Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Jackson Kentucky
353 am EDT Friday Jul 31 2015
Short term...(today through saturday)
issued at 345 am EDT Friday Jul 31 2015
07z surface analysis shows cooler and drier high pressure building
into east Kentucky from the west. This has cleared the sky of any
clouds while the drier air is limiting the fog development so far.
It is also supporting a decent ridge to valley temperature
difference with readings ranging from near 70 on the ridges to
around 60 in the sheltered valleys. Dewpoints show a bit more room
for temperatures to drop through the rest of the night with most places
in the upper 50s and lower 60s while winds are light to calm.
The models are in good agreement aloft through the first part of
the weekend as they show troughing deepening north of the Great
Lakes and extending its influence south into our area. This will
result in some slow and gentle height falls across the Ohio
Valley with only minor bits of energy moving past in broad
northwest flow. The NAM is a bit stronger with this trough later
in the period than the European model (ecmwf) and GFS. Accordingly...will favor
more of a model blend that discounts the NAM/S solution.
Sensible weather will be under the benign control of high pressure
today into Saturday. A cold front will lose its definition
Saturday night as it passes through the Ohio Valley with little
more than a brief increase in clouds expected...along with another
shot of dry air. The reinforced high will keep pleasant weather
around through the day Saturday. The cooler nights under the high
pressure will support some limited patchy fog in the deeper
valleys early this morning and again Saturday morning.
Used the shortblend model as a starting point for the T/TD/wind
grids through the day followed by the superblend into Saturday.
Did make some significant adjustments to temperatures this morning
and tonight with respect to ridge and valley differences once the
inversion is in place. As for probability of precipitation...kept them low and in line
with the MOS guidance.
Long term...(saturday night through thursday)
issued at 350 am EDT Friday Jul 31 2015
The extended forecast period begins on Saturday night with the long
wave pattern showing a ridge over the western Continental U.S. And a trough
developing over the east. With the trough still digging...models
suggest that the shortwaves or main track will still remain to the
north or over the the Great Lakes region. So will expect a dry
Saturday night and Sunday especially with surface high in place.
Heading into Monday...the pattern becomes a bit more pronounced
as the long wave trough over the east digs with another wave
moving through to impact the area by the afternoon. The surface
cold front moving through on Tuesday slows and becomes a west to
east stationary boundary over eastern Kentucky. This feature then
becomes a focus for showers and thunderstorms as through the
Tuesday to Thursday time frame several shortwaves move through
the Ohio Valley.
This does pose a problem through the period as the GFS and Euro are
slightly different in timing but the super blend would suggest a
busy period each day. Have decided to stay close to the super
blend solution but add some diurnal trends to the forecast. This
pattern in place does make conditions favorable for mesoscale convective system/S mainly
towards the end of the extended.
Aviation...(for the 06z tafs through 06z Friday night)
issued at 140 am EDT Friday Jul 31 2015
High pressure will continue to build across eastern Kentucky
overnight. Along with light winds and a few clouds at 5k feet...
some MVFR fog will be possible at the sme...sjs...and sym taf
sites between 08 and 13z...although expect that any IFR or worse
fog will be limited to the deeper river valleys...thanks to
larger dewpoint depressions in place tonight compared with last
night. VFR conditions will return everywhere after 13z...with
light northwest winds and mostly clear skies on tap through the
rest of the taf period.