Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 180032
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
732 PM EST Sun Dec 17 2017

.Forecast Update...
Issued at 732 PM EST Sun Dec 17 2017

Patchy drizzle is already occurring across the area so did a quick
update to get drizzle in the grids a little earlier than originally
planned. No other changes.

&&

.Short Term...(This evening through Monday night)
Issued at 230 PM EST Sun Dec 17 2017

As of mid afternoon, regional radar imagery showed an area of
showers generally along and east of the I-65 corridor across the
lower Ohio Valley. Readings were in the low to mid 40s with overcast
skies.

The main forecast concern in the short term is drizzle and fog late
tonight through Monday and its impact on temperatures. For the
remainder of this afternoon, plan on the back edge of the
precipitation to quickly move east, giving way to just cloudy skies
by late afternoon. As we head into this evening, the low levels of
the atmosphere will begin to moisten and saturate from the surface
to about 850 mb. Upstream observations show plenty of 500 to 1000 ft
ceilings with 3-5 mile visibilities. RAP and HRRR soundings show
good signals for drizzle beginning toward midnight. Tonight`s
temperatures won`t drop too much with the widespread cloud cover.
Plan on lows in the low 40s.

Drizzle, fog, and low clouds will start the new work week. We should
stay socked in the stratus for most of the day as well. This should
keep our highs held down to the low to mid 50s. Some breaks in the
clouds are possible late in the day and into Monday night but
overall not optimistic that we`ll see much clearing. Lows Monday
night will stay in the low to mid 40s.

&&

.Long Term...(Tuesday through Sunday)
Issued at 235 PM EST Sun Dec 17 2017

Several weather systems to keep tabs on in the long term period, the
first being Wednesday. Confidence in the overall forecast starts
above average early on then drops considerably by next weekend and
Christmas.

An upper level system coming from the southwest US will lift toward
the Tennessee Valley by late Tuesday into Wednesday. Rain showers
are likely to spread into Tennessee and southern Kentucky late
Tuesday then across more parts of central Kentucky Wednesday
morning. The trend in the model cycles has been to the north, and
the latest model consensus brings in precipitation chances up to the
Louisville metro now. However, the highest chances (greater than 50
percent) remain confined closer to the Tennessee border. There`s
good agreement that the rain will exit Wednesday afternoon or
evening. Plan on highs to be in the upper 40s to middle 50s. Right
now, up to 1/2 inch of rain could be possible along the KY/TN
border.

A deep upper level trough is then forecast to develop across the
central US. This will act to bring ridging across the southeast US
and warmer temperatures. Thursday`s highs could reach the upper 50s
to near 60, with lower 60s possible across southern Kentucky.

A strong cold front is then forecast to approach the area late
Friday into early Saturday. The 17.12z models generally have the
frontal passage late Friday. Showers will become likely ahead of the
front during the afternoon or evening hours then a more widespread
band of showers will accompany the frontal passage. Soundings show
the potential for marginal MUCAPE (100-500 J/kg) developing so
couldn`t rule out a few thunderstorms at this time. By early
Saturday morning, crashing temperatures behind the front could
briefly turn any remaining precipitation over to a mix or wet snow
west of I-65.

For Christmas Eve and Christmas Day, the forecast confidence drops
off. This cycle of models continue to struggle with the strength of
a building southeast US ridge. The ECMWF and CMC kept a stronger
ridge with a more active, but warmer, zone of weather from the Texas
Gulf Coast through the lower Ohio Valley into the Great Lakes. The
GFS was a colder, but drier solution. It remains too early to
pinpoint details and the best message we have is to continue to
closely monitor the forecast this upcoming week for any holiday
travel preparations.

&&

.Aviation...(00Z TAF Issuance)
Issued at 629 PM EST Sun Dec 17 2017

Sfc-850 RH will remain high through much of the TAF period.
Ceilings, already MVFR at the start of the TAF at most locations,
will lower tonight to IFR, possibly with some LIFR during the early
morning hours especially at BWG and LEX. The low level moisture will
remain in place on Monday so low clouds will persist through the
day, though there should be enough mixing to push ceilings back up
into MVFR.

Winds will come in from the southwest at 5 to 10 knots with surface
ridging to our east and southeast and a cold front approaching from
the northwest by the end of the period.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...13
Short Term...ZT
Long Term...ZT
Aviation...13


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