Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 240734
Area Forecast Discussion
National Weather Service Louisville KY
334 AM EDT SUN JUL 24 2016
.SHORT TERM (Now through Monday)...
Issued at 310 AM EDT Sun Jul 24 2016
Early morning sat/obs reveal partly cloudy skies across the region.
A large MCS is currently moving eastward across northern IL and IN
and into southern Michigan. The cloud tops have been warming over
the last few hours and the latest high-res model continue to take
this system eastward and perhaps sinking southeastward a bit into
Ohio later this morning. Temperatures remain warm early this
morning with most locations in the middle to upper 70s. In the
urban areas, temperatures are still in the 80s (owing to the urban
heat island effects). For the remainder of the overnight hours,
expect partly cloudy skies to continue. A steady stream of high
cirrus associated with the MCS to our north will continue to work
southward. Temperatures across the region look to bottom out in the
middle 70s with upper 70s in the urban areas.
For today, it looks to be another mostly dry day across the region.
Convective allowing models still suggest that isolated showers and
storms will be possible this afternoon. Some of these models are
suggesting that outflow from the MCS to the north of the region this
morning may serve as an effective trigger across the region this
afternoon. For now, have kept PoPs in the isolated category, but
we may have to increase this later today depending on how far the
outflow gets. Another forecast challenge will be high temperatures.
The MCS to the north is providing the area with a thin veil of
cirrus. This will overspread the region today cutting down on
insolation. Overall, we think we`ll see temperatures similar to
yesterday, but may be a degree or so cooler in the north due to the
aforementioned cirrus shield. Highs look to top out in the 90-95
degree range. With those temps and dewpoints in the 70s, it will
feel closer to 100 in most locations. With regards to the Heat
Advisory, current feeling is that we`ll be hard pressed to see
criteria east of I-65. For that reason, have gone ahead removed
most counties east of I-65 from the advisory for the afternoon
hours. The best chances of seeing criteria would be across our
western sections. For tonight, we`ll see another dry and warm night
with lows cooling into the lower-mid 70s.
For Monday, we`ll see heights start to fall aloft as a mid-level
trough axis swings into the region. Associated surface cold front
will push in from the north and serve as a focus for convection
during the afternoon/eve. The models continue to show a bit of a
slow down with the front, so the highest chances of convection will
likely be across the northern areas with lesser chances down toward
the TN border region. While dewpoints will likely be higher during
the period, the associated cloudiness and expected precipitation
will likely keep temps down which will result in lower heat indices
for the afternoon. Highs will likely warm into the upper 80s to
around 90 in most locations.
.LONG TERM (Monday Night through Saturday)...
Issued at 333 AM EDT Sun Jul 24 2016
...Stormy Pattern Setting Up for Much of the Upcoming Week...
The upper level ridge that has been in the headlines of late is
expected to break down and retrograde westward through the work
week. As this occurs, height falls will be seen across the eastern
US as a large/baggy trough axis develops. This will place the Ohio
Valley in a northwesterly flow pattern with plenty of chances of
convection as we head through the week. The transition to a wetter
pattern is not really all that surprising as this has been a
recurring theme for the last 8-10 weeks.
Deterministic and ensemble data suggest daily convective chances as
multiple perturbations move through within the mean flow. The
ensemble QPF plumes remain rather noisy, but do suggest that the
highest PoP chances may be centered around Tuesday and again on
Thursday as stronger perturbations may move through the area at that
time. Precipitable water values will remain in the 1.75-2.00 inch
range through the period. Thus, storms that move through will have
plenty of moisture and will dump copious amounts of rainfall. Strong
convection will be possible as we`ll have diurnal rises in
instability throughout the week. Main hazards would be heavy
rainfall and damaging winds with the strongest storms. QPF amounts
are difficult to pin down. The synoptic scale models generally have
widespread QPF painted across the region throughout the period. Area
rivers and streams are in good shape as of right now, but are
running about 1-3 feet above normal pools. If heavy rain becomes
more commonplace/widespread as the week unfolds, we could start to
see hydro problems crop up in some areas.
High temperatures through the period will be seasonal with daily
highs in the upper 80s and overnight lows in the lower 70s. The
blended model guidance and multi-model consensus are in relatively
good agreement here with not too much spread.
.AVIATION (06Z TAF Update)...
Issued at 130 AM EDT Sun Jul 24 2016
A stagnant weather pattern has the TAF sites in the doldrums as a
flat upper level ridge covers the southern half of the U.S. The
upper pattern actually looks more typical of the tropical horse
latitudes, with variable winds at or below 10 kts through the lowest
30 thousand feet of the atmosphere.
With no appreciable pressure gradient at the surface and no defined
pockets of energy aloft in the weak flow, there is only diurnal
surface heating to drive the weather this forecast period. Surface
dewpoint depressions place cloud bases in the VFR range...perhaps
initiating around 040 before rising to 050 with an occasional broken
ceiling during the afternoon. Cannot rule out isolated
thunderstorms that manage to break through the warm cap that will
otherwise will keep flat cumulus limited to about 2000 feet of
growth, but with no surface focal point to key on - and little
movement of any that develop - confidence is too low to even include
VCTS until they form.
KY...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for