Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 180229

Area Forecast Discussion
National Weather Service Louisville KY
929 PM EST Fri Nov 17 2017

.Forecast Update...
Issued at 927 PM EST Fri Nov 17 2017

Starting to see some light showers show up on regional radars at
this hour in western portions of the CWA. These showers are
developing in response to isentropic lift and a strengthening low
level jet which is aiding to enhance a theta-e ridge over western
KY/southern IL. Coverage of showers should increase over the next
few hours.

Additionally, surface temperatures have been steadily going up over
the past few hours thanks to strong warm air advection, and think we
can safely assume we`ve hit our "low" temperatures for the evening
as temperatures steadily climb into tomorrow morning.

Only major update to the forecast was to start precipitation for
parts of central KY a few hours sooner given radar trends.
Otherwise, rest of forecast looks on track.


.Short Term...(This evening through Saturday night)
Issued at 235 PM EST Fri Nov 17 2017

...Gusty Winds Saturday and Saturday Evening...

Low pressure now is over Kansas with a High pressure center to our
east. The gradient in between will tighten tonight, starting to
bring in some warmer and more moist air. It will be one of those
fall nights where the lowest temperature will be early this evening
and then steadily rise under those southerly winds. NAM is pulling
up a strong low-level jet of 60-70 knots over southern IN in the 06-
09Z time frame. GFS is weaker, with the RAP in between...around 60
knots. Would not be surprised to see some of those winds mix down
early in the the current advisory starting at 12Z looks

That low-level jet should kick off some rains and perhaps isolated
storms along/north of the Ohio River before daybreak. After
daybreak, we should get more showery before a line of storms.
Precipitable water values come up to around 1.4 inches...which is
pretty high for this time of year. A more solid line of showers
should come through just ahead of the cold front in the mid to
late afternoon hours. Soundings indicate some limited instability
that should produce scattered thunder along that line. Stronger
winds are expected just behind the front, with gusts likely to
around 45 mph from the west and northwest. The gradient across our
area should relax pretty quickly behind this surge, so the timing
of the end of the advisory looks good for our region.

As for cloud cover behind the front, model RH fields in the 900-950
mb layer hold back moisture and keep that thin layer saturated
through daybreak Sunday. Previous forecast hung on to this cloud
layer through that time period and see no reason to deviate from
that at this point. Model statistical guidance has not been handling
this trapped moisture very well thanks to how thin the layer is.

.Long Term...(Sunday through Friday)
Issued at 235 PM EST Fri Nov 17 2017

After a couple days earlier in the week advertising a headache for
next week, the models have stabilized around a quiet solution for
the midweek. It looks like we`ll have a quasi-zonal flow, so
temperatures should moderate closer to normal and, at least for now,
Thanksgiving looks good. The only potential break in that zonal flow
comes Wednesday, but again this looks dry for now.


.Aviation...(00Z TAF Issuance)
Issued at 620 PM EST Fri Nov 17 2017

LLJ will ramp up this evening and create some LLWS issues for all
TAF sites. Additionally, showers will expand in coverage overnight
from the west, and we`ll see cigs/vis degrade as the moisture works
eastward. Winds will also increase in strength out of the
south/southwest through the overnight hours, and remain quite strong
heading into Saturday morning and afternoon. A cold front will move
through the region tomorrow afternoon, and isolated to scattered
thunderstorms could be possible along the front, though confidence
in timing of storms and cold front remains low. Winds will switch to
the west/northwest behind the cold front and remain strong and gusty
Saturday afternoon and evening.


IN...Wind Advisory from 7 AM EST /6 AM CST/ to 10 PM EST /9 PM CST/
     Saturday for INZ076>079-083-084-089>092.

KY...Wind Advisory from 7 AM EST /6 AM CST/ to 10 PM EST /9 PM CST/
     Saturday for KYZ023>043-045>049-053>057-061>067-070>078-081-



Short Term...RJS
Long Term...RJS
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