Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 061739
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1239 PM EST Thu Mar 6 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Friday)...
Issued at 310 AM EST Thu Mar 6 2014
Southern stream upper low is gaining organization, with light precip
breaking out over the Natural State. As this system continues to
organize, a monster surface ridge extending from eastern Canada into
Wisconsin will keep us high and dry, with the precip well suppressed
over the Deep South.
Wednesday morning`s fog and stratus were really all that kept max
temps from exceeding the warmest guidance values. Low-level
thickness progs suggest today`s max temps will be several degrees
warmer, and we have not seen any fog or stratus overnight, so will
continue the theme of temps running just above the warmest guidance.
Even with the impressive recovery from Monday`s highs in the 20s,
today`s forecast highs in the upper 40s to mid 50s will still be a
few degrees below climo.
By tonight the surface ridging over the Ohio Valley breaks down just
enough to leave a very sloppy and weak wind field. Expect fairly
substantial fog and stratus to develop, especially west of I-65
where the winds are the weakest. Will include fog in the grids and
products, but not jump on any dense fog yet. With temps below
freezing it could end up presenting a freezing fog issue, so stay
tuned. Weak surface and upper ridging will set up a mild and dry
Friday, with highs well into the 50s.
.LONG TERM (Friday Night through Wednesday)...
Issued at 245 AM EST Thu Mar 6 2014
Taking a look at multi-model time series plots of heights, temps,
and thicknesses indicates models are in fairly good agreement on the
large-scale pattern. We will continue a warming trend into the first
half of next week, although there will be a slight cool down Sunday
behind a cold frontal passage. Then, troughing will build across our
area for the latter half of next week, cooling the region and
sending temps below normal. However, there are signs this cool down
will not last too long.
For the weekend, we are still facing a cold frontal passage Saturday
evening and overnight. Moisture still looks limited, yet combined
with adequate forcing should still squeeze out some very light
precip. Expecting mainly rain as temperatures range from lower 50s
in the north to around 60 across the south Saturday afternoon. There
is still a small chance of a rain/snow mix on the very tail end, but
soundings are favoring a cold rain becoming drizzle as 850-500 hPa
moisture dissipates. Precip should exit the area around or just
after midnight. Temperatures are expected to drop into the middle
20s north to middle 30s south by daybreak Sunday morning. A few
slick spots cannot be ruled out Sunday morning where roadways remain
wet, but QPF is looking rather light.
Sunday through Tuesday will feature west-northwesterly flow at mid
levels, with southwesterly low-level flow. The forecast trend has
been drier through this period, so will continue with a dry and
warming forecast. Temperatures Sunday will be middle 40s to low 50s
in the wake of the frontal passage, but then we warm into the 50s
and 60s Monday and Tuesday. Wednesday appears to be a transition
day, as an upper-level trough and associated large-scale forcing
approach from the west. Models have slight differences in timing and
strength, but the signal is present. This will increase rain
chances, perhaps as early as Tuesday night, as well as initiate our
overall pattern change for the latter half of the week.
.AVIATION (18Z TAF Update)...
Updated at 1235 PM EST Thu Mar 6 2014
VFR conditions should prevail for the rest of the afternoon as
high-level clouds cruise through the region, primarily across
southern and eastern Kentucky, although reaching as far north as the
Ohio River. The clouds are in thanks to a low pressure system
tracking across the SE US from the Gulf, and NE into the
Atlantic. As the low makes its progression through tomorrow, high
pressure will build into the Ohio Valley behind it, allowing for
winds to go light to calm by the pre-dawn hours Friday, drier air
aloft to filter in, and clouds to temporarily clear out. Given the
low-level moisture that is progged to linger in the area, with
some assistance from the remaining ground moisture, fog looks to
continue to be a decent probability at all three terminals,
particularly at the fog-prone BWG location. The question is how
quickly the clouds clear out with the low and given this
uncertainty, have bumped up the ceilings just a bit until a better
handle can be grabbed. Feel fairly confident that fog will form,
with support from the GOES-R simulated fog product, but just not
sure how low the terminals will go. At least MVFR can be expected,
with a good chance of IFR conditions at LEX and BWG. Through
midday Friday, model soundings keep the terminals with a low
stratus deck, struggling to clear by mid-afternoon. More clouds
can be expected by tomorrow night as a frontal boundary approaches
the region but is beyond the scope of this TAF issuance. As such,
expect the winds to veer from an easterly component this afternoon
to a more south to southwesterly component by late tomorrow.