133 
FXUS63 KLMK 082359
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
659 PM EST Fri Mar 8 2019

...Updated Aviation Discussion...

.Short Term...(This evening through Saturday)
Issued at 301 PM EST Fri Mar 8 2019

...Breezy with Strong to Severe Storms Possible Saturday...

The morning snow is becoming a distant memory today as warmer air 
works into the region. Most obs in the area generally range from 
upper 30s to mid 40s with lots of overcast skies. Some showers are 
ongoing near the TN/KY border now, and should persist through the 
next several hours before tapering off this evening.

Overnight, we should remain dry. A stationary front will remain 
draped across the lower Tennessee Valley, and most of the 
precipitation associated with that front will stay south of the KY 
state line. Clouds/stratus will linger here overnight, and we could 
see some patchy fog or mist develop late.

Strong low pressure ejects out of the Plains tomorrow and heads 
toward the Midwest, setting the stage for potential active and 
severe weather. We'll start out the morning well north of the warm 
front, but as the low slides MO/IA/IL, we'll see the warm front try 
to gradually lift northward. Most models indicate some showers and 
elevated convection moving into our area between 12-15z Saturday. 
The main threat with the morning storms will be heavy rainfall, as a 
substantial surface inversion will eliminate any wind/tornado threat 
despite strong shear profiles. Can't rule out some small hail in the 
stronger storms, though the lack of dry air in the mid levels of the 
atmosphere won't be very conducive for bigger hail in the morning.

As we head into the afternoon hours, models begin to surge a 
corridor of +60 dewpoint air into western Kentucky and southwestern 
Indiana as the warm front lifts northward. Drier air aloft may allow 
for a lull in showers/storms and potentially some breaks in clouds 
to form in these areas. It's during this timeframe that we'll begin 
to see a transition from elevated instability to surface based 
instability as the near-surface CIN is eroded. Storms then look to 
form in the warm sector ahead of a pre-frontal trough in far western 
KY and southern IL, tapping into the surface based instability. 
Storm mode via high-res models indicate a mix of linear/bowing 
segments and discrete convection as it pushes eastward. Model 
forecast hodographs within the warm sector show substantial long, 
clockwise curvature, indicating very strong low level shear and 
veering with height. This will result in an environment with ample 
storm relative helicity that will be supportive of a potential 
tornado threat, assuming any surface based instability can be 
realized.

But that's the big question for tomorrow... how far north and east 
does the surface based instability translate? Most models indicate 
that the peak surge of higher dewpoints and surface based 
instability will be west of I-65, with a gradual waning in those 
parameters after 00z. There appears to be a small window of 
opportunity in our region for severe storms, from late afternoon 
into early evening, where a zone of surface based instability and 
shear parameters could align. Storms in this zone would be capable 
of all facets of severe weather, including damaging straight line 
winds, heavy rainfall (resulting in localized flooding), hail, and 
isolated tornadoes. The tornado threat will have to watched 
especially closely with any discrete supercells that form within the 
warm sector. A number of high-res models show storms weakening as 
they approach the I-65 corridor, which makes sense given the sub-par 
thermodynamics along and east of this area. Still can't rule out 
isolated severe storms east of I-65, but the overall thermodynamic 
environment just won't be very supportive of it. Think the current 
SPC Day 2 Outlook highlights the severe threat very well.

In a nutshell, here's what we're thinking for specifics of the 
potential severe setup:

* Timing: 4pm - 10pm
* Storm mode: Mix of linear/bowing segments and discrete storms
* Threats: Straight-line damaging winds, heavy rainfall, and hail, 
  with an isolated tornado threat, mainly west of I-65.

One other thing worth mentioning... with such strong wind fields in 
place, it won't take a lot of mixing to get some stronger gradient 
wind gusts to reach the surface. Went ahead with a wind advisory 
mainly south of the I-64 corridor and west of the I-65 corridor, 
where the best potential for +40mph gusts will be during the 
afternoon and early evening hours.

.Long Term...(Saturday night through Friday)
Issued at 230 PM EST Fri Mar 8 2019

...STRONG STORMS POSSIBLE MID-LATE NEXT WEEK WITH POTENTIAL FOR MORE 
HEAVY RAINFALL...

A quiet period of weather will get us started Sunday and continue at 
least through Tuesday. With the cold front clear of the region 
Sunday morning, expect this period to linger around normal 
temperature wise as well.

Then we flip the active weather switch back on again midwekk, with 
temperatures rising well above normal and winds picking up from the 
southeast and then south as another low pressure center develops 
across the Central Plains and moves into the Midwest. The GFS/GEFS 
hints at some warm advection type showers Tuesday night as this 
switch turns on. Will cap pops in the 20-30 percent range for this 
potential and as most other models, including the FV3 keep us dry.

Our eyes then turn to the cold front dragging behind this surface 
low. Model start time for storms to move into our area range from 
Wednesday afternoon through night. With the flow aloft becoming 
parallel to the front, it looks like this boundary could stall and 
even back up as further waves travel through that flow. The 
CMC/GEFS/Euro all keep some QPF in through Friday though the GFS and 
FV3 both push it east more quickly. Previous forecast was similar 
and SuperBlend keeps pops lingering into our I-75 zones into the 
daytime Friday. Will not stray too far from that thinking for now. 
In doing that, will keep Wed to Thu night above normal and then drop 
temperatures back to normal to close out the work week.

&&

.Aviation...(00Z TAF Issuance)
Updated at 635 PM EST Fri Mar 8 2019

MVFR/IFR conditions are expected this evening with HNB/SDF 
deteriorating to IFR tonight as well.  Low cigs and some light fog 
are expected tonight as we sit in a moist low level environment to 
the north of a warm front.  Drier conditions will exist at HNB/SDF 
so they may not see much light fog but will most likely experience 
IFR cigs later tonight.  The warm front will lift north through the 
area tomorrow morning bringing the first of multiple rounds of 
showers/storms.  South of the front tomorrow afternoon, southerly 
winds will become gusty with continued chances for showers and 
storms.  The best time frame for strong storms will come tomorrow 
late afternoon through the end of the TAF period. These may contain 
heavy rainfall reducing flight conditions to IFR/LIFR and strong 
winds. Showers/storms should diminish just beyond the end of this 
TAF period.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...Wind Advisory from 1 PM EST /noon CST/ to 10 PM EST /9 PM CST/ 
     Saturday for KYZ023-024-026>028-053-061>064-070>076.

&&

$$

Short Term...DM
Long Term...RJS
Aviation...AMS