Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 170709
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
309 AM EDT Thu Apr 17 2014
.SHORT TERM (Now through Friday)...
Issued at 308 AM EDT Thu Apr 17 2014
In the near term, a batch of high level cloudiness will continue to
push eastward through the region this morning. These clouds will
preclude full radiational cooling this morning. Temperatures across
the region will vary this morning...depending on elevation. While
most ASOS and KY mesonet stations are generally in the lower 40s,
the valley locations have decoupled and have readings in the middle
30s. The higher ridge top locations are still quite warm with
middle to upper 40s being noted across far south-central KY. Expect
temperatures to continue their nocturnal cooling trends with most
locations dropping into the upper 30s to lower 40s. Some cooler
spots may get briefly close to freezing. Current frost advisory
will be kept going...though frost will likely be limited to the
valley and low elevation areas that decouple...and those areas will
be generally east of I-65. Some scattered areas of frost will be
possible in the low-lying areas west of I-65.
For today, surface high pressure ridge across the eastern US will
continue to move eastward. This will result in a more southerly
wind flow developing across the region. High cloud cover this
morning should thin out as the day goes on resulting in mostly sunny
conditions. Combination of insolation and increasing southerly flow
will result in temperatures warming about another 8-10 degrees over
yesterday`s highs. Feel that readings in the 63-68 degree range
For tonight, an upper level trough axis across the Plains will move
eastward into the Ohio Valley. This feature will bring increasing
cloudiness into the region overnight and into Friday. There is not
a lot of time for moisture to get advected back up into the region
and there is not much support for lift. So, the chances of
precipitation for the overnight period look pretty small. Lows will
feature a gradient across the area. Lowest readings will be in the
Bluegrass region with upper 30s to around 40. Readings in the
central and west will be in the middle 40s.
For Friday, upper trough axis will swing through the region.
However, upper jet streak will drive southwest of the region and
result in an upper level cut off low developing across the
southeastern US. Much of Friday will be mostly cloudy across the
region. Main forcing for precipitation will be located well south
of our area, but combination of modest height falls aloft combined
with a little insolation may produce some isolated showers across
the region. For now, have backed off on the PoPs during the day
with just a slight chance expected. Afternoon readings will be very
near seasonal normals with highs in the 65-70 degree range.
.LONG TERM (Friday Night through Wednesday)...
Issued at 254 AM EDT Thu Apr 17 2014
The start of the long term period will feature split flow aloft
across the Ohio Valley, which will transition to more of a western
trough/eastern ridge pattern by the middle of next week. This
transition within the upper-level pattern will make for a rather
benign long-term period, with moderating temperatures being the main
focus, along with one system Monday into Tuesday.
The system mentioned above in the short term section will be pushing
east of the region by Saturday, making way for a rather pleasant
weekend. After partly cloudy skies on Saturday and highs in the
lower 70s, temperatures will moderate into the middle 70s by Easter
Sunday with mostly sunny skies. Have nudged temperatures up a bit
in this timeframe from the previous forecast, given the recent cool
bias seen in guidance under mostly sunny skies with a rather dry
low-level airmass in place. Would like to see a bit more turbulent
mixing to see things really exceed guidance (surface winds will be
rather light), but a degree or so warmer seems reasonable at this
The latest guidance suite has trended quite a bit slower with the
system Monday into Tuesday. Dprog/dt fields show this trend is not
just on the 00Z cycle, it has been there the past few runs.
Therefore, have trimmed back pops Sunday night into Monday. Given
the expected later arrival, temperatures should get a bit warmer
Monday afternoon. Look for highs in the middle 70s, perhaps higher
if there is less cloud cover than currently anticipated.
The PV anomaly and associated weak surface reflection will push
through Monday night into Tuesday. High pressure over the Gulf of
Mexico will largely limit the moisture return ahead of this system.
This lack of low-level moisture along with generally unimpressive
dynamics means the precipitation will likely fall in the form of
scattered showers, with perhaps a few isolated thunderstorms.
The cold front will push east by Tuesday night, but the airmass
behind it won`t be too much cooler. Upper-level ridging will
begin to build in Wednesday through the end of the workweek, which
will allow temperatures to moderate. Will go with highs in the
middle and upper 70s for now, but would not be surprised to see
readings exceed 80 degrees by the latter half of next week.
.AVIATION (06Z TAF Update)...
Issued at 110 AM EDT Thu Apr 17 2014
High pressure ridge axis is currently centered along the eastern
coastline of the US this morning. The ridge axis should continue to
move off to the east throughout the period resulting in a more south
to southwesterly flow developing across the Ohio Valley later this
morning. For the remainder of the overnight period, the forecast is
simply an extension of the previous one. Band of mid-high level
cirrus will continue to march eastward across the terminals
overnight resulting in BKN250 conditions. Winds are expected to
remain light and variable at KSDF and KBWG...with a light easterly
to east-southeasterly component over at KLEX. High clouds are
likely to scatter out later this morning...though VFR are expected
throughout the day. Surface winds will pick up more from the south
to southwest throughout the day with speeds of 8-10kt.
KY...FROST ADVISORY until 9 AM EDT /8 AM CDT/ this morning FOR