National Weather Service Raw Text Product

066 
FXUS63 KLMK 122257
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
556 PM EST SAT JAN 12 2013

.Mesoscale Forecast Update...
Issued at 556 PM EST Sat Jan 12 2013

Strong cluster of thunderstorms is currently moving through
southwestern Indiana.  This area of storms is located along a
quasi-stationary boundary extending from NE Texas through central
Indiana.  Combination of mid-level height falls and an approaching
low-level jet seem to be forcing the convection.  Low-level bulk
shear values of 55-65kts extend from SE MO northeastward into SW
Indiana.  This southwesterly low-level flow combined with a
southerly surface flow is resulting in SFC-3km SRH values of 350-450
m2/s2 across southwest Indiana.  We have been tracking a cluster of
strong to severe thunderstorms across west Kentucky this afternoon.
The storms have been exhibiting supercellular characteristics at
times as they moved south of Paducah and now just exiting the
Evansville area.  The storms are coincident with the strongest shear
and instability, but they are moving northeastward into a slightly
more stable atmosphere as they head northeastward toward central
Indiana.

Strong to severe thunderstorms look to be limited mainly to our
northwest CWA over the next hour or so...specifically Dubois and
possibly northwestern Orange county.  Heavy rainfall...wind gusts to
50 MPH and frequent lightning will be possible with this activity.
In addition, given the wind shear and elevated storm relative
helicity fields a tornado threat does exists across Dubois and
western Orange counties for the next hour or so.

&&

.Short Term (Now through Sunday Night)...
Issued at 320 PM EST Sat Jan 12 2013

...Flood Watch in Effect through Sunday Evening for areas along and
west of I-65...

The well advertised precip event is still on track.  A cold front
currently sits well to our west with pre-frontal waves/isentropic
lift out ahead of the front causing steady shower activity over
south central and east central KY this afternoon.  This activity is
expected to move northeast into northern KY and southeast IN through
the evening hours but become more scattered in nature.

The area of precip that will be of most concern for our area later
tonight was setting up near the front from southern IL/western KY
southeast to northeast TX.  This will be the band of heaviest precip
which looks like it may initially move through our southwest Indiana
counties this evening before shifting more northwest of our area.
Embedded t-storms have been observed so will keep a slight chance of
thunder mentioned in the forecast.  This area of rainfall will move
back eastward into our western section after Midnight tonight with
the heaviest rains approaching the I-65 corridor toward sunrise as
an area of low pressure rides northeast along the front.  Steady
moderate to at times heavy rainfall with embedded thunder will then
move east through the area during the morning hours and early
afternoon hours.  The latest GFS and SREF guidance suggests a
secondary wave will then arrive during the afternoon hours causing
steady precip, heavy at times, to continue tomorrow afternoon.   By
Sunday evening, though, precip should start making its way eastward
out of the area.  Model soundings are still indicating plentiful
deep layer moisture and unseasonably high PWATS.  We'll see a strong
LLJ and be in the entrance region of a strong upper level jet as
well.  All of these factors point toward heavy precip and potential
flooding.  Thus, the flood watch will remain in effect through
tomorrow evening for areas along and west of I-65.  Total QPF
amounts from rains today through Sun evening should range from 1.5-3
inches area wide with locally higher amounts possible especially in
the axis of best forcing or where t-storms occur.  Minor river
flooding and some areal flooding will be possible.  See the hydro
discussion below for more details.

Temperatures should be quite mild tonight in the 60s for much of the
evening.  The cold front will cross the area Sunday afternoon
bringing in cooler air, but not enough to change us to wintry
precip.  Temps will fall into the upper 30s and 40s as the front
passes tomorrow afternoon/evening.  Precipitation should end Sunday
evening as plain rain around or shortly after Midnight.  Colder air
will continue to invade the region so lows Sunday night will get
down into the lower 20s to mid 30s.  Locations that reach the lower
to mid 20s Mon morning may experience some slick spots if lots of
water still exists on the ground/roadways.  We'll have to keep an
eye on that.

.Long Term (Monday - Saturday)...
Issued at 300 PM EST Sat Jan 12 2013

By Monday morning precipitation from the last of the waves over the
weekend will have exited the eastern portion of the forecast area.
However, the boundary will remain stalled to the southeast. By
Monday afternoon into Monday evening another wave will move
northeast along the boundary. This still looks to bring some
precipitation to the southeastern portions of the forecast area.
However, have cut way back on the areal extent of this precip for
this forecast.

