241 
FXUS63 KLMK 280643
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
243 AM EDT Tue Jul 28 2020

.Short Term...(Today and tonight)
Issued at 225 AM EDT Tue Jul 28 2020

Well...the 2 big synoptic weather features are an upper low over 
Hudson's Bay and amplifying Western USA Ridge. Jet stream energy and 
cold air aloft will carve out trough over Finger Lakes region of W 
NY over to the Green Mtns over to Acadia NP ME. This will increase 
the W ridge with 595 m center anchored near Grand Canyon NP AZ. 
Ridge will amplify Nwd through Crater of the Moon NM ID to Glacier 
NP MT into the Canadian Rockies. This will cease the monsoon hyetal 
season for awhile with lots of high "dry heat". 

Well...for our CWA...Cool Front draped across the I 64 corridor and 
continues to produce some sct shra. With slow moving front this will 
continue along with some low clouds due to weak isentropic lift and 
deep llvl moisture.  The stratus will start burning off during mid 
to late morning. 

2 distinct weather areas today across the CWA.  Areas north of the 
front will have a bit of humidity reprieve with northwest winds 
ushering in some less sultry air.  Srn IN will see dew points 64-68 
F...much nicer than the lower 70s DPs over the past several days. 
Model soundings drop PWATs down to 1.2" at SDF by this evening, not 
too shabby for late July. 

South of the front muggy air and convergence will be focus area for 
storms cranking back up across S KY. Soundings have typical summer 
profile...with PWATs of 1.7-1.9". Heavy rainfall will remain the 
primary hazard.

Looks like front will be around BG Parkway by Noon...so focusing 
majority of PoPS along and south of the BG Parkway with highest 
across the bottom 3 tiers of downstate KY counties to TN border. 
Seems like 40-60% PoPS look reasonable.

By tonight...PoPS will be shifting southward and decreasing after 
sunset downstate.  Tonight's issue may be fog with low level moisture 
and crossover temps occur with valley and river fog. 

Weather Tidbits...

Today in 1997 was the Ft Collins Flash flood which killed 5 with 20 
ft wall of water.  

Tomorrow in 1945 B-25 hit 79th floor of Empire State Bldg in heavy 
fog killing 3 crew members and 11 in building.

&&

.Long Term...(Wednesday through Monday)
Issued at 230 AM EDT Tue Jul 28 2020

An active stretch of weather is expected for the Ohio Valley through 
the weekend as a stalled frontal boundary will continue to trigger 
shower and thunderstorm development, and multiple waves of mid-level 
disturbances arrive by the late work week and weekend. 

On Wednesday, the stalled frontal boundary situated east-west will 
dissect our CWA, giving the best chance of showers and storms to be 
south of the boundary. South-central Kentucky counties look to have 
the best chance of precip given the greater moisture and 
instability. With roughly 1000 J/kg of DCAPE and PWATs of 1.8-2.0 
inches, some heavy downpours and localized flooding should not be 
out of the question. 

A parade of mid-level shortwaves to the Ohio Valley will begin on 
Thursday. The Euro guidance suggests a sfc low will develop over the 
Ozarks in response to a 500 mb shortwave trough with a 500 mb 
vorticity lobe. This sfc low will propagate eastward along the 
stalled stationary boundary and eventually progress across the CWA 
Thursday night/Friday morning. Widespread showers and thunderstorms 
will be possible as we will see quite an increase in PWATs in the 
neighborhood of 2.5 inches. While CAPE will be best to our SW, we 
will still have marginal instability and wind shear to work with. 
Overall, thinking these showers and storms pose more of a flooding 
risk than severe threat. 

By Friday evening, another mid-level disturbance to our west 
generates another sfc low in the KS/MO/OK/AR region. As the first 
sfc low moves off to our east Friday evening, the second sfc low 
will be approaching from the west. This second low will bring 
showers and storms Saturday and Sunday. On Sunday, the low will 
continue to progress NE away from the CWA, draping an east-west warm 
front and north-south cold front across the Ohio Valley. As the warm 
front lifts northward, an 850mb LLJ will develop in the warms 
sector, increasing moisture advection with PWATs around 2.1-2.3 
inches. In response to the LLJ, expect gusty SSW winds on Sunday 
along with showers and storms until the cold front passes. Once the 
front passes, we should begin to dry out for Monday.

&&

.Aviation...(06Z TAF Issuance)
Issued at 110 AM EDT Tue Jul 28 2020

Well...WSR-88D has widely sct shra with most concentration around 
HNB right now. Based on HRR trends will keep SHRA vcnty in HNB and 
perhaps BWG for the next 6 hrs with weak frontal boundary in S IN. 
slides into the region. 

Challenge is really the IFR/MVFR stratus possibilities especially 
with HNB and the I-64 corridor.  Some of the data showing weak 
isentropic ascent with condensation pressure deficits maximized at 
950 mb. Still analyzing the data for low clouds. 

Confidence in the predictability of these showers and storms will be 
focused on BWG today as front slides south. If BWG picks up one of 
these brief IFR/MVFR reductions in visibility. Precip should 
decrease significantly after sunset.  

Classic decoupling tonight with light winds and radiational 
inversion (in late July) and possible crossover temps at HNB.  Will 
have 6SM BR at SDF for now 10-12z late tonight.


&&

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

$$

Short Term...JDG
Long Term...CJP
Aviation...JDG