Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 251044
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
644 AM EDT Mon May 25 2015

...Updated Aviation Discussion...

.SHORT TERM (Now through Tuesday)...
Issued at 303 AM EDT Mon May 25 2015

An upper level trof above the Ozarks and vorticity stretched out
along the lower Mississippi Valley have been producing showers and
thunderstorms to our west throughout the overnight hours.  These
features will head northeast today and will spread showers and
embedded thunderstorms through southern Indiana and central
Kentucky.  While severe weather is not expected, high precipitable
water values and deep warm cloud depths suggest locally heavy
downpours will be possible.  The best chances for rain still appear
to be during the first half of the day west of I-65 and this
afternoon to the east.  Despite a warm start to the day, clouds and
rain will prevent temperatures from rising much.  Will continue with
going forecast of highs around 80.

Convection should taper off this evening, and then regenerate after
midnight as the next wave, positioned near El Paso TX this morning,
starts to enter the region from the west.  It will be another warm,
muggy night with lows 65 to 70.

On Tuesday that upper wave will cross the region over the course of
the day, resulting in shower and thunderstorm activity.  Though wind
fields will be a little stronger on Tuesday, instability does not
look very impressive -- especially if we have widespread convection
in the morning. SWEAT Index remains AOB 300 all day.  Wet bulb zero
is fairly high, there`s not much dry air aloft, and mid-level lapse
rates remain fairly weak. The occurrence of strong/severe storms
will be highly dependent on just how much surface destabilization we
can realize.  If we see less shower/storm activity in the morning
than currently expected, and a few more holes in the clouds to allow
some insolation, then the potential is there for some stronger
storms.  Confidence, at this point, is somewhat lower than usual for
Tuesday.

With or without strong/severe storms Tuesday, locally heavy
downpours will certainly be a possibility.

Temperatures Tuesday should be similar to Monday (depending greatly
on how much rain and/or sun we receive), and we`ll go with max temps
around 80 once again.

.LONG TERM (Tuesday Night through Sunday)...
Issued at 250 AM EDT Mon May 25 2015

The main focus in the long term is precipitation chances each day as
a moist and seasonably warm airmass holds over the lower Ohio
Valley.

The synoptic pattern Tuesday night is expected to feature a weak
shortwave trough passing through the lower Great Lakes. In addition,
the right entrance region of a 300 mb jet will be favorably
positioned over the region, providing weak but sufficient forcing
for ascent. Some elevated instability is noted in the soundings, so
will continue to carry 30 to 50 percent POPs during the overnight.
Another mild night with lows 65 to 70.

Though the main upper level forcing moves off to the north/east
Wednesday, the moist and warm airmass will result in 1500 to 2000
J/kg of SBCAPE by afternoon in a mostly uncapped environment. This
supports diurnally driven thunderstorms for the afternoon to early
evening hours. Shear environment is very weak, so not anticipating
any strong organized convection. Highs 78-82.

25.00z deterministic and ensemble guidance show a weak shortwave
trough moving through southern Indiana Thursday, which may be enough
of a focus for shower/storm enhancement during the afternoon.
Moisture/instability not as favorable though, so kept POPs mainly in
the 30 to 40 percent range.

Thursday night into Saturday, forecast models are agreeing that the
southeast US upper ridge and surface high begin to build back over
the region. This could result in a drier period and for now carried
20-30 percent chance of afternoon showers/storms. 850mb temps nudge
up a degree or two these days, so highs 85-88 are expected with
overnight lows in the mid/upper 60s to around 70.

Saturday night into early next week, models begin to show the
central Plains trough advance eastward again while a surface front
slowly approaches from the northwest. There is uncertainty in how
fast the southeast US ridge breaks down, allowing this system to
approach the local area. A time trend analysis suggests the ridge
may hold longer into the weekend. As a result, a model consensus of
30 to 40 percent POPs seem reasonable at this time but could end up
being lowered later if trends in more/stronger ridging continue.
Plan on near normal temperatures of highs in the low/mid 80s and
lows in the 60s.

&&

.AVIATION (12Z TAF Update)...
Updated at 644 AM EDT Mon May 25 2015

An upper wave currently over the lower Mississippi Valley will head
northeast today and will bring showers and embedded thunderstorms to
the region. Ceilings, and occasionally visibilities, will be low-end
VFR or high-end MVFR.  Southerly winds will become gusty, with 3-sec
speeds of 20-25 knots possible.

Convection will taper off by late afternoon at SDF/BWG and early
evening at LEX.  Redevelopment will then be possible at after
midnight tonight and into Tuesday morning as another wave comes in
from the southwest.

&&

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

$$

Short Term........13
Long Term.........ZT
Aviation..........13




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