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Area Forecast Discussion (AFD)

Issued by Louisville, KY (LMK)

FXUS63 KLMK 211045

Area Forecast Discussion
National Weather Service Louisville KY
645 AM EDT Wed Aug 21 2019

...Updated Aviation Discussion...

.Short Term...(Today and tonight)
Updated at 315 AM EDT Wed Aug 21 2019

...More Strong Storms Possible Later This Evening...

Things are currently quiet across the CWA this morning as evening 
convection has pushed well out of the area and diminished. Forecast 
soundings and observed AMDAR soundings show a notable inversion, and 
this is expected to persist for the remainder of the morning and 
into the afternoon. Above the inversion, there is still some 
instability as MUCAPE values around 500 J/KG at the moment. It is 
interesting to note that hi-res models were hinting at some 
convective development east of I-65 toward the pre-dawn hours, 
likely associated with a weak LLJ uptick. Still can't rule out this 
scenario playing out, but recent runs of the HRRR have backed off 
this thought. Included a slight chance east of I-65 for a few hours 
this morning, but otherwise expect dry conditions once the subtle 
LLJ exits and there is no trigger to get parcels above the inversion.

Assuming the inversion does hold as suggested by forecast soundings, 
the bulk of the day should be hot and dry once again. Expect most 
highs to reach the low to mid 90s. 

By early evening, a W to E oriented cold front trailing from an 
eastern Canada storm system is expected to drop south toward our 
region, and capping should begin to weaken across our western CWA. 
Ahead of the cold front, strong instability is expected to develop 
across our western CWA by late afternoon/evening. HREF probs suggest 
likely values over 3000 J/KG of BL CAPE, along and west of I-65. 
Likely values over 2000 J/KG can be expected across the rest of the 
CWA by evening. Overall deep layer shear will be lacking and 
displaced well to the north of our region, so the scattered to 
numerous storms that are expected to develop should be pulse in 
nature. However, given the strong updrafts localized wet microburst 
potential will be there along with localized heavy rain. Some hail 
is also possible, but should mostly be a sub-severe type of threat. 
The SPC Marginal Risk looks pretty good given the lack of deep layer 
shear. The threat for scattered storms should last off and on for 
most of the overnight so will keep fairly high pops in for that time 

.Long Term...(Thursday through Tuesday)
Updated at 330 AM EDT Wed Aug 21 2019

Thursday through Friday...

An elongated cold front will push through the region Thursday and 
likely stall out over south-central/southern Kentucky through the 
end of the week as an upper level trough moves across the upper 
Great Lakes and into the northeastern CONUS. This will bring chances 
for showers and storms throughout Thursday and Friday. There looks 
to be moderate instability as the front moves through, with SBCAPE 
values around 2000 J/kg across much of the area during the day 
Thursday and Friday, and decent wind shear with 0-6 km values up to 
30-35 kts. As a result, storms will be mostly pulsey in nature, with 
some organized storm clusters possible. Main storm threats will be 
strong winds, frequent lightning, and heavy rainfall. SPC has added 
most of the area to a marginal risk Thursday. 

Temperatures will cool through the end of the week with highs in the 
low to mid 80s and lows in the 60s by Friday.  

Saturday through Tuesday...

Weak zonal flow looks to take over in the beginning of the weekend 
as the upper level trough pushes off of the east coast and upper 
level ridging dominates the north-central CONUS. At the surface, a 
high pressure system will build over the northern Great Lakes. 

Previously, models were hinting at drier conditions for the weekend, 
however, the 00Z GFS and 12Z ECWMF are suggesting that a weak cut-
off low will be meandering around the region this weekend, bringing 
slight chances of precipitation Saturday and Sunday, mainly to 
southern Kentucky where the environment is less capped. Placement 
and timing are variable between models though, resulting in low 
confidence. Models then show a stronger upper level trough moving 
across the region Sunday night into Monday, bringing more 
shower/storm chances. The GFS is much more aggressive with the 
strengthening of the upper level trough as compared to the ECMWF, so 
am leaning towards a blend of the two solutions.  

Temperatures will remain pleasant this weekend, with dewpoints in 
the 60s and highs in the low to mid 80s. We will then warm-up for 
the beginning of next week, with highs pushing into the mid to upper 


.Aviation...(12Z TAF Issuance)
Updated at 645 AM EDT Wed Aug 21 2019

Have seen some fleeting fog on webcams at HNB this morning, but the 
main story is LEX where minimums have been occurring for a couple of 
hours. Expect improvement fairly quickly with sunrise this morning, 
with VFR returning.

Otherwise, expect VFR today with diurnal cumulus developing and a 
steady SW wind. Today's cumulus cloud bases should be around 4 K 
feet, with tops up around 7 or 8 k feet. Looks like a cap should 
keep storm chances in check for most of the day, but another complex 
could come into the area from the west later in the evening. Handled 
this with continued prob30 mention.




Short Term...BJS
Long Term...JML