Area Forecast Discussion
Issued by NWS Louisville, KY

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107
FXUS63 KLMK 171131
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
631 AM EST Tue Jan 17 2017

...Updated Aviation Discussion...

.Short Term (Now through Wednesday)...
Issued at 330 AM EST Tue Jan 17 2017

The main batch of showers out ahead of a cold front was clearing
portions of western Kentucky early this morning. Surface analysis
placed the surface low over Chicago, with a cold front extending
south through eastern Illinois and the Jackson Purchase.
Temperatures were holding fairly steady, mainly in the upper 50s to
around 60 degrees.

The main batch of rain is associated with good low-level moisture
transport and convergence out ahead of the surface boundary.
Favorable upper-level divergence was also noted on the SPC
mesoanalysis page. It will be breezy at times this morning as the
LLJ pushes through. KLVX radar currently shows 45 kts at around 3
kft. Wind gusts to around 20-25 mph are certainly possible. These
stronger winds push east of central KY and southern IN from mid-
morning into the afternoon as the front moves through.

Highs today won`t warm too much above current readings, topping out
in the upper 50s to mid 60s prior to the frontal passage. Expect a
drying trend from west to east from mid-morning through early
afternoon. Some meager instability exists, so still can`t rule out
an isolated rumble of thunder along and ahead of the cold front.

Quieter weather is expected tonight and Wednesday. Despite the
frontal passage, winter is not expected to return. Lows will drop
into the mid 30s to low 40s tonight. Some patchy drizzle is possible
given the persistent low-level moisture. Wednesday looks dry,
however, with ridging pushing through the Ohio Valley. Most
locations will warm to around 50 degrees.

.Long Term (Wednesday Night through Monday)...
Issued at 300 AM EST Tue Jan 17 2017

...Highly amplified pattern with above normal temperatures and
frequent rounds of rain during extended period...

Model overview/synoptic pattern...

Models continue to advertise a highly amplified/meridional pattern
in much of the long range period, with actually rather good
agreement throughout between models. This lends more confidence in
expected pattern evolution and forecast details within our model
blended solution. Granted, exact details invariably will vary, but
the overall synoptic setup, which features a few significant rainy
systems, is rather consistent among models at this time.

Thursday thru Friday...

Models suggest shortwave energy coming out of the southwestern U.S.
will carve a significant mid-level low over the central U.S.
Thursday, as an associated shortwave trough south of the low
eventually takes on a negative tilt as it rotates northeast into our
area Thursday night and Friday. This system will interact with a pre-
existing baroclinic zone from the TN Valley to lower MS Valley. As a
result, expect rapid moisture transport northward across the lower
OH Valley as the southerly low-level jet increases in response to
the approaching trough. This will create widespread rain, moderate
to locally heavy at times, Thursday afternoon and especially
Thursday night. Soundings show marginal lapse rates aloft, but with
strong forcing and a decent low-level/upper-level jet configuration,
there will be convective elements within the rain, with possibly a
few rumbles of thunder. Precip will push northeast out of our
forecast area by Friday afternoon as the shortwave passes by.

Saturday thru Monday...

After the late week system, another major system will be hot on its
heels. Deep-layered southerly flow will develop across the OH Valley
with a few rounds of rain expected. Difficult to exactly time
episodes of rain, but rain should move into our southern counties
Saturday night with numerous showers Sunday and Sunday night when
our region will be within the exit region of a pronounced jet streak
to our south and west. Periods of moderate to heavy rain appear
probable. In addition, model soundings show a little better
instability Sunday, so scattered thunderstorms may accompany the
showers. Interesting, both the GFS and especially the ECMWF have
what appears to be a significant mesolow moving northward out of TN
into central KY and southern IN Sunday afternoon or night (depending
on the model). This could enhance low-level shear and gusty wind and
even convective potential if this pans out. The deep mid-level
system meanders east on Monday, with still some showers around then.

Tuesday thru Wednesday...

Precip will exit our region Tuesday, but by Wednesday, models show
yet another upper low approaching from the west. Early indications
with this system suggest another round of showers by Wednesday, but
less widespread and lighter than the earlier systems.

Temperatures...

Daytime highs and nighttime lows will remain at or above normal
through the extended period. Highs Thursday afternoon should range
through the 50s, then upper 50s to mid 60s Friday, through the 60s
Saturday, lower-mid 60s Sunday, 50s Monday, then a little cooler
Tuesday with highs in the 40s (closer to normal). Highs will be
influenced by the amount of clouds and rain each day.

&&

.Aviation (12Z TAF Update)...
Issued at 631 AM EST Tue Jan 17 2017

Low pressure crossing Lower Michigan will swing a cold front through
central Kentucky today and push showers east of the TAF sites by mid
day. Drier air this afternoon should provide several hours of VFR
flying conditions, though SDF may remain just below 3k`. Low clouds
will move back in from the northwest tonight. We could see some
patchy drizzle tonight as well but it should be very light.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

Short Term........EBW
Long Term.........TWF
Aviation..........13



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