Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 251713
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1213 PM EST Wed Feb 25 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1130 AM EST Wed Feb 25 2015

12Z GFS matches up well with the NAM on timing and location for
precip tonight. Dry low-level air will take a few hours to saturate
despite returns on radar. Given this information and the timing in
those and other high-res model runs being a little slower than the
previous forecast, have started the winter weather advisory at 00Z
instead of 22Z. That product has been updated along with the rest of
the forecast package for this change.

Issued at 935 AM EST Wed Feb 25 2015

12Z NAM coming in with a similar forecast for snowfall tonight.
Trended QPF forecast towards those numbers as well as latest
high-res guidance. New snow forecast looks pretty similar to
previous one, so no changes at this time to the advisory in place.
Will look again as the GFS and other models come in. Otherwise
tweaked forecast towards current obs and sent out a zone update.

.SHORT TERM (Now through Thursday)...
Issued at 310 AM EST Wed Feb 25 2015

...Light Accumulating Snow Likely for Portions of South Central KY
Tonight...

First of all, removed light flurries/freezing drizzle from this
morning`s forecast.  Clouds have remained in the 4-5 kft level with
a dry layer between these lower clouds and the sfc.  Thus, no precip
was being generated.  The latest high-res models have a good handle
on this set-up while the 0Z GFS was too moist in low levels.

With the 0Z NAM and other high res models in mind, think that low
clouds will linger east of I-65 early this morning.  We should see a
period after sunrise of only partly cloudy or perhaps mostly sunny
skies through the morning hours before cloud cover begins to build
back into the area closer to noon.  The rest of the day will remain
cloudy as weather systems approach from the south and northwest.
Highs should top out in the low to mid 30s with most locations
rising above freezing.

==========================
Accumulating Snow Tonight:
==========================

Tonight a low pressure system crossing the Gulf states will spread
moisture northward into our area.  At the same time, another low
pressure system will dive southeast out of the upper Plains states
weakening as it pushes into the Midwest. Models continue with the
scenario that these system will stay independent of each other.

The southern stream system will affect our area first, spreading
light snow into south central KY this evening.  We`ll be on the
northern edge of the snow shield with this system and it will be
difficult to nail down exactly how far north the light snow area
will extend.  Any moisture being transported into central KY or
southern Indiana will have to overcome a good dry layer initially
before precipitating.  Think that enough saturation will occur in
low levels for light snow to occur along and south of the parkways
in southern and central KY.  It may also snow over southern Indiana
and north central KY tonight but think that it`s less likely that
far north.

The next challenge with this forecast is pinning down snowfall
amounts.  There is still a wide range of solutions among short range
models.  All models seem to indicate that the Lake Cumberland region
will have the best chance at accumulating snowfall.  However, some
have as little as a few tenths while others indicate a few inches.
The last 3-4 model runs have trended farther north with the snow
shield and have consistently painted an area of 1-2 inches across
south central KY mainly from Scottsville/Glasgow areas into the Lake
Cumberland region.  So feel a Winter Wx Advy is in order for these
locations for tonight.  Will likely keep a Special Wx Statement for
other areas over central KY and maybe southern Indiana as there is
still low confidence in the exact northern extent of the snow
shield.  Debated including Bowling Green in the Advy as well, but
decided against it at this time since precip amounts have been
consistently lower farther west.  However, if model runs later today
shift the precip axis, Bowling Green could be added to the Advy.
Also, Lexington and Richmond areas may end up being close to the 1
inch snowfall mark as well if a soln similar to the 0Z NAM plays
out.  Will re-evaluate Advy boundaries later today.

=========================

For Thursday, we should see a relative lull in snow over the area
during the morning hours after sunrise as we sit in the cull between
weather systems.  Left over moisture and forcing from the northern
stream system looks to cause some snow shower activity over the
region Thurs afternoon.  Also, better upslope flow may result in
enhanced snow shower activity over east central KY late in the day
Thursday.

Temperatures on Thurs will start in the upper teens to mid 20s and
max out in the mid 20s to lower 30s.

.LONG TERM (Thursday night through Tuesday)...
Issued at 300 AM EST Wed Feb 25 2015

The last in a series of arctic fronts will arrive Thursday night.
Forecast soundings show steepening lapse rates late Thursday with
lingering moisture between 3 and 9 kfeet through around 10z Friday.
This may be sufficient to produce some light snow or certainly some
flurries through the early morning hours Friday. Will raise chances
for light snow to 30% early Friday. North winds around 10 to 12 mph
will continue through Friday morning with temperatures falling
rapidly into the low teens by dawn Friday. Low clouds will tend to
erode and Friday will become partly cloudy. Highs Friday will
struggle to reach 20 across our northern counties, and will reach
the mid 20s to our south.

High pressure will migrate from northern Missouri towards Ohio
Friday through early Saturday. Light north winds Friday will become
easterly by Saturday morning. Under mostly sunny skies, temperatures
will begin to moderate Saturday, reaching the lower to mid-30s.

Upper air pattern will begin to change late Saturday as a
disturbance diving south across the western states will carve a
positively tilted trough across the Intermountain West. Flow will
become more zonal across the Lower Ohio Valley. Clockwise low level
flow around high pressure over the mid-Atlantic will bring southerly
winds, warmer temperatures, and increasing moisture beginning
Sunday.

A series of disturbances will originate early next week from this
western trough, with the trough itself expected to eject
northeastwards across Missouri early Tuesday. The first of these
features will bring cloudiness and rain Sunday. This precipitation
may start out as a wintry mix, but change to all rain by Sunday
afternoon. Temperatures by Sunday afternoon will warm substantially
into the lower to upper 40s, south to north. A weak boundary may sag
south towards central Kentucky Monday, with winds becoming
northeasterly across southern Indiana. However mid and upper flow
will stay from the southwest, and precipitation chances will
continue.

Substantial rain may develop Tuesday as low pressure develops across
Missouri and begins its track northwestwards. A surge of mild air
will bring Tuesday`s highs well into the 50s.

&&

.AVIATION (18Z TAF Update)...
Issued at 1210 PM EST Wed Feb 25 2015

Mid and upper clouds will continue to increase through the day ahead
of a couple of weather systems. Winds are faily light at this time,
but will become more northeasterly late this afternoon and then
northerly overnight. The chance for light snow should be along and
south of a BWG/LEX line starting late in the evening. MVFR
conditions should be at each of the sites as the moisture increases,
but the BWG/LEX stand the best chance to get close to IFR, between
midnight and daybreak. Clouds should stick around behind the snow
chance, as low level moisture profiles stay saturated. Could even
have patches of light snow into Thursday, though accumulations, if
any, or would be light.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...WINTER WEATHER ADVISORY from 6 PM this evening to 6 AM CST
     Thursday FOR KYZ073>078-081-082.

IN...NONE.
&&

$$

Update.........RJS
Short Term.....AMS
Long Term......JSD
Aviation.......RJS




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