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Area forecast discussion 
National Weather Service Louisville Kentucky
713 PM EDT Tuesday Oct 13 2015

..updated aviation discussion...

Short term (now through Wednesday night)...
issued at 257 PM EDT Tue Oct 13 2015

Quiet weather is expected through the short term period under
northwesterly flow aloft and surface high pressure building in from
the west. For the rest of this afternoon, clouds over the northern
portion of the forecast area will shift off to the east and
dissipate this evening. These clouds have resulted in temperatures
being held in the lower to mid 60s in the north, though they could
go up a few degrees over the next couple of hours.

For tonight, high pressure will still be west of the area and winds
will stay up in the 3-5 knot range. Thus, we will not see ideal
radiational cooling despite clear skies. Lows will still drop into
the lower to mid 40s with some upper 30s in the traditional cool
spots. Highs Wednesday will be a couple degrees warmer than today,
in the upper 60s to lower 70s. The setup for radiational cooling
will be a bit better Wednesday night into Thursday morning and thus
have forecast lows a degree or two cooler than tonight. Very
isolated instances of frost in sheltered areas cannot be ruled out
Thursday morning. However, guidance is a bit variable on whether
some return flow will set up before daybreak. If it does, this would
keep temps a bit warmer.

Long term (thursday through tuesday)...
issued at 323 PM EDT Tue Oct 13 2015

..frost and light freeze likely this weekend...

A broad northwesterly flow aloft will keep temperatures below normal
and the area generally dry at the beginning of the forecast period.
The latest data continue to agree with a mid-level wave pushing
through the region late Thursday into Friday which will usher in
another in a series of cold fronts. Will likely see a few showers
along the front late Thursday night and early Friday morning.
Overall precipitation coverage is still low confidence as there is
not much in the way of moisture to work with. For now, have kept
the slight chance pops going in the forecast for now, but did drop
pops a bit across southern Kentucky. Highs Thursday should warm into the
mid-upper 60s in the north with upper 60s to the lower 70s across
the south. Mid-upper 60s are likely on Friday before temperatures
fall in the evening as colder air arrives. Temperatures Saturday
morning will likely drop into the 30s region wide. A few mid 30s
will be possible at the typical colder locations. Some patchy frost
will be possible Saturday morning, though it would seem to be
limited to our northern areas.

For the weekend, Saturday will be a cool/crisp fall day across the
region. With mostly sunny skies, deep cold air advection aloft will
keep highs well below seasonal normals. Highs in the lower-mid 50s
are likely across southern Indiana and across the Bluegrass region
of central Kentucky. Upper 50s to around 60 degree readings will be
seen across southern Kentucky. With a large surface high moving overhead
Saturday night and Sunday, we should see very good radiational
cooling Sat night/Sun morning. Lows will generally be in the lower
30s region wide, with the typical colder/sheltered locations
dropping into the upper 20s. A widespread frost looks increasingly
likely with some areas seeing the first freeze of the fall season.
Forecast confidence here continues to increase with respect to frost
and freeze conditions. The 13/12z GFS ensemble probabilistic
forecast of temperatures less than 32 degrees across portions of southeast
in/Bluegrass of cky is running above 75%. Temperatures will remain
cool on Sunday with low-mid 50s for highs in the north and upper 50s
to around 60 in the south. A little bit of a return flow will set up
Sunday night which will likely produce a gradient of temperature
across the region. Lows in the west look to cool into the upper 30s
while another threat of frost and low 30s looks likely across the

The return flow pattern really looks to set up in earnest on Monday
as the flow aloft GOES a bit more zonal. Highs Monday look to warm
into the mid 60s in the east and upper 60s in the west. Temps look
to return to the upper 60s to around 70 by Tuesday which is near
climatology for this time of the year.


Aviation (00z taf update)...
issued at 705 PM EDT Tue Oct 13 2015

VFR conditions expected for the valid taf period, with only few-sct
cirrus. Winds are not expected to completely decouple tonight, which
will keep the boundary layer just mixy enough to avoid any fog
concerns, even though temps are expected to cross over the afternoon
dewpoints at sdf and Lex. West winds will pick up slightly again Wed
afternoon, but should remain just under 10 kt.


Lmk watches/warnings/advisories...


Short term........eer
long term.........Mj

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