area forecast discussion
National Weather Service Louisville Kentucky
728 am EDT Sat may 18 2013
..updated aviation discussion...
Short term (now - sunday)...
issued at 252 am EDT Sat may 18 2013
Currently, the center of the upper low appears to be across north
central Tennessee. There is a band of light to moderate showers
moving northeast from south central Kentucky associated with a
trowal ahead of the upper low. This feature is clearly identified on
300 k isentropic analysis. There is also a precipitable water maxima along this
axis around 1.5 inches. Have forecast this feature to slowly move
north-northeast through the early morning hours and pivoting to a more west-northwest-east-southeast
orientation as it nears the I-64 corridor. Will watch along this
boundary through the late morning into the afternoon as this will be
the best focus for scattered showers and storms. Right now have the
highest concentration of showers and storms along a line from
Madison, in to Lexington, Kentucky to Jackson, Kentucky this afternoon. Further
southwest will only include an isolated chance of a shower and
thunderstorm as a batch of drier air evident on water vapor imagery
slides east southeast across south central Kentucky behind the upper
low. Cannot completely rule out an isolated thunderstorm, however as
this area will see the best heating later today.
Overall, most areas that see a shower or storm should expect a tenth
to a quarter of an inch. However, areas along the line mentioned
above might expect between a quarter and three quarters of an inch
of rain. A bit concerned about individual heavy rainers as 1.5"
pwats are impressive and forecast soundings indicate tall and skinny
profiles with little in the way of flow through the column. However,
thinking forecast soundings may be a little overdone. Will monitor
through the day.
High temperatures should range into the mid and upper 70s today,
with a few spots around bwg around 80.
As we move into the this evening and tonight, best coverage along
the axis mentioned above will gradually diminish as upper low starts
to move east. Meanwhile, an upper level ridge axis will begin to
build in across western Kentucky. Will go briefly dry by around midnight
through dawn as this occurs. Do expect skies to become at least
partly
cloudy through the overnight, allowing temperatures to drop into the
low and mid 60s.
Sunday will see an increase in diurnally driven convection once
again with focus in the eastern County Warning Area nearest the meandering upper low
and in the SW County Warning Area where a weak warm frontal boundary will be
positioned. Again, expecting only scattered coverage. Environment
will likely be more unstable so will have to watch for heavier rain,
and cloud to ground lightning. Highs on Sunday should range in the
upper 70s east to low to mid 80s west.
Long term (sunday night - friday)...
issued at 249 am EDT Sat may 18 2013
An upper trof will sit over the plains for much of the week before
finally starting to drift to the east Thursday/Friday.
Accordingly, surface low pressure and its attendant features will
also initially remain off to our west and north before beginning a
slow eastward trek.
Atlantic high pressure ridging into the southeast United States will
continue to pump warm and muggy air northward into the Tennessee and
Ohio valleys. Upper level ridging, a sufficient cap, and lack of a
strong trigger should keep US dry Monday. On Tuesday the cap
appears to weaken enough that some afternoon convection may be able
to sprout.
By Wednesday the plains storm system will begin to edge far enough
east that thunderstorm chances will be a little better than on
Tuesday, especially by afternoon and evening.
Thursday and Friday we'll still be in the warm and muggy air mass
with the upper trof passing by to our north and possibly a weak
surface boundary in the region. Thunderstorm chances will be less
on Thursday than they were on Wednesday, and less still on Friday,
but can't be completely ruled out.
We could see a few strong storms Tuesday afternoon, if we can get
enough sunshine for destabilization. Better chances for strong
storms exist on Wednesday as we get positioned under the right
entrance region of a small upper jet and winds increase in the mid
and lower levels as well. However, lapse rates are still not very
impressive and clouds may hamper surface instability. Nevertheless,
if we're going to get strong storms this week, right now Wednesday
looks like the best chance.
As for temperatures, models are wanting to bring some very warm
readings in for highs on Monday...into the lower 90s, which is 15
degrees above normal and near record levels. However over the past
couple of days clouds have done a very good job keeping temperatures
down. We won't see as much cloudiness on Monday as we have
recently, but still would like to shade the forecast a little cooler
than guidance (which agrees with ensemble numbers), keeping maxt in
the middle and upper 80s for now.
Highs Tuesday and Wednesday should be in the lower and middle 80s
with more clouds and showers than what we see on Monday. Highs
Thursday/Friday may only be in the 75 to 80 degree range with the
upper trof passing by.
&&
Aviation (12z taf issuance)...
issued at 720 am EDT Sat may 18 2013
Upper low moving across the area continues to bring extensive cloud
cover and scattered light rains to our region. Bwg has yet to drop
into the IFR range, although is making progress as latest obs have
been more solidly into the low MVFR range. Will carry IFR ceilings
through around midday, before improvement to MVFR occurs.
Lex will be in the best position to see numerous showers and
scattered thunderstorms today as an area of convergence occurs NE of
the upper level disturbance. Have depicted the best time for -tsra
to occur in the tafs.
Sdf will likely see scattered showers and storms through the day,
although overall coverage should be less and will hold off on
nailing down a specific time until confidence is higher. Will only
mention thunderstorms in the vicinity for now. Otherwise, expect there could be a brief
period of MVFR ceilings just after sunrise, with conditions
improving again by midday. Overall, expect light easterly and
southeasterly winds.
&&
Lmk watches/warnings/advisories...
in...none.
Kentucky...none.
$$
Short term.......bjs
long term........13
aviation.........Bjs
