Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 271333
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
933 AM EDT Sun Jul 27 2014
Issued at 932 AM EDT Sun Jul 27 2014
Updated the forecast this morning to account for ongoing trends.
Convection continues to develop across central KY early this morning
as the low-level jet continues to impinge upon a lingering outflow
boundary/effective weak warm front. Much of this convection remains
elevated at this time due to overnight convection and surface
temperatures in the lower 70s. However, the capped warm sector has
already pushed ENE into western Kentucky (into BWG as of this
writing) and will continue to try and push northeast into central KY
through the late morning and early afternoon hours. It appears the
best chance for renewed surface-based convection will be along a
pre-frontal trough, which is currently just south of Saint Louis
northeast toward Indianapolis.
The storms that can form will be fighting a decent mid-level cap,
and with effective shear of 50-60 knots oriented orthogonal to the
surface forcing, these factors will favor initial supercell
development. With the EML advecting in dry air aloft and steep
mid-level lapse rates, large hail appears to be the main threat
along with damaging winds. An isolated tornado is also possible
given mostly speed shear in the low-levels, but the greatest tornado
threat will likely reside across eastern KY where low-level flow
will be more favorably backed. It must be said, all of this is
quite conditional if we can see some breaks in the clouds before the
trough moves in. It appears the better diurnal heating by the time
the trough moves in will be south of the Ohio River, with the
greatest threat appearing to be across south-central KY. Certainly a
complex forecast, and will continue to update as needed.
.SHORT TERM (Now through Monday)...
Issued at 359 AM EDT Sun Jul 27 2014
...Severe weather threat continues this morning through much of
The MCS that rolled through the forecast area late Saturday night
has not stopped convection from re-firing in a line extending
currently from roughly Daviess County, IN southeastward through
Elizabethtown, KY. These storms have developed near theta-e
advecting in from the west, along with an increase of low-level
PWATs, per the CIMMS NearCast model. This cluster has all of the
features of being severe; however, latest available AMDAR soundings
show a shallow stable layer, which may help to keep the worst of the
winds aloft. Regardless, the concern is certainly there that despite
that these storms should be primarily elevated, they seem to be able
to overcome the layer and go surface-based. An additional concern
that was not present with the previous MCS is that a directional
shear component has been added to the increase in speed shear as the
low-level jet ramps up and surface southerly winds persist.
Continued uncertainty exists for the exact evolution of today`s
storms, although given how easily convection was able to develop
overnight and how quickly the local atmosphere was able to recover
behind the MCS, this is concerning given all of the other parameters
that will line up to create a severe threat for much of central KY
and south-central IN. The worked over atmosphere has not stopped
storm development. Models are showing 0-6km bulk shear today will be
increasing from approximately 30kts. in southern KY to 50kts. north
of the Ohio River to 40kts in the south to 60kts. in the north by
late today. SBCAPE, while some already exists this morning, will
increase to over 2500 J/kg under the sun today. The focus of where
storms will develop and how they`ll move will be a short-term,
mesoscale based forecasting approach as they ride leftover
boundaries and wherever the greater instability sets up, which
currently looks to be in southern and eastern KY. Hi-res models are
showing multiple rounds of storms but clearing out by late this
afternoon. Think this will be more dependent on the timing of the
front. The mode early on could be discrete supercells, congealing
into potentially a broken line as they merge and coalesce with one
another. The primary concern for any severe storms today will be
damaging winds and heavy to torrential rainfall, with secondary
concerns for hail and potentially an isolated tornado.
Highs today are expected to reach the upper 80s in the north and the
low 90s in the south, despite any cloud cover as the WAA pipeline
remains at full blast until the fropa.
Tonight through Monday:
Once the well-advertised cold front pushes through (expected to be
through the forecast area by tonight), the storms will go with it,
leaving clearing skies and a dry forecast for the overnight period.
However, clouds will clutter the skies once more on Monday with a
chance for showers, especially in the Bluegrass region and locations
east of I-65. This is as the upper low spins down into the region,
which will also bring significantly cooler temperatures. Look for
lows to range from the lower 60s in the north to the upper 60s in
the southeast. Highs on Monday will range from the mid 70s in the
north to around the 80 degree mark in the south.
.LONG TERM (Monday Night through Saturday)...
Issued at 245 AM EDT Sun Jul 27 2014
An amplified pattern over the CONUS will persist this week with
troughing noted over the Midwest providing unseasonably cool
Tues-Thurs we`ll be dry with sfc high pressure in the area.
Tuesday`s highs will flirt with record cold highs which are in the
70s at climate stations. Forecast highs for Tuesday range from
73-79 across the area. We`ll then see a little bit of a warm-up
into the upper 70s and lower 80s for Wed/Thu. Night time lows will
be in the upper 50s and lower 60s.
By Friday, the pattern looks to attempt to become more a of a split
flow with an upper low attempting to be cut off over the Midwest.
As shortwaves increase in the trough and upper low toward the end of
the week, rain/storm chances will re-emerge with on and off
showers/storms possible through the weekend.
.AVIATION (12Z TAF Update)...
Issued at 651 AM EDT Sun Jul 27 2014
Difficult forecast for today as ongoing convection causes
uncertainty in how convection will evolve later today. A surface low
is progged over central IL and moving toward the NE. Aloft,
upper-level low pressure is rotating down from the NW as a deep
Canadian trough primes to take over the region.
Strong to severe thunderstorms will continue to threaten all three
terminals but given the uncertainty in timing, have not included
specifics other than VCTS (but even this is likely to change
throughout the day). Amendments will need to be made as storms
develop and threaten the terminals. The fropa is expected to have
cleared all three terminals sometime or shortly after 00Z Monday and
will take with it storm activity.
Winds will be a concern during the day as 15 to 20 knot
southwesterly gradient winds are expected with higher gusts. Winds
could be higher in or around any storms.