Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 141534
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1034 AM EST SUN FEB 14 2016

...Forecast Update...
Updated at 1030 AM EST Sun Feb 14 2016

Early batch of snow streaked across the area this morning, laying
down a quick dusting in many locations, with a few spots pushing a
half inch. If nothing else this will serve to tighten up the
temp/dewpoint spreads so we won`t lose as much QPF when the heavier
band arrives this afternoon.

Current forecast is well on track with the snow chances really
ramping up between 17-19Z as it spreads in from SW-NE. Will likely
see mesoscale banding, and heavy thundersnow has been reported near
PAH and CGI, so may need to look at opening a bigger range for
local variations in snow totals. Will handle most of these issues
through our warning/advisory and DSS products, but do expect a quick
zone update closer to noon to clean up wording.

.SHORT TERM (Now through Monday)...
Issued at 400 AM EST Sun Feb 14 2016

...WINTER STORM TO BRING ACCUMULATING SNOW TO THE REGION TODAY AND
TONIGHT...

===================================
Short Term Synopsis
===================================

Several mid-level waves will roll through the Ohio Valley in the
short term period bringing numerous rounds of precipitation to the
region.  The first in the series of waves will arrive later this
morning and will bring a period of light to moderate snow to the
region today and tonight.  As that wave passes off to the east, a
secondary and stronger wave will push eastward from the Plains and
into the Ohio Valley late on Monday.  Ahead of this system, a
southerly fetch of moisture and warmer air will push into the region
resulting in the precipitation changing over to plain rain during
the day on Monday.  Slightly colder air will attempt to filter back
into the region Monday night resulting in the rain changing back
over to or mixing with snow before ending.  The final wave, a strong
clipper system, will drop into the region during the day on Tuesday
bringing another round of mixed precipitation to the region.

===================================
Model Trends/Preference/Confidence
===================================

Short term model trends with regards to QPF have trended upward
across the region in recent runs.  This is especially true with the
the NAM and GFS solutions.  On the other hand, QPF from the normally
consistent Euro has trended downward in the last run.  The multi-
model consensus continues to indicate the axis of heaviest QPF
mainly across the southern half of KY and then arcs it northeastward
through the east KY coalfields into WV.  A sharp decreasing gradient
of QPF appears to be a trend especially in areas north and northwest
of the Ohio River.

Overall model trends in surface temperatures have not changed
appreciably over the last few runs.  Temperatures at the beginning
of the model simulations are a bit warmer than in previous forecasts
given that initial observed temperatures are warmer out across SE
MO/W TN/S KY.  The multi-model consensus does keep temperatures cool
enough to produce snow across the region today and tonight. However,
the trend is for warmer air to flow northward into the region late
tonight and on Monday resulting in precipitation changing from snow
over to a wintry mix and then plain rain.

As for model preferences, a multi-model consensus blend including
the previous forecast will be used.  We will lean heavily on a
GFS/NAM SREF blend on QPF and temperature forecasts.  This will
result in slightly more QPF and snowfall in the forecast while
maintaining a large amount of continuity from the previous forecast.

Forecast confidence in precipitation type and amounts are high for
today and tonight.  Forecast confidence decreases markedly for
Monday and Tuesday as lower confidence on surface air temperatures
and depth of remaining cold air in the lower atmosphere result in
lower confidence on precipitation type.

===================================
Sensible & Societal Impacts
===================================

As the first upper level wave passes through the region today and
tonight, we expect snow to break out to the west of the region and
then head eastward into our forecast area.  Large scale synoptic
scale ascent will increase across the region as we`ll be in the
right exit region of an approaching jet streak.  Model proximity
soundings show steepening lapse rates and good omega values through
the DGZ suggesting that snow will start off initially as light, but
the become moderate to heavy at times during the mid-late afternoon
and evening hours.  It is possible that we could see some banding
features develop across the region.  The most likely place for this
would be in the area between the WK/BG Parkways and the Cumberland
Parkway.  Lighter intensity snow is likely further north across our
southern Indiana counties.