Precipitation type is still quite a bit in question with this system
on Monday night. Soundings from the latest model runs are showing
that there will be ice crystals aloft, as opposed to previous runs
which were not as saturated at colder temperatures. There will still
be a rather deep warm layer for the precip to fall through, however,
before reaching the ground. Surface temperatures will be close to
freezing, but could remain a degree or two above. Thus, some snow
could reach the ground mixed with the rain. Sleet may be possible as
well. If temperatures are freezing or below at the sfc, freezing
rain is not out of the question. However, will hold off on
mentioning more than a rain/snow mix for now given the big
uncertainty in the forecast.

Precipitation will move out of the area on Tuesday morning and the
rest of the long term will be much quieter. Flow aloft will become
quasi-zonal with systems passing mainly to the north or the south of
the forecast area. Dry conditions look to prevail through the
remainder of the week. High temperatures will generally be in the
40s with lows in the 20s.

&&

.Aviation (18Z TAF Issuance)...
Issued at 1250 PM EST Sat Jan 12 2013

MVFR conditions are expected for most of the TAF period.  A slow
moving cold front is expected to slowly move toward the region
tonight and pass through the region tomorrow bringing multiple waves
of rain through the area as multiple disturbances ride along the
front.

One initial wave of rain and low MVFR to at times IFR cigs are
moving over central KY affecting BWG/LEX early this afternoon.
Expect light to at times moderate rains as well as variable flight
conditions from IFR to MVFR through around 22Z at BWG/LEX.

We'll then see a break in the moderate, steady rains at all TAF
sites this evening with conditions improving to MVFR.  Lingering
light showers will still be experienced throughout the TAF sites
this evening though.

After 0Z, winds will pick up at the sfc and aloft as a LLJ
accompanies a low pressure riding northeast along the front.  Did
increase sfc wind gusts throughout the overnight hours.  Debated on
adding LLWS to the TAFs as well due to a 45-50 kt LLJ.  However,
since the BL will be pretty mixy and gusty overnight felt that a
true LLWS situation was not likely.

Steady rains, moderate to heavy at times, will make their way back
into the TAF sites after 9Z tonight as the cold front approaches
with flight conditions deteriorating to low end MVFR and then IFR
after 12Z.

The fropa will occur tomorrow afternoon so did include that
timing for SDF.  It's beyond the BWG/LEX TAF period however.

Finally there is a slight chance for thunder at the TAF sites
tonight into tomorrow morning ahead of the front, but felt it too
slim to mention at this point.

&&

.Hydrology...

Unseasonably warm, moist air continues to be pooled into the Ohio
Valley behind an aggressive warm front that traversed through
yesterday. This has been setting up for decent amounts of rain to
fall ahead of an approaching cold front from the west as the
atmosphere is laden with moisture. Precipitable water values are
forecast to reach levels at or above max (approximately 1.45 for
this time of year) and given the other meteorological parameters
falling into place, should yield highly efficient, numerous rain
showers. The best timing for the heaviest amounts of rain looks to
be overnight tonight into tomorrow, generally beginning to decrease
in coverage Sunday night as the frontal boundary moves through. QPF
totals are anticipated to be at the highest over the next 24 hours
with a range from about 1.5 to 3 inches and locally higher amounts
will be possible.

What this all translates to is the possibility for some minor areal
(see the issued Flood Watch for more details) and river flooding to
occur along prone banks. The location to watch initially looks to be
Dundee on the Rough River in the Green River basin. Current forecast
trends take this river level above action stage by as early as
tomorrow morning. Additional spots to watch over the next 24 to 36
hours include locations along the Green and Salt River basins as
well as small creeks and streams. This includes Rochester, Alvaton
(Drakes Creek), Woodbury, and Boston (Rolling Fork River). As the
precipitation moves off toward the north and east, additional basins
will be under close observation as the rain flows downstream.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...FLOOD WATCH THROUGH SUNDAY EVENING FOR INZ076>079-083-084-
     089>092.

KY...FLOOD WATCH THROUGH SUNDAY EVENING FOR KYZ023>030-053-061>063-
     070>075.

$$


Mesoscale........MJ
Short Term.......AMS
Long Term........EER
Aviation.........AMS
Hydrology........LG