301 
FXUS63 KLMK 091615
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1115 AM EST Sat Mar 9 2019

.Forecast Update...
Issued 1100 AM EST Sat Mar 9 2019

Elevated convection developing along and ahead of the warm front is 
now in play for a few locations west of I-65. Leading band runs from 
near Jasper to Elizabethtown to Lake Cumberland, with another band 
just getting into the Bowling Green area and seemingly aligned with 
the warm front itself. POPs really ramping up for most of the area 
in the next hour or two, pretty much on schedule with the previous 
forecast. Thunder potential seems to be well handled, but we will 
push an update to legacy forecasts soon, mainly to clean up wording. 
Hourly temp curves have been adjusted in the hi-res products to show 
a sharper and slower warm front. 

Late afternoon SVR potential is largely unchanged, as it remains 
conditional on getting sfc-based instability. still seems like we 
can do that mainly south of I-64 and west of I-65, with a little 
wiggle room in line with SPC slight risk.

&&

.Short Term...(Today and tonight)
Issued at 308 AM EST Sat Mar 9 2019

Currently, a solid stratus deck resides over the region with temps 
sitting in the 30s to low 40s. Seeing some patchy fog mainly across 
our southern half of the CWA. For the most part, it seems transient 
on webcams and obs are mostly ranging between 1 and 5 SM. A few 
spots have gone below a mile, but not planning any special mention 
at this time. Will continue to monitor.

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

A strong and negatively tilted shortwave trough is expected to eject 
out of the Plains and into the Great Lakes region later this 
afternoon into this evening. The associated ~990mb surface low will 
follow the same trajectory. As this occurs, a warm front currently 
situated over southern TN will lift north through our CWA by this 
evening, establishing a weak but notable warm sector over the 
region. Although the warm sector will be short-lived, it will be 
accompanied by a very impressive kinematic setup. The exit region of 
strong mid/upper level jetting will overspread the region later this 
afternoon into the evening, creating strong forcing and low level 
jet response around 70 knots! The overall setup will create a 
situation where several rounds of convection will move through the 
region from later this morning through late this evening. Initial 
convection this morning into the early afternoon will likely be 
elevated in nature given a strong inversion near the surface, 
however as we move into the afternoon and especially the early 
evening hours, storms will likely be able to become more surface 
based. Bottom line, the severe threat gradually increases through 
the day.

Instability remains the big question mark, and there are several 
initial obstacles to overcome to even get to the point where meager 
surface based values will be possible. 1.) Getting the warm front 
north this afternoon. 2.) Overcoming late morning and early 
afternoon elevated convection, including heavy sky cover. Do think 
we'll be able to overcome these as models agree that strong 
advection should win out by afternoon and evening. The latest data 
continues to hint at a weak and narrow instability axis developing 
by late afternoon/early evening and moving into area mainly along 
and west of the I-65 corridor. This instability axis will generally 
be around 500 J/KG of SB CAPE or less, but there could be a few 
pockets greater than 500 J/KG, especially down toward the Bowling 
Green region. Generally, the warm sector will be characterized by 
peak temps reaching the low to mid 60s, with peak dew points mostly 
in the 55 to 60 degree range later this afternoon into the evening.

The intense low level jet combined with the strong and veered mid 
levels produces some long and looping hodographs. The resulting SRH 
values (both 0-1 and 0-3km) will grab your attention, with values 
that would easily support rotating discrete cells in the presence of 
strong enough updrafts. In addition, any linear segments will likely 
bow out along with potential for mesovortices. Bottom line, shear 
isn't in question, and really hasn't been all cool season as you 
might expect. Hi res models seem to depict mostly a combination of 
discrete cells and linear segments for storm modes, which seems to 
fit the shear profile and weak instability.

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

* Timing: 2pm - 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 and across 
  southern KY.
* Confidence: High if we are able to destabilize

Given multiple rounds of showers and storms, can't rule out some 
isolated flooding problems in addition to the other threats. Any 
heavy rainfall will be brief as storm motion will be quite fast 
which should be the main limiting factor. Will message as a threat, 
but overall have most spots around 1 inch of QPF with locally higher 
amounts.

