Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 281047

Area Forecast Discussion
National Weather Service Louisville KY
647 AM EDT Sun May 28 2017

...Updated Aviation Discussion...

.Short Term (Now through Monday)...
Issued at 315 AM EDT Sun May 28 2017

...Strong Storm Chances Later Today Conditional Upon Destabilizing...

Trailing stratiform rain from MCS now over the northern Gulf Coast
states will slide across southern KY for the remainder of the
overnight, so will continue high Pops there with a small chance for
an embedded rumble of thunder. Overnight rainfall, and expected
rainfall on Sunday are not enough to warrant the Flash Flood Watch
continuing. So, will let that fall off in coordination with JKL.
More on the Sunday precipitation below...

Once southern KY precipitation ends, we should see a relative dry
period through the remainder of Sunday morning and early afternoon.
As we move toward late afternoon, a shortwave and it`s associated
surface low over the southern Great Lakes will drag a cold front
near the area. Despite what is expected to be fairly heavy cloud
cover throughout the day, models show modest to moderate
destabilization by late afternoon. Most models suggest ML CAPE
values around 1000 J/KG, but a couple of models suggest values
closer to 2000 J/KG. Given the amount of cloud cover and that SW
surface wind will just be advecting old cold pool air from overnight
convection, feel the lower instability values are a better bet.
Instability will play a big factor because vertical shear profiles
are more than sufficient for organized updrafts, and even some
splitting/rotating storm modes given the long-straight hodograph. If
we are able to destabilize, still can`t take the threat of a few
severe storms off the table. Most likely place for this would be
over southern IN and northern KY late afternoon into the evening.
SPC has us in a Marginal Risk that is ultimately conditional upon
destabilizing. Otherwise, expect mostly cloudy skies with highs
topping out in the upper 70s and touching 80.

Shortwave trough axis and cool front move through overnight, with
shower and storm chances ending from west to east. Overnight lows
should drop into the upper 50s and low 60s by dawn on Memorial Day.

Still expecting a dry and pleasant Memorial day with plenty of
sunshine and highs on either side of 80. The dry relief will come
thanks to a mid level dry slot wrapping into a deep occluded low
over Lake Superior, and post-frontal surface high pressure.

.Long Term (Monday Night through Saturday)...
Issued at 315 AM EDT Sun May 28 2017

Monday Night - Wednesday...

Deep and occluded cyclone centered over Lake Superior will slowly
meander into eastern Ontario through Tuesday night. Mid level dry
slot that had been over the area will push SE Monday night and a
weak front will approach from the NW. Models have been hinting at
some potential light showers ahead of this front on Tuesday, and
will only mention small chances mainly across southern IN in the
morning, and across east central KY in the afternoon. A second front
looks to swing through on Wednesday as another shortwave rotates
around the parent trough. So, will leave slight chances for a shower
overnight Tuesday, and a chance for a few showers and storms on
Wednesday as instability looks a little better. Look for highs
around 80 and lows in the upper 50s to near 60 during this time.

Wednesday Night - Thursday...

Have higher confidence that the front will be through the area
during this mid-week time frame, with dry NW flow aloft and surface
high pressure briefly in control. So, will continue a dry forecast
with lows in the mid to upper 50s and highs in the upper 70s to
around 80.

Thursday Night - Saturday...

Overall placement of upper and surface features to end the work week
becomes a bit muddy, but there is a general idea that a strong storm
system will drop out of Canada and into the Great Lakes, dragging a
cold front into the Ohio River Valley. Expect to see some unsettled
days (Fri-Sat) ahead of this feature with scattered thunderstorm
mention. Highs should continue mostly in the upper 70s to near 80,
with lows in the low 60s.


.Aviation...(12Z TAF Issuance)
Issued at 645 AM EDT Sun May 28 2017

BWG came in last hour with a low fuel-alternate MVFR cig, and latest
GOES MVFR fog probabilities shows a growing area in the BWG/LEX
corridor for this potential. FFT briefly was IFR, but has gone back
to VFR. Given proximity, went ahead and put in tempo groups with
these lower cigs. Next operational concern will be storm development
late this afternoon and into the evening hours ahead of a cold
front. By late evening those should be done and we look to go VFR.




Short Term........BJS
Long Term.........BJS
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