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Area forecast discussion 
National Weather Service Louisville Kentucky
1005 PM EST Sat Feb 13 2016

..forecast update...
Updated at 1000 PM EST Sat Feb 13 2016

Not many changes to the forecast this evening. Forecast
temps/dewpts overnight look pretty much on track. Only made minor
tweaks to those. The latest forecast data suggests we could see
some light snow around or just afternoon sunrise, but the main
accumulating snows should still hold off until the afternoon/evening
hours tomorrow.

..initial thoughts on 21z sref/0z NAM for snowfall...

There is still a good deal of spread amongst model quantitative precipitation forecast/snowfall
amounts for the coming snow sun-early Mon. The 21z sref has come up
a bit on quantitative precipitation forecast amounts over north central Kentucky with snowfall amounts
close to the same or slightly lower than previous runs. The 0z NAM
has come up on quantitative precipitation forecast amounts over central Kentucky but mainly for Monday
when much of the area will be mainly in the rain sector of this
system. The 0z NAM actually pulls the heavier snow axis down into
northern Tennessee for sun/Sun night.

So with model data still shifting, confidence is not high enough to
make any changes to the current winter wx advy and forecast snowfall
amounts. Will await the latter half of 0z models to hopefully shed
more light any trends for this forecast.

Short term (now through Sunday night)...
issued at 333 PM EST Sat Feb 13 2016

..accumulating snow likely Sunday into Sunday night...

An upper wave will move overhead, bringing widespread precipitation
to the region Sunday and Sunday night. Snowfall rates will likely
start out slow in the morning, with only minor accumulations, if
any.

During the afternoon and evening hours the snow should increase as
we get under the right entrance region of the upper jet. Soundings
show high relative humidity near the warm end of the dendritic growth zone while
temperatures and wet bulbs at the surface remain slightly below
freezing. 850-700 fn convergence will increase significantly, with
the strongest frontogenesis and best moisture supply over Kentucky.
Mid-level lapse rates increase enough to suggest mesoscale banding
will be possible. Slightly negative epv aloft co-located with high
relative humidity and on the warm edge of the dgz, with surface temperatures of 25-
30, also support heavier snow with large, wet flakes.

This all easily supports issuing an advisory, which, after
collaboration with neighboring offices, we have done. In
general,right now it looks like amounts of 1-3" north of I-64 and 2-
4" south of I-64 are reasonable. The mesoscale banding suggests that
we could see a few amounts higher than 4", primarily east of I-65
and south of the Blue Grass Parkway. However, coverage and
confidence aren't enough for a watch yet. Wpc shows the chance of
=>4" as being less than 50%. If confidence increases in warning
level snowfall, then a headline upgrade can be issued.

After the snow Sunday into Sunday evening, temperatures will begin
to rise Sunday night ahead of the next system that will move through
early in the long term. Also, Sunday night we will begin to lose
moisture aloft where temperatures are cold enough for snow
production, especially across southern Indiana and north central
Kentucky. While there may be some seeder-feeder assistance from a
shallow layer of higher clouds at first, it looks like glaciation
will reduce significantly overnight. So, a transition to drizzle or
light rain will be possible, beginning in the Bowling Green region
towards midnight and working its way northeastward, reaching just
shy of the Louisville and Lexington areas by daylight Monday
morning. It's possible we may see a brief period of freezing drizzle
during the transition, but it shouldn't have much impact as warm air
quickly brings surface temperatures and wet bulbs above freezing.

Temperature wise, we'll have another cold one tonight as the Mercury
drops into the teens. A few single digit readings will be possible
in the northern Blue Grass and the usual cold spots. Highs on Sunday
will range form the mid 20s in the Blue Grass to around the freezing
mark southwest. As mentioned previously, temperatures will climb
Sunday night, with the entire lmk County Warning Area in the 30s for sunrise on
Monday.

Long term (monday through saturday)...
issued at 331 PM EST Sat Feb 13 2016

An upper shortwave trof will approach on Monday and move overhead
Monday night, while surface low pressure passes by to our south. The
light precipitation late Sunday night will get reinvigorated as we
experience strong upper divergence under the right rear quad of the
upper jet. 700-500 frontogenesis will increase significantly in
conjunction with deep moisture, especially in the afternoon and
evening over eastern Kentucky, along with strong q-vector
convergence ahead of positive vorticity advection in the base of the approaching upper trof.

Surface wet bulbs will be above freezing all day in Kentucky, and
near freezing in southern Indiana. Going with a middle-of-the-Road
solution (on a very wide road) for maxt Monday gets US into the 40s
areawide. So, it looks like the transition to liquid that began late
Sunday night will continue into Monday morning, with everyone seeing
plain rain Monday afternoon. Given instability parameters and
general synoptic set-up, mesoscale banding appears less likely
Monday than Sunday.

Sunday night incoming cold air will change the precipitation back to
light snow as it tapers off. No significant accumulations are
expected either before the transition Monday morning or after the
transition Monday night.

A clipper will then shoot through the area Tuesday
afternoon/evening. This will bring a mix of light rain and snow to
the region. Will simply use surface temperatures to determine ptype
in the grids for now.

High pressure will dominate Wednesday-Thursday with dry weather. No
Arctic cold, though, with highs Tuesday in the 40s and Wednesday in
the 50s.

A storm system will then barrel through the Great Lakes Friday and
Saturday and will bring a chance of showers to the region. Thunder
looks unlikely at this time. Highs on Friday will be in the 60s, and
in the 50s Saturday.

&&

Aviation (00z taf update)...
updated at 630 PM EST Sat Feb 13 2016

VFR conditions are expected for the next 10-12 hrs with mid and
upper level clouds increasing ahead of the next weather system. Late
tonight into tomorrow morning an upper level wave will dive south
into our region and interact with a southern stream weather system.
This will cause snow to overspread the region Sunday morning with
flight conditions in light to at times moderate snow reduced to
MVFR/IFR by Sun afternoon/evening. Will need to refine these times
as the event draws closer, but after 18z MVFR/IFR cigs/vsbys will be
likely. Winds will turn light tonight and then east-southeast between 6-8 kts
for sun during the daylight hours.

&&

Lmk watches/warnings/advisories...
Kentucky...Winter Weather Advisory from 7 am EST /6 am CST/ Sunday to 10 am
EST /9 am CST/ Monday for kyz028>043-045>049-053>057-
063>067-074>078-081-082.

Winter Weather Advisory from 4 am EST /3 am CST/ Sunday to 7 am
EST /6 am CST/ Monday for kyz023>027-061-062-070>073.

In...Winter Weather Advisory from 7 am Sunday to 10 am EST Monday for
inz077>079-090>092.

Winter Weather Advisory from 4 am EST /3 am CST/ Sunday to 7 am
EST /6 am CST/ Monday for inz076-083-084-089.

&&

$$

Update.........Ams
short term.....13
long term......13
aviation.......ams

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