LMK issues Area Forecast Discussion (AFD) at Nov 18, 9:45 PM EST906
FXUS63 KLMK 190245
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
945 PM EST Mon Nov 18 2024
.KEY MESSAGES...
* Showers arrive tonight into tomorrow ahead of a cold front. A
few storms are possible.
* High confidence in cold and breezy conditions the second half of
the week with the strongest gusts likely on Thursday.
* A mix of rain and light snow showers will be possible late
Wednesday night through Thursday night. Significant snowfall
accumulations are not expected with minimal impacts, if any.
&&
.UPDATE...
Issued at 945 PM EST Mon Nov 18 2024
Currently dry across the area, with the focus for precip located
across southern IL and far western KY. Overall forecast remains in
good shape, with earliest onset of precip around or shortly after
midnight. Expect light showers to spread eastward overnight and into
tomorrow morning. While an increasing LLJ will support ample shear
parameters, we will be lacking low level instability. Some rumbles
of thunder could be possible, but better chances for gusty showers
exist. Breezy southerly flow will result in continued WAA regime, so
temps overnight will be much warmer than normal, with most seeing
temps in the 50s. Forecast remains in good shape, so no changes are
planned.
&&
.SHORT TERM /THROUGH TUESDAY/...
Issued at 308 PM EST Mon Nov 18 2024
The low pressure system over the central Plains will continue to
move northeast into the upper Midwest through the afternoon and
overnight. The associated cold front will draw closer to the region
tonight bringing showers and a few storms. These showers and few
storms will continue to push through the region, until the front
passes in the late afternoon on Tuesday into the evening. The
environment is CAPE limited, however there is a small axis of weak
MUCAPE along the line which supports some thunder mention.
Additionally, there is modest speed and directional shear, which
will allow the line of showers and storms to remain somewhat
organized as it continues across the Ohio Valley. With a stronger
storm, could see heavy rainfall (given high PWATs of 1.6-1.9 inches,
thanks to plentiful Gulf moisture) and gusty winds. Agreement
amongst high-res ensembles is low, however, the idea is present. Any
strong storms would remain isolated and highest chance is west of I-
65.
In the overnight hours, a 45-55kt LLJ will move into the region from
the west, allowing winds to increase overnight. These winds, coupled
with additional cloud coverage will limit cooling overnight. Low
temperatures over the Bluegrass will cool into the mid 50s and
elsewhere into the upper 50s and low 60s.
During the day, this LLJ will remain over the region keeping winds
breezy up to 25 mph. Temperatures will remain 12-15 degrees above
normal tomorrow with highs in the upper 60s and low 70s. Bust
potential for temperatures is over the western portion of the
region, if the front moves through a little faster than anticipated.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 308 PM EST Mon Nov 18 2024
Synopsis...Complex pattern aloft will develop during the medium-
range period as shortwave energy phasing over the Northern Plains
will result in a deep upper low rotating across the Great Lakes/
Ohio Valley towards the Atlantic Ocean the rest of the workweek. The
forcing provided by several embedded vorticity maxima rotating
around the upper low amid sufficient low-level moisture and cold air
advection will promote cold rain showers and light snow chances the
second half of the week. By the weekend, a warming and drying trend
is anticipated as the upper low departs to the east and anomalous
mid-level ridge over the West slowly stretches across the Central
US, while weakening. Finally, Pacific shortwave appears to move
inland and flatten the weakening ridge to reach the Ohio Valley by
the beginning of next week.
Model Evaluation/Confidence...Generally speaking, there is good
consensus on the timing and position of the deep upper low; however,
timing and intensity of embedded shortwaves is still uncertain which
might influence the development and position of surface features.
The latest CMC and GFS runs have similar Geopotential and Vorticity
output while the ECMWF is slightly faster with PV energy more
concentrated around the upper low. There is better confidence in the
weekend forecast with uncertainty increasing once again early next
week as model solutions diverge. In this case, the WPC Cluster Phase
Space shows the deterministic CMC and GFS agreeing on a shallow
shortwave trough moving atop of the ridge while the ECMWF depicts a
stronger ridge and overall is slower and favors trough amplification
across the West. It is noted that previous ECMWF runs resembled more
a GFS-like solution.
Tue Night - Wed Night...There is a brief pause in the rain shower
activity Tuesday night as frontal showers move east of the area.
However, the leading wave associated with the deep upper low will
quickly swing by the region later on Wednesday and carry light rain
chances, although timing of showers is pending better model
agreement. Westerly winds will also pick up on Wednesday afternoon
with gusts around 25 mph as a weak surface low develops along the
Great Lakes and the pressure gradient strengthens. GFS forecast
soundings are hinting at steepening lapse rates Wednesday afternoon
below cold air advection aloft, opening the possibility of mix down
the stronger momentum aloft. As a result, a few gusts could reach or
overcome the 30-mph threshold if there is sufficient cloud breaks.
Last but not least, a few flurries could be spotted late Wed night
across southern Indiana and northern Kentucky.
Thursday - Friday...Best chance of flurries or light snowfall stays
for the Thursday-Thursday Night timeframe as persistent cold air
advection supports an almost below-freezing profile. Actually, a mix
of cold rain and light snow/flurries is likely during the day as
near-surface temperatures stay above freezing with mostly wet light
snow in the overnight periods. GFS forecast soundings and ECMWF p-
type meteograms boost confidence in that scenario. As for
accumulations, above-freezing pavement and near-surface air
temperatures throughout this period will not allow any significant
snowfall accumulations with probably an overnight dusting in grassy
areas and elevated surfaces. Windy conditions will linger Thursday
and also Friday with the strongest winds forecast on Thursday
afternoon, especially across the Bluegrass where the highest
probability of achieving 40-mph gusts resides, according to both
ECWMF EFI and maximum wind gust probability. Temperature wise, highs
will be 5 to 10 degrees below normal while lows remain near the
seasonal average.
Weekend & Next Week...Slow warm-up trend during the weekend and
early next week with highs climbing to the 50s on Saturday and close
to 60 in Sunday given increasing warm air advection as winds turn to
the south on Sunday. Lows, on the other hand, will continue on the
chilly side, but gradually move. More sunshine is anticipated this
weekend, especially on Saturday. For next week, temperatures will
continue on the rise while liquid rain chances return to the
forecast, but low confidence in onset timing given model
disagreement.
&&
.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 653 PM EST Mon Nov 18 2024
Deteriorating conditions are expected tonight as a cold front
approaches from the west. First, LLWS will arrive as a LLJ moves
over the area. LLWS will be most likely between 06-12z. Increasing
rain coverage and lowering ceilings will occur tomorrow morning,
with flight categories forecast to drop to MVFR. Rain intensity
should be fairly light, so confidence on vis restrictions remain on
the lower side. Southerly winds ahead of the front will be gusty,
but should relax behind the front and become more westerly later in
the period.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...CJP
SHORT TERM...SRM
LONG TERM...ALL
AVIATION...CJP
Source:
LMK issues Area Forecast Discussion (AFD) at Nov 18, 9:45 PM EST---------------
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