Heavy Snow and Winter Weather in Kentucky, March 11 to 12, 2018

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1038 PM EDT Sun Mar 11 2018

.UPDATE...
Issued at 1037 PM EDT SUN MAR 11 2018

Precip is causing airmass to wetbulb fairly quickly. Despite
temperatures being in the mid 30s to near 40 degrees, we are still
getting reports of rain changing over to snow across portions of
the western CWA. As such, loaded the latest observed
temperatures into the near term forecast then reran the weather
at a slightly higher temp threshold for all snow and snow/rain
mix. This resulted in the rain/snow mix making it across portions
of our CWA this hour and expands it eastward in the coming hours.
Based on some reports, this might still be a bit slow but is still
more representative than ongoing forecast. All updates have been
published and sent to NDFD/web. This change was not significant
enough to warrant a new forecast package, however an updated WSW
product was issued last hour to reflect latest forecasted snowfall
amounts.

UPDATE Issued at 916 PM EDT SUN MAR 11 2018

Have been watching the latest model guidance as it comes in
throughout the evening to see how they are comparing to the
current radar trends, and how they are changing from the day
shift. Latest trends have been to put the axis of highest
pops/QPF/snow slightly farther north than originally forecast,
and slightly increase the QPF. QPF before 6Z (mainly rain) has
also increased, especially over the SW. Tried to incorporate
these trends in the near term forecast for pops/qpf overnight.
Left snow ratios the same from the afternoon forecast, as they
seem to be in good shape, with most of the CWA 11:1 or lower, and
the valley ratios slightly lower to account for slightly warmer
temps. After rerunning the snowfall we did increase amounts to
around 6 inches in some locations. Luckily highest amounts in
warning criteria still line up well with the ongoing warning.
Can't rule out some isolated locations just outside of the warning
seeing warning criteria amounts, but given the latest snowfall
forecast and the fact that there is still so much uncertainty,
confidence is not high enough to expand the warning at this time,
so will leave remaining areas in the advisory. Will continue to
closely monitor how snow continues to set up just to our west as
we head throughout the overnight and continue to adjust the
forecast as needed.

In addition to the snowfall updates, also loaded in the latest
observations to make sure the near term forecast for temps, dew
points, and winds was on track with current conditions. Also
reran the weather grids to change wording to coverage instead of
chances since precip is ongoing. All changes have been published
and sent to NDFD/web. A new forecast package was sent out to
reflect snowfall changes. An updated advisory and warning will
follow shortly as well.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 415 PM EDT SUN MAR 11 2018

A mid level low is approaching the Lower OH Valley region from MO
and the MS Valley region. Ahead of the system, the March sun has
warmed most locations into the 50s with the exception being the
high elevations near the VA border.A few locations near the TN
were near 60 before the clouds have increased.

The mid level low is expected to move southeast into the TN Valley
tonight and the Southern Appalachians early on Monday morning.
Meanwhile an northern stream trough will be moving into the
northern Great Lakes. These systems are not expected to phase with
the souther mid level low moving off the South Carolina coast on
Monday evening when a northern stream shortwave will also move
through the OH valley. As the upper low moves into the Central
Great Lakes and Ontario late in the period the southern mid level
low will open up and begin to merge with the Great Lakes system
with another weak shortwave approaching East Ky late in the
period.

With the system almost encroaching on the Commonwealth,
uncertainty remains greater than usual. There are some limiting
factors, including initially warm ground as temperatures reached
at least the 50s in most areas. The second will be a column
cooling to near isothermal near 0C in the lowest several thousand
feet as a deformation zone is expected to develop well north of
the surface low over western and central KY and move into the
area late as the mid and upper level system works through the TN
Valley and approaches East KY tonight. Cold advection as well as
lift and wetbulbing should all work to gradually cool the column
to near isothermal 0C as noted in the lowest several thousand feet
and the surface air temperatures to near freezing. Ground temps
will lag this somewhat though with rates at times likely moderate
to heavy at least in any banding, and with snow falling at night,
accumulations are anticipated with ridges favored.

