
The strength of this system and amount of available moisture and
thermal profile are in question. Nevertheless, the GFS and GEM
suggest that some rain could redevelop over at least the southern
and eastern half of central KY Tuesday afternoon, which could change
to some wet snow Tuesday night as the thermal profile cools. Our
blended grids reflect the GFS/GEM solution. Too early to tell if any
accumulation would occur if this scenario plays out as suggested. On
the other hand, the latest ECMWF is less enthusiastic about this
possibility. Lows Tuesday night should be in the upper 20s and lower
30s, with highs Wednesday only around 40 east, and mid 40s west,
quite chilly for the first day of spring on Wednesday.

The next system arrives around Saturday with a potential influx of
deep moisture and isentropic lift leading to potentially widespread
showers and a few thunderstorms. Then yet another system could bring
additional rain Monday-ish. If all these systems bring rain and some
storms to our area over the next week, then will have to remain
aware of some potential water issues by the end of the period.


.Aviation...(06Z TAF Issuance)
Issued at 150 AM EDT Sat Mar 17 2018

Early this morning, the first TAF concerns will be LLWS at
SDF/LEX/BWG and t-storm chances at BWG.  A strong LLJ and line of
convection ahead of an approaching low pressure system will move
through the region during the pre-dawn hours.  BWG looks to be most
affected with LLWS and a t-storm chance, but the LLJ could be decent
at SDF/LEX as well early this morning.  Winds at 2 kft look to be
from the SW at 35-38 kts with sfc winds east-southeast between 5-8
kts.  T-storms at BWG could reduce flight conditions to MVFR/IFR if
strength is maintained as they progress east from western KY. Will
need to monitor.

After this line of convection passes through this morning, expect
VCSH throughout the rest of the morning hours.  Also a warm front
will slowly move north through central KY today settling somewhere
over north central KY this afternoon.  Along and north of the front
at SDF/LEX/HNB, expect showery conditions, light/vrb winds, and IFR-
MVFR conditions throughout the day.  This afternoon SDF/LEX stand
the best chance at a few t-storms as a sfc low passes through. At
BWG, a few t-storms will also be possible this afternoon along with
gusty southwest winds.

Convection should end late tonight after passage of the low pressure
with conditions returning to VFR.




Short Term...TWF
Long Term....TWF
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