Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 200351
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1051 PM EST Sun Feb 19 2017

.Forecast Update...
Issued at 1051 PM EST Sun Feb 19 2017

Several sites in the area have already dropped to 1/4-1/2SM, quite a
bit earlier than climatology. There is some concern over the ability
to maintain very low visibilities through the night since we`ll have
cirrus spilling in from the west and we`re not under the center of
the surface high. CONSShort and GLAMP, which are usually not shy
about bringing in low visibilities, have been keeping us above
advisory level overnight. However, it is worth noting that those
models were not doing very well with their visibility
initializations, being late to the party as vsbys in reality started
to drop.

It`s difficult to disregard actual observed visibilities this low
this early in the evening. Also, the GLAMP does seem to be catching
up, and the 03Z run has trended foggier. So, will go ahead with an
advisory over most of the region. Will leave out southern Kentucky
for now, where there was more mixing Sunday afternoon.

Many thanks to JKL, ILN, IND, OHX, and PAH for a great collaborative
discussion!

Issued at 733 PM EST Sun Feb 19 2017

Almost all of the earlier low clouds have dissipated, leaving clear
skies in their wake. Have beefed up fog wording late tonight into
early Monday morning from "patchy" to "areas."

&&

.Short Term...(Tonight through Monday night)
Issued at 205 PM EST Sun Feb 19 2017

The main forecast challenges in the short term period are
fog/stratus trends tonight and high temperatures Monday.

As of mid afternoon, surface analysis showed high pressure across
central Tennessee and Kentucky extending from the Gulf Coast through
the southern Great Lakes. Visible satellite continued to show
stubborn stratus stuck in a low level inversion but recent imagery
does indicate holes and breaks developing with afternoon mixing and
drying aloft. The stratus remains mainly along the Ohio River
counties, which is where temperatures have remained in the 50s to
near 60 while sunnier locations have risen into the low/mid 60s.

For the remainder of the afternoon and evening, expect a slow
erosion of the stratus layer across southern Indiana and central
Kentucky. Don`t think all areas will clear out by sunset this
evening but a lot more folks should see some sun. If so, readings
may reach the low/mid 60s before sunset.

Tonight`s concern is centered on fog and/or stratus potential. With
upper level ridging and the surface high only expected to move to
eastern Kentucky and the Appalachians, wind fields through 700 mb are
forecast to be light, less than 5-10 mph. Where skies do clear, the
residual moisture and low T/Td spreads will favor fog formation
while the lingering stratus may expand/redevelop in place. Some of
the fog could be locally dense toward Monday morning, impacting the
morning commute. Out of the available guidance, the highest threat
area for dense fog seems to be across southeast Indiana, down into
the Bluegrass and Lake Cumberland region, or mainly along/east of I-
65.

For Monday, the upper ridge axis swings overhead while the surface
high moves further toward the mid-Atlantic. We`ll get a southerly
wind component, though it`s expected to be more from the southeast
than south or southwest. If fog/stratus does develop, it may take
some time to burn off again (similar to this morning). This would
greatly impact highs again. The 19.12z guidance did show a downward
trend in highs, so went ahead and lowered highs a few degrees from
previous forecast, or right near 70 for most locations. Do think
we`ll see more sunshine, especially in the afternoon.

&&

.Long Term...(Tuesday through Sunday)
Issued at 210 PM EST Sun Feb 19 2017

The main focus in the long term period is the unseasonable warmth
and threat for stronger storms on Friday.

A weak shortwave trough will approach the region on Tuesday but as
it does so it`ll lose a lot of its upper level support. Add in
meager moisture return/transport ahead of this system and overall
precipitation chances will stay in the 30-40 percent range.

Expect a very mild day on Wednesday with highs in the low/mid 70s.
Some of the guidance suggests some locations in the upper 70s but
stayed with a model consensus for now. Temperatures through the
remainder of the work week look unseasonably warm as well with upper
60s to low 70s possible each day through Friday.

