LMK issues Area Forecast Discussion (AFD) at Dec 13, 9:28 PM EST ...Forecast Update...974
FXUS63 KLMK 140228
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
928 PM EST Fri Dec 13 2024
...Forecast Update...
.KEY MESSAGES...
* Widespread soaking rain late Saturday through Sunday.
* Another widespread soaking rain Monday into Monday night with
isolated thunder. Possible ponding and nuisance flooding.
* Cold temperatures return late next week. Low confidence in light
snow showers Thursday and/or Friday.
&&
.UPDATE...
Issued at 927 PM EST Fri Dec 13 2024
Quiet evening expected across the area as brief upper ridging and
the western fringes of surface high pressure hang on. Current
satellite imagery does show a relative clearing of upper clouds,
however expect a resurgence of another batch of upper clouds between
Midnight EST and 5 AM EST from west to east. This is the precursor
to tomorrow's system that will be rolling in later in the afternoon
and evening. As a result, do expect the best cooling of to occur
during this relative clearing, before the upper clouds arrive once
again through the pre-dawn hours. By that time, temps will likely
flat line.
Tomorrow starts off dry, with light E winds picking up to a more
steady SE surface wind. Makes sense given the warm front that is
currently bisecting our CWA. This feature lifts northward tomorrow,
especially once the low level jet kicks in. Temps should be warmer
tomorrow given a deep position in the warm sector. Look for low to
mid 50s everywhere, with perhaps some upper 50s down near Bowling
Green. Light rain arrives from W to E late afternoon into the early
evening.
&&
.SHORT TERM /THROUGH SATURDAY/...
Issued at 301 PM EST Fri Dec 13 2024
Shortwave ridging and warm advection aloft has resulted in a fairly
thick cirrus canopy across the Ohio Valley today. A weak inverted
sfc trof extending SW-NE across central Kentucky has kept chilly
northeast winds across southern Indiana and the northern part of
central Kentucky, where temps are still struggling to get out of the
30s without the sunshine assist. Farther south, low-level warm
advection has pushed readings to near 50.
Still expecting this sfc feature to wash out by this evening, with
light E-SE winds throughout. Limited confidence in the temp forecast
tonight, especially in the east where the models like some clearing.
Opened up the range in min temps slightly by working the low end of
guidance across the Bluegrass region, but more pronounced clearing
in the east could result in an even larger spread in temperatures.
Main impact in the short-term is the arrival time of precip Saturday
afternoon/evening as a vertically stacked but progressive cyclone
kick ENE out of Kansas. Low-level dry air in place means we will
have to wait for the main low-level jet/warm conveyor belt, which
seems to be slowing down a bit with each model run. Will keep the
forecast dry through the morning and at least the early afternoon,
with precip finally spreading in from the Wabash Valley and the
Pennyrile between 18-21Z, and just reaching the I-65 corridor by 00Z
Sunday. Low-level winds coming around to SE by midday should allow
temps to climb into the 50s before the rain arrives, even with
plenty of cloud cover.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 301 PM EST Fri Dec 13 2024
Synopsis...The medium range period will mostly feature quasi-zonal,
progressive flow aloft as a series of periodic shortwave troughs
move across the northern half of the CONUS, boosting precipitation
chances and hosting above-normal temperatures. The first (shallower)
wave is expected to cross the Ohio Valley on Sunday with the
attendant surface low weakening as it tracks the Mid Mississippi
Valley. On the other hand, the second wave will be stronger and more
amplified with strengthening surface low tracking through the Upper
Midwest Monday while a sharper cold front extends southward. Then,
low-amplitude, mid-level ridge quickly transitions over the Ohio
Valley Tuesday into Wednesday leading to amplification in the second
half of the week as anomalous upper ridge builds over the West and
longwave trough develops over the East.
