Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 181357
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
956 AM EDT TUE JUN 18 2013
Issued at 955 AM EDT Tue Jun 18 2013
Morning cloud cover across the southeast forecast area should keep
highs temperatures several degrees under readings to the northwest.
Bumped highs up a couple of degrees in the latter region given good
heating getting started now. Still think initiation in that area
will hold off till at least mid afternoon so have tweaked pop grids
to cover that. Also reduced afternoon chances across the south,
where lack of heating should limit coverage. The NARRE and to a
lesser extent the latest HRRR agree with this scenario.
As for severe chances, shortwave trough over northern Iowa should
move to the Chicago area by late afternoon. Falling heights ahead of
this trough should bring cooler air aloft. Afternoon forecast
soundings indicate less moisture to work with and CAPEs not as high
as yesterday, but lower wet-bulb zeroes. With drier air in the mid
levels, think damaging wind gusts and hail will be the main threats
as storm clusters develop over the north and move southward.
Issued at 635 AM EDT Tue Jun 18 2013
Area of light rain continues to shift slowly eastward this morning.
Main area of rain should be east of I-65 after 12Z and then exit the
I-75 corridor by mid-morning. Drier air to the northwest will move
into the region this morning which should allow skies to partially
clear from the west to the east. Current forecast has this well in
hand, so only minor updates were made to the grids to better time
the exit of the rainfall this morning.
.SHORT TERM (Now through Wednesday)...
Issued at 324 AM EDT Mon Jun 18 2013
Radar continues to show widespread light rain continuing across the
forecast area this morning. Convectively induced MCV continues to
push through middle Tennessee this morning with the heaviest
activity mainly staying to our south. Some moderate rain showers
will be possible across our southern Kentucky counties over the next
few hours...and a rumble of thunder or two can not be ruled out.
Elsewhere, light rain is beginning to diminish across our northwest
and western sections. Expect to see precipitation come to an end
toward sunrise over our northwest sections. Additional convection
is forecast to develop just to our northeast...between Indianapolis
and Covington later this morning...according to our local WRF model
run. Indeed, convection has developed over the last hour in this
general area. This activity is forecast to slide southeast and may
affect our far NE counties after sunrise. However, the local WRF
shows this activity decaying in the 13-14Z time frame. Temperatures
this morning will continue to be nearly steady state with lower to
middle 60s in the north and upper 60s to around 70 in the south.
Patchy fog will be a possibility in the typical low-lying and fog
prone areas until sunrise.
Somewhat of a complicated and overall low confidence forecast today
regarding cloud cover and additional convection. Widespread
convective debris will initially limit our solar insolation this
morning...keeping morning temperatures in the lower to middle 70s.
However, as the afternoon wears on, we should see cloud cover
decrease...especially across the west and northwestern sections
which will allow temperatures to warm into the lower to middle 80s.
Real question mark is over the east...where cloud cover may keep
temperatures in the upper 70s to around 80. Should clouds break up
faster, temperatures in future forecasts may need to be increased
As we heat up, we will destabilize once again thanks in part to
slightly cooler mid-level temperatures which will allow lapse rates
to approach 7 C/km. The afternoon heating combined with dewpoints
in the 60s should yield a moderately unstable atmosphere resulting
in isolated-scattered convection to develop across the region. With
this in mind...plan on keeping isolated-scattered PoPs in the
forecast for this afternoon.
More interesting convective development is possible late this
afternoon and evening as mid-level wave dives down from the Dakotas
into the Ohio Valley. As this feature pulls into the region, it
will encounter the moderately unstable and weakly sheared
atmosphere. Overall shear is not that great as we will be located
on the southern edge of the westerly flow with values pegged at 35
to maybe 40 kts. Latest high resolution NAM...WRF...and LMK WRF
models all develop convection across central Indiana this afternoon
and then drop it southeast into our southern Indiana counties by
this evening. This activity should continue into areas south of the
Ohio River early this evening, but is expected to weaken with the
loss of heating and increasing PBL stability. Some storms could be
on the strong to severe side this afternoon across our northern
sections. Based on the severe parameters of shear/instability that
damaging winds and near severe hail would be possible. Overall, feel
that the threat is likely to be more to our north where the stronger
shear would be located (up around the I-70 corridor). After the
activity dissipates, clear to partly cloudy skies are expected for
the overnight period with lows in the lower-middle 60s.
More quiet and tranquil weather looks likely on Wednesday with
afternoon highs warming into the lower to middle 80s.
.LONG TERM (Wednesday Night through Monday)...
Issued at 252 AM EDT Tue Jun 18 2013
The long term will be fairly quiet with just occasional slight
chances for thunderstorms. At the surface high pressure will slide
east of the region early in the period and we will then remain in
between the high pressure to the east and low pressure to the west.
Aloft a ridge will build from Texas to the Lower Mississippi River
Valley and then shift slowly eastward.
Mainly dry conditions are expected through the long term. A few
different weak disturbances may bring a slight chance of showers
thunderstorms to south central Kentucky on Friday, to northeastern
portions of the forecast area on Sunday, and to the whole area on
Monday. These storms are not expected to be widespread at this time.
Temperatures will warm into this weekend. Highs Saturday through
Monday are expected to top out in the upper 80s to lower 90s. Lows
will go from the lower 60s on Thursday morning to upper 60s and
lower 70s this weekend.
.AVIATION (12Z TAF Update)...
Issued at 645 AM EDT Tue Jun 18 2013
Widespread rain shower activity continues to press eastward this
morning. The rain has already cleared KSDF and will clear KBWG and
KLEX within the next hour or so. After that, VFR conditions are
expected across the region for the remainder of the morning and into
the afternoon hours.
Some isolated-scattered convection will be possible later this
afternoon due to convective heating. In addition, a mid-level
disturbance is forecast to drop into the region from the NW later
this evening and may spawn additional convection across southern
Indiana which may affect KSDF and KLEX after 19/00Z.