Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
624 am EDT Sat Aug 1 2015
..updated aviation discussion...
Short term (now through sunday)...
issued at 250 am EDT Sat Aug 1 2015
An early morning surface analysis revealed high pressure extending
west to east across Kentucky while aloft water vapor imagery and 500
mb heights showed troughing over the Great Lakes region. The airmass
across the region remained quite dry, confirmed by the iln 01.00z
sounding precipitable water of 1.06 inches. Mostly clear skies prevailed over
southern Indiana and central Kentucky with light/variable winds.
For today, plan on sunny skies and seasonable Summer temperatures
for the first day of August. Readings will top out in the upper 80s
to around 90 degrees, a degree or two within the highs observed
Friday. Middle afternoon mixing will bring dewpoints down into the middle
50s to around 60, making for low humidity and rather pleasant Summer
Plan on more benign weather tonight with lows in the 60s. A couple
of dry, efficient mixing days should limit fog formation across the
south. On Sunday, winds will begin to turn to the south ahead of an
approaching shortwave and cold front. Any influence across the
forecast area from this feature looks to hold off until after Sunday
evening. Plan on another seasonably warm day with sunny to mostly
Long term (sunday night through friday)...
issued at 259 am EDT Sat Aug 1 2015
The long term will be characterized by a persistent low amplitude
ridge west/trough east pattern, resulting in seasonable temperatures
and occasional thunderstorm chances as waves move through. Moisture
will be on the increase as the dry surface high that has been
overhead recently weakens and slides off to the east.
The European model (ecmwf) is showing the most run-to-run consistency and has done
well in recent verification. GFS less consistent but showing signs
of catching up to the European model (ecmwf). So, this forecast package leans a
little more toward the European model (ecmwf) Camp.
Though the plains nllj will be weak at first, it will gradually
strengthen and shift eastward each successive night. By Tuesday
night and Wednesday night it will be strong enough and far enough
eastward that we may begin to feel the effects of mesoscale convective system remnants
moving in from the west. Also, a surface cool front that will come
in from the northwest early in the period and remain quasi-
stationary from west to east across the region through at least middle
week will act as a Focal Point for convection. Wednesday now looks
like the best day for showers and storms as a weak wave moves along
the front. Lots of timing changes can occur that far out in the long
term, though, so this may change. Will keep probability of precipitation at the high end of
chance for now.
Temperatures will be near seasonal norms. Tuesday appears to be the
warmest day as the eastern trough flattens a bit and allows heights to
rise. Humidity levels will increase over what we've seen the last
couple of days as well.
Aviation (12z taf update)...
issued at 620 am EDT Sat Aug 1 2015
VFR conditions will prevail at the taf sites through the period with
generally clear skies and light northwest winds thanks to high pressure at
the surface and a drier than normal air mass. Some high cirrus may
spill over the area later today into tonight...otherwise plan on
benign weather and VFR conditions through at least Sunday afternoon.