The consensus of the 12Z guidance as well as convective allowing
models and even HREF ensemble point toward an area of heavier qpf
from central KY extending into western counties generally north
of KY 80/Cumberland Parkway and the I 64 corridor with the band
probably moving into these counties and then weakening and moving
east across the area such as indicated by the GFS as the surface
low begins to reorganize further southeast or off the southeast US
coast. Both models have a max in qpf from near Estill and Jackson
counties extending east into the area. The NAM qpf is generally
the greatest during the past two runs. In some of our western
counties, the probability of reaching low end warning amounts of
4 to perhaps 5 inches, especially on ridges increased over the
past 12 to 24 hours. Coordination with surrounding offices and
WPC to upgrade a few of the western counties in a warning. Even
though these amounts are at the lower end of the warning criteria,
what snow that does fall should be very wet with ratios initially
near or even below 8:1 considering thermal profile near 0C
somewhat limited presence of dendrites expected and warm ground
but then trend toward 10:1 before ending.

A few counties have also been added to the advisory over the
southwest and southeast with impacts to the morning commute
anticipated. Over the far southeast, the impacts may be limited
to 1500 to 2000 feet MSL elevations and above. The end time of the
southeast was also adjust further into Monday a bit.

Otherwise, behind the steady precipitation, a relative lull is
anticipated before the next wave moves into the OH Valley late in
the day or Monday evening. Isolated to scattered snow showers are
anticipated with this.

Temperatures should be below normal on Monday with snow on the
ground and the colder airmass in place. Lows should reach the 20s
in all areas on Monday night when 850 mb temperatures should reach
near -8C.

.LONG TERM...(Tuesday through Sunday)
Issued at 246 PM EDT SUN MAR 11 2018

The extended will feature a short period of colder than normal
temperatures and chances for rain and snow Tuesday through Wednesday
evening, as a large trough of low pressure aloft continues to move
slowly up the eastern seaboard. There will also be the possibility
of rain and snow showers late Thursday night through early Friday
morning, as an area of low pressure moves out of the Plains and
across the Ohio and Tennessee Valley regions. Temperatures will warm
enough for all rain to occur across the area Friday through Sunday,
as another area of low pressure forms over the Tennessee valley and
moves off to the east.

A period of much warmer weather is on tap for the end of the
upcoming work week into the weekend. The warmer weather will be the
result of winds shifting to the south and southwest Thursday night
and Friday. After seeing daytime highs only make it into the 30s for
most locations Tuesday and Wednesday, the warm up should begin in
earnest midweek. Thursday's highs should top out in the 50s, as
winds begin to shift from the west to the southwest across the
region. Friday and Saturday should be even warmer as winds should be
out of the southwest or south by then. Highs on each of those days
are expected to max out in the upper 50s and lower 60s and the low
to mid 60s respectively. Winds are expected to be brisk and gusty
for the first few days of the extended as well.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 809 PM EDT SUN MAR 11 2018

A surface low pressure system, currently over southern TN, will
continue to shift ENE and affect much of eastern Kentucky
overnight and into the first part of the day tomorrow. OVC CIGS
have taken hold of the TAF sites, and will continue to lower to
MVFR and possibly IFR in the next few hours. Rain is also
encroaching upon the TAF sites, and will encompass all the TAF
sites in the next few hours. This rain will transition over to
snow as temperatures drop to and below freezing, generally between
3 and 9Z. Rain, and especially the snow, could have high rates at
times, reducing VIS to MVFR or potentially lower throughout the
night. Snow accumulations are still somewhat uncertain at this
time, but could vary between an inch and 4 inches at the TAF
sites. The snow will be of the heavy and wet/slushy variety. Snow
will taper off from west to east mainly after 12Z, with all
precip exiting and conditions expected to improve back to VFR
generally by 17Z. Winds will be breezy out of the north during
the TAF period, especially during the overnight as the low passes
close by. Sustained winds between 7 and 12 mph will be likely at
KJKL and KSJS, while the more exposed sites of KSYM, KLOZ and
KSME could see sustained winds between 8 and 15 mph with some
higher gusts possible.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM EDT Monday for KYZ044-050>052-
060-079-080-104-106-109-112-114-116.

Winter Storm Warning until 9 AM EDT Monday for KYZ058-059-068-
069-108-111.

Winter Weather Advisory from 2 AM to 10 AM EDT Monday for KYZ088-
107-110-113-115-117>120.

