Scientific Forecaster Discussion
fxus63 klmk 120109
Area forecast discussion
National Weather Service Louisville Kentucky
809 PM EST Mon Nov 11 2019
issued at 808 PM EST Mon Nov 11 2019
Portions of northern Kentucky and central Kentucky west of I-65 are seeing a
changeover from rain to snow as of this writing. Reports of brief
sleet mixing in with rain and snow have been common in the
transition zone. Louisville has switched over to all snow, but Road
surface temps remain above freezing.
Areas in southwestern Indiana such as Huntingburg, Jasper, and
French Lick are seeing temps dip below 30 degrees now. We'll likely
see Road deterioration accelerate in those areas due to colder Road
sfc temps. Indot RWIS stations are reporting Road temps in the low
to mid 30s in SW Indiana. These areas were also cooler earlier in
the day due to the position of the front and more cloud cover.
Elevated Road sfc temps in Louisville have dipped as low as the
upper 30s so far, but Road surfaces on solid ground are running
about 10 degrees warmer than that.
So expect Road sfc temps to lag the air temperatures as it gets
colder tonight. Roads will be mainly wet as snow begins in central
KY, but roads could become quite slick closer to midnight and
especially during the early morning hours of Tuesday.
Light accumulations are still on track for tonight, and given the
presence of gusty winds and the arrival of much colder air for
Tuesday, the current headlines look good.
Issued at 545 PM EST Mon Nov 11 2019
Sfc cold front is already pushing into the Lake Cumberland region,
where temperatures are still hovering in the upper 50s at Kentucky mesonet
stations in Cumberland and Clinton counties. Northwest of the
boundary, temperatures are falling several degrees each hour in
southern in and central Kentucky. Temperatures are now around the freezing
mark near Jasper and French Lick in Indiana.
West-central Kentucky and southern in have been seeing a relative lull in
precip rates over the past 30-60 minutes. The rain to snow line has
effectively pushed partially through our southern in counties, and
brief light snow has been reported in DuBois, Orange, and Washington
counties so far. Whenever precip rates pick back up across these
areas, expect light snow to be the primary precip type.
However, the main band of moisture/lift in the dgz currently
stretches from roughly Mount Vernon Illinois to Indianapolis. This band of
enhanced moisture does sag southeast with time, but the lift
diminishes somewhat as better forcing moves off to the northeast
across Ohio. Overall, The Heart of this light snow event still
begins around 00-01z. We will see pretty substantial reductions to
visibility even in lighter snow thanks to gusty northwest winds. Gusts of
25-35 mph will be common.
Short term...(this evening through tuesday)
updated at 300 PM EST Mon Nov 11 2019
..light snow accumulations tonight...
..Record cold temps Tuesday...
While most of the morning and early afternoon has consisted of clear
skies and seasonal temps, cloud cover has steadily begun building
into the region as the cold front continues to edge past the Ohio
River. Given the lack of cloud cover this morning, most of our County Warning Area
has managed to climb into the low 60s, however, as we head into late
afternoon and evening, temps will steadily be on the downward trend.
In regards to precip, light rain is already been observed in a few
counties near the Tennessee border. Coverage in southern in and central Kentucky
should ramp up between 20-23z. At around 00-02z, snow will start to
become mixed with rain in southern in and north central Kentucky. Shortly
thereafter, any mixed precipitation will transition to all snow,
especially as temps drop below freezing. Snow will persist until
around 06z for our northeastern counties and gradually tapper off at
our southern/southeastern counties by daybreak.
At this time, totals looks to remain around an inch for most of the
County Warning Area. However, models soundings do show good frontogenetical forcing,
coupled with ample lift, and moisture, so some localized heavy bands
resulting in totals near 1.5 inches can't be completely ruled out.
These accumulations will mostly be confined to grassy and elevated
surfaces though, as Road temperatures will take a bit longer to cool
off. Additionally, gusty northwest winds behind the front should
help to keep Road surfaces dry. However, the well below freezing
temperatures Tuesday morning will cause any remaining water to
freeze, so isolated slick spots are certainly possible during the
morning commute. As a result, the Winter Weather Advisory has been
expanded to included all counties in our cwa, given the expected
snowfall totals and possible impacts to commute.
Otherwise, Tuesday is forecast to be dry and unseasonably cold.
Morning lows will range from the mid teens to low 20s, with wind
chill values in the single digits, while afternoon highs remain
below freezing. A few flurries may still exist for the northern
Bluegrass region, as cold air advects over Lake Michigan, but no
additional accumulations are expected at this time.
Long term...(tuesday night through monday)
updated at 234 PM EST Mon Nov 11 2019
High pressure with Arctic origins will settle near the region
tomorrow night, setting up our coldest night of the season so far.
Most guidance has morning lows Thursday falling into the mid-teens,
but would not be surprised to see a few single digit readings in
some of the colder valleys in the County Warning Area with the dry air (single
digit dewpoints) that will be in place.
By Wednesday, the high will drift off to the east, and flow across
the region will turn more southerly. Quiet and dry weather can be
expected in the long term, as most systems avoid impacting the area,
and any shortwaves that do dive toward US lack deep moisture to aid
in precipitation development. Temperatures will gradually climb
heading into the weekend, though they will remain below
Aviation...(00z taf issuance)
issued at 550 PM EST Mon Nov 11 2019
The Arctic front has pushed through the terminals, with temps
falling off quickly behind it. Ceilings have dropped into fuel-
alternate, and even IFR at hnb. Expect sdf, then Lex and bwg to
also drop into IFR as the evening progresses.
Perhaps the biggest challenge will be precip type, as the intensity
has decreased enough that most of it continues to fall as light
rain. As the rates pick up again this evening, we should see a
change to snow with IFR vis. Will likely initialize sdf and Lex with
a light mix, with tempo groups for IFR vis in the intervals of
heavier snow showers.
Precip will taper off either side of midnight at hnb and sdf, and
later but still well before daybreak at Lex and bwg. Ceilings should
improve fairly quickly once the precip shield departs. Snow will be
accompanied by north-northwest winds gusting around 25 kt, and we'll see gusts
stay up near 20 kt through most of the night before diminishing
around midday Tuesday.
in...Winter Weather Advisory until 8 am EST /7 am CST/ Tuesday for
Kentucky...Winter Weather Advisory until 8 am EST /7 am CST/ Tuesday for