Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 041451
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
951 AM EST Wed Dec 4 2013
Issued at 940 AM EST Wed Dec 4 2013
Quick update this morning to account for latest trends. Scattered
showers over northern part of forecast area is associated with
initial warm advection/isentropic lift zone. This area will continue
to lift northward rapidly late this morning and afternoon, with
little or no showers expected behind it. Therefore, will continue
with a dry afternoon.
Patchy morning fog and low clouds continue at this time, but both
should lift this afternoon as surface winds begin to gradually
increase in response to surface pressure gradient. High temps this
afternoon are greatly dependent on whether any sunshine can break
through clouds as low clouds begin to lift. Current thinking is that
it should stay mostly cloudy over many areas, with partial clearing
possible over south-central Kentucky. Thus, will continue with mid
60s north and around 70 south for highs, but will monitor.
No changes at this time for the storm systems for late this week.
Will evaluate 12z model data and make decisions from there.
.SHORT TERM (Now through Thursday)...
Issued at 255 AM EST Wed Dec 4 2013
Today and tonight will be the relative calm before the storm, but
far from a quiet weather pattern. Plenty of stratus around due to
abundant moisture from the surface up through about 800mb. Between
that and a mid-level warm front that will lift through the Ohio
Valley this morning, expect the clouds to stick around with a decent
chance for light rain. By afternoon we should see stronger low-level
winds, resulting in better mixing which will lift the stratus deck.
Skies will remain mostly cloudy but the afternoon will take on a
less dreary feel, with highs climbing well into the 60s on breezy
south winds. This forecast is a few degrees below MOS guidance due
to the extensive cloud cover.
Deepening surface low over Iowa will lift NE across Lake Superior
overnight, driving the long-awaited cold front into the Ohio Valley
by daybreak on Thursday. POPs will increase accordingly, starting in
our southern Indiana counties, with categorical rain on Thursday
across almost the entire area. Given the strong front and nearly
neutral stability aloft, will also include a rumble of thunder from
just before daybreak through about noon. Non-diurnal temp curve
tonight into Thursday as we should flatline in the lower/mid 60s
until the front arrives, and then rapidly fall with the frontal
passage. By late Thursday afternoon most locations should be in
the 40s, with a few upper 30s over southern Indiana while Lake
Cumberland is still in the 50s.
.LONG TERM (Thursday night through Tuesday)...
Issued at 335 AM EST Wed Dec 4 2013
...Heavy Rainfall and Wintry Weather for the Latter Half of the
Thursday Night - Saturday...
Cold air behind our departed cold front will begin to filter across
the forecast area, undercutting warm and moist flow aloft. Most areas
will continue to see all rain on Thursday night, however still
expect a changeover north of the Ohio River before dawn, where
freezing rain, sleet, and snow will be possible. Temperatures
through the column will continue to cool, with the changeover zone
(sleet, snow, freezing rain) sliding into central Kentucky by Friday
afternoon, and the all snow line to locations along the Ohio River.
Colder air aloft will quickly enter late Friday evening, quickly
changing p-type to all snow for most locations. The southeast CWA
will see a mix, but the intensity and coverage will be waning as
deep moisture departs with the system. Precip for all locations
appears to end around midnight Saturday, with a dry yet cold
Saturday on tap.
Still expect the biggest impacts from any frozen precipitation to be
along and north of the Ohio River, with lesser impacts south of the
river. Frozen precip amounts will remain tricky, with uncertainty
still present within the model data. However, guidance is beginning
to converge, with possibly some areas in our far northern tier of
counties seeing 2-4 inches of snow by Friday night and lesser
amounts south. This appears to be one of those systems that will
create a sharp gradient across our southern Indiana counties. Will
run with 2-4 across our far north to around 1 inch along the Ohio
River, with lesser amounts further south. Southern Kentucky will see
the most rainfall where at least 2 to 3 inches of rain will fall,
and locally higher totals are possible given the anomalous moist
airmass that will be in place just ahead of the front. Flooding
problems may become a concern in this area as a result. Refer to
hydro discussion in this product.
