Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
645 am EDT sun Apr 26 2015
..updated aviation discussion...
Short term (now through monday)...
issued at 230 am EDT sun Apr 26 2015
The synoptic pattern early this morning features split flow aloft,
with an amplifying trough over the eastern Continental U.S.. this trough and
the associated northwest flow will be the main player in the short
term period, bringing seasonably cool conditions but dry weather.
The area of low pressure that brought the severe weather yesterday
continues to push well east of the region as it fills in. In its
wake, northerly winds are advecting in drier air into the
commonwealth. Therefore, despite a few isolated showers very early
this morning, think any precipitation will come to an end by dawn.
Clouds will hang tough through the morning hours, but should begin
to mix out late this morning into the afternoon as we mix to 4-5k
feet. Therefore, do expect to see some sunshine this afternoon
which will help push highs into the low and mid 60s despite the
For tonight, the surface gradient will relax a bit, allowing winds
to go light. Skies will be clear, so think that there will be
pretty good conditions for radiational cooling. There should be
just enough of a gradient to keep winds from going calm everywhere.
Given these factors, think that the typically cool/sheltered
locations will likely drop into the mid/upper 30s, but most
locations will remain in the upper 30s/lower 40s. There may be some
patchy frost in the typically cooler/sheltered locations, but at
this time the frost does not look widespread enough to warrant any
headlines. The day shift will take another look and update this
thinking as needed.
Otherwise, skies will start out mostly sunny on Monday. A trough
will be diving through the north/northwest flow aloft on Monday
across portions of Ohio and eastern Kentucky. Model forecast soundings
suggest there will be enough low-level moisture with this feature to
produce some strato-cu, mainly across the northern Bluegrass region
in the afternoon. Therefore, temperatures there will be in the
upper 50s/low 60s, with mid 60s expected elsewhere under more
Long term (monday night through saturday)...
issued at 300 am EDT sun Apr 26 2015
Blocky and fairly amplified pattern will continue for most of the
upcoming week, with a fairly persistent eastern Continental U.S. Trof and split
flow to the west. Main challenge comes around midweek, as a southern
stream system makes its way across the deep south, and a northern
stream impulse dives into the Great Lakes. In order to get even
light precip in the Ohio Valley, we would need to see some phasing
between these two systems. At this time, it appears that the
southern stream system will scoot past to our south on Wednesday,
and only warrants a 20-30 pop mainly in the Lake Cumberland region.
Northern stream system dives southeast behind it, and GFS and European model (ecmwf) both
hint at a fujiwhara interaction that could force the northern stream
low's trajectory far enough west to bring precip into east-central
Kentucky on Thursday. Will not include a pop just yet but it bears
watching. By Friday and Saturday, the quiet weather pattern
continues as an upper ridge starts to build in from the plains,
allowing temps to recover to exceedingly pleasant levels for the
first weekend in may.
Aviation (12z taf update)...
updated at 645 am EDT sun Apr 26 2015
The low cigs experienced overnight will improve through this morning
at all sites as drier air and VFR conditions build into the region.
VFR cigs have already pushed into ksdf and should be into klex
within the next hour or two. The drier air will be slower to work
into kbwg, but cigs should slowly rise through the morning hours,
going VFR by the early afternoon. Otherwise, winds today will be
out of the north, going light and variable tonight as high pressure
builds into the region.