Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 250514
AFDLMK

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

...Updated Aviation Discussion...

...Forecast Update...
Updated 945 PM EDT Sun May 24 2015

Warm and increasingly moist southerly flow has taken hold over the
Ohio Valley, with temps staying up this evening in a mixy boundary
layer. NW-SE oriented band of showers and T-storms has developed and
sits along and just south of I-24 from Paducah to near Nashville.
However, this precip is lifting nearly due north, and doesn`t really
extend east of I-65. Therefore, the going forecast is pretty well on
track, with slight or low chance POPs in our western counties
beginning late this evening and continuing past midnight. Toward
daybreak, we could see precip chances increase and/or expand
eastward as the low-level jet starts to translate eastward into our
area.

.SHORT TERM (Now through Monday Night)...
Issued at 301 PM EDT Sun May 24 2015

A subtle warm front has lifted north of our CWA, with a surge in
deeper moisture over our western CWA showing up on SPC mesoanalysis
and visible satellite. Will continue to keep a 20% chance of a
shower or storm through the afternoon across western tier or two of
counties. Soundings do appear to show a mid level inversion around
15 K feet, which could be a limiting factor for any development.
Otherwise, temperatures are on track to top out in the low and mid
80s and south winds will continue to gust up around 20-25 mph at
times.

Steady S flow will continue overnight with increasing mid and upper
clouds. Expect fairly mild lows as a result, only bottoming out in
the upper 60s and low 70s in most spots. The far east may bottom out
in the mid 60s around Midnight, before potentially climbing a bit
toward dawn.

A 40-50 knot low level jet will ramp up over the area tonight
underneath the right entrance region of a weak upper jet. The
moisture transport and weak forcing associated with this will allow
for increasing shower/storm chances across our west toward dawn.
Expect whatever is ongoing at daybreak to slowly progress east and
weaken as it does so. Precipitation chances for the rest of the day
will then be dependent on the morning convection and any
redevelopment along differential heating, likely focused more across
our eastern CWA. More subsident and worked over airmass to the west
is expected to have less coverage and a few breaks in the clouds
possible. Can`t rule out a stronger storm or two as 0-6 km shear
should be between 25-30 knots, which is marginally sufficient for a
multicell cluster. However, instability is expected to be fairly
meager 1000 J/Kg or less, so not expecting severe. Main threat will
be brief heavy downpours and gusty winds. Gradient winds themselves
will be quite steady with gusts up around 25 mph possible.

High temperatures will be tricky, but generally thinking the west
will have some trouble recovering from morning convection so will
keep them in upper 70s. Meanwhile, the east will have some time to
heat up so will go with low 80s.

Scattered convection mainly in the east should wane in the evening
hours, with a relative lull through the first part of Monday night.
However, expect isolated to widely scattered shower/storm chances to
again get going toward dawn. Another mild night is in store with
lows in the 65-70 range.

.LONG TERM (Tuesday through Sunday)...
Issued at 300 PM EDT Sun May 24 2015

Not too much change in the overall extended forecast period with
this forecast issuance.  We`ll see the upper level ridge break down
and shift to the eastward on Tuesday which will allow a mid-level
wave to push into the region.  This should result in widespread
shower and thunderstorm development.  Moisture profiles indicated
that we`ll see relatively deep saturation so heavy rainfall looks to
be a good possibility.  Wind fields aloft are strong, but
instability looks to be questionable given anticipated morning
convection.  Thus, think overall severe weather threat is rather
marginal at this time.  However, if we did see some breaks in the
clouds in the afternoon, we could attain sufficient instability for
strong convection.  This will be something to watch over the next
few days.   It will be rather breezy on Tuesday due to the pressure
gradient, so winds of 15-20 mph with gusts up to 25 mph will be
possible.  We did keep temps down slightly for Tuesday based on
expected cloud cover.  Highs in the upper 70s to the lower 80s still
look reasonable.

By Wednesday, main forcing looks to be to our east, with a slightly
drier atmospheric profile.  Diurnally driven convection looks likely
with iso-sct convection in the afternoon/eve.  Temperatures easily
climb into the upper 70s to lower 80s, with overnight lows in the
lower-middle 60s.


For the remainder of the work week, some upper level ridging will
try to build back into the region.  Flow aloft weakens slightly, so
overall progressive pattern looks to slow down a bit.  Typical of a
summertime pattern, we`re likely to see scattered diurnally driven
convection during the afternoon hours.  Highs should be a little
warmer with low-mid 80s in most areas with overnight lows in the
60s.

As we head into the weekend, model guidance reveals the typical day
6-7 spread in their solutions.  Upper level ridging looks to hold
into Saturday as a stronger trough moves out of the Intermountain
west.  This looks to pose a risk of additional showers/storms
Saturday afternoon, with much better chances of precipitation
holding off until Sunday.  Highs Saturday look to warm into the 80s
again, but will be a bit cooler on Sunday with highs in the upper
70s to around 80.

QPF amounts for the period look to be rather excessive out to our
west with the main bulk of precipitation extending from Texas
northeastward into the Midwest.  As mentioned above, our main
precipitation chances look to come on Tuesday and Sunday.  QPF
amounts of 2-3 inches will be likely over the coming week.  The
higher amounts will be out across the west, and the lower bounds out
over the east.  This rain, falling over the week looks to be spaced
out enough to preclude hydrologic issues at this time.

&&

.AVIATION (06Z TAF Update)...
Updated at 114 AM EDT Mon May 25 2015

The pre-dawn hours will be breezy with a tight surface gradient
between high pressure off the East Coast and low pressure over the
Midwest, and a low level jet streaming from the lower Ohio Valley to
the Great Lakes.  As a result of the stronger winds just off the
surface, as predicted by the models and shown on recent AMDAR
sounding out of SDF, will continue with borderline LLWS at the
western TAF sites (nearer the LLJ).

An upper wave currently over the lower Mississippi Valley will head
northeast today and will bring showers and embedded thunderstorms to
the region.  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 SDF after
midnight tonight as another wave comes in from the southwest.

&&

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

$$

Update.........RAS
Short Term.....BJS
Long Term......MJ
Aviation.......13





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