LMK issues Area Forecast Discussion (AFD) at Jan 5, 4:07 PM EST
423
FXUS63 KLMK 052107
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
407 PM EST Sun Jan 5 2025
.KEY MESSAGES...
* Major winter storm continues across the Ohio Valley, with the
heaviest mixed precip and ice accumulations expected this evening.
Isolated thunder could result in locally higher precipitation
totals, even if ice accumulation is not increased significantly.
* A period of freezing drizzle is likely overnight, with an
additional 1 to 2 inches of snow possible Monday.
* Bitterly cold temperatures are expected this week as an Arctic
airmass overspreads the region. Forecast confidence on the cold
temperatures is very high while there is increasing confidence in
sub-zero temperatures for some Thursday morning.
* Another wintry system is possible next weekend, though forecast
confidence in accumulations and impacts is low at this time.
&&
.SHORT TERM /THROUGH MONDAY/...
Issued at 407 PM EST Sun Jan 5 2025
Winter storm moving through the Ohio Valley is undergoing a
transformation as the sfc low approaches Memphis and a low-level jet
surges northward into the Pennyrile. Warm nose has punched far
enough north that the snow has mostly changed over to freezing rain
and sleet roughly up to Interstate 64. A pocket of convection
associated with the LLJ has generated a fair bit of lightning, and
the main effect of that will be to locally enhance precip rates.
Since the precip type is governed by the warm nose rather than a
lack of ice aloft, we expect it to remain rain/freezing rain with a
bit of sleet. While this will increase precip totals, the intensity
will limit the efficiency of ice accumulation, so it's not a
significant change in impact. Will include mention of thunder late
this afternoon west of I-65 and into this evening along the KY/TN
border as the sfc low pushes through.
Precip type this evening will be mostly if not entirely liquid,
which means freezing rain north of a line from Hartford to
Hodgenville to Berea. From there northward to the I-64 corridor,
including Jasper, Louisville, Frankfort, and Lexington, widespread
damaging ice accumulations of a quarter to half inch, with locally
higher amounts, are likely. With wind gusts around 20 mph overnight,
significant impacts to trees and power lines are in play.
Precip rates will diminish significantly after about midnight as the
dry slot punches in, but we could see lingering freezing drizzle for
much of the night. Look for the final act of this long-duration
winter storm on Monday as the upper low opens up and pushes eastward
across central/southern Indiana, with a deformation band to drop an
additional 1 to 2 inches of snow, mainly in southern Indiana and
north central Kentucky.
Cold temperatures spill into the region on gusty northerly winds, so
would not expect any real recovery in temps. If anything, look for
falling temps especially south of the Bluegrass Parkway. By early
afternoon most locations should be just below freezing.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 407 PM EST Sun Jan 5 2025
Synopsis...Large-scale pattern around the CONUS consisting of broad
upper high over the eastern Caribbean, amplified ridge across the NE
Pacific, and cur-off low meandering Newfoundland will promote
persisting negative upper-height anomalies and shortwave energy
intrusion along most of the Lower 48 this week. At the surface,
Arctic high pressure will gradually drop from Canada to the Central
Plains by midweek and slowly progress towards the Ohio Valley and
the East Coast the rest of the week. As a result, bitterly cold
temperatures and mostly dry weather are expected the rest of the
week. However, another storm system might impact the forecast area
next weekend as a northern-stream shortwave trough coming from
Canada tries to phase with a southern-stream closed over located
over the Dessert Southwest. The resultant surface low will track
across the Gulf Coast potentially leaving the Ohio Valley under
another round of wintry weather.
Model Evaluation/Confidence...As stated in the previous forecast
package, confidence in gelid temperatures for the Tuesday-Thursday
timeframe is increasing given lingering snowpack and slightly
modified airmass accompanying the Arctic surface pressure. There is
high confidence that coldest morning will occur on Thursday given
position of the surface high center over the Ohio Valley and
clearing skies. The second half of the forecast is still uncertain
as models do not agree on the wave phasing west of the region, which
limits timing and QPF confidence for the potential winter system
next weekend. Modelwise, latest runs of GFS/ECMWF/ICON have snow
shield transitioning over the Lower Ohio Valley Friday into
Saturday. On the other hand, the CMC has a similar scenario but for
Sunday since it does support wave phasing and therefore the southern-
stream low ejects later. Finally, the UKMET resembles the CMC un-
phased solution, but the latter has a further south low track and
does not support as much as QPF as the former models.
Monday Night...DGZ saturation will be decreasing as the storm system
ejects to the east. Scattered flurries will probably be ongoing
Monday evening and rapidly decline towards Tuesday morning as
subsidence depletes moisture aloft. Expect temperatures to plummet
overnight amid persistent cold air advection and the freshly
deposited snowpack.
Tuesday - Thursday...Mostly to cloudy conditions will continue
Tuesday and most of Wednesday as wrap-around moisture translate
through the region under light westerly surface winds. There is also
a conditional probability for isolated flurries if a seeder-feeder
mechanism realizes as mid-level clouds stream over low-level
stratus. No additional snowfall accumulations are anticipated from
that activity if it materializes. Biggest headline for this week
will be the bitterly cold temperatures with below-freezing highs
every day and single-digit lows Wednesday and Thursday mornings.
Additionally, given the snow depth, continuous below-freezing
temperatures, and clearing skies accompanying the surface high
pressure, near-zero to slightly negative lows cannot be ruled out
Thursday morning. Greatest probability (>70%) for such gelid values
are focused along the Ohio River and southern Indiana.
Friday - Sunday...Slight temperature warm-up next week as the next
storm system tracks south of the area, but lows will be in the 20s
with highs barely over the freezing mark. As discussed above, there
is still disagreement on timing and QPF of potential precipitation.
It is worth noting that whatever solution is desired (GFS/ECMWF/ICON
vs. CMC vs. UKMET), the favored precipitation type is snow with a
couple of inches not out of question at this point.
&&
.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 107 PM EST Sun Jan 5 2025
Winter storm is well underway with IFR ceilings across the board,
and LIFR vis in moderate to heavy snow at SDF, LEX, HNB, and RGA.
BWG is under the warm nose and has mostly seen freezing rain for
much of today.
As the warm nose progresses northward, expect to see more sleet
mixing in by 19-20Z at SDF and HNB, and 20-21Z at LEX and RGA.
Eventually precip will switch to FZRA around sunset, with this
evening as the peak period to accumulate ice glaze. The exception to
all this will be BWG, where it will warm up just enough to
transition to plain rain around 19-20Z.
Late this evening we lose ice aloft, but low-level saturation
persists and will support at least intermittent FZDZ overnight. ENE
winds will eventually back to NNE, except for a period of SW winds
at BWG before daybreak when the sfc low passes.
Monday morning look for NNW winds increasing to near 15 kt, with 20-
25 kt gusts in the deeper cold advection. IFR vis possible in
scattered snow showers through at least midday.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Winter Storm Warning until 7 PM EST /6 PM CST/ Monday for
KYZ023>043-045>049-053>057-061>067-071-074>078-081-082.
Winter Weather Advisory until 6 PM CST Monday for KYZ070-072-
073.
IN...Winter Storm Warning until 7 PM EST /6 PM CST/ Monday for
INZ076>079-083-084-089>092.
&&
$$
SHORT TERM...RAS
LONG TERM...ALL
AVIATION...RAS
Source: LMK issues Area Forecast Discussion (AFD) at Jan 5, 4:07 PM EST (https://mesonet.agron.iastate.edu/p.php?pid=202501052107-KLMK-FXUS63-AFDLMK)
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