Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 241123
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
623 AM EST Wed Dec 24 2014
...Updated Aviation Discussion...
Issued at 440 AM EST Wed Dec 24 2014
Instead of showers and storms, we so far are having drizzle and fog
form along the frontal boundary. Visibilities have gone down to less
than a mile over parts of the western half of the forecast area. The
sensor at KLOU just dropped down and visibility on area webcams is
dropping as well. Have expanded the fog in the grids some, but this
fog wording already was in the zones. May have to issue an SPS
should this fog trend continue. Still expect the returns on radar to
increase as we get lift from a low-level jet and with a brief period
of lift from a departing upper jet over the Great Lakes now.
.SHORT TERM (Now through Thursday)...
Issued at 300 AM EST Wed Dec 24 2014
Low pressure will travel along a frontal boundary stretching
north/south across our western forecast area this hour. Have a thin
band of low clouds and some fog reports along this band. Flow aloft
should push this boundary slowly eastward through the day today as
the surface low gets into the eastern Great Lakes. Winds should
start gusting behind the surface low as the pressure contours are
packed more tightly behind the system. Decided to issue a wind
advisory for later this afternoon and a few hours into the evening
over the Bluegrass region after collaboration with neighbors.
Advisory criteria is sustained 30 mph for a couple of hours and/or
40 mph gusts any time. Do not have close to either criteria in my
current forecast for the rest of the region, so did not want to
issue a blanket areawide advisory.
Precip chances will linger even behind the front, as an elongated
vortmax behind it takes its time passing through the forecast area.
There is still some question about if there will be deep enough
moisture available tonight to get more than drizzle, but if it does,
we could see some light snow showers. Forecast liquid equivalent
look to be too light and ground temperatures too warm to have snow
accumulations in the grids, so this does not look like an impactful
Clouds should linger into the day Christmas. Highs should get to
near normal levels despite the cloud cover.
.LONG TERM (Thursday night through Tuesday)...
Issued at 304 AM EST Wed Dec 24 2014
Thursday Night - Friday Night...
The upper pattern will feature amplified troughing the western CONUS
with low amplitude and broad ridging over the eastern CONUS to end
the week. At the surface, high pressure will generally hold over the
mid Atlantic Coast. This upper ridge/surface high pattern over the
Ohio Valley will result in dry conditions and pleasant temperatures.
Thursday night will actually feature good radiational cooling
conditions with lows around 30 east to the mid 30s west. Expect
milder temperatures Friday night in the mid 30s to around 40. Expect
highs on Friday to range between 50-55.
Saturday - Sunday...
Upper level flow flattens out over the CONUS through the weekend,
with SW flow dominating over the eastern US. The general model
agreement is that low pressure will slide through the Great Lakes on
Saturday with the trailing cold front sliding through our area
sometime Sunday. Ahead of this feature, expect warm advective rain
chances to pick up across our west as early as Saturday morning and
peaking Saturday night and Sunday just ahead of and along the front.
At this point, highest chances look to be across south central KY,
with lesser chances along and north of the Ohio River as northward
advance of deep moisture gets cut off.
Temperatures will again be mild on Saturday with low to mid 50s
expected. Lows will mostly be in the upper 30s and low 40s Saturday
night. Sunday temperatures will be tricky and dependent on frontal
passage, but will generally go with a cool down and highs in the 40s.
Temp profiles support all rain through this point in the forecast.
Sunday Night - Tuesday...
Confidence lowers as we enter the new week, however there is a
general consensus on the overall pattern. This pattern will feature
the surface boundary that had passed through our area waffling in
the vicinity of the Ohio Valley as it remains nearly parallel to the
upper flow. Meanwhile, there is a signal that the southern stream
will become active with a surface low developing over the Gulf Coast
states, and then travel up the Appalachians to our SE. This could be
a wet pattern for us if the placement of the boundary is correct.
This pattern could also bring a wintry mix into play along and on
the north side of the surface boundary so we will need to pay
attention to the evolution of this setup over the coming days. That
said, not to excited about the model performance of late, and given
the complexity of the setup won`t mention more than rain chances
across the southern half of the CWA and periods of rain/snow mix
across our north through Monday. Monday night and Tuesday could
bring better chances for scattered snow showers across much of the
area as colder air filters in behind the departing low. In fact,
there is a signal for a shot of much colder air just in time for the
New Year. Stay tuned.
.AVIATION (12Z TAF Update)...
Issued at 620 AM EST Wed Dec 24 2014
Low pressure near SDF this hour will continue moving north
northeast. Winds will be variable until that lows pulls a little
further away, when more solid southwesterly winds will kick in,
becoming gusty, especially at KLEX late this afternoon. As for cigs,
have a narrow band of LIFR cigs west of a KSDF/KBWG line that may
creep eastward in the next hour or two. In addition, the low moving
across looks to bring in additional showers. Have removed the
thunderstorm wording for now, given the very light returns. Cigs
likely will remain low, but should rise to MVFR at some point during
KY...WIND ADVISORY from 1 PM this afternoon to 9 PM EST this evening