Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 180703

Area Forecast Discussion
National Weather Service Louisville KY
303 AM EDT Tue Jul 18 2017

.Short Term...(Today through Wednesday)
Issued at 247 AM EDT Tue Jul 18 2017

Surface obs and analysis reveal a very subtle southwest to northeast
oriented boundary across southern Indiana and western Kentucky this
morning. This boundary has surprisingly fired off some weak, low-top
showers over northwestern portions of the CWA, despite recent AMDAR
soundings showing dry air and a weak cap in place around 850mb. The
HRRR does seem to have a decent handle on the showers, and has the
activity slowing drifting off to the east through the morning before
dissipating near sunrise. See no reason to deviate from this so will
keep the forecast close to the HRRR solution.

The weak surface boundary will slowly drift eastward this afternoon
and serve as a focal point for redevelopment of afternoon showers
and storms. Model soundings do show a weak cap in place this
afternoon, but surface convergence near the boundary should be
enough to get isolated showers/storms going. Not expecting any
severe weather today, but with weak deep layer shear, storm movement
will be slow, so some isolated heavy downpours are a possibility.
Any shower/storm activity should begin to dissipate near sunset and
give way to a mostly clear and mild evening.

Upper level ridge over the central US will begin to drift closer to
our region tomorrow, and result in temperatures being a few degrees
warmer than today. With dewpoints in the upper 60s to low 70s, the
heat index will be in the mid to upper 90s, with the highest values
along and west of I-65.


.Long Term...(Wednesday night through Monday)
Issued at 257 AM EDT Tue Jul 18 2017

Upper level ridge will continue to build into the region late in the
week, with the core of the warmest air aloft staying west of the
region. GEFS 850mb temperature anomalies still showing about 1
standard deviation above normal for the lower Ohio Valley, and
looking at forecast soundings and model data, afternoon temperatures
Thursday through Saturday will generally be in the low to mid 90s,
with urban centers being a tad warmer. Dewpoints will also be high
during this period, generally upper 60s to low 70s, and with large
scale subsidence associated with the ridge, we won`t have a lot in
the way of clouds or storms to cool things down. This will result in
afternoon heat index values hovering around 100 degrees, give or
take a couple of degrees, with large urban areas possibly getting
close to 105 degrees. The highest heat index values will generally
be along and west of I-65.

Thankfully, there are some indications we will see a break from the
heat by the late weekend timeframe, as an upper level trough and
associated cold front take aim at the lower Ohio Valley and bring
some welcome precipitation to the region. The general trend of the
models has been to push back precipitation chances and the cooler
air to later time periods over the past several runs, so confidence
in timing is low. However, the GFS/ECMWF/Canadian all have the cold
front pushing through or stalling over the region by early next
week, so confidence is above average that we will see showers/storms
and a cool down by some point next week.


.Aviation...(06Z TAF Issuance)
Issued at 1245 AM EDT Tue Jul 18 2017

Light/variable winds and VFR conditions will prevail through the
valid TAF period as upper ridging continues to build. Ceilings will
remain unrestricted with only FEW-SCT diurnal cu. A few isolated
showers/storms over southern Indiana will dissipate overnight before
getting close enough to impact SDF.




Short Term...DM
Long Term...DM
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