758 
FXUS63 KLMK 061703
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1203 PM EST Sat Feb 6 2021

Updated Aviation Discussion...

.Forecast Update...
Issued at 1045 AM EST Sat Feb 6 2021

Forecast remains on track this morning. Minor tweaks made to 
temperatures given a slower warming response with the cloud cover 
over central Kentucky... otherwise, still expecting to see highs top 
out in the upper 30s in southern Indiana and low to mid 40s across 
central Kentucky. Far southern Kentucky could see highs briefly hit 
the upper 40s by late afternoon. Clouds will continue to increase in 
coverage and thickness ahead of our next system tonight.

&&

.Short Term...(Today and tonight)
Issued at 330 AM EST Sat Feb 6 2021 

Current satellite imagery shows thinning band of cirrus over 
southern KY while a band of mid-level clouds streams across southern 
IN and northern KY. Continue to see some light snowfall and flurries 
out of this mid-deck as area surface observations indicate lowest 
levels have saturated enough for precip to reach the ground. 
However, not expecting more than a dusting with these snow showers 
as they diminish over the next couple of hours. Otherwise relatively 
quiet weather in store for the first part of the day with increasing 
cloud coverage throughout the day ahead of an approaching system. 
Temperatures will warm into the upper 30s to lower 40s across 
southern IN and northern KY and into the mid to upper 40s across 
southern KY. 

As we move into this evening, expect a couple waves of energy 
swinging across the TN Valley and Great Lakes region to bring 
increasing precipitation chances to the area. Precipitation will 
begin to move in shortly after sunset, when temperatures across 
northern portions of the area will be in the lower to mid 30s and 
temperatures across southern KY will be in the lower 40s. This will 
result in p-type starting as snow along and north of I-64, rain 
across southern KY, and a rain/snow mix between the Parkways and I-
64. As temperatures continue to crash overnight however, expect 
precip to changeover to all snow between 12-3 AM EST. Snow will 
then continue overnight before ending from west to east towards 
sunrise Sunday morning. Accumulations will generally be around a 
half inch or less, but higher amounts to around an inch will be 
possible mainly along and north of I-64 as well as across the 
eastern edge of our CWA. With temperatures ranging from the upper 
teens over southern IN to the upper 20s across southern KY, any 
wet surfaces may freeze and create slick spots.

.Long Term...(Sunday night through Friday)
Issued at 339 AM EST Sat Feb 6 2021

A very challenging, complex, low confidence forecast as the region 
sits in the battleground between air masses to our north and south.

Sunday and Sunday night Canadian high pressure will nose 
southeastward into the region with dry, cool weather. Highs on 
Sunday will be in the 30s but we'll drop into the mid teens to lower 
20s Sunday night with partly cloudy skies. Monday a warm front will 
set up from a weak area of low pressure over the TX/NM border to the 
central Appalachians. During the day precipitation associated with 
this feature will remain to our north. However, Monday night into 
Tuesday morning the boundary is expected to slip southward as a cold 
front as low pressure rides along it, bringing us some light 
precipitation. Will stick with rain/snow mix in the forecast for 
now, however it should be noted that soundings over southern Indiana 
and north central Kentucky show little if any ice nucleation aloft 
given a shallow layer of low level moisture while surface 
temperatures fall into the middle and upper 20s...suggesting 
freezing drizzle or light freezing rain may be a possibility by the 
Tuesday morning commute. Something to keep an eye on.

Mid-week confidence remains low, similar to previous forecast 
packages, as we sit between cold air and more vigorous mid/upper 
energy to our north and more temperate air to our south. CFSv2 16 
member ensemble mean shows cold air spilling from Alaska and Canada 
into the Plains/Great Lakes/Midwest and a baroclinic zone setting up 
from the Ozarks through the Tennessee Valley to the mid-Atlantic. 
EPS and GEFS are similar but have the baroclinic zone slightly 
farther north, more over the Ohio Valley than the Tennessee. The 
location of this zone will have an impact on how much precipitation 
we receive and what type of precipitation we receive depending on 
how deep into the cold air we are at the surface and aloft.

Tuesday-Tuesday night we're in between systems but ensembles do show 
the possibility of some very light precipitation in the area so will 
continue to carry a low PoP with very low QPF. Right now will prog 
highs Tuesday afternoon ranging from around freezing in southern 
Indiana to near 50 along the Tennessee border...which provides a 
good illustration of how we are treading the tightrope between cold 
and warm. A shift of just a hundred miles in that temperature 
pattern will spell huge differences in the forecast, especially as 
we continue into mid- and late-week.

Speaking of which, Tuesday night-Wednesday night the operational GFS 
brings significant wintry weather to the region in two waves. The 
first wave would come late Tuesday night into Wednesday morning and 
has support from the CMC and now from the latest ECMWF as well. The 
second wave would then come in Wednesday night and possibly into 
Thursday. Though the models have not done a great job with the 
extended over the last few days and there is still some run-to-run 
inconsistency showing up as the models struggle with the transition 
zone, this is something to keep a close eye on with the GFS/EC/CMC 
all starting to come together. We'll have southerly low level flow 
bringing warmth and moisture northward overrunning a surface trough 
from the Mississippi Delta to the central Appalachians and flowing 
above above shallow cold northeasterly winds at the surface coming 
off of Canadian high pressure stretching from the northern Plains to 
New England. This set-up would encourage impactful winter weather.

Thursday-Friday low pressure is expected to lift from the western 
Gulf into the upper Ohio Valley and bring us another chance of 
precipitation and once again the advancement, or lack thereof, of 
the cold dome to our north will make a big difference in the 
resulting precipitation type. Operational GFS is a little more 
aggressive with the late week cold invasion than the model mean and 
there is a 58 degree spread in 2m temperatures Friday evening among 
the model members at Louisville. Will lean on what the NBM delivers 
for now...plenty of other fish to fry in the meantime.

Thanks to neighboring offices for collaboration this morning.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1201 PM EST Sat Feb 6 2021

VFR conditions will be in place at the start of the forecast period, 
but flying conditions will decline tonight as a system moves in from 
the west. Rain and/or snow showers will begin shortly after 00z for 
TAF sites west of I-65, and eventually spread to the I-75 corridor 
after midnight. Cigs/Vis will drop to MVFR levels, perhaps briefly 
hitting IFR levels, for several hours. Visibilities will improve 
after the rain and/or snow moves out, but MVFR cigs will linger well 
into tomorrow morning before drier air from the northwest scatters 
out the stratus deck.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...DM
Short Term...JML
Long Term...13
Aviation...DM