Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 082145
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
545 PM EDT Tue Jul 8 2014
Issued at 530 PM EDT Tue Jul 8 2014
Well, after an hour on shift a few observations of note. The
synoptic front is still just north of the Ohio River between HNB and
BMG with sfc trough from MSL to TYS and back into WV. Upper Trough
producing light showers just north of I 70 in IN. Overall, storms
are having a arduous time overcoming warm upper troposphere and am
downplaying storms and downplaying the severe risk. In facts dew
points have mixed out into the low to mid 60s except across from HNB
to HOP. Took off the top news web article for severe weather risk.
Worst case scenario would be a strong isolated storms with heavy
rain and lightning. My plan is to drop pops to isolated everywhere
by 615, but will want to watch the radar and satellite trends for
another half hour.
.SHORT TERM (Now through Wednesday Night)...
Issued at 309 PM EDT Tue Jul 8 2014
The synoptic pattern this afternoon features an amplified ridge
across the western CONUS, with a trough building into the Great
Lakes. A rather potent mid-July shortwave trough can be seen on
WV imagery, diving southeast through portions of OH/IN/IL/MO. This
trough will be the main focus of the short term period.
Overall, am going to downplay the severe weather threat for this
afternoon/evening. A strong outflow boundary from this morning`s
convection has pushed the better low-level moisture (70+ dewpoints)
much further east of the region. In its wake, dewpoints have fallen
into the mid to upper 60s at best. Latest SPC mesoanalysis data
valid at 18Z depicts only meager instability remaining, with MLCAPEs
in the 500-1000 J/kg range, a far cry from the 2000+ J/kg guidance
forecast for this time yesterday. That being said, we have seen
quite a few breaks in the cloud cover this afternoon, and dewpoints
are slowly trying to recover. This in addition to the strong
mid-level wave pushing in will help to increase instability some
this afternoon, mainly across south-central KY.
There will likely be two areas of convection, one is associated with
the weaker band of showers/storms that is currently developing along
the synoptic front across portions of southern IN. Another area of
showers/storms is just now starting to fire across portions of
south-central KY. In this second area, there are many lingering
outflow/differential heating boundaries that will serve as the
triggers for storms this afternoon/evening. Think this secondary
area, south-central KY, will be the best chance for a few strong to
marginally severe storms. This region will reside in the better
moisture/instability, which should aid in storm intensity. However,
the overall lack of instability due to the lower-than-expected
dewpoints and weak surface convergence should tend to limit the
overall threat despite good deep layer shear as the mid-level wave
pushes in (30 to 40 knots 0-6km shear). The main threat with any
strong to marginally severe storm in this area will be locally
damaging winds and perhaps some small hail.
Convection should push to the south during the overnight hours as
the synoptic front slowly pushes south through the state. Overnight
lows will be a bit tricky give some expected cloud cover (especially
across southern KY), but mid to upper 60s seem reasonable.
Wednesday and Wednesday night look to be dry across the Ohio Valley
as high pressure builds into the region. Guidance suggests that
some strato-cu may develop tomorrow as cooler air collides with
lingering low-level moisture. Therefore, have upped cloud cover a
bit for tomorrow afternoon. Highs should top out in the middle 80s,
with overnight lows falling into the low and mid 60s.
.LONG TERM (Thursday through Tuesday)...
Issued at 236 PM EDT Tue Jul 8 2014
The first couple days of the long term look to be quiet as high
pressure slides from the Great Lakes to the Northeast. The afternoon
hours on Thursday and Friday will see temperatures in the 80s with
dew points in the mid 50s to lower 60s -- pretty nice for mid July!
As the high moves off we`ll get into warm, moist return flow at the
surface, while small upper disturbances move overhead Friday night
and Saturday night/Sunday. As a result, scattered thunderstorms
will enter the forecast by the weekend. Storm chances will be a
little better on Sunday than on Saturday. High temperatures on
those days will be around 90 with dew points around 70, so the
weekend will be a more hot and muggy than Thursday/Friday.
A more significant upper trof will move through Monday/Monday night
along with a surface cold front. Thunderstorms are a good bet on
Monday, and some strong storms may be possible Monday afternoon and
evening. High temperatures should again be around 90.
It does look like the front will be progressive and will push
cleanly through the region, leaving us dry on Tuesday with afternoon
temperatures peaking only in the lower and middle 80s.
.AVIATION (18Z TAF Update)...
Issued at 108 PM EDT Tue Jul 8 2014
Outside of any thunderstorm activity, VFR conditions are expected to
prevail through the TAF period. Currently, WSW to W winds continue
to remain quite brisk at all sites, gusting to around 20 knots at
times. This will likely continue through the mid afternoon hours,
before gusts start to wind down. Convection is expected to develop
this afternoon, but coverage is a bit in question. Think the best
coverage will likely be near KBWG, with only isolated to widely
scattered coverage expected at KLEX and KSDF. Therefore, will
continue with just VCTS wording at these two sites. Vsbys will
likely be reduced to MVFR or IFR within any thunderstorm.
Convection will wind down at KBWG late this evening. Otherwise,
expect a partly to mostly cloudy night. Depending on how convection
plays out this afternoon, there may be some light fog at KBWG, but
given the uncertainty will leave this out for now.