Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 271732
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
132 PM EDT Mon Mar 27 2017

.Forecast Update...
Issued at 1025 AM EDT Mon Mar 27 2017

Updated the forecast to adjust POPs and t-storm chances.  The area
of showers/storms associated with a warm front will continue to move
northeast this morning with the front.  A few t-storms this morning
have had pea size hail and that possibility will continue with this
first batch of convection.

As we get into the afternoon hours, the threat for severe weather
will increase.  Moisture/temps will rise south of the warm front
especially over central KY and destabilization is expected.  The
amount of destabilization from early-mid afternoon is a bit
uncertain given morning convection and some cloud cover, however,
still think that at least 1000-1500 j/kg of CAPE is achievable over
most of the area...up to 2000 j/kg in south central KY.  So with
this instability and given 30-40 kt deep layer shear, severe storms
are certainly possible with the best timing between roughly mid
afternoon through midnight.  Based on the latest guidance, storms
could start a bit early in the 2-4pm time frame west of I-65.
However, the main threat for most areas still looks to be 5pm-
midnight.

Severe Wx Threats remain the same.  Damaging winds is primary. Large
hail and an isld tornado are possible as well.  Will need to watch
left over boundaries from this morning`s convection and the actual
warm front position as they may provide a focus for any isld spin
ups and enhancements of storms in general.

Issued at 700 AM EDT Mon Mar 27 2017

Warm advection band of showers and thunderstorms currently lifting
quickly northeast into western KY oriented NW to SE. This activity
is on the nose of the 850 mb LLJ/strongest moisture transport.
Nudged precip/thunder arrival an hour or two earlier in the grids to
account for faster motion.

These showers and storms will likely push into the western CWA
around 12-13z. Severe weather is not likely with morning convection,
but brief heavy rainfall, gusty winds, and lightning are possible.

&&

.Short Term...(This evening through Tuesday night)
Issued at 245 AM EDT Mon Mar 27 2017

...Strong to Severe Storms Possible This Afternoon and Evening...

Today`s mid-level feature of interest can be seen spinning in
eastern Kansas on WV imagery early this morning. This progressive
wave is forecast to eject due east across the OH Valley today into
tonight. Meanwhile, in the low levels, a surface low was analyzed
over eastern Oklahoma early this morning, with a subtle surface
boundary extending eastward into the TN Valley. Over NW Arkansas by
12z, the surface low is forecast to move northeast to southern IN by
late tonight. As this occurs, moisture return gradually ramps up in
the warm sector of the system. Surface dewpoints are forecast to
rise into the mid to upper 50s,  with 60 dewpoints possible in the
SW forecast area.

The atmosphere begins to destabilize by mid to late morning. Most
areas will stay dry through 15z. Latest hi-res models do suggest
isolated to scattered warm advection showers/storms moving into the
forecast area after 14-15z. Plenty of cloud cover throughout the day
will also help to suppress surface heating a bit. The latest RAP/GFS
soundings suggest MLCAPE values in the 500-1000 J/kg range, with the
higher values further to the south and west. This aligns well with
SPC`s Day 1 Outlook, which features a Slight Risk for central
KY/southern IN and an Enhanced Risk across western KY/TN.

Deep layer shear is also sufficient for sustaining organized
convection, with 0-6 km values of 35-40 kts. Most likely storm modes
are multicells and linear segments. Some bowing linear segments will
be possible, and the main severe hazard is damaging winds. However,
given the proximity of the surface low as it tracks roughly along
the Ohio River this evening, there is some potential for an isolated
tornado or two to spin up. RAP soundings show some backing of the
surface flow this evening, with effective SRH maxing out near 200-
250 m2/s2.

As far as timing, severe weather looks possible mainly from 5 pm -
midnight EDT. Low pressure moves east of the area by 12z Tue, and
some showers could linger into Tuesday morning east of I-65. Highs
will reach the low to mid 70s this afternoon, with lows in the mid
to upper 50s tonight. Tuesday will be cooler, but still a bit warmer
than normal, with highs in the mid 60s to around 70 degrees.

&&

.Long Term...(Wednesday through Monday)
Issued at 415 AM EDT Sun Mar 26 2017

The middle portion of the week will feature quiet weather, with a
dry forecast Tuesday evening through Wednesday evening. This is our
next brief window of upper level ridging before the next low
pressure system cycles through in this active flow pattern. Highs in
the mid 60s to low 70s Wednesday will warm into upper 60s to mid 70s
for Thursday.

Rain chances ramp up on Thursday as a deep upper trough approaches
the region, maxing out Thursday night into Friday morning. There is
at least a slight chance for storms during this period as well.
Decent agreement between 27.00z GFS/ECMWF on the cold front clearing
the forecast area Friday afternoon. Highs on Friday should be in the
mid to upper 60s, with cooler air filtering in behind the front.
Lows will drop into the 40s Saturday morning. Saturday is the
coolest day over the next week, with highs in the low to mid 60s.
Timing the next potential for precip is quite uncertain, but looks
to arrive by late Sunday or Monday. Sunday could end up dry, with
highs in the mid to upper 60s.

&&

.Aviation...(18Z TAF Issuance)
Issued at 131 PM EDT Mon Mar 27 2017

Main threat for this afternoon and early evening is the threat of
thunderstorms, some of which could be strong to severe. A warm and
moist airmass is moving into the region ahead of a surface low
moving into the mid Mississippi River Valley. Showers and storms are
already ongoing across SE Missouri/W Tennessee/N Mississippi and
will quickly move into our area this afternoon.

BWG will see the first round of storms as early as 2 PM CDT, with
the best threat lasting until 8 PM CDT. Lightning, brief heavy rain,
gusty winds, and hail are the main threats. Expect reduced
visibilities and ceilings at times.

SDF/LEX timing for the biggest threat should occur between 5 PM and
10 PM EDT. Lightning, brief heavy rain, and gusty winds are the main
threats. Expect reduced visibilities and ceilings at times.

Main storm threat diminishes around the latter part of the timing
windows mentioned above, however may be followed by shower activity
into the overnight. A return to dry conditions should return shortly
after midnight as a weak cold front swings through and winds veer
to the SW and W. Concerned about some low ceilings as we move toward
dawn on Tuesday and will advertise fuel-alternate prevailing. Can`t
rule out IFR toward dawn but will hold off mention until confidence
is higher.

&&

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

$$

Update...AMS
Short Term...EBW
Long Term...EBW
Aviation...BJS


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