Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 261434
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
934 AM EST Mon Jan 26 2015
Issued at 934 AM EST Mon Jan 26 2015
Will let the Traveler`s Advisory drop off at 10 AM EST since the sun
is up. Some slick spots will linger so continue to use caution while
traveling this morning.
Will shift the focus westward and into the afternoon as another
round of light wintry precipitation drops quickly south out of the
western Great Lakes. Light snow is already dropping south into
northern Illinois and will continue to work toward our area by late
this afternoon and more solidly into the evening and overnight.
Right now best area of focus looks to be along and west of I-65
where light snow around a half an inch can be expected by dawn on
Think light snow could start an hour or two earlier than expected
because initial mid deck of clouds may "seed" our lower stratocu
deck with ice crystals. Either way, will likely be issuing a Special
Weather Statement to highlight the new area of concern after the
Travler`s Advisory expires. Did not want to do so until then to
.SHORT TERM (Now through Tuesday)...
Issued at 303 AM EST Mon Jan 26 2015
...A few slick spots this morning with additional light snow
accumulations possible tonight into Tuesday...
The synoptic pattern early this morning features an amplified
regime, with a western ridge and downstream trough across the east
coast. This pattern will continue through the short term period,
with a weak system diving through the building trough aloft to
contend with tonight into Tuesday.
The forecast is pretty much panning out as expected early this
morning, as a compact clipper pushes out of the region. A weak
deformation band has formed just behind the cold front, back enough
into the cold air to bring a very brief shot of snow for locations
across southern IN/north-central KY. Hi-res guidance shows this
band continuing to trek east through the morning, but never really
getting its act together. Isentropic analysis from the synoptic
models depict this as well. Therefore, think this band will likely
only produce a dusting at best across areas east of I-65 this
morning, with most locations seeing nothing more than a brief period
of some flakes flying.
Even with just a dusting, that could be enough to re-wet the
roadways, freezing again as temperatures fall into the 20s this
morning. The gusty winds should help dry things out, but still
think there will be a few slick spots, especially on elevated and
less-traveled roadways. Therefore, will continue with the SPS
through the morning hours. If the snow band picks back up in
intensity, or if we start getting reports of more widespread issues,
this may be upgraded to a Traveler`s Advisory.
Otherwise, clouds will stick around through much of the day today as
moisture remains trapped under a low-level inversion. With
northwesterly winds and the expected cloud cover, will keep highs
confined to the middle 30s.
Attention will then quickly shift to a weak system, slated to move
in this evening and last through Tuesday morning. This system
actually looks to come in two parts, with one PV anomaly moving
through late this afternoon into this evening, helping to saturate
the mid/upper levels. Snow will be hard to come by with this
initial wave, as the low-levels will be quite dry. However, a
second PV anomaly will dive southeast into the Ohio Valley tonight
into Tuesday morning, this one having a weak surface reflection with
it. Cross-sections depict the ascent never really gets deep, with
much of the overnight lift confined from the surface up through
about 700mb. A weak frontogenetical circulation just to the north
of the surface low looks to set up somewhere along and just to the
west of the I-65 corridor. It is in this region that snowfall
totals could approach a half inch, with a localized inch amount not
completely out of the question. The main limiting factor to higher
amounts will be a lack of moisture (only a few hundredths of an inch
of QPF) and that the bulk of the lift will be below the DGZ, which
should cut down on ratios. Timing with this system will be
problematic though, given the light snow looks to be fall just
before and into the morning commute. Will not issue any product for
this system quite yet given the ongoing snow/black ice potential,
but will pass concerns along to the day shift.
Otherwise, any light snow will come to an end by mid-morning
Tuesday. Highs will recover into the mid 30s to lower 40s.
.LONG TERM (Tuesday Night through Sunday)...
Issued at 257 AM EST Mon Jan 26 2015
High pressure will cross the region Tuesday night and Wednesday,
bringing us chilly conditions. Lows Wednesday morning will range
from the teens in the Blue Grass to the lower 20s west of I-65.
Low pressure advancing eastward from the Plains will arrive in the
vicinity of Chicago by Thursday morning, with a cold front dropping
down to Texas. This system will bring showers to the region
Thursday (possibly starting as a light rain/snow mix before the sun
comes up). Warm air will surge northward ahead of the cold front,
but with frontal passage likely occurring here sometime during the
day, it`s tough to say how warm temps will get before fropa. Will
stick with the mid 40s to low 50s we`ve been advertising recently.
Behind the front Thursday night moisture will leave as cold air
comes in, possibly leading to a brief changeover to light snow as
the precipitation ends.
We`ll get a brief respite Friday and Friday night as high pressure
moves through, with seasonable temperatures.
The weekend is a mess as the models grapple with both northern and
southern stream systems, with the OV in between. Since there will
likely be *something* in the region, feel we should have some sort
of PoP in the forecast. Since confidence is low, though, will keep
PoPs small for now.
.AVIATION (12Z TAF Update)...
Issued at 544 AM EST Mon Jan 26 2015
The light precipitation from earlier this morning has ended, leaving
just IFR/MVFR cigs. Think all cigs will remain fuel-alternate MVFR
through the morning hours, perhaps improving to VFR briefly this
afternoon into early this evening. However, yet another system will
dive southeast tonight, bringing lower cigs and lower vsbys due to
light snow. KSDF and KBWG will be most affected, with MVFR
cigs/vsbys, perhaps IFR vsbys at times especially at KBWG. Will
leave KLEX VFR tonight for now, given they look to be on the eastern
edge of the precipitation shield. Gusty northwesterly winds this
morning will relax through the day today as the pressure gradient
declines over the region.