Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
1259 am EDT sun Jul 13 2014
..updated aviation discussion...
Short term (now through Sunday night)...
issued at 300 PM EDT Sat July 12 2014
Upper air pattern at 500mb will begin its long advertised
amplification early Sunday as an unseasonably deep trough builds
southwards north of Lake Superior in response to full latitude
ridging across the Canadian rockies.
Currently, a warm front lies from near Chicago southwards to western
Kentucky. Earlier this morning widespread thunderstorms developed
along this boundary across Illinois. These storms have weakened
throughout the morning hours as they have moved east into
progressively more stable air. One exception is the current
scattered thunderstorms in western Kentucky. Think that these will
propagate mainly south. They may affect some of our far western
counties west of I-65 by late afternoon.
Southern Indiana will remain mostly cloudy through mid afternoon due
to remnant mid-level debris from earlier convection to our
northwest. These will tend to erode by late afternoon or early
evening and skies will likely become partly cloudy.
Expect a warm and increasingly humid overnight period as developing
southwesterly flow will bring higher dewpoints. Lows will range from
near 70 to the lower 70s, with our warmest temperatures over urban
areas and southern Indiana.
A surface trough will approach southern Indiana late Sunday.
Moisture convergence and pwats exceeding 1.7 inches will lead to
very unstable conditions during the afternoon hours. Scattered to
perhaps a broken line of storms will develop over central or
southern Indiana during the mid to late afternoon hours, and sag
southeast through the evening and overnight hours. Increasing
mid-level flow may bring a threat of isolated damaging winds along
and north of I-64 during the afternoon and evening hours. The slow
southward movement of the surface trough may allow for localized
During the overnight hours and into early Monday morning, scattered
to numerous showers and storms will continue over central Kentucky,
slowly edging southwards as the surface trough edges south.
Sunday will become hot and humid, with highs in the lower 90s.
Overnight lows early Monday, probably modified by rainfall. Will
fall into the upper 60s.
Long term (monday through saturday)...
issued at 317 PM EDT Sat Jul 12 2014
Monday through Wednesday night...
Unsettled weather is very likely early in the extended period as
major amplification of the upper air pattern across North America
commences. This weather pattern has been well advertised in the
model data for the last week or so...and model convergence has
become stronger with each successive run. A surface cold frontal
boundary will be on the northern edges of our forecast area by
Monday morning. This front will sag through the Ohio Valley during
the day on Monday and pass south of the Kentucky/Tennessee border Tuesday
morning. Periods of strong convection look likely during the day on
Monday. However, convective evolution is still quite murky as much
will depend on previous day convective evolution and the role of
outflow and mesoscale boundaries.
Current data suggests that convection will likely be ongoing from
Sunday night across southern Indiana and northern Kentucky.
Additional convection is expected to develop once again during the
afternoon...mainly across central and southern Kentucky.
Thermodynamic and kinematic profiles suggest damaging winds and
large hail will be the main severe weather threats...though a low
probability tornado threat remains. Storms should continue into
Monday night and will end from northwest to southeast with the passage of the
front. Much cooler and drier air will then push into the Ohio
Valley for the remainder of the period. Highs Monday will be
conditional on cloud cover and associated precipitation. Current
guidance suggests highs in the 83 to 88 degree range. Temperatures
should fall into the 60s by Tuesday morning. Highs on Tuesday will
be well below normal with readings only warming into the 73 to 77
degree range. Lows Tuesday night will be refreshingly cool with
lows in the Lower-Middle 50s. A few of our typically colder
locations could touch the upper 40s. Dry and cooler than normal
conditions will persist into Wednesday with highs in the 73-78
degree range with overnight lows back into the Lower-Middle 50s
Thursday through Saturday...
Large cyclonic gyre over Quebec is forecast to lift northeastward
and fill during the long term period. The large eastern US trough
axis will shift to th east on Thursday as heights slowly rise from
west to east. Temperatures will moderate some by Thursday with
readings warming into the 74 to 79 degree range...though some areas
in southern Kentucky may hit the 80 degree mark. Lows Thursday night not
be as cool with readings generally in the upper 50s to the lower 60s.
By Friday and Saturday, recent deterministic and ensemble solutions
suggest that a weak perturbation will drift across the
mid-Mississippi Valley and into the Ohio Valley. This will likely
bring a swath of showers and storms from the Red River valley
northeastward through the Tennessee Valley. Depending on the
strength of the high and upper level flow, this activity may only
affect the southern half of our forecast area. For now, plan on
keeping slight chance pops in across the south for Friday-Saturday
with drier conditions from the parkways and points north. Highs
Friday should warm into the upper 70s to the lower 80s, with lower
80s being the rule by Saturday.
Aviation (06z taf update)...
issued at 1255 am EDT sun Jul 13 2014
Mainly VFR conditions are expected overnight, with the exception of
possibly some light fog at bwg towards sunrise. Otherwise, winds
will be light out of the S to south-southwest overnight with just a mid level
cloud deck. Winds will pick up out of the SW through the morning
hours. Sustained wind speeds will be 10-12 knots today with gusts up
to 20 knots.
A front will slowly sag southward across the region late this
afternoon into the evening hours. Showers and thunderstorms are
expected to develop along this front during the late afternoon hours.
They are expected to affect sdf during the late afternoon and Lex by
the early evening hours. Will carry thunderstorms in the vicinity for now to account for
this. Think this front will be slow moving enough that the storms
will not affect bwg until the very end of or just after this taf