Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 290512
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1212 AM EST Thu Jan 29 2015
...Updated Aviation Discussion...
Issued at 933 PM EST Wed Jan 28 2015
Models show a decent area of precipitation associated with a vortmax
moving through the area early tomorrow morning. Have increased pops
a bit around the 12Z time frame for these showers, but kept chances
at 50% or less. Still think we should warm up to above freezing
before this precip begins to fall. Otherwise, just minor edits were
made to bring the forecast in line with current observations.
.SHORT TERM (Now through Thursday Night)...
Issued at 306 PM EST Wed Jan 28 2015
Surface high pressure over Ohio has provided the region with sunny
skies this afternoon. After starting the morning off in the upper
single digits to the lower teens, temperatures have warmed into the
lower 30s over the northeast/Bluegrass with mainly lower 40s along
and west of the I-65 corridor. Mostly clear skies are expected this
evening and temperatures will likely cool off back into the upper
20s to the middle 30s.
For tonight, clouds will be on the increase late tonight as the next
weather system approaches from the west/northwest. Temperatures will
likely experience their minimum values after midnight and then start
to rise as southwesterly winds and cloud cover increase. Some weak
lift may generate a few light rain showers toward dawn, but it
appears the bulk of precipitation will likely hold off until after
sunrise. Lows tonight will likely bottom out in the mid-upper 20s
in the east/northeast and in the lower 30s in the west.
For Thursday, surface low pressure system will move from the Midwest
into the Great Lakes with a trailing cold front slicing through KY
during the late morning and into the early afternoon. Gusty
southwest winds will be likely in the morning and we should see a
shift to the west and then northwest during the afternoon hours.
Sustained winds of 15-20 MPH will be the rule with gusts up to 30-35
MPH at times. A band of showers will likely develop along the
actual frontal boundary with the best coverage along and east of the
I-65 corridor. Temperatures will spike out ahead of the front. The
model guidance still has quite the spread in high temperatures.
Using the multi-model consensus, highs look to top out in the
mid-upper 40s in the north with upper 40s to the lower 50s in the
south. Warmest air will likely stay along and south of the
Cumberland Parkway during the afternoon hours. Behind the front,
temperatures will fall from NW to SE with readings dropping in the
upper 30s by evening.
For Thursday night, surface cold front should clear the state by
mid-evening. A cold northwesterly flow will continue across the
region with winds slowly subsiding through the overnight period.
The high resolution models suggest that plenty of light snow showers
will be likely from east-central IN down through east-central KY.
These showers will be forced by the lagging upper trough and
increasingly steep lapse rates. Best chances of snow will be mainly
east of I-65 and across the Bluegrass region of central Kentucky.
Minor accumulations of less than an inch will be possible which may
result in some travel issue late Thursday night and early Friday as
surface temperatures drop into the mid-upper 20s.
.LONG TERM (Friday through Wednesday)...
Issued at 309 PM EST Wed Jan 28 2015
...Wintry Mix Possible Late This Weekend...
Friday is expected to start out with low level moisture trapped
under the inversion. Perhaps a few flurries could be squeezed out
before low clouds scatter out by afternoon. With the heavier cloud
cover and steady NW winds through much of the day, temps should
struggle staying in the 30s. The surface high center settles near
our NE CWA Friday night with cold overnight lows in the upper teens
and low 20s. Saturday continues the dry trend as high pressure
scoots off to our east under dry NW flow aloft. Will see a decent
recovery in temperatures with highs in the upper 30s NE to low 40s
Confidence continues to be low for the end of the weekend storm
system as models change with every run. Have seen a fairly dramatic
shift in data with the 12z GFS/ECMWF which have come in later with
the upper jet phase. That results in a weaker surface low moving
across the CWA. This weaker surface low leads to a colder solution
due to less warm air being drawn up ahead of it. The end result is a
snowier system, at the expense of less overall deep moisture to work
with. In contrast, the GEM has continued to come in warmer with a
stronger surface low right over our CWA. The end result of this
solution would be onset of precipitation later in the day on Sunday
and much warmer. P-type would be much more rain changing to a little
snow on the back side. It should be noted that the GEM was the
extreme cold solution only 2 days ago, and now it is on the warm
side of the envelope. That doesn`t necessarily mean that it is wrong.
Decided to lean a bit toward the GFS/ECMWF solution for now to keep
the forecast somewhat consistent. As a result, the overall trend of
the ongoing forecast swings back toward a bit colder with light snow
beginning across much of the area on Saturday night into Sunday
morning. Would likely see a rain line work northward through the day
on Sunday, with the northern half of our CWA mostly snow or a
rain/snow mix. Then, a changeover back to snow crashing south the end
the event Sunday night. This overall setup would bring light accums
to the area, however confidence is not overly high in this playing
out yet. Will continue to play things conservative until models
Monday through Wednesday look mainly dry and cold as surface high
pressure builds in. If any snow is on the ground Monday, highs may
not make it out of the 20s in many spots. Lows Monday night are
expected mostly in the mid and upper teens. Tuesday is expected to
recover back into the 30s, along with a milder Tuesday night back in
the 20s. A southern stream system could organize to our south on
Wednesday, with low chance mention for some wintry precipitation
across our south.
.AVIATION (06Z TAF Update)...
Issued at 1205 AM EST Thu Jan 28 2015
Surface low currently across southeastern Iowa will push toward
Chicago overnight, bringing a cold front through the TAF sites
during the morning hours. Ahead of this, pressure gradient has begun
to tighten up with southeasterly winds sustained around 15 kts. Plan
on a wind shift to the south and southwesterly toward dawn. A very
strong 55-60 knot jet between 2-3 kft is expected to develop across
the area creating LLWS conditions at all TAF sites from around 09z
Showers ahead of the front are slated to come through during the
morning to early afternoon hours. Surface winds are expected to mix
down to 15 knots, with gusts 20 to 25 kts. Expecting mainly VFR
clouds during the frontal passage. In the wake of the front and
surface low, ceilings will be on the lowering trend, likely dropping
into the MVFR range by late afternoon. There are signals that
fuel-alternate ceilings may be reached at SDF/LEX by mid-evening,
lasting through Thursday night. Lingering low-level moisture
combined with steep lapse rates could result in isolated snow
flurries or even a brief period of drizzle/freezing drizzle after
30.00z. Confidence in this occurring is low but bears watching.