994
FXUS63 KLMK 180824
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
424 AM EDT Sat May 18 2024

.KEY MESSAGES...

*   Dense Fog Advisory through 1000 AM EDT.

*   Showers and a few thunderstorms tapering off by this evening.

*   Dry weather arrives Sunday with unseasonably warm temperatures
    Monday and Tuesday.

*   Showers and thunderstorms return Tuesday night into Wednesday.
    Confidence remains low in the potential for severe weather.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 424 AM EDT Sat May 18 2024

Early morning satellite imagery showed mostly clear skies across
southern Indiana and much of central Kentucky.  The only cloudiness
we had was down in our far southeast across the Lake Cumberland
region where a few showers continued.  Otherwise, dense fog has
developed across the region.  The fog is not all that widespread
with the greatest concentration across the Bluegrass region of
central Kentucky back to the southwest along and just south of the
Parkways.  Some patchy dense fog has developed as far north as
southern IN.  With skies remaining clear and winds continuing to
slack off, guidance suggests that fog will become more widespread as
we head towards sunrise.  Given the dense nature of the fog, a Dense
Fog Advisory was issued earlier and will continue until 10 AM EDT.

For today, we`ll see the fog this morning mix out by mid-late
morning with partly cloudy skies becoming commonplace.  Overall flow
pattern across the region will remain quite stagnant as upper level
troughing will remain in place across the region.  It will be a
muggy day across the area.  As temperatures warm, model soundings
show a relatively uncapped airmass in place.  Recent model trends
continue the idea of suppressing rain chances further south.  Based
on latest NAMnest and HRRR runs, the best chances of precipitation
today look to be south of the KY Parkways.  Area proximity soundings
show poor lapse rates and very weak shear which suggests that
convection will be relatively unorganized.  Nonetheless, scattered
showers and a few storms will be possible with locally heavy
rainfall and lightning being the main hazards.  Highs on the day
will be in the upper 70s to the lower 80s.

For tonight, upper ridging will build into the region from the west
resulting in drier conditions and mostly clear skies.  We`ll run the
risk of seeing some more fog again given the clear skies, light
winds, and wet ground.  Overnight lows will be in the lower 60s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 424 AM EDT Sat May 18 2024

Synopsis...The medium range period will be characterized by
amplification of the large scale flow that will initially favor dry
and increasingly hot conditions through early next week with active
weather starting on Wednesday. After a weak, southern-stream
shortwave trough moves away from the region Saturday into Sunday,
mid-level ridge will stretch from Texas into the Northeast US in
response to strengthening dome of high pressure over Mexico and
upstream energy phasing. The resultant mid-level cyclonic
circulation will be conformed by upper low over southern Canada and
a series of shortwave troughs ejecting across the Midwest by the
middle of next week. Of particular interest is the leading shortwave
trough and attendant surface low as they will push a cold front
towards the Ohio Valley on Wednesday, raising the chances of strong
to potentially severe storms.

Model Evaluation/Confidence...Overall, deterministic global models
(ECMWF/CMC/GFS) are in good agreement on how the synoptic features
will evolve through Tuesday. As expected, forecast confidence starts
to diminish on Wednesday and thereafter given the fairly complex
wave interaction between the Canadian upper low and parade of
shortwave troughs. Nonetheless, most recent runs have an overall
better consensus on the position of the occluding surface low and
timing of the frontal passage on Wednesday. Correspondingly, CSU and
NCAR severe weather guidance continue highlighting low probabilities
of severe storms for Wednesday. Another wave of heavy rainfall might
be in place late next week (probably Friday) but confidence in
specifics at this time is rather low to mention any significant
weather.

Sunday - Tuesday...Dry and increasing hot weather is anticipated
during this period. First of all, rain chances for Sunday have
greatly decreased compared to yesterday forecast. The influence of
the building mid-level ridge and surface high pressure over the
region will keep rising motions confined below a 700-mb capping
inversion while pronounced dry layer settles in on the mid levels.
As the surface high pressure moves to the Mid Atlantic and the next
storm system approaches from the Midwest, low-level winds will turn
to the south on Monday and southwest on Tuesday enhancing the warm
and humid air influx. Highs both days should be in the mid to high
80s with urban areas probably reaching the 90 degree mark. Although
a cu field will develop each afternoon, rain chances will be
negligible given the dry and stable environment. Only exception
would be Tuesday afternoon and evening when a few light showers
might move in ahead of the cold front. Last but not least, hydro
guidance has changed radically as HEFS now reflects less than 10% of
minor river flooding for Rochester and Woodbury. This reduction was
primarily driven by recent rainfall trends and forecast
accumulations of less than an inch in the aforementioned river
basins.

Wednesday...Convection-allowing and parameterized models depict two
distinct waves of rainfall on Wednesday. The first wave, probably
subsevere, should arrive Wednesday morning as overnight convection
weakens and outruns the best frontal forcing roughly stalled along
the Wabash Valley as the shortwave and attendant surface low moves
farther away to the north. The second and strongest wave should
begin along and ahead the effective frontal boundary in the
afternoon hours and translate across the forecast area in the
evening. In this case, timing of convection will be key as earlier
storm activity will tap into daytime instability to produce better
chances of organized, strong convection. Overall, forecast space
parameters agree with CSU and NCAR algorithms having a greater
severe threat along and north of the OH river.

Thursday - Friday...Daily rain chances will continue the second half
of the week with potential for heavy rainfall on Friday as another
system tracks over or close to forecast area. Localized areal and
river flooding cannot be ruled out.

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 424 AM EDT Sat May 18 2024

Main concern for the overnight is the clear skies and wet ground
from recent rainfall.  Visibilities have started to tank over in the
east with a mix of low cloudiness and fog developing.  Looking at
the latest guidance, it appears that we`ll see fog develop at the
terminals overnight and have subsequently lowered cig/vsbys down in
to IFR and below for the overnight, especially in the 18/08-12Z time
frame.  After sunrise, cigs/vsbys will quickly rise through the IFR
and MVFR range before becoming VFR by late morning.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Dense Fog Advisory until 10 AM EDT /9 AM CDT/ this morning for
     KYZ023>043-045>049-053>057-061>067-070>078-081-082.
IN...Dense Fog Advisory until 10 AM EDT /9 AM CDT/ this morning for
     INZ076>079-083-084-089>092.

&&

$$

SHORT TERM...MJ
LONG TERM....ALL
AVIATION.....MJ