As far as the ongoing Wind Advisory headline goes, confidence is 
fairly low. It seems that by the time we get our warm sector 
established to the point where some of the stronger winds aloft can 
be mixed down, we'll be under the threat for convective winds. So, 
not really sure whether the Wind Advisory helps messaging at that 
point or is just confusing. The bigger gradient wind issue may be 
with post cold frontal winds as lapse rates steepen and strong low 
level jetting is still around through the overnight. Will likely 
leave the afternoon/evening Wind Advisory as is for now, but not 
sure the gradient winds out ahead of storms will be strong enough 
given the initial low level inversion.

.Long Term...(Sunday through Friday)
Issued at 250 AM EST Sat Mar 9 2019

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

Sunday through Tuesday Night...

Quiet period of weather is expected in the Sunday through Tuesday 
time frame.  Surface high pressure is expected to dominate the 
weather pattern over the Ohio Valley with a general quasi-zonal flow 
aloft.  Highs during the period will warm into the lower to middle 
50s with overnight lows in the upper 20s to the lower 30s.  Lows 
Tuesday night should average a little milder with mid-upper 30s 
expected.

Wednesday through Friday...

By mid week, the upper pattern is forecast to become amplified once 
again with a sharp upper trough axis moving out of the western US. 
Downstream ridge is expected to expand a bit which should result in 
much warmer conditions for Wednesday.  We may see a few light 
showers early Wednesday as the ridge builds, but by and large 
Wednesday looks to be dry, but breezy.  Highs look to warm into the 
mid-upper 60s west of I-65, with lower-mid 60s over our Bluegrass 
region.

By late Wednesday, sharp upper trough looks to take on a negative 
tilt over the Plains.  This will result in lee side cyclogenesis 
east of the Rockies with a low pressure center rapidly moving from 
the southern Plains up into the Midwest.  The overall track of this 
particular system is a bit more west than this weekends system. 
Arcing cold front will push into the region early Thursday. However, 
as this front heads east, it looks to become aligned with the flow 
aloft which would allow it to slow down considerably and perhaps 
stall a bit over the Ohio Valley.  Showers and thunderstorms (some 
strong) are likely across the region on Thursday and continuing into 
Thursday night.  The front does look to make some eastward progress 
by Friday resulting in a nice drying trend to end the week.

Main concern with the Thursday system is the potential for heavy 
rainfall.  We'll have a deep moisture plume directed off the Gulf 
and multiple perturbations will likely bring waves of precipitation 
to the region. An inch or two of rainfall looks likely with this 
system and that could result in some hydro issues across the region. 

Highs Thursday should warm into the mid-upper 60s.  Cooler air will 
push in late Thursday and early Friday behind the front with 
readings falling into the 40s by Friday morning.  Highs Friday will 
likely top out in the upper 40s to the lower 50s.

&&

.Aviation...(12Z TAF Issuance)
Updated at 627 AM EST Sat Mar 9 2019

A warm front remains south of the TAF sites at this hour, and seeing 
widespread IFR as a result. In addition to the ceilings, 
visibilities will likely vary between IFR/MVFR through much of the 
morning, but will improve as the warm front begins to lift north. 
Further north at HNB/SDF, it should be mainly ceiling restrictions 
with less in the way of vis restriction.

The warm front will lift north over the region later this morning 
through the afternoon with steady E winds becoming SE and S through 
the day. Magnitudes will increase and become strong by afternoon 
with sustained 15 to 25 mph, gusting between 30 and 40 mph. Ceilings 
should rise back to low MVFR by late morning or early afternoon, 
along with widespread rain and scattered storms overspreading the 
area. Expect MVFR ceilings/vis to prevail for much of this time, but 
will also likely go back to IFR periodically in stronger showers and 
storms. A few severe storms are possible later this afternoon into 
the evening.

A strong cold front moves through by late evening with surface winds 
veering to a SW component and still gusting. Winds won't be quite as 
strong but could still see some 25-35 mph gusts through the end of 
the TAF cycle. MVFR ceilings will quickly clear out overnight behind 
the strong cold frontal passage.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...Wind Advisory until 10 PM EST /9 PM CST/ this evening for KYZ023-
     024-026>028-053-061>064-070>076.

&&

$$

Update...RAS
Short Term...BJS
Long Term...MJ
Aviation...BJS