Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 110431
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1231 AM EDT Fri Jul 11 2014

...Updated Aviation Discussion...

...Forecast Update...
Issued 939 PM EDT Thu Jul 10 2014

Two changes for this update: the first was to account for the clouds
currently streaming across the southern third of the forecast area,
thanks to a passing disturbance from AR into MS. These clouds are
expected to continue to thin and clear out overnight, leaving mostly
clear skies across the entire forecast area as much drier air aloft
pushes in overhead. The other change was the mention of patchy fog
in valleys/near rivers/other prone locations. Could be enough
low-level moisture lingering and with the calm winds and plenty of
radiational cooling expected under the mostly clear skies, added up
to a potential for some development.

Issued at 623 PM EDT Thu Jul 10 2014

Updated PoPs across the very southeastern portions of the forecast
area to account for the slightest chance for shower activity over
the next couple of hours with the possibility for a rumble of
thunder or two. All activity will wane after sunset and have
maintained the dry forecast for tonight as such.

.SHORT TERM (Now through Saturday)...
Issued at 312 PM EDT Thu Jul 10 2014

Surface frontal boundary currently bisecting the region this
afternoon.  Overall, not that much of a dew point gradient behind the
front...except in our northeast where some light northeasterly winds
are pushing down a bit of drier air down into the Ohio Valley.
Water vapor loop shows a weak mid-level wave pushing through the
Ohio Valley. This feature will continue to lift northeastward this
afternoon and evening.  Isolated to scattered showers and
thunderstorms will continue to be possible...mainly across our
east-central sections.  This activity will diminish toward sunset
with all areas seeing a return to mostly clear conditions by
mid-late evening.  Afternoon temperatures, outside of the showers,
were in the lower to middle 80s.  As the evening wears on,
temperatures will fall into the upper 70s.

Surface high pressure will build into the region overnight and hold
sway across our area on Friday.  This will result in a mostly clear
night and a mostly sunny day on Friday.  Lows tonight look to cool
into the upper 50s across southern Indiana and into the lower 60s
across Kentucky.  Highs Friday will warm into middle 80s with most
areas seeing temperature ranges from 83 to 88.  The warmest areas
look to be across the south and southwest where some upper 80s will
be found.  Clouds will be on the increase Friday night as another
wave approaches from the northwest.  At this time, it appears that
mid-high level cloudiness will increase a bit.  Lows will cool back
into the lower-middle 60s.

.LONG TERM (Saturday Night through Thursday)...
Issued at 305 PM EDT Thu Jul 10 2014

...Active and very changeable weather conditions expected...

The main weather story during the extended period will be the highly
anomalous upper low/trough that models agree upon and rotate south-
east out of Canada into the Great Lakes early next week. Active
convective weather is likely across the Ohio Valley ahead of this
system over the weekend and early next week, with much cooler
weather behind the system by mid next week.

At the start of the period Saturday, a corridor of instability and
embedded thunderstorms should exist from about Nebraska to western
Ohio Valley, on the north and east periphery of a large upper ridge
over the southern Plains states. Models for the last few runs have
shown that mid-level clouds from this activity should move into our
northern forecast area on Saturday, and a couple showers are
possible early on. Otherwise, any spotty showers should end during
the day as the air mass remains relatively stable (compared to our
north and west). With some afternoon sun, high temperatures should
reach the upper 80s in southern IN to lower 90s in south-central KY.

For Saturday night, there are no definable forcing mechanisms, and
with nocturnal cooling, conditions should be dry. Only exception
could be parts of southern IN by Sunday morning for any convection
upstream that propagates southeastward toward/into the area. For
now, will only carry isolated convection in this area.

On Sunday, increasing low-level moisture and air mass destabilization
will commence, mainly over southern IN and north-central and east-
central KY. While most convective activity should again remain north
and west of our area, scattered afternoon storms are possible.
Capping and less instability should keep much of south-central KY
dry on Sunday. Afternoon temperatures Sunday will be the hottest of
the extended period, with reading at or above 90, and could approach
the mid 90s in spots.

Convection should increase Sunday night and Monday across the area.
With warm advection, deep moisture (precip water values increasing
to around 2 inches), and west-northwest moderate flow aloft, pattern
suggests that some MCS activity or a few convective clusters could
develop upstream and propagate toward southern IN and northern KY
late Sunday night/Monday morning. This would be ahead of the main
cold front associated with the upper trough. Given nocturnal
thunderstorms, strong wind gusts would be less likely to occur but
not out of the question, but locally heavy rain is likely.

On Monday, storms should continue moving southeast across the area,
possibly redeveloping on outflow boundaries. Convective evolution
Monday is tough to discern given probability of some morning
activity and associated convective boundaries, which could sweep
instability south into southern KY in the afternoon, similar to what
happened this past Tuesday. Nevertheless, with the synoptic cold
front still to the north and west, at least scattered renewed cells
may develop late Monday afternoon over northern sections of forecast
area. Locally heavy rain and strong convective wind gusts are
possible Monday depending on instability and low-level lapse rates.

As the synoptic cold front approaches and flow aloft increases in
response to the upper trough Monday night, models differ on what
will happen. Latest GFS develops a new band of thunderstorms (QLCS)
along the front, while ECMWF hints that most activity will be with
the residual convective boundary farther south, while GEM hints that
a narrow second band could form north with more activity south.
Given forcing, could see another line develop along main front, but
tenuous for now so will include generic chance POPs over entire
area. Any secondary band could contain strong storms.

Cold front moves through on Tuesday which will clean out any
leftover precip and usher in much cooler, lower humidity air. Expect
highs in the mid or upper 70s mid week with lows in the 50s, or 10
or more degrees below normal. Given the cool trough aloft and
surface heating during the afternoon, spotty diurnal showers could
occur, but much of this should stay just to our north so will keep
mid-week forecast dry.

&&

.AVIATION (06Z TAF Update)...
Issued at 1215 PM EDT Fri Jul 11 2014

Well...VFR fcst with High pressure over the Wolverine State which is
keeping light N-NE sfc flow early Friday morning. This 1024 mb
anticyclone center will move to the Empire State with the sfc ridge
from ME to KY. This will switch sfc winds to light easterly by this
evening and and to light SWLY by Sat morning.

Will have to watch BWG obs and web cams for some MIFG and HZ
around daybreak. Otherwise some few CU during the day and some sct CI/CS.
Convective feature over the Mo/MS River Valley will spill mid deck
clouds on Saturday.

&&

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

$$

Update.........lg
Short Term.....MJ
Long Term......TWF
Aviation.......JDG




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