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Area forecast discussion 
National Weather Service Louisville Kentucky
1217 am EST Sat Jan 31 2015

..updated aviation discussion...

Short term (now through Saturday night)...
issued at 305 PM EST Fri Jan 30 2015

Afternoon satellite imagery and observations reveal mostly sunny
skies across southern Indiana and central Kentucky. Kentucky mesonet
temperatures show readings generally in the middle to upper 30s
across the north with lower 40s across the south. We expect
temperatures to Max out in the next hour or so and then slowly fall
as we head into the evening. Mostly clear skies are expected this
evening with temperatures dropping into the 20s.

High pressure will move into the region overnight providing the area
with mostly clear skies along with light winds. Temperatures will
fall into the Lower-Middle teens in the NE/Bluegrass region to
around 20 in the I-65 corridor and points southwest.

Saturday will find the area starting off with mostly sunny
conditions. Clouds will be on the increase throughout the day with
most locations going partly to mostly cloudy by late afternoon.
Highs look to warm into the upper 30s to the lower 40s.

Cloudy skies are expected Saturday night and precipitation with an
approaching storm system will start to overspread the region. Model
proximity soundings from the models suggest a wintry mix of
rain/snow/sleet across the south, with mostly snow across the
north/northeast. For now, plan on keeping the wintry mix in the
forecast as the overall evolution of this storm still contains quite
a bit of uncertainty. Lows Saturday night are expected to drop into
the upper 20s to the very low 30s.

Long term (sunday through friday)...
issued at 325 PM EST Fri Jan 30 2015

..significant snow accumulations looking unlikely Sunday into

The synoptic pattern at the start of the long term period will
feature an amplified ridge across the West Coast, with split flow
over the central and eastern Continental U.S.. there will be one main system
of note in the long term period, with another weaker system slated
to move through towards the end of next week.

The period will start off with a phasing system just to the west of
the Ohio Valley, with a weak pv anomaly (and associated Pacific
moisture) ejecting out of the southern stream combining with a more
dynamic pv anomaly quickly diving through the northern stream. The
end result will be a deepening surface low, which looks to track
across the Ohio Valley into the mid-Atlantic.

The 30/12z guidance has continued the theme of a more northern
solution with the surface low. The Gem had been the southern
outlier, but is now in pretty good agreement with the
NAM/GFS/gefs/ECMWF solutions in bringing the surface low across
northern Kentucky/southern in, which will allow all of the lmk County Warning Area to rise
above freezing as the heaviest precipitation falls. Looking at the
30/15z sref members, there were several outliers of 3+ inches in
previous runs, but now they've all come in significantly lower, with
no real extreme outliers left. Therefore, confidence is increasing
in a warmer solution. To keep at least some forecast continuity and
to account for the small potential the guidance may correct a bit
back to the south, took the new data and blended it with about 20%
of the previous forecast, but this still resulted in significant
changes to the sensible weather and impacts.

On Sunday morning, any light wintry mix will quickly transition to a
cold rain as surface warm advection commences. Precipitation will
gradually increase through the day, likely peaking in the 18-00z
timeframe as the best isentropic ascent associated with the
low-level jet spreads across the region. Have gone with 100% pops
in this time period. It is likely that parts of southern Kentucky will
get into the 50s on Sunday, with upper 30s/lower 40s expected across
southern in.

As the low deepens and shifts east, cold air will quickly spill into
the region on northwesterly surface winds. This cold air will
interact with the deeper moisture across portions of southern
Indiana, where it appears an inch or so of accumulation may be
possible. However, further southeast, the cold air will lag behind
the deeper moisture, meaning just some scattered snow showers are
likely to fall as the main trough axis swings through. Could see
some minor accumulations (less than an inch) with this activity, but
nothing significant is expected at this time. In addition to the
snow shower activity, the brisk northwest winds will help drop wind
chills into the single digits Monday morning.

Otherwise, high pressure will build into the region on Monday.
Given no expected significant snowpack, have upped temperatures a
bit for Monday now putting them in the 20s and lower 30s, still
below normal. However, the upper-level flow will quickly turn more
zonal by midweek, which will allow for a moderating trend Tuesday
into Wednesday. Highs on those days will be in the 40s, perhaps
pushing into the lower 50s on Wednesday out ahead of yet another
cold front. This cold front looks to swing through Wednesday night
into Thursday, bringing a light wintry mix and another shot of
cooler air. Will continue to monitor this system as there is a
signal of a southern stream system which could potentially phase
with this incoming surface front/northern stream into a bigger
system, but at this time that appears likely to occur well off the
the east.


Aviation (06z taf update)...
issued at 1210 am EST Sat Jan 31 2015

An approaching disturbance will bring thickening and lowering clouds
to the area beginning late this morning. Although ceilings will
lower, they will remain VFR through 00z Sunday morning.

Ceilings will remain VFR at bwg through the entire taf period with
no precipitation. However, light rain or a light rain/snow mix may
develop after 00z Sunday across southern Indiana and the northern
Bluegrass. This area of precipitation may stay north of sdf and Lex
through 06z Monday. Will put vcsh in taf for sdf after 00z to
account for possibility of light precipitation. Ceilings at sdf and
Lex will most likely stay VFR through 06z Sunday.

South winds under 5kt through late morning will stay southerly at
around 5 to 8kt through Saturday evening.


Lmk watches/warnings/advisories...


Short term........mj
long term.........Kjd

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