Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 151121

Area Forecast Discussion
National Weather Service Louisville KY
621 AM EST Mon Jan 15 2018

...Updated Aviation Discussion...

.Short Term...(Today through Tuesday)
Issued at 312 AM EST Mon Jan 15 2018

...Another round of light accumulating snow is expected through

A surface low will cross the southern Great Lakes through Tuesday,
bringing a couple rounds of snowfall to the region. Currently seeing
the first round of light snow associated with isentropic lift as the
mini warm sector of the clipper system gets established over our
region. We should start to see a light southerly wind component over
the next several hours as the warm front develops and lifts north of
the area. A dusting to a half an inch of snow is possible through
sunrise, mainly along and north of I-64. We picked up a quarter of
an inch here at the office with a 25:1 snow ratio, and seeing some
light accums on area webcams. Best chance for around a half an inch
of snow is across the northern tier of counties, where the Winter
Weather Advisory is already in effect. The strongest radar returns
look to traverse that region over the next 3 hours, so looks good.
Plan on no changes to the ongoing headlines as timing still looks
pretty good for the next segment to go into affect around mid to
late morning.

Expect a brief lull around sunrise through mid to late morning
before the next round of snowfall moves into the area from the west.
This round of precipitation will be associated with the left exit
region of a 120 knot upper jet. This feature is expected to nose
into the area, and then slowly pivot as the upper vort max rotates
into the western Great Lakes. A bit concerned that this slow
pivoting will allow for some slightly higher snow totals in our
southern IN and west central KY counties as the resulting
frontogenetical banding persists through early to mid afternoon.
Obviously not expecting 25:1 snow ratios at that time given the
daylight hours, but 15:1 still seems like a good bet given the cold
antecedent conditions, and good lift and saturation through the DGZ.
So, expect a swath of slightly higher snow totals in southern IN,
west central KY, and extreme north central KY where 2 to locally 3
inches are possible.

As we move into the late afternoon and evening hours, widespread
snow is expected to shift from northern to central KY. Models have
been consistently showing a weakening trend during this time, and
this appears to be associated with the behavior of the upper jet and
it`s orientation. As the upper jet pivots, the core will slide over
the area likely hurting the overall lift and frontogenesis for a
brief time. Then, as we move deeper into the overnight and into
Tuesday the jet axis will now feature the right entrance region over
southern and SE KY where an enhancement in snowfall is expected as
better frontogenesis and lift through the DGZ commence. So, also
have a swath of 2 to locally 3 inches down in that region roughly
along and east of a Glasgow to Richmond, KY line. North of that line
from Glasgow to Richmond, up to near the Ohio River expect lesser
totals due to the weaker jet support as the core rotates through the
area. Will go with around an inch in most spots, locally up to 2.

It may seem a bit odd, but given the setup of the upper jet it feels
like this system could slightly overachieve in our NW, underachieve
in the center part of the CWA, and then slightly overachieve in our
far SE. Will be interesting to watch how it all progresses.


Expect a mid level dry slot over southern IN and north central KY
for a period on Tuesday, before low level moisture returns to the
area. Given that this moisture will be situated in the DGZ, the
lightest of QPF values will still be able to produce additional
flurries and/or light snow showers. Some lingering light accums will
be possible through Wednesday morning.

Did want to talk about the Arctic air behind the cold front. Temps
drop into the single digits and low teens tonight, along with a
steady NW wind. This will result in the lowest wind chill values
down in the -10 to 0 range. Best chance for values near criteria
will be in our southern IN and north central KY counties. An
additional Wind Chill Advisory might be needed for that area for
Tuesday morning. Will consider than add this info to the ongoing WSW
for now. Tuesday highs only struggle into the low and mid teens
given the fresh snow pack.

.Long Term...(Tuesday night through Sunday)
Issued at 312 AM EST Mon Jan 15 2018

Tuesday Night - Wednesday...

The upper trough will slowly rotate through the region, with
lingering low level moisture situated in the DGZ. We`ve seen this a
couple times already this winter, and expect we`ll have some
lingering light snow showers capable of some light accums into
Wednesday morning. With snowpack and a very cold airmass in place,
Wednesday morning will be quite cold with dangerously cold wind
chills. Expect lows in the 0 to 5 degree range and just enough wind
to drop the lowest wind chill values into the -10 to 0 range. High
pressure builds into the area by Wednesday afternoon with clearing
skies and temps "warming" into the low 20s.

Wednesday Night - Friday Night...

NW flow aloft will transition to a more zonal pattern by the end of
the work week. Meanwhile, high pressure at the surface will traverse
to the east. This will bring a "warming" trend with temps rising
around 10 degrees from the previous day. Highs Thursday will be
around or just above freezing, reaching the low 40s by Friday. After
lows in the single digits Wednesday night, low Thursday night will
be around 20.

Saturday - Sunday...

The warming trend will continue into the weekend, bringing well
above normal temps, and even the chance for thunderstorms to end the
weekend. A strong shortwave will eject out of the west CONUS, with
lee cyclogenesis occurring over the central Plains. This will result
in the a wide open flow of warm/moist air out of the Gulf into our
region. Initially, we`ll see light showers with isentropic lift,
however as get toward Sunday night or Monday, expect widespread rain
with a chance at some thunderstorms. Highs on Sunday could approach
60 degrees!


.Aviation...(12Z TAF Issuance)
Issued at 620 AM EST Mon Jan 15 2018

An arctic cold front will press southeastward and push through the
forecast area this afternoon and this evening.  Snow showers will
accompany this feature as it pushes through.  Cigs/Vsbys will start
off the period in the VFR range, but should decrease into the MVFR
range later this morning and into the afternoon hours.  Some
temporary drops into the IFR range will be possible at
KHNB/KSDF/KLEX from this morning into this afternoon.  KBWG may see
some drops into the IFR range late this afternoon and into the
evening hours.  The snows will bring an accumulation with them and
will likely lead to snowcovered ramps and runways.  Snow showers
will end this evening at KSDF and KHNB but will likely persist at
KBWG and KLEX into the late night hours.  Winds will start off out
of the southeast this morning and then switch to the southwest and
become gusty.  Wind gusts of 20-25kts will be possible throughout
the day and into the evening hours.


IN...Winter Weather Advisory until 4 PM EST /3 PM CST/ this afternoon
     for INZ076>079-083-084-089>092.

     Wind Chill Advisory from 1 AM EST /midnight CST/ to noon EST /11
     AM CST/ Tuesday for INZ076>079-083-084-089>092.

KY...Winter Weather Advisory until 4 PM EST this afternoon for

     Wind Chill Advisory from midnight tonight to 11 AM CST Tuesday
     for KYZ023.

     Winter Weather Advisory from 1 PM EST /noon CST/ this afternoon
     to 10 AM EST /9 AM CST/ Tuesday for KYZ036-037-040>043-

     Winter Weather Advisory from 10 AM EST /9 AM CST/ this morning
     to 10 PM EST /9 PM CST/ this evening for KYZ023>029-038-039-



Short Term...BJS
Long Term....BJS
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