Temperatures will continue to fall through the day Friday. Might see
a very small diurnal trend near Lake Cumberland, but for the most
part, highs will occur in the morning. Lows Friday night will range
from lower teens across the northwest to upper 30s across the
southeast CWA. Highs Saturday will struggle to reach the middle 20s
across the northern CWA, especially if there is snow. South-central
Kentucky should edge up into the lower and middle 30s.
Saturday night through Tuesday...
Will have to contend with two more southern stream systems Saturday
night through Monday. Moisture will lift northward quickly across
much of central Kentucky by Sunday morning. With the deep southwest
flow and a nice upper jet streak entrance region over the area,
potential is there for significant precipitation again. Warmer air
aloft will ride over our low-level/surface cold airmass Sunday.
Precipitation will fall mainly as rain (possibly light snow/sleet at
onset on northern edge), but should then freeze as it encounters the
cold ground. So, a hazardous icing event is possible depending on
actual temps Sunday morning and precipitation rates. By afternoon,
surface temps should rise into the mid 30s to lower 40s over central
Kentucky changing freezing rain to rain. However, as mentioned in
the previous forecast, the low-level cold air may not scour out as
much as expected, which keep ice a larger threat. Southern Indiana
could remain with more icing.
This system exists Sunday night, but a final shortwave will cross
the area Monday night which could reinvigorate a quick shot of more
precipitation. The more aggressive ECMWF favors rain southeast
sections of central Kentucky transitioning to snow before ending,
with snow possible across northern areas. The GFS shunts moisture
more off to the east, but with still wintry precipitation quite
possible over eastern forecast area. This second system also has a
good jet streak right entrance region signal at this time. With
several systems before this last one, will not try to get too
specific this far out in time.
Arctic air will move into the Ohio Valley by Tuesday and Wednesday
of next week. High temps should only be in the 20s (could be even
lower especially if there is any snow cover), with lows by Wednesday
morning in the single numbers to lower teens very possible.
Issued at 315 PM EDT Tue Dec 3 2013
A prolonged period of precipitation is forecast this weekend. The
first batch is expected starting Thursday morning through Friday
night. A stalled front south of Kentucky will allow several waves of
precipitation over the weekend. There will be another batch of
precipitation starting Saturday night through Sunday night as the
front finally pulls out of the region. In the north, the
precipitation will be a mixture of freezing rain, sleet, and snow.
However in the south, it will be mainly rain. This rain will
accumulate over the weekend to cause minor flooding on rivers and
streams in southern and central Kentucky.
Up to four inches of liquid precipitation is expected over this
period with a few spots in the south seeing over four inches. This
rain could cause minor flooding in parts of the Kentucky, Green, and
.AVIATION (12Z TAF Update)...
Updated at 615 AM EST Wed Dec 4 2013
IFR stratus has become well established again at SDF and BWG as
abundant low-level moisture lingers in the lowest 6000 ft of the
atmosphere. LEX is far enough east to miss the best moisture
pooling, and has been able to stay MVFR, albeit below fuel-alternate
thresholds. Backing of the surface winds over Kentucky, as well as
the latest temps, suggest that the warm front is sharpening and not
too far southwest of BWG.
Still looks like that warm front will trigger light precip as it
lifts NE across Kentucky this morning, but confidence is too low to
carry anything more than VCSH. Stratus/fog will remain the bigger
impact on operations, as any precip will likely be too light to even
improve the visibility.
Expect gradual improvement to MVFR by late morning and finally VFR
conditions for the afternoon and evening as gusty south winds bring
better mixing. Gusts will be either side of 20 kt, actually a bit
higher this afternoon and then dropping just below this evening.
Mixing should be sufficient to keep us VFR or high-end MVFR until
around midnight. Precip moves in ahead of the cold front by 07-09Z
Thursday, and will quickly drop ceiling/vis into fuel-alternate MVFR
if not IFR.
Planning period at SDF will see fropa, with a sharp wind shift to
WNW and gusts picking up toward 20 kt. Otherwise will remain MVFR in