Model Evaluation/Confidence...Overall, there is relatively high
confidence in the large-scale pattern evolution through Wednesday
based on different runs from deterministic model guidance. This
consensus increases confidence in timing and type of precipitation
of the first two waves while also confirming the upward temperature
trend anticipated for the coming days. On the other hand, forecast
confidence decreases by the middle of next week as consulted
deterministic model guidance starts to diverge in regards to
shortwave phasing timing and placement. Such differences could
affect timing, placement, and intensity of a potential third wave of
precipitation. Although confidence is lower during the last half of
the forecast, one way or another all models reflect amplified trough
over the East with some ensemble members (and event control run)
showing a small chance of snow Thursday and/or Friday.
Sat Night - Sunday...Light to moderate rainfall will be moving
through southern Indiana and central Kentucky Saturday night into
Sunday morning as the shallow mid-level wave crosses the region and
weakening surface low barely pushes a cold front over the Lower Ohio
Valley. Even though a 50-knot low-level jet will accompany this
system, a lack of instability and established surface inversion will
inhibit any severe weather chances. Only threat (still minimal)
would be sporadic lightning chances overnight as decent mid-level
lapse rates and better forcing aloft overspread the forecast area.
Forecast soundings from GFS indicate mid-level drying on Sunday
which agrees well with subsidence due to rising upper-level heights
as a mid-level ridge quickly moves eastward from the Southern
Plains. That being said, cloudy skies and drizzle/light rain chances
will continue throughout Sunday give the presence of enough low-
level moisture and any mesoscale forcing from the stalled front.
Monday...Second, stronger wave will impact the area with potentially
heavier showers and slightly higher thunderstorm chances. Based on
the PV advection signal, upper-level dynamics, and overall timing of
the precipitation shield, expect persistent moderate rainfall Monday
afternoon into the evening with localized heavy rainfall. As a
result, widespread accumulations should range between 0.5 to 1.5
inches with narrow swaths closer to inches or more; however, there
is considerable disagreement where the highest rainfall could end
up. Therefore, will carry possible ponding and minor flooding issues
due to wet antecedent conditions. Lightning chances will also
increase compared to the Sunday morning wave as, especially if there
are some cloud breaks in the morning the render a few hundreds of
surface-based instability. In addition, sustained warm air advection
could substantially erode the surface inversion to a point that
surface winds turn gusty (around 20-30 mph), especially during the
afternoon. Some enhanced gusts of 30+ mph cannot be rule out with
strongest cores.
Tuesday...Mid-level ridge and surface high pressure will allow dry
weather to return to the area. Weak cold air advection component
under west winds will lower temperatures a few degrees, but still
run above average for this time of the year.
Wednesday - Friday...Model disagreement limits predictability and
inclusion of timing or intensity details during this period.
Nonetheless, pattern amplification yields certain confidence to
mention the possibility of initially rainfall followed by cold air
intrusion and low confidence for brief periods of light snow.
&&
.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 643 PM EST Fri Dec 13 2024
A mostly quiet TAF cycle ahead, although we do begin to see
deteriorating conditions toward the end of this window, especially
at the western sites (BWG/HNB/SDF). For the overnight, expect broken
upper clouds with a light east wind as a warm front sets up over our
region. Around sunrise through mid to late morning, we may see a
brief LLWS component at BWG as the 35 knot low level jet overspread
our area on top of the surface warm frontal boundary. Getting
roughly 50 degrees of veering in the lowest 2 K feet, along with
speed shear of 30-35 knots.
By midday or so, surface winds pick up out of the SE around 7 to 12
mph with thick mid and upper clouds. By late afternoon and early
evening, ceilings lower to near MVFR with light rain onsetting from
WSW to ENE across the area. Eventually, we'll find our way to MVFR
conditions, but it will likely be after this TAF cycle ends. Look
for those conditions in future updates for later Saturday
evening/night.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...BJS
SHORT TERM...RAS
LONG TERM...ALL
AVIATION...BJS
Source:
LMK issues Area Forecast Discussion (AFD) at Dec 13, 9:28 PM EST ...Forecast Update...---------------
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