Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 210254

Area Forecast Discussion
National Weather Service Louisville KY
954 PM EST Mon Nov 20 2017

.Forecast Update...
Issued at 950 PM EST Mon Nov 20 2017

Quiet evening across the Ohio Valley, with return flow gradually
increasing. Temps are already close to forecast lows, but low-level
jet is near 25 kt and will continue to increase through the night,
so expect steady temps for the rest of the night. This lines up well
with the going forecast, so no changes planned.


.Short Term...(This evening through Tuesday night)
Issued at 246 PM EST Mon Nov 20 2017

Mostly sunny conditions were noted across the region this afternoon.
Afternoon temperatures ranged from the upper 40s over the Bluegrass
region to the lower 50s over central and southern KY.  Quiet weather
is expected to continue with winds becoming more southerly as the
afternoon and evening roll onward.  We should see temperatures fall
into the upper 30s to the lower 40s this evening before bottoming
out in the low-mid 30s overnight.  With the high to our east, we
should see more of a southwesterly wind overnight which should keep
our atmosphere well mixed and allow temps not to be as cool as what
we saw this morning.

For Tuesday, a surface low pressure system will move into the James
Bay area with a trailing cold front dropping into the region by mid-
late evening.  It still doesn`t appear that we`ll get much in the
way of deep moisture advection ahead of the system, so just an
increase in clouds is expected as the system passes through.  Highs
during the day look to warm into the lower 50s across southern
Indiana with mid-upper 50s being seen across much of Kentucky.
Frontal passage still looks to be on target for Tuesday evening.
Best chances of precipitation look to be well to our northeast
across Ohio and into West Virgina.  Skies should clear late as high
pressure builds into the region.  Low temperatures look to drop into
the upper 20s across southern Indiana and far northern KY.  Lows in
the lower 30s look reasonable across southern KY.

.Long Term...(Wednesday through Monday)
Issued at 246 PM EST Mon Nov 20 2017

Wednesday through Monday...

Surface cold front is forecast to be well east of the region with
high pressure building in behind it.  With clearing skies, lows
Wednesday morning should bottom out in the upper 20s in the northern
sections to the low 30s in the south.  Wednesday looks to be a very
good travel day in terms of weather.  Mostly sunny skies are
expected.  Temperatures will be below normal with highs in the upper
30s to around 40 across southern Indiana and far northern Kentucky.
Across the central and southern parts of Kentucky, highs of 40-45
will be seen.  Cold high pressure will pass over the region
Wednesday night allowing Thanksgiving morning lows to cool into the
middle 20s.  Some of the outlying cold spots could drop a bit
further if we have little if any clouds and light winds.  Dry
conditions are expected on Thanksgiving Day with a slight moderation
in temperatures over Wednesday.  Highs should warm into the lower to
middle 40s over southern Indiana and northern Kentucky.  Across
southern Kentucky highs of 44 to 49 look reasonable.  Dry and cold
conditions will be seen early Friday morning with lows in the upper
20s to the lower 30s.

By Friday, high pressure center is forecast to be to the east of the
Ohio Valley along the southern Mid-Atlantic states.  We should get
into a return flow ahead of an approaching cold front.  With a
southwesterly wind and a good amount of sun, we should warm up into
the low to middle 50s.  Aforementioned cold front is forecast to
swing through Friday night.  This will bring a period of windy
conditions and some shower activity.  The best chances of showers
look to be mainly across central Indiana and Ohio, but some of these
showers could scrape far northern KY during the period.  Lows Friday
night will cool into the lower 40s with highs on Saturday remaining
mild with middle to upper 50s expected.  A few 60s may be seen in
southern KY.

A colder airmass will work in Saturday night with lows dropping into
the lower 30s.  Sunday looks to be a blustery day with strong
northwesterly winds.  We`ll probably see a bit of stratocumulus
across the northeastern Bluegrass region with clearer skies down
across our southwest sections.  We might be able to squeeze out a
flurry or two, but we suspect more widespread snow shower/flurry
coverage will be seen across much of Ohio and into West Virgina.
Highs will struggle to reach the lower 40s in many areas. Clouds
look to clear out Sunday night as another Canadian high drops in
and lows will cool into the lower-mid 20s.   Monday looks to remain
cold as well with highs in the upper 30s to the lower 40s. Consensus
blend looks way too warm through here and we`ve undercut temps a
bit.  Would suspect to see further downward trends in the blended
data in subsequent forecasts.

Week Two and Beyond...

While the Thanksgiving holiday weekend will end on a cold note,
conditions look to rapidly warm as we head into next week. From a
global scale, long range models continue to show the global weather
oscillation to be in the phase 1 and 2 which means we`ll be in a low
atmospheric angular momentum (AAM) state.  We`ve seen rather weak
low AAM state over the last week or so.  That, combined with some
limited blocking has led to a wavy northern hemispheric pattern with
transient periods of cold and warmth.  This wavy state looks to
continue next week with another possible amplification in the NOAM
pattern by mid-late week.  Past week of Hovmoller signal analysis,
supported by other organic techniques are decent agreement with a
strong signal passing through in the 11/29 to 12/1 time frame.  This
has some support from the long range dynamical models of the GFS and
Euro.  Both of those models show a very windy and mild pattern
setting up by midweek with a run at 60+ temps again followed by a
cold front which may bring another round of showers and storms to
the region.  Following that system, a period of colder conditions
looks to follow as we move into December.  It`s unclear if that cool
will hold given the progressive pattern.  The long range models have
struggled with warming things up too fast, only for successive
forecasts to come in cooler.

Looking further ahead into December, QBO values look to remain
rather negative which would suggest a blocky pattern emerging. There
are some early indications of some upper atmospheric warming near the
pole which would promote a stronger -AO pattern developing.   The
GFS and Euro runs do suggest that the stratospheric vortex may get
perturbed somewhat leading to an increased chance of colder air
pushing into the mid-latitudes.  Organic forecast techniques suggest
a rather stormy period setting up for mid December with implications
of a much colder period developing.  Something to watch come into
focus in the next few weeks.


.Aviation...(00Z TAF Issuance)
Issued at 545 PM EST Mon Nov 20 2017

VFR conditions expected through the valid TAF period with only few-
sct cirrus. S-SW return flow will increase through the period, with
winds staying just shy of 10 kt overnight. Low-level jet cranks up
to around 40 kt which is borderline for LLWS, but in the absence of
a strong inversion the change is gradual enough not to mention.
Winds increase to 10-15 kt Tue morning, with gusts just over 20 kt
during the warmer part of the afternoon.




Short Term...MJ
Long Term....MJ
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