LMK issues Area Forecast Discussion (AFD) at Sep 10, 3:06 AM EDT799
FXUS63 KLMK 100706
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
306 AM EDT Tue Sep 10 2024
.KEY MESSAGES...
* Hazy skies continue today due to smoke aloft.
* Warming temperatures and drying conditions through mid week.
* Francine expected to bring rain chances Thursday into the weekend,
though forecast confidence remains low in rainfall amounts.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 305 AM EDT Tue Sep 10 2024
Surface high pressure drifting from the Ohio Valley to the East
Coast will provide the region with light winds and cloud-free skies
today with a very dry atmosphere in place, though thin smoke is
expected to remain overhead between 6 and 14k' above the surface.
With the high slipping eastward and weakening, a slight increase in
thicknesses, and plenty of sunshine, temperatures should be a few
degrees higher than yesterday, in the middle and upper 80s.
Afternoon humidity levels will once again be very low.
A quiet night is in store tonight with nearly calm winds as cirrus
well ahead of Francine spreads northward into Kentucky. Lows will
mostly be in the 50s.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 305 AM EDT Tue Sep 10 2024
Wednesday and Wednesday Night...
An upper level trough will move onshore the Pacific NW on Wednesday,
with downstream ridging expected to build across the central and
eastern CONUS. Surface high pressure will have shifted east toward
the northeastern U.S. coast by Wednesday afternoon, though return
flow should hold off until late Wednesday into Thursday, with a dry
air mass remaining in place across the region. Dry air combined with
a downslope component from E/SE low level flow should allow for the
warmest temperatures of the extended forecast period in most
locations Wednesday afternoon, especially if incoming high clouds
from TC Francine remain relatively thin and/or scattered.
On Wednesday evening, thicker upper level clouds from TC Francine
should stream from south to north across the Tennessee and Ohio
valleys. This extra cloud cover, combined with increasing light
winds overnight as the pressure gradient strengthens should help
limit overnight cooling compared to previous nights, with more mild
low temperatures expected Thursday morning.
Thursday into Next Weekend...
The remnants of TC Francine are expected to be the main weather
maker across the Ohio and Tennessee valleys from Thursday into next
weekend. As upper ridging continues to strengthen over the Great
Lakes into Thursday, a subtle shortwave extending from the main
trough out west into the southern Plains is expected to help lift
Francine northward into the lower and mid-Mississippi Valley
Thursday into Friday. The influence from the upper shortwave is
expected to wane on Friday, resulting in a considerable slowing in
Francine's forward movement as it runs into the heart of the upper
ridge. Ensemble cluster analysis shows generally good agreement in
the storm's positioning through Friday, with most guidance stopping
Francine's northward progress near the confluence of the Ohio and
Mississippi Rivers. At this point, the upper closed low associated
with Francine's remnants will begin to weaken and meander slowly
across the Tennessee Valley through the weekend as steering currents
are expected to remain weak.
As would be expected, ensemble metrics of moisture advection and
precipitable water are anomalously high for Thursday into Friday as
Francine moves closer to the region. On the east side of Francine's
remnants, 850 and 700 mb southerly flow are in excess of the 99th
percentile of climatology, drawing rich moisture from the Gulf of
Mexico up into Kentucky and Indiana. Accordingly, tropical showers
and storms with locally heavy rainfall are expected to move across
the region starting Thursday afternoon (southern KY) and continuing
into at least the first part of the weekend. Histograms of ensemble
QPF still show large amounts of spread: while median precipitation
amounts continue to range from 1-2" across much of the area, there
are both significant probabilities of less than 1/4" (especially in
the KY Bluegrass), as well as greater than 3". Furthermore, since
ensembles cannot resolve convection, the usual caveat of localized
higher amounts would still apply. In short, there is high confidence
in rainfall late this week and this weekend; however, whether or not
the remnants of Francine will bring significant drought relief
remains uncertain.
The potential for spin-up tornadoes with the remnants of TC Francine
will be very low, but cannot completely be ruled out given the
continued spread in storm track. At this time, it appears that
appreciable instability should be confined to the Tennessee valley
and the Deep South, with most sounding profiles showing deep
saturation, limiting instability. The concern will be that initially
strong mid-level flow will provide ample shear, though this too will
weaken as the storm loses intensity Friday into Saturday.
Increased moisture in the lower troposphere will lead to smaller
diurnal ranges in temperatures from Thursday through the weekend.
While milder lows and cooler highs are expected during this period,
there continues to be a range of some 15-20 degrees among the
ensemble guidance for many of these days, with wetter solutions
producing cooler highs and milder lows while drier solutions produce
warmer highs and cooler lows. Forecast confidence in temperatures
remains low from Thursday through the beginning of next week.
&&
.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1244 AM EDT Tue Sep 10 2024
High pressure drifting slowly from the Ohio Valley to the East
Coast will keep our winds light and skies cloud-free through the TAF
period. Some smoke is possible again today and tonight, primarily in
the 6-14k' layer.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
SHORT TERM...13
LONG TERM...CSG
AVIATION...13
Source:
LMK issues Area Forecast Discussion (AFD) at Sep 10, 3:06 AM EDT---------------
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