Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 312241
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
541 PM EST Sat Jan 31 2015
...Updated Aviation Discussion...
.SHORT TERM (Now through Sunday Night)...
Issued at 250 PM EST Sat Jan 31 2015
...A few slick spots possible Monday morning...
The synoptic pattern this afternoon features split flow aloft, with
a strong PV anomaly diving southeast through the northern Plains,
which will interact with a weaker southern stream disturbance across
the southern Plains. These two systems will phase, leading to the
deepening of a surface cyclone over MO tonight. This system will be
the main focus of the short term period.
For this evening, isentropic ascent will increase across portions of
MO/IL/IN in response to the approaching strong PV anomaly. This
forcing will overspread portions of IN, perhaps clipping southern IN
into extreme northern KY in the 23-06Z timeframe. However, any
falling precip will need to overcome quite a bit of dry air in the
low-levels before it makes it to the ground. Therefore, think
anything that falls will be quite light and confined mainly to
southern IN. Can`t rule out a stray shower further south, but the
dry air is more likely to win out there. Forecast soundings for
Madison, IN depict the dry low-levels may be enough to wet bulb the
column to get some sleet or even some snow, but given the light
nature of the precip and temperatures remaining at or above
freezing, do not expect many issues on area roadways.
Otherwise, the early morning hours on Sunday will be dry, as the
initial wave of isentropic ascent lifts northeast. However, by the
mid to late morning, a low-level jet of 50-60 knots will ramp up
over the Ohio Valley, helping to pump plentiful moisture into the
region. At the surface, southerly winds will increase to 20-25 mph,
with gusts approaching 30 mph at times. This will help temperatures
climb into the low 50s (with 40s expected over southern IN).
Widespread rainfall will break out in the afternoon through the
evening hours as the surface low and associated cold front pass
through. Rainfall amounts are expected to be around 0.50-0.75
As the surface low slides east, cold air will rapidly spill into the
region early Monday morning. Isentropic analysis depicts a
weakening deformation band may attempt to pivot southeast into
northern portions of the region Monday morning, which coupled with
the passing trough axis, should be enough ascent to spawn some snow
showers on the back side of the departing system as the column
cools. Overall, not expecting much snow with this as deep moisture
will be limited and forcing will be brief, but a quick dusting to a
half of an inch will be possible. Given these snow showers will be
falling near rush hour as temperatures crash into the 20s, slick
spots will certainly be possible on the morning commute. This is
something we will continue to monitor in coming forecasts.
.LONG TERM (Monday through Saturday)...
Issued at 250 PM EST Sat Jan 31 2015
Still looking at some snow showers Monday morning as the upper
trough crosses the region. Forecast soundings show a brief period
where deeper moisture will be over the region, and that moisture in
the prime growth zone for snow dendrites, so we could see some
moderate snow showers around daybreak. This activity should end
quickly though as the trough axis shifts east of us and pulls that
moisture away. It will leave a day and night with below normal
temperatures before we moderate back to above normal for mid week.
Still watching how a couple of systems will affect us Wednesday
night/Thursday. The Euro keeps a surface low going well south of the
region, into the Gulf and crossing south Florida Thursday, thus not
shooting any moisture ahead of a northern stream system. The GFS and
GEM continue to phase these two systems, as the surface low crosses
closer to the Gulf coast. This would bring some precipitation into
our area, which has a better chance of being snow. The European
solution is not a typical surface track for this time of year, so
will lean more toward the GFS solution, which is a good compromise
of the two.
For Friday and Saturday we should be dry. The system moving through
Thursday will push us back below normal through Friday for
temperatures, and we should return closer to normal for Saturday.
GFS and Euro both advertise some light QPF along a warm front just
to our north late Saturday, but will keep us dry for now.
.AVIATION (00Z TAF Update)...
Issued at 541 PM EST Sat Jan 31 2015
High pressure over North Carolina will reach far enough back to the
west to dominate our weather tonight, resulting in light winds and
VFR conditions. Clouds around 10,000 feet will increase and thicken
as a storm gathers to our west.
On Sunday intensifying low pressure will travel roughly a MCI-SDF
route. Rain will move into the terminals and make for a very wet
afternoon. Ceilings will likely lower into MVFR by mid to late
afternoon. Of most concern, though, will be southerly winds that
will gust over 20kt, especially at LEX and BWG.
The low will continue to the east Sunday evening and swing its cold
front across central Kentucky, switching the gusty winds to the
WSW. Light rain will continue.