Winter Weather Advisory from 2 AM to 9 AM EDT Monday for KYZ083-
084.

&&

UPDATE...JMW
SHORT TERM...JP
LONG TERM...AR
AVIATION...JMW

Hazardous Weather Outlook...UPDATED
National Weather Service Jackson KY
240 PM EDT Sun Mar 11 2018

KYZ044-050>052-060-079-080-104-106-109-112-114-116-122145-
Fleming-Montgomery-Bath-Rowan-Menifee-Pulaski-Laurel-Elliott-
Morgan-Magoffin-Breathitt-Owsley-Clay-
Including the cities of Flemingsburg, Camargo, Jeffersonville,
Mount Sterling, Owingsville, Morehead, Frenchburg, Burnside,
Somerset, London, Sandy Hook, West Liberty, Salyersville,
Jackson, Booneville, and Manchester
240 PM EDT Sun Mar 11 2018

...WINTER WEATHER ADVISORY IN EFFECT FROM MIDNIGHT TONIGHT TO
9 AM EDT MONDAY...

This hazardous weather outlook is for portions of eastern Kentucky.

.DAY ONE...Tonight.

Rain will mix with and then change to snow late tonight, with
light accumulations expected.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Any lingering snow will taper off on Monday morning, with total
snowfall of 1 to 3 inches for most locations.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

KYZ058-059-068-069-108-111-122145-
Estill-Powell-Rockcastle-Jackson-Wolfe-Lee-
Including the cities of Irvine, Ravenna, Clay City, Stanton,
Brodhead, Mount Vernon, McKee, Annville, Campton, and Beattyville
240 PM EDT Sun Mar 11 2018

...WINTER STORM WARNING IN EFFECT FROM 11 PM THIS EVENING TO 9 AM
EDT MONDAY...

This hazardous weather outlook is for portions of eastern Kentucky.

.DAY ONE...Tonight.

Rain is expected to change to snow late tonight, with accumulation
of wet heavy snow expected.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Any lingering snow will taper off on Monday morning, with total
snowfall of 2 to 5 inches expected for most locations.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report snowfall tonight and Monday
morning.

KYZ088-107-110-113-115-117>120-122145-
Harlan-Johnson-Floyd-Knott-Perry-Leslie-Letcher-Martin-Pike-
Including the cities of Cumberland, Harlan, Paintsville,
Prestonsburg, Wheelwright, Hindman, Pippa Passes, Hazard, Hyden,
Jenkins, Whitesburg, Inez, Coal Run, Elkhorn City, Pikeville,
and South Williamson
240 PM EDT Sun Mar 11 2018

...WINTER WEATHER ADVISORY IN EFFECT FROM 2 AM TO 10 AM EDT
MONDAY...

This hazardous weather outlook is for portions of eastern Kentucky.

.DAY ONE...Tonight.

Rain will mix with or change to snow late tonight, with light
snow accumulations possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Any lingering snow will taper off on Monday morning, with total
snowfall of half an inch in some valleys to 2 to 3 inches on
rides.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report snowfall on Sunday night and
Monday morning.

KYZ085>087-122145-
Whitley-Knox-Bell-
Including the cities of Corbin, Williamsburg, Barbourville,
Middlesboro, and Pineville
240 PM EDT Sun Mar 11 2018

This hazardous weather outlook is for portions of eastern Kentucky.

.DAY ONE...Tonight.

Rain may mix with or change to snow late tonight, with light snow
accumulations possible, mainly on ridges.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Any lingering snow will taper off on Monday morning, with total
snowfall of a half an inch or less for most locations.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report snowfall on Sunday night and
Monday morning.

KYZ083-084-122145-
Wayne-McCreary-
Including the cities of Monticello, Stearns, and Whitley City
240 PM EDT Sun Mar 11 2018

...WINTER WEATHER ADVISORY IN EFFECT FROM 2 AM TO 9 AM EDT
MONDAY...

This hazardous weather outlook is for portions of eastern Kentucky.

.DAY ONE...Tonight.

Rain will mix with and then change to snow late tonight, with
light snow accumulations possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Any lingering snow will taper off on Monday morning, with total
snowfall of around an inch, especially on the ridges.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report snowfall on Sunday night and
Monday morning.

HAL/JP