On Thursday, a deepening trough over the west will develop a surface
low over the central Plains. Its warm front will begin to lift
across our region. Introduced the chance of thunderstorms for
Thursday and Thursday night as most of the 19.12z models show 500 to
800 J/kg of MUCAPE. Some elevated thunderstorms are possible
Thursday night.

That central Plains low quickly deepens as it races toward the Great
Lakes region Friday. The lower Ohio Valley is expected to be well
within the warm sector and models show dewpoints climbing into the
upper 50s to low 60s. This could help fuel modest instability on the
order of 1000 J/kg and combined with an impressive wind field, there
is a chance for stronger to severe storms Friday and Friday
afternoon across portions of central Kentucky and southern Indiana.

There`s still plenty of time for things to change, but the SPC
outlook for day 6 /Friday/ looks good for a chance of severe
weather. Too early to pinpoint exact storm mode/threats but damaging
winds look most likely if severe weather were to occur.

In the wake of that system, cooler air will surge back into the area
sending readings back to near normal for late February. A model
consensus of highs in the 50s and lows in the 30s/40s looks good at
this point.

&&

.Aviation...(00Z TAF Issuance)
Issued at 630 PM EST Sun Feb 19 2017

The stratus from earlier today is finally completely gone from the
TAF sites. This leaves us with clear skies, light winds, and surface
high pressure centered over eastern Kentucky at 23Z. Although the
exact center of the high will be to our east and we should see some
cirrus spill in from the northwest late tonight, we will still have
very light surface winds with upper shortwave ridging directly
overhead and mostly clear skies synoptically. So, fog still appears
to be a good possibility tonight. The computer models are hitting
fog pretty hard at SDF/LOU and LEX, which makes sense as the
lingering cloud cover during the daylight hours allowed dew point
depressions to remain tighter there relative to areas that saw more
sunshine. Will include significant vsby reductions at those sites,
along with some temporary IFR ceilings. Will also, however, include
reduced vsbys at BWG. They will have a good radiational cooling set-
up and they got down to 1/4SM this morning with less favorable
conditions, plus they are notorious for fogging up in these sorts of
situations.

The fog and low clouds should mix out by mid morning, followed by
benign weather for the rest of the forecast package.

&&

.Climate...
Issued at 200 PM EST Sun Feb 19 2016

Record temperatures for the next few days.

Louisville:
Mon. Feb. 20 record warm low: 55 (1994)
Mon. Feb. 20 record high:     76 (2016)
Tue. Feb. 21 record warm low: 51 (1878)
Tue. Feb. 21 record high:     70 (1930*)
Wed. Feb. 22 record warm low: 61 (1922)
Wed. Feb. 22 record high:     71 (1992*)

Lexington:
Mon. Feb. 20 record warm low: 54 (1994)
Mon. Feb. 20 record high:     72 (2016*)
Tue. Feb. 21 record warm low: 54 (1997)
Tue. Feb. 21 record high:     71 (1874)
Wed. Feb. 22 record warm low: 55 (1922)
Wed. Feb. 22 record high:     70 (1922)

Bowling Green:
Mon. Feb. 20 record warm low: 55 (1994)
Mon. Feb. 20 record high:     75 (2014*)
Tue. Feb. 21 record warm low: 54 (1897)
Tue. Feb. 21 record high:     75 (1930*)
Wed. Feb. 22 record warm low: 55 (1961*)
Wed. Feb. 22 record high:     74 (1922)

Frankfort:
Mon. Feb. 20 record warm low: 47 (1949)
Mon. Feb. 20 record high:     73 (2016)
Tue. Feb. 21 record warm low: 47 (1906)
Tue. Feb. 21 record high:     72 (1997)
Wed. Feb. 22 record warm low: 49 (1935*)
Wed. Feb. 22 record high:     72 (1922)

* means most recent occurrence, record occurred in previous years as
  well

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Dense Fog Advisory until 9 AM EST /8 AM CST/ Monday for
     INZ076>079-083-084-089>092.

KY...Dense Fog Advisory until 9 AM EST /8 AM CST/ Monday for
     KYZ023>043-045>049-053>057-061>067.

&&

$$

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


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