Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 012016
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
316 PM EST Sun Mar 1 2015

.SHORT TERM (Now through Monday Night)...
Issued at 200 PM EST Sun Mar 1 2015

...Freezing Drizzle Possible Overnight Across South-Central KY...

The synoptic pattern this afternoon features an active southern
stream with several embedded shortwaves while pieces of northern
stream energy pass across the Great Lakes region. At the surface,
high pressure is centered across Kansas. After the morning wintry
mix for southern Indiana and northern Kentucky, temperatures have
warmed nicely into the mid 30s to mid 40s as of mid afternoon.
Scattered rain showers tracked through the area, dropping between
0.10 and 0.25" of liquid so far.

Hi-res models are handling the current activity fairly well, so
leaned on those solutions for this evening. Mid-level frontogenesis
will continue a few more hours before moving off to the east. Low
clouds and drizzle will be the main weather story for most this
evening before a cold front arrives, bringing another sharp decline
in readings overnight. Plan on lows mid 20s to around 30 by daybreak
Monday.

For tonight, main concern is the potential for light wintry
precipitation along and south of the KY Parkways as low to mid level
frontogenesis sets up from northwest TN to east central Kentucky
associated with a secondary shortwave lifting through TN. At the
same time, northwest to north winds will funnel in colder air at the
surface, dropping temperatures to near or below freezing after
midnight. This has been a consistent signal the past few days and
the 01.12z soundings support the idea of sub-freezing boundary layer
temperatures and a loss of ice saturation aloft with a warm nose in
between. The increasing signal for frontogenesis adds support for
the threat of light freezing drizzle, after midnight to mid morning
Monday, or about when surface temperatures warm above freezing. QPF
is light overall and the greater threat looks to be just south of
the KY border, but areas from Butler to Russell County southward are
the most likely LMK areas to see a period of freezing drizzle. SREF
probabilities for 0.01" or more of ZR are running 50 to 70 percent.

As a result, added drizzle/freezing drizzle to areas south of the KY
Parkways with the possibility for a light ice accumulation of a few
hundredths. Today`s relatively warmer, above freezing temperatures
and wet roads negate some of the potential impacts but untreated
secondary surfaces may develop slick spots for the Monday morning
commute. Will go with a SPS for now, but the evening shift may need
to see if an advisory is warranted depending on how quickly surface
temperatures are dropping.

Refreezing wet roads could pose a problem across the entire area
late tonight as well as readings fall into the mid 20s to around 30.
Increasing north winds and slightly drier air should help dry up
roads, but the less traveled, secondary and sheltered locations may
have some slick spots as well.

For Monday, surface high pressure moving across the Ohio Valley will
continue funneling drier air into the region such that we`ll see
some breaks in the clouds by late morning into the afternoon,
especially for southern Indiana and northern Kentucky. Plan on highs
top out in the mid 30s to low 40s, north to south. Monday night into
Tuesday morning the high shifts to the east and easterly to
southeasterly flow sets up by Tuesday morning. Increasing isentropic
lift and warm air advection could spread precipitation to areas
along and west of I-65 by early Tuesday morning. Soundings show that
we`ll have a sub freezing boundary layer and a warm nose aloft, so
once again there is concern for light freezing rain at the onset.

.LONG TERM (Tuesday through Sunday)...
Issued at 300 PM EST Sun Mar 1 2015

...Active Weather Period Shaping Up for the Ohio Valley...

A fast moving surface low will race from the central Plains on
Tuesday morning into Quebec by Wednesday morning, and will drive a
cold front into the Ohio Valley. Ahead of this front, strong Gulf
moisture return and low-level warm advection will feed plenty of
warm and moist air into the region, with precipitable water values
well over 1 inch as temps approach 60 degrees. Low-level jetting and
isentropic lift will make for 24 hrs of categorical POPs.

Main weather hazard will be heavy rainfall, especially over central
and southern Kentucky. The window for heavy rainfall does not seem
to last as long, given the faster trends with the Arctic front.
However, QPF is over 2 inches for a good chunk of Kentucky, and that
coincides with where the heaviest rain fell last weekend, and the
heaviest snow earlier that week. Still anticipate at least minor
flooding impacts, which are detailed in the Hydrology section.

Will continue to carry embedded thunder Tuesday and Tuesday night,
given the strength of the low-level jet and elevated instability
showing up in forecast soundings. However, not expecting any
substantial severe threat as surface-based instability is lacking.

Cold front comes through before dawn on Wednesday. Recent model runs
continue to trend faster with the Arctic air spilling into the Ohio
Valley, which would yield a changeover to snow during the day on
Wednesday as temps will nosedive for 24 hrs or more. We could see
another wave ride along the front late in the day, and if sufficient
cold air is in place, accumulating snows are possible mainly across
central and southern Kentucky. This forecast is still beyond the
scope of where we would put out actual snowfall numbers, but it
bears watching. Main factor that limits confidence is a NAM solution
that is much warmer through the day on Wednesday and keeps the
potential for wintry precip over Indiana.

A quiet pattern will set up on Thursday as Canadian high pressure
builds in, and then will continue through the weekend as the surface
high settles over the Deep South and the upper pattern flattens out.
Expect cold temps Thursday and Friday, especially if there is any
snowpack, followed by a moderating trend over the weekend.

&&

.HYDROLOGY...
Issued at 315 PM EST Sun Mar 1 2015

Light precipitation and warmer air continued to melt the snowpack
this afternoon over our area and keep soils saturated. The remaining
pack contains anywhere from about a half inch up to two inches of
liquid in a few locations. Temperatures will fall below freezing
tonight but will rise to similar values as today`s on Monday.

A new storm system will move into the region Monday night. At this
time, it appears that southern Indiana will see one to two inches of
rain on Tuesday and Wednesday, where Kentucky will collect about a
half inch more. Since soils will be saturated from snow melt, the
new rains could trigger flooding.

It appears that flooding on the major rivers would likely start
around midweek and continue into the weekend. This would affect the
Salt, Green, Licking, and Kentucky river basins. Minor flooding on
the Ohio River could occur as well. Residents in flood prone areas
should closely monitor water levels over the coming days and be
prepared for possible flooding by mid to late week.
&&

.AVIATION (18Z TAF Update)...
Issued at 1210 PM EST Sun Mar 1 2015

Initial band of precipitation working through central Kentucky early
this afternoon as ceilings continue to lower to MVFR fuel-alternate
levels. Expecting scattered showers to persist through the afternoon
as weak lift and saturation remains. There are still signals of IFR
ceilings moving into the area or developing toward sunset, though
confidence is not that high in this occurring. A secondary wave is
expected to bring additional precipitation to south-central
Kentucky, impacting BWG late this evening through early Monday
morning. As surface temperatures fall to near freezing, this may end
up as light freezing rain or freezing drizzle. At SDF/LEX, drier
north winds will help lift ceilings to MVFR by early Monday morning
then to VFR or scatter out mid/late morning.

&&

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

$$

Short Term........ZBT
Long Term.........RAS
Hydrology.........CMC
Aviation..........ZBT






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