Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 260238
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
938 PM EST Wed Feb 25 2015
Issued at 938 PM EST Wed Feb 25 2015
Will go ahead and trim the northern tier of counties out of the
Winter Weather Advisory. This leaves Monroe, Cumberland, Russell,
and Clinton counties still in it. The atmosphere is struggling to
saturate, however still expect a quick shot of light snow as the
weakening deformation zone and associated frontogenesis slide across
our southern CWA between 03 and 09Z. Looking upstream at the OHX
VWP, the area has finally saturated down to 1-2 K feet, however yet
to see snow on the obs there. Just feel the window is too short for
any accumulations over a half inch in the counties removed from the
advisory, however a dusting is still possible so will slide the SPS
south to cover the counties removed from the WSW. Will also trim a
tier of counties of the northern edge of the SPS.
In the advisory area, have lowered expected totals a little more,
with between a half inch and inch possible. Updated products coming
Issued at 724 PM EST Wed Feb 25 2015
What had been a closed upper low over the southern Plains is now
opening up as it crosses the lower Mississippi River Valley. Will
watch as mid level deformation/frontogenesis and the northern
fringes of the precip shield rapidly lifts NE across the mid south
overnight, dealing a glancing blow to our southeastern CWA.
The Winter Weather Advisory for extreme southeastern portions of our
CWA just went into effect at 7 PM EST/6 PM CST. Snow has not started
falling yet, although we are within 2 to 3 hours of the becoming
more of a reality. Looking at the 00z OHX sounding, there is still a
significant dry layer below 700 mb to overcome so light returns that
have already started to overspread our area will take a while to hit
the ground. Overall, forecast is on track although feel the advisory
may be a tier of counties too far NW. Won`t make any changes to the
headline at this time, but think the best chance for up to an inch
will be near Lake Cumberland, with a half an inch or less toward the
western portions of the headline. Any snow that falls should stick
so still expect some slick conditions for the morning commute.
Further NW across central KY, a light dusting of snow is still
possible so will likely re-issue the Special Weather Statement for
this region. No expecting many impacts, however a few slick spots
will be possible for the morning commute. Look for the updated
headlines to be out shortly.
.SHORT TERM (Now through Thursday Night)...
Issued at 250 PM EST Wed Feb 25 2015
...Light Accumulating Snow Likely for Portions of South Central KY
Winter storm system now organizing over the central Gulf coast, as a
potent shortwave moves along the Arklatex. 88D showing some returns
coming up into southern TN. Forecast models continue to show the
chance for snow as limited to south of the Bluegrass and Western KY
parkways for tonight. After running through forecast QPF and snow
ratios, am barely getting an inch of snow by daybreak Thursday for
our advisory area. As the values are close, will continue to hold
onto the advisory for now, to leave some room for error.
We should get a brief break from snow chances as that first system
departs and our next one comes in from the northwest. Forecast
soundings would call for more of a snow shower type setup, but
moisture is limited and it does not look as squally as a setup we
had a week or two ago with snow showers and stronger winds behind a
front. The best chance would be in the afternoon and continue into
the evening hours. Snows should be light enough for totals of just a
few tenths of an inch, so no need for an advisory at this time.
Temperatures tonight will fall into the low to mid 20s for most
locations, though upper teens are possible across the north.
Thursday highs should get back above freezing closer to the TN
border, whereas mid to upper 20s will rule southern IN and our
northern counties in KY. The warmer temperatures may make for a
brief mix of snow/rain showers down south during the day. Then
Thursday night we crash again as another cold high pressure builds
in from Canada. Lows should range from the single digits to the mid
teens, some 20 degrees below normal.
.LONG TERM (Friday through Wednesday)...
Issued at 300 PM EST Wed Feb 25 2015
Friday through Saturday...
Arctic high pressure will dominate as a 1040+ mb center moves east
from Iowa to Pennsylvania. The weather pattern will be quiet, but
still unseasonably cold. Highs on Friday will struggle to crack 20
along and north of I-64, with double-digit departures from normal
continuing on Saturday. Biggest question is just how well we radiate
on Friday night. GFS is quite bullish while the NAM is the mildest
as it keeps the high center to our north and west. Recent history
has not seen temps drop as dramatically as advertised by the models,
but the NAM seems to be an outlier solution. For now will split the
8-10 degree difference, which will still be enough for single digits
and wind chills just below zero in our north.
Saturday night through Wednesday...
Expect a progressive and active zonal pattern as a series of
disturbances will eject out of a southwestern CONUS trof. Best
chances for precip will be Sunday and Sunday night as one impulse
phases just enough with the northern stream to really tap the Gulf,
and then Tuesday and Tuesday night with another mid-level
disturbance running up and over the top of a flat Gulf of Mexico
ridge. The pattern will be milder, but still below normal as the
Sunday/Sunday night precip will be primarily cold rain, with snow
possibly mixing in, especially at night.
Precip type will again be in question at onset with the second
system early Tuesday. Model forecast soundings and our actual temp
forecast suggest that freezing rain is a possibility. However this
far ahead of time, will keep it rain/snow and make tweaks as needed
later. Temps do recover to near normal during the day on Tuesday,
and should remain warm enough that precip type is not an issue.
.AVIATION (00Z TAF Update)...
Issued at 608 PM EST Wed Feb 25 2015
Split upper level flow will keep the TAF sites mainly between two
winter systems this evening and tomorrow.
Could see a few flurries at BWG between 9 PM and Midnight CDT
this evening, however the bulk of the activity will stay to the SE.
In the meantime, expect to stay VFR with increasing low and mid
level clouds and a light NE surface wind. Then, expect MVFR or worse
ceilings shortly after sunrise with flurries hanging around and a
steady NNW wind.
Won`t mention flurries this evening because they wouldn`t have any
impact, however can`t rule out a few floating around this evening.
Otherwise, expect a light NE wind to gradually back to N and then NW
through the period, with MVFR or worse ceilings settling in just
before sunrise. Expect those ceilings to persist through the day
with some flurries early and light snow showers possible toward the
end of the forecast cycle.
Will keep this forecast dry tonight, with increasing low and mid
clouds and light NE winds becoming more northerly. Could see some
MVFR ceilings as we near dawn, followed by some flurries through the
morning and afternoon. Snow showers will then be possible to end the
forecast cycle Thursday evening, along with a steady NNW wind.
KY...WINTER WEATHER ADVISORY until 6 AM CST Thursday FOR KYZ075-078-