Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 050234
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
934 PM EST Tue Mar 4 2014
Issued 934 PM EST Tue March 4 2014
Low stratus has continued to form over southern Kentucky this
evening and it appears that the clouds may have some staying power,
so we upped sky cover numbers for the overnight hours in the far
south. With snow cover and nearly calm winds there could be some
patchy fog, either through the lowering of the stratus cloud deck`s
bases or, if we lose the low clouds, radiational fog could form
after midnight once the cirrostratus moves off to the east. Either
way any fog would be patchy and light. Will restrict fog chances to
the south where dew point depressions are narrowest.
.SHORT TERM (Now through Wednesday)...
Issued at 240 PM EST Tue Mar 4 2014
The flow aloft will be zonal tonight through tomorrow, transitioning
to southwesterly tomorrow night as a wave dives into the lower
Mississippi River Valley. Dry and somewhat warming conditions are
expected through this time frame.
Temperatures will remain tricky tonight and tomorrow given the snow
on the ground. Last night stayed warmer than expected due to high
clouds and some winds. Tonight winds will be light and variable to
calm, but there will still likely be some clouds. Think there will
be a gradient of temps from the teens in the north to the lower to
mid 20s across south central Kentucky. Tomorrow should be quite a
bit warmer with highs ranging from the upper 30s to upper 40s.
Clouds will be on the increase tomorrow afternoon into evening as
the upper wave drops nearer to the area. Lows will range from the
lower 20s to around 30.
.LONG TERM (Wednesday Night through Monday)...
Issued at 300 PM EST Tue Mar 4 2014
Confidence is fairly high in an upper trough, possibly closed off,
passing across the Deep South Thursday. Most of the models indicate
moisture associated with this system will remain well south and east
of the region. The NAM is an outlier here, bringing a stronger
closed low up the Appalachians and consequently some rain on the
north side of this system. Given ensemble and most model support,
will keep the forecast dry for now.
With that system past, our next chance for precip chance will come
with another upper low, this time progged to be a little farther
north than the Thursday system. This low will not be in a rush to
move east though, with models showing some light QPF possibly
Saturday over the north and across the rest of the region Saturday
night, but again slight chances.
Sunday through Tuesday`s forecast will depend on how quickly that
upper low can get going and get past us. Think the blended model
forecast for pops is too high given the amount of uncertainty in the
models, so will cap pops at slight chance for Monday night and
Temperatures will be close to normal each day, with Thursday being
the coldest day.
.AVIATION (00Z TAF Update)...
Updated at 919 PM EST Tue Mar 4 2014
Low stratus has returned to much of southern Kentucky, including
BWG. The airport is right on the northern edge of the stratus deck,
making for a challenging TAF since a very slight shift in the edge
of the clouds will mean a huge difference in forecast flying
As mentioned earlier, there is model support for fog tonight,
especially across southern and western Kentucky. However, actual
conditions show a widespread field of low stratus from southern KY
into the mid TN and MS Valleys. Low stratus tends to inhibit fog
formation, and it`s conceivable that the models are confusing fog
for low clouds.
However, stratus build-down may be a possibility. As air
temperatures drop tonight, surface temperatures are expected to
hover within a couple degrees of the cross-over temperature at BWG.
Dew points are already fairly high in the area, in the mid 20s, plus
the ground is covered in wet snow. Checking obs over the past few
hours from surrounding sites, ceilings have already begun
lowering...having lowered around 400 to 600 feet during that time.
So, given all this, will update the BWG TAF to show low stratus
continuing through the night, with ceilings dropping into IFR
category late. Will also bring in some MVFR BR.
It`s important to note that this is not a particularly high
confidence forecast. If the edge of the clouds shifts even just a
small amount in either direction, large changes in conditions at the
airport would be realized.
Updated at 608 PM EST Tue Mar 4 2014
Dry air flowing into the region from high pressure to our north and
west will keep the TAFs well VFR for SDF and LEX during this
forecast period, with cirrus as the main cloud type. Calm winds
overnight will become northeasterly around 5 to 9 knots on Wednesday.
At BWG winds will be calm tonight and skies will clear after
midnight. Dew points are higher here and cross-over temperatures
may be met. Some model data are very bullish on fog formation. Will
go ahead and introduce a TEMPO for MVFR BR during the pre-dawn hours.