Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 010820
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
320 AM EST Sun Mar 1 2015

.SHORT TERM (Now through Monday)...
Issued at 257 AM EST Sun Mar 1 2015

...A Light Wintry Mix Will Continue This Morning...

The heaviest precipitation overnight has been confined to points
along and north of the Ohio River. Some lighter returns across
central Kentucky resulted in some reports of light rain/snow/sleet
earlier tonight. The main forecast concern for the short term period
will be precipitation type and accumulations through mid morning.

Temperatures across the forecast area this morning range from the
mid 30s across south central Kentucky to the upper 20s across
southern IN and portions of north central KY. Think that most of the
precipitation right now across southern IN is light snow, though
some higher reflectivities a bit ago probably indicated some sleet
mixing in. AMDAR soundings from around 645Z at SDF show the warm
nose aloft has worked into at least central KY with values up to
around +2C. This warm layer should continue to work northward. Will
continue to carry a mix of snow, freezing rain, and a chance for
some sleet across southern IN and north central KY this morning.
Further south any precipitation is expected to be in the form of
rain.

As winds turn to southerly this morning, temperatures will warm with
all areas expected to be above freezing by 15Z or so. Thus the area
of potential mixed precipitation will shift northward quickly from
12Z on. Prior to that, however, cannot rule out an additional inch
or so of snow across the far northern tier of the advisory with
light accumulations of snow and/or a glaze of ice to the south. Some
slick spots still look to be possible early this morning.

A cold front will push through the area this evening. Precipitation
should be moving out as the cold air is moving in. Still think there
will be a chance for a wintry mix or a brief changeover to snow as
the precip moves out tonight. Any accumulations from this should be
fairly minor.

Clouds will begin to clear Monday as high pressure continues to
build in. Highs will range from the mid 30s to the lower 40s.

.LONG TERM (Monday Night through Saturday)...
Issued at 311 AM EST Sun Mar 1 2015

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

The latest global models continue to show a rather progressive
pattern aloft with a very active southern jet stream.  This setup
will result in a very wet pattern that features a brief warm
up...followed by a return of colder air back into the region.

Surface cyclogenesis is still progged to occur over the lower Plains
within the lee of the Rockies early in the period.  This low will
then race from the Plains into the Great Lakes while dragging a
surface cold front through the region.  Out ahead of this system,
large scale warm air advection combined with strong moisture
advection will bring a very wet period of weather to the region.
Precipitation is expected to re-develop and build northeastward late
Monday night and early Tuesday.  Out ahead of this precipitation,
the atmosphere will be largely cold...with subfreezing temperatures
over part of the region.  Thus, the initial precipitation for a
limited time early Tuesday looks to remain in a wintry mix across
the northern forecast area...with plain rain across the south.
Temperatures will warm on Tuesday with the WAA in full swing which
should result in temperatures breaking 60 across the south with
low-mid 50s up across the north.

Severe chances still look rather low across the region as surface
based instability will be confined to areas to our south.  Some
localized surface based instability may develop across southern KY,
but in general, it appears that elevated instability will be more
widespread across the region.  So, we will continue to go with
embedded thunder in the forecast.  Total quantitative precipitation
still remains somewhat of a challenge.  While the overall amounts
projected from the models continues to decrease with each run, we`re
still seeing quite a bit of variability in the amounts.  In general,
we still feel that total QPF amounts of 2-3 inches will likely be
realized across the region.  This rainfall, falling on melting
snowpack and saturated grounds will likely lead to flooding issues.
Please see they Hydrology section for further details.

The second aspect of this weather system will be the potential for
wintry weather on Wednesday as colder air pushes into the region.
The surface frontal boundary looks to pass through the region
Wednesday morning, with modified Arctic air sinking southward into
the region.  However, a sustained west-southwesterly flow aloft will
likely continue spread moisture up into the region, resulting in
light to moderate snows across the area.  Highs for Wednesday will
likely be very early in the day with a non-diurnal temperature
free-fall throughout the day.  We would not be surprised to see a
30-40 degree temperature fall throughout the day.  Some accumulating
snows look likely on Wednesday across the region with this activity.

From Thursday onward, the weather looks to be rather quiet with
mostly clear nights and mostly sunny days.  Highs will remain well
below normal with readings on Thursday staying in the 20s with 30`s
and 40s returning by Friday-Saturday.  Overnight lows will be cold
as well with single digit and teens Thursday morning and 20s by
Friday/Saturday morning.  Lows could be a little colder on Thursday
morning depending on the amount of snow we see on Wednesday.

&&

.HYDROLOGY...

Issued at 317 AM EST Sun Mar 1 2015

We still have quite a bit of snowpack in the area that contains
about a half inch in the south with an inch and a half to two inches
of liquid content up in our northern areas.  With warmer
temperatures expected through the period, we expect a bit of
melting.  Light to moderate rainfall with today and tonight`s system
will add less than a half inch but may result in some rises on area
creeks and streams due to runoff.

The secondary storm system for Tuesday is where we expect to see
hydrologic problems increase.  The latest model forecasts continue
to show a slight downtrend in total precipitation.  However, we`re
still looking at a solid 2-3 inches of rainfall along with continued
snowmelt.

Given the current rainfall projections, flooding on the major rivers
would likely start around midweek and continue throughout the
remainder of the week.  The latest forecasts continue to suggest
that the axis of heaviest rainfall will likely fall across much of
central KY...south of the Ohio River.  This would affect the Salt,
Green, and Kentucky river basins.  We will continue to closely
monitor stream levels and rainfall over the coming week.  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 (06Z TAF Update)...
Issued at 1157 PM EST Sat Feb 28 2015

The chance for any wintry precipitation overnight will be the main
concern for this forecast. Any frozen precipitation will then change
to all rain by around 12Z with rain continuing off an on through the
rest of the day.

For SDF a batch of rain and sleet moved through over the last hour.
For now the airport is in a clear slot. The latest mesoscale models
suggest that SDF will remain dry for at least the next couple of
hours. Thereafter, some freezing rain and maybe some sleet could
move in. Temperatures are hovering right above freezing right now,
but could fall a degree or two before beginning to rise around
sunrise. The timing of freezing rain in the TAF was shortened based
on the latest guidance.

At LEX light returns showing up right now on radar will shift off to
the northeast shortly. Still think LEX could have a very short window of
very light freezing rain in the morning before changing to all rain.

BWG should stay out of the wintry precipitation. Rain looks to start
there by mid morning and continue off and on through the day.

All sites will saturate aloft overnight with cloud bases lowering.
MVFR cigs are expected to develop by 12Z with IFR cigs developing by
mid to late morning. Winds will eventually shift to
south-southwesterly today then to the west to northwest eventually
late Saturday night.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...WINTER WEATHER ADVISORY until 10 AM EST this morning FOR KYZ032.

IN...WINTER WEATHER ADVISORY until 10 AM EST /9 AM CST/ this morning
     FOR INZ076>079-083-084-089>092.

&&

$$

Short Term........EER
Long Term.........MJ
Hydrology.........MJ
Aviation..........EER





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