Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 211121

Area Forecast Discussion
National Weather Service Louisville KY
621 AM EST Sun Jan 21 2018

.Short Term...(Today through Monday)
Issued at 315 AM EST Sun Jan 21 2018

Now - Tonight...

A deep longwave trough was over the Four Corners region this
morning, with zonal flow aloft over the Ohio Valley. A well defined
baroclinic zone was located on the leeward side of the Rockies. The
cyclone will strengthen as it moves into the Plains over the course
of the day. Low and mid-level winds will take on more of a
southwesterly component between low pressure and low-level ridging
near the Southeast coast.

Temperatures are very mild this morning thanks to that southwest
flow in the low levels, with readings generally in the upper 40s to
low 50s. A modest 850 mb moisture transport maximum runs from east
Texas up through Arkansas, southeast Missouri, and curving slightly
along the Ohio River. This 35-40 kt LLJ will continue to stream
warm, moist air into the region. Radar is quiet at the moment, with
only a few light sprinkles earlier. But isolated to scattered light
rain will be possible from mid-morning through the rest of the day.
Hi-res models suggest an area of enhanced moisture, along with the
low-level jet, will result in spotty light rain from mid-morning on.
This evening, the better chance for any light precip lifts into
southern Indiana. Many areas will stay dry tonight. Temperatures
should stay largely in the 50s overnight with a southerly breeze
that ramps up toward dawn on Monday.


Strong shortwave trough and mature surface cyclone lift from the
Plains into the Midwest on Monday, sending a cold front through the
forecast area. Surface dewpoints are forecast to peak in the upper
40s in a narrow band of deep moisture along the boundary.
Instability is pretty meager, with forecast soundings showing a cap
through the morning hours. Blended guidance suggests 10-15 percent
thunder probability, so may go ahead with a slight chance in the
southeast. But mainly gusty rain showers are expected. Latest QPF
guidance continues to trend downward a tad, with around a third of
an inch possible. No flooding issues are expected. Winds will remain
quite breezy into Tuesday. Monday will be very mild, with highs in
the upper 50s to lower 60s prior to onset of rain.

.Long Term...(Monday night through Saturday)
Issued at 320 AM EST Sun Jan 21 2018

Monday Night and Tuesday...

Rain should cut off fairly quickly behind the cold front Monday
evening, with temperatures falling overnight. Lows should dip into
the mid to upper 30s. The potent shortwave trough swings through
overnight as well. Some very light rain associated with wrap-around
moisture may be possible near and north of I-64 Tuesday morning. But
the bulk of the day looks dry in a cold advection pattern with gusty
west winds. Highs will be limited to the low 40s. Winds could gust
as high as 30-35 mph.

Tuesday Night - Saturday...

Dry NW flow aloft and surface high pressure dominate through mid
week, before progressive upper ridging builds over the area late in
the week. This will be a dry stretch with steadily warming
temperatures. Highs Wednesday in the low to mid 40s will give way to
low to mid 50s by Friday.

Rain chances return to the area Friday night and Saturday. Another
deep upper trough is forecast to swing into the Plains during this
time frame. We`ll likely see another surge of Gulf moisture into the
area ahead of this feature. Medium range guidance is also suggesting
a secondary surface low could develop near Arkansas and track
through Kentucky sometime late in the weekend, with a shot of cold
air on the backside of the system. Forecast confidence is low at
this point, but it`s something to watch.


.Aviation...(12Z TAF Issuance)
Issued at 615 AM EST Sun Jan 21 2018

Both synoptic and hi-res models remain quite pessimistic with
ceilings under modest S-SW flow and low-level near-saturation
extending up through 800mb. Confidence is limited as the low
ceilings haven`t quite come in as advertised in guidance, so if
anything may adjust ceilings upward or key on most likely timing for

An axis of enhanced moisture is poised over the Wabash Valley, and
still appears on track to cross over the TAF sites late this morning
into early afternoon. Still look for HNB to go into IFR, and SDF to
fuel-alternate, though it may not be as long-lasting as previously
thought. Also will not include any precip, as drizzle has been
spotty at best and hasn`t had any impact to ceiling or vis. LEX will
drop into MVFR, but BWG should stay VFR as this slug of moisture
passes mainly to the north.

Stronger forcing comes into play toward Monday morning as low
pressure gets more organized over the central Plains. Will see POPs
ramping up after midnight, especially for HNB and SDF. Ceilings will
walk the line between MVFR and VFR, but any restrictions to
visibility will hold off beyond the SDF planning period. South winds
will increase to a solid 10 kt overnight, with breezy conditions
expected by midday Monday.




Short Term...EBW
Long Term...EBW
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