Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 211522
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1122 AM EDT Thu Aug 21 2014
Issued at 1120 AM EDT Thu Aug 21 2014
Isolated showers have begun to develop in southern Indiana and the
northern Bluegrass this morning. These have remained fairly weak
this morning as SPC mesoanalysis shows some capping over the area.
This should decrease over the next hour or two while instability
increases. Mesoscale models show most of the activity today from now
through mid to late afternoon. The best chance for any stronger
storms will be over the Bluegrass this afternoon. These should move
out by early evening with dry conditions through the remainder of
the evening. Went ahead and decreased pops late this afternoon and
this evening based on the current model trends. Otherwise, just
minor tweaks made to the grids.
.SHORT TERM (Now through Friday)...
Issued at 300 AM EDT Thu Aug 21 2014
500mb ridging will continue over the Lower Mississippi Valley
through late Friday, with northwesterly 500mb flow just off to our
northeast across Ohio and central Indiana. Hot and humid conditions
will continue through Friday with highs in the lower to mid 90s, and
overnight lows only falling into the lower to mid 70s.
A disturbance currently analyzed over the Dakotas will round the top
of the ridge today and move southeast, crossing northern Illinois
late this afternoon or evening.
Current forecast soundings show elevated instability still present
over southern Illinois and Indiana attm. A small cluster of
thunderstorms currently entering southwestern Indiana should weaken
some as radar shows an outflow boundary moving ahead of the
strongest convection. Also, an analysis shows weaker instability
present near and east of Interstate 65. However, some of these
showers or thunderstorms may maintain enough integrity to bring rain
to portions of southern Indiana along the Ohio River west of
Louisville through the early morning hours.
This afternoon will become quite unstable, especially near a weak
elevated warm front forecast to stretch southeast across central
Indiana and southern Ohio. Scattered strong to possibly severe
storms are anticipated this afternoon, the bulk of which will stay
to our north and northeast closer to this boundary. Any afternoon or
evening storms that do move across southern Indiana or the northern
Bluegrass will produce gusty winds and localized very heavy
Scattered storms will diminish overnight, although residual
instability and humid conditions may some storms to persist through
the early morning hours. Scattered afternoon and evening storms are
likely to our north and east again Friday afternoon.
Highs today will range from the upper 80s across the northern
Bluegrass to the lower 90s near Bowling Green. After a muggy night,
highs Friday will generally rise a couple of degrees more.
.LONG TERM (Friday Night through Wednesday)...
Issued at 245 AM EDT Thu Aug 21 2014
...Heat, Humidity, and Generally Unsettled Weather This Weekend...
Heat and humidity still look on track as a strong ridge builds over
the Ohio Valley this weekend and stays anchored over the region
through the beginning of next week. Models have backed off of the
h85 temps slightly...now 18-22 degrees C vs 20-24 degrees C in
previous runs. However, high temperatures should still solidly
reach the 90-97 degree range Sat-Mon with locations along and west
of I-65 most likely to see highs in the mid to upper 90s. With
dewpts expected to remain quite moist in the lower 70s, resultant
heat indices should top out in the upper 90s to low 100s each
afternoon Sat-Mon. Taking into account a hot day in store for
Friday as well, a heat advisory may be needed mainly west of I-65
for this prolonged period of hot weather. Will need to consider
that with today`s afternoon forecast package. However, afternoon
showers/storms may keep things a bit cooler than forecast so will
need to take that into consideration as well.
As previous forecaster noted, the ridge will be a dirty ridge
allowing for convection to fire mainly at peak diurnal heating
during the afternoon and evening hours each day. Mid range models
are keying in on a signal that would produce a good complex of
storms to our north late in the day Friday and dive into the Ohio
Valley Friday night into early Sat morning. Will have the best
areal coverage and highest POPs (50%) in the long term period Fri
night/Sat. Model soundings indicate that the greatest threat from
these storms would be heavy rainfall and dangerous lightning.
However, isld small hail and strong winds may also occur. Rounds of
isld-sct storms will be possible Sat-Tues during the
afternoon/evening hours with no organized severe threat anticipated
at this point.
By Wed an upper trough will attempt to break down the ridge over the
Midwest. The strong ridge will be hard to break down however so
it`s not clear as to when significantly cooler temps and better
precip chances will arrive. At the very least though, it should
provide cooler temps with highs in the upper 80s and lower 90s for
the middle of next week. Will keep low POPs 20-40% in the forecast
despite model timing and strength differences.
.AVIATION (12Z TAF Update)...
Issued at 645 AM EDT Thu Aug 21 2014
Warm humid weather with light southwest winds will continue today
and tonight. South southwest winds around 5 to 7kt this morning will
become southwesterly around 7 to 9kt this afternoon, before becoming
light southerly this evening through early Friday morning.
VFR flying conditions are anticipated outside of any isolated
thunderstorms that may affect SDF or LEX as early as the mid-morning
hours today. Coverage of any convection this afternoon will be
scattered and disorganized and difficult to time. Due to only
scattered POPs, will keep thunder out of the TAFs at this point.
Some light haze may affect the LEX and BWG terminals early Friday