-- Discussion containing changed information from previous version are highlighted. --
874
FXUS63 KLMK 220503
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
103 AM EDT Sat Jun 22 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Above normal temperatures expected again on Saturday.

*   Scattered showers and storms possible Sunday, and again by the
    middle of next week.

*   Heat Index may rise above 100 degrees on Tuesday.

&&

.UPDATE...
Issued at 922 PM EDT Fri Jun 21 2024

Evening observations show clear to partly cloudy skies across the
region.  The main area of clouds was across portions of south-
central Kentucky and these clouds will continue to move southeast
overnight.  Mid-evening temperatures had cooled down into the upper
70s and lower 80s in most locations, however the urban heat islands
were still in the upper 80s to around 90.  Quiet weather is expected
overnight with skies going mostly clear.  Lows will drop into the
lower 70s in many locations, though a few valley locations could see
some upper 60s (68-69).  The urban heat islands will remain warm
with mid-upper 70s.

After taking a look at high temperatures over the past few days,
it`s pretty clear that the modeling has a pretty bad warm bias.  The
models simply under did the cloud cover and didn`t take into account
the rather lush/green vegetation that we had in place.  Now, the
dryness over the week has led to the lawns browning up a bit, but
overall, we`re still pretty green.  The previous forecast had highs
in the upper 90s for tomorrow and that looks to be overdone.  Using
persistence and assuming a little less cloud cover, given that the
ridge builds slightly more over our area, current thinking is that
highs need to be lowered quite a bit.  Overall, high temps Saturday
will probably 1-2 degrees higher than what we saw this afternoon. In
fact, the latest NBM guidance has come down quite a bit.  For now,
will go with the CONSShort guidance for temps which will result in
highs in the lower 90s, with the urban areas pushing 95-96.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 315 PM EDT Fri Jun 21 2024

As expected, the center of a strong mid-level ridge was centered
over the Tennessee Valley as a 1022mb sfc high was stacked below.
This has help to provide continued hot weather across the Ohio
Valley. As of 2pm, temperatures were already near or into the low
90s with heat index values per the KYMeso showing mid/upper 90s.
Visible satellite imagery was showing mainly scattered cumulus
field over the area with some high broken clouds near the Ohio
River. This may help to just slightly limit afternoon highs but in
the overall scheme of things it won`t make much of a difference in
how hot it feels. Highs are still expected to be in the mid/upper
90s and with Td in the upper 60s/low 70s heat index values will
likely range 98-102.

Overnight into tomorrow the upper ridge will weaken slightly as it
presses southward and becomes more oblong west-east stretching
from the Desert Southwest across the Deep South. This will give us a
more zonal flow over the region aloft. At the surface, high pressure
will remain located just off to our southeast as weak sfc low
develops over the Central Plains and works into the Great Lakes as
an upper level shortwave works along the northern peripheral of the
ridge and into the Ohio Valley by tomorrow night. Little relief from
the heat as we go overnight as lows only bottom out in the low/mid
70s with upper 70s in our urban areas. Given the warmth we will be
a few degrees of the record warm lows.

As the sfc low and associated cold front approaches the Ohio Valley
during the day tomorrow, sfc pressure gradient will tighten helping
to increase the winds out of the southwest between 10-15 mph. Heat
and humidity will continue for another day with highs once again in
the mid/upper 90s and heat index values in the upper 90s to low 100s
once again. Likely will see more scattered to broken cumulus in the
afternoon. Forecast looks to remain dry thanks to a capping
inversion between 800-700mb but have silent PoPs just around 10
percent to our east along the I-75 corridor.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 315 PM EDT Fri Jun 21 2024

Though no drought exists in Indiana or Kentucky at this time, much
of Indiana is now considered "abnormally dry", and the region would
benefit from some rainfall. A cold front will push through the Ohio
Valley Sunday afternoon and evening, providing a bit of hope for
some wetting rains. Though the more anomalous moisture and stronger
dynamics associated with this system will be off to our northeast
ahead of a vort max crossing the Great Lakes, the boundary should
still be able to spark scattered storms in southern Indiana and
central Kentucky. Seasonally sufficient instability will be in place
along with typical late June weak deep layer shear and mid-level
lapse rates/capping. Nevertheless, dry mid-levels and steep low
level lapse rates may support gusty winds with the strongest
precipitation loading, and SPC SREF shows a 60% chance of DCAPE of
1000-1500J/kg. The tallest cores may produce some brief local sub-
severe hail given WBZ heights around 10k` and quite a bit of dry air
in sounding progs.

Monday looks dry behind the departing front with weak high pressure
overhead. High temperatures both Sunday and Monday will once again
be in the 90s, but humidity levels will be slightly more tolerable
on Monday with surface dew points 4-8 degrees lower than the
readings around 70 degrees we`ll see on Sunday.

Tuesday return flow behind Monday`s small area of high pressure will
bring some moisture and instability back to the region with isolated
summertime afternoon thunderstorms not an impossibility. Conditions
outside in that return flow will be quite uncomfortable Tuesday
afternoon, with temperatures in the middle and upper 90s, the heat
index peaking over 100 degrees for many (especially along/west of I-
65), and moderate/high WBGT of 84-86F.

Better chances for rain, however, will arrive Wednesday and
Wednesday night as another cold front enters the picture from the
northwest. As with Sunday`s system, some strong to severe storms
will be possible.

High pressure moving from Saskatchewan/Manitoba through the Great
Lakes to New England will give us a brief break from the 90s on
Thursday with highs in the middle and upper 80s. However, it looks
like we`ll bump back up to around 90 to finish the work week.

Though drought has not developed in Indiana or Kentucky yet, these
rain chances, especially on Sunday and Wednesday, will be very
important to keep drought at bay given the expected hot
temperatures. CPC temperature outlooks are leaning warmer than
normal through early July with drought development possible from
southern Illinois through much of Indiana to western Ohio as we
approach Independence Day, and a moderate risk of excessive heat
throughout the Ohio Valley June 30 - July 1.

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
-- Changed Discussion --
Issued at 102 AM EDT Sat Jun 22 2024

VFR conditions are expected through the upcoming TAF period.
Surface and upper level ridging will remain in control of the
weather in the short term period. Mostly clear skies and light winds
overnight. May see a little light fog over at HNB between 08Z and
12Z. After sunrise Saturday, winds will shift to the southwest with
speeds generally under 10kts for the day. In the afternoon, diurnal
Cu will begin to form around 5kft.
-- End Changed Discussion --

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
KY...Air Quality Alert until midnight EDT tonight for KYZ029>031.
IN...Air Quality Alert until midnight EDT tonight for INZ091-092.
-- End Changed Discussion --

&&

$$

UPDATE...MJ
SHORT TERM...BTN
LONG TERM...13
AVIATION...SRM