Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 201428
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1028 AM EDT Sun Apr 20 2014
Issued at 1027 AM EDT Sun Apr 20 2014
Forecast is on track for the most part this morning, although did
update to lower afternoon dew points along and east of I-65 for this
afternoon. Forecast soundings show potential for drier air to mix
down again. The lowest dew points could drop into the low and mid
30s, and this will yield relative humidity values in the 20-25%
range in many spots east of I-65. Although conditions will be quite
dry for several hours this afternoon, surface winds will be much
lighter than yesterday so not anticipating an elevated wildfire
threat at this time.
.SHORT TERM (Now through Monday)...
Issued at 300 AM EDT Sun Apr 20 2014
A gorgeous Easter Sunday is on tap across the Ohio Valley, as
upper-level ridging and an associated surface high maintain control
of the sensible weather. This ridge will slowly push east through
the short term period, allowing a PV anomaly to approach from the
west toward Monday afternoon/evening.
With the surface ridge in place today, skies will remain mostly
sunny, with just a few cirrus clouds passing by. While these weak
winds will limit turbulent mixing to some extent, still believe we
will mix sufficiently to once again bring drier air down this
afternoon. Therefore, have lowered dewpoints a bit for this
afternoon, which puts them in the upper 30s to lower 40s. This dry
airmass coupled with the copious sunshine will once again yield
temperatures above guidance today. Have gone anywhere from 4-6
degrees above MAV/MET guidance, which puts highs in the upper 70s
and lower 80s. The dry airmass coupled with the warm temperatures
will mean RH values falling near 25% for a few hours this
afternoon. However, winds will be very light throughout the day
which should limit the wildfire danger.
High clouds will be on the increase tonight as the aforementioned
system approaches. The increasing cloudiness and a tightening
pressure gradient should help to hold temperatures up a bit more
than previous nights. Will go with lows in the upper 40s and 50s.
On Monday, isentropic ascent will increase in response to the
approaching PV anomaly. Guidance continues to remain split on the
amount of pre-frontal activity associated within this region of
lift, with the GFS/Euro wetter than the NAM/GEM. Forecast soundings
depict a pretty deep dry layer between 600-800mb. Given the forcing
is not too impressive and the moisture feed being quite limited,
have leaned toward the drier NAM/GEM solution, bringing only slight
chances of precip into the western CWA by 00Z Tuesday. Temperatures
will be largely dependent on the timing and amount of cloud cover
streaming into the region. Given overall thinking of a drier
solution, will bump temperatures up a bit which puts them in the
upper 70s and lower 80s.
.LONG TERM (Monday Night through Saturday)...
Issued at 300 AM EDT Sun Apr 20 2014
Progressive pattern aloft for most of the coming week, with two main
systems to affect the Ohio Valley.
First, a low-amplitude upper trof will push a weak cold front
through the Ohio Valley Monday night and early Tuesday, bringing
fairly decent rain cahnces with it. Nocturnal timing does not
support surface-based CAPE, but we may see just enough elevated
instability to support scattered thunder. Wind fields are also not
impressive so severe potential is quite limited. Went on the high
end of guidance for Mon night low temps given typical cool bias in
pre-frontal southerly flow.
Shortwave ridging aloft with a modest surface high nosing in from
the Great Lakes for mid-week. Coolest morning will be Wednesday, but
at this point we are keeping forecast mins in the lower/mid 40s.
Would need the high to ridge a little more strongly into the Ohio
Valley to get any widespread readings in the 30s.
Next system will be Thursday night into Friday, and is trending a
bit faster as models show a bowling-ball upper low moving across the
Great Lakes. Latest solution has a few impulses pinwheeling around
this low, with the lead impulse pushing a cold front through the
Ohio Valley Thursday night/Friday morning. Will keep POPs limited to
the chance category and mainly focused on Thursday night/Friday.
Temps in the latter half of the week will trend back to the high
side of normal, especially at night with the front moving through.
.AVIATION (12Z TAF Update)...
Issued at 640 AM EDT Sun Apr 20 2014
VFR conditions will prevail through the period. High pressure will
remain in control over the Ohio Valley through the next 24-30
hours. This means winds will be rather light and variable today,
with only a few passing cirrus or diurnal cu. This cirrus shield
may increase a bit toward this evening and overnight, but it will be
of no impact to aviation operations.