Previous forecasts indicated the potential for 2-4 inches of
snowfall for the area with today and tonight`s activity.  Given the
upward tick in the model QPF, we have increased snowfall amounts
across our central and southern sections with this forecast update.
Our current forecast will feature a gradient of snow across our
north with a general 2-3 inches of snow across our southern Indiana
counties.  Snowfall amounts are expected to increase as one heads
south of the Ohio River with a general 3-5 inches of snowfall across
central sections of KY.  With this increase in snowfall, a few
changes are needed in terms of headlines.

After coordinating with surrounding offices, a Winter Storm Warning
will be hoisted for much of central and southern KY.  In general,
the warning will be for areas south of I-64 in KY and then curve
southwestward south of the Ohio River into western KY.  North of the
warning, a Winter Weather Advisory will continue for far northern
sections of north-central KY and all of southern Indiana.

The snow intensity and coverage is likely to diminish by mid-late
evening as upper level forcing pushes off to the east.  In general,
we should see the main precipitation band push southward into
Tennessee this evening.  With the loss of moisture in the DGZ we
could see the potential for freezing drizzle to develop across the
region for a period of time.  However, as the night wears on, low-
level warm air advection out ahead of the next wave pushing in from
the west will allow surface temperatures to warm.  Band of precip
across TN will likely lift back northward in the form of a mix of
rain/snow and eventually change over to plain rain during the day on
Monday as surface temperatures warm above freezing.  There remains
quite a bit of uncertainty on how much temperatures will warm given
the expected snowfall Sunday afternoon/eve.  However, all model
guidance has been predicting temperatures warming well above
freezing.  For now, have trended temps slightly colder than the
multi-blend guidance and with readings warming into the mid-upper
30s.  We will have to watch for the potential for heavy rainfall
down across our southeastern sections during the day on Monday.  The
multi-model guidance suggests and inch or so of liquid precip
falling during the day on Monday.

Main shield of precipitation will move off to the east Monday night
with some colder air working in behind it.  This will result in a
brief change over back to snow before precipitation ends.  At this
time, it does not appear that significant accumulations will occur
with this activity.  After a brief lull in the weather, a final wave
will drop down into the region during the day on Tuesday.  This will
bring yet another round of mainly rain to the region as low-level
warm air advection ahead of the system will keep thermal profiles
warm through the period.  As the system departs to the east Tuesday
night, some colder air may arrive in time for another brief period
of snow to occur.  Highs Tuesday look to warm into the lower 40s
with overnight lows cooling back into the lower 30s.

.LONG TERM (Monday Night through Saturday)...
Issued at 300 AM EST Sun Feb 14 2016

Wednesday will mark a period of overall drier weather and moderating
temperatures as a trough along the east coast moves offshore,
allowing ridging to build into the Ohio Valley by the end of the
week.  After temperatures in the 40s on Wednesday, they will warm
into the low/mid 60s by Friday!  A weak cold front may bring some
light showers to the region Friday afternoon into Saturday, but
temperatures should continue to run well above normal through the
upcoming weekend.

&&

.AVIATION (12Z TAF Update)...
Updated at 601 AM EST Sun Feb 14 2016

VFR conditions will prevail this morning before conditions quickly
deteriorate by early this afternoon as snow moves through the
region.  This snow will be moderate at times, helping to reduce cigs
and vsbys into the low-end IFR or even LIFR range.  The best chance
for prolonged LIFR conditions will be at KBWG and KLEX where the
heaviest axis of snow will fall.

Otherwise, the snow will taper off in intensity overnight.  However,
warm air overrunning the fresh snowpack will keep some cig and vsby
restrictions going.  As we lose saturation aloft, can`t completely
rule out a brief period of FZDZ at KSDF or KLEX late in the period,
but do not have high enough confidence to include mention at this
time.

&&

.LMK Watches/Warnings/Advisories...
KY...Winter Weather Advisory until 10 AM EST /9 AM CST/ Monday for
     KYZ023-030>037-042-043.

     Winter Storm Warning until 10 AM EST /9 AM CST/ Monday for
     KYZ024>029-038>041-045>049-053>057-061>067-070>078-081-082.

IN...Winter Weather Advisory until 10 AM EST /9 AM CST/ Monday for
     INZ076>079-083-084-089>092.

&&

$$

Update.........RAS
Short Term.....MJ
Long Term......MJ
Aviation.......KJD


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