Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 212332
Area Forecast Discussion
National Weather Service Louisville KY
732 PM EDT THU JUL 21 2016
...Updated Aviation Discussion...
.SHORT TERM (Now through Friday Night)...
Issued at 240 PM EDT Thu Jul 21 2016
...It`s getting hot out there...
Fairly uncertain forecast given that most models have had poor
initialization with current system over the Great Lakes. As of early
afternoon, this system is moving southeast across southern Lake
Michigan. Cloud tops have warmed a little with the main line, but
new development across the northern Lower Peninsula is helping them
cool again there.
The flow around the ridge centered over the Great Plains would argue
for this system to start turning more southward by this evening. At
that point it will be moving into a much drier airmass, with GFS
forecast soundings having precipitable waters this evening in the
1.3-1.4 inch range over our Bluegrass counties. Thus will lean
towards a drier forecast for us tonight and tomorrow morning. A
question mark then will be how far south any remaining boundaries
get for Friday afternoon`s heat. That boundary could bring in some
more moisture for our east, not to mention bring focus for
additional development out of that heat. Thus will keep in isolated
to scattered storms for the late afternoon and evening hours.
Subsequent timing of convection will depend on how things progress
in the near term. So will have to transition more to an ensemble
approach for the rest of the period, not getting into specific
details, because they are too far out to focus on right now.
Given that there is a better chance for storms not to provide
widespread cooling relief Friday, the focus will remain on the heat.
Heat indices for the afternoon look to peak in the 105-110 degree
range along and west of I-65. Have done a slight eastward extension
of the advisory area for tomorrow to better match up with ILN and
OHX. For ILN...our criteria for an advisory is higher than theirs.
Am not as confident we will hit that criteria, around 105+, along
the border with them, but the national map will look better for it,
and cause less confusion. The extension closer to OHX is in an area
where there is less chance for rain to cool things down, so 105+
looks better there.
.LONG TERM (Saturday through Thursday)...
NZUS01 KLMK DDHHMM
Issued at 230 PM EDT Thu Jul 21 2016
...Continued Hot and Humid Likely Through This Weekend...
Saturday, the GEFS and SREF place the ridge across the Desert
Southwest with a ridge axis through KS and MO and into our west. Our
being on the edge will mean a chance even for hard to time and
forecast systems to move southeast and south into the region. The
latest deterministic models (NAM/GFS/GEM/00Z ECMWF) all have precip
somewhere in the area for the day. The ensembles have this too, but
with a high spread, offering the chance for no precip. Location of
ridge of high pressure normally would mean less of a chance across
our south and west, so will continue a gradient there. Given
continued lower confidence, and pops in the scattered/chance range,
heat still looks like a good bet. Heat indices should top out
similar to Friday.
The pattern really doesn`t change much for Sunday, with the same
thinking in mind...a question mark between rain chances and heat. It
is quite possible on either day for areas of southern Indiana and
central Kentucky to get a break from the heat. May have to extend
the heat advisory into Sunday or further, but we still have time to
decide on that.
As we get into Monday, the GEFS indicates the ridge will shift
slightly southward, as a shortwave trough moves into the Midwest.
This trough should provide a better focus for storms to develop over
the region. The question mark then will be how far south this front
gets. The GEFS pushes the best rain chances into our southern
counties Tuesday and Wednesday before bringing them back north again
Thursday. Will lean toward this thinking.
With these thoughts in mind and thinking of the heat, a later day
start to storms would mean having another day of higher heat indices
Monday. We should get more of a break for Tuesday on though, given
more cloud cover if the boundary remains over us, or less humidity
should it be to our south.
.AVIATION (00Z TAF Update)...
Issued at 732 PM EDT Thu Jul 21 2016
Thunderstorms over eastern Indiana have been struggling to survive
as they move to the SSE, and this trend is expected to continue. As
a result, storm chances at SDF/LEX this evening are too low for
inclusion of SH or CB in the TAFs.
Of perhaps greater concern is the growing MCS over Wisconsin. Upper
flow would take this activity SSE towards the Ohio Valley, possibly
reaching SDF around 08Z on its present vector. However, the current
feeling is that it will probably develop more southward into extreme
instability over northern Illinois. Also, the low level jet that is
feeding into it right now is expected to collapse overnight. So,
right now it appears that the complex will remain largely to SDF`s
northwest. Will need to keep an eye on it, but will refrain from
including it in the SDF TAF quite yet.
Could see some high-end MVFR BR or HZ at BWG around dawn in the
stagnant, humid atmosphere.
Scattered thunderstorm development will be possible just about
anytime on Friday. Nothing to hang one`s hat on for enough
confidence to include anything in the TAFs yet. Of the TAF sites,
SDF looks to stand the best chance of TS tomorrow.
KY...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for KYZ023>030-
Heat Advisory from noon EDT /11 AM CDT/ Friday to 8 PM EDT /7 PM
CDT/ Saturday for KYZ031>034-038-046-054-064-065-076-077-
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ076>078-
Heat Advisory from noon Friday to 8 PM EDT Saturday for INZ079.