Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 171942
AFDLMK

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

.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...(18Z TAF Issuance)
Issued at 1220 PM EST Sun Dec 17 2017

Back edge of the wave of light rain showers is about to hit HNB, but
in its wake will be trapped low-level moisture that will bring poor
flying conditions for later this afternoon through the rest of the
period. Expect ceilings to drop to IFR levels for most sites late
tonight, though SDF will hover closer to the MVFR/IFR threshold. We
may see some drizzle overnight as well, to lower vsby`s. Conditions
will improve slowly Monday afternoon.


&&

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

$$

Short Term...ZT
Long Term...ZT
Aviation...RJS


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