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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KLMK 050304
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1004 PM EST Thu Mar 4 2021

.Forecast Update...
Issued at 1004 PM EST Thu Mar 4 2021

Surface high pressure nosing in from the north and a dry atmosphere
will provide us with light winds and clear skies overnight. It will
be chilly with the mercury falling into the middle and upper 20s in
most places, about 5 to 10 degrees colder than normal. No changes to
the forecast needed.

&&

.Short Term...(This evening through Friday)
Issued at 225 PM EST Thu Mar 4 2021

Current satellite shows clear skies across the region as regional
observations show temperatures in the low 50s across southern
Indiana and into the low 60s across southern KY. Surface analysis
shows a weak cold front stretched W-E across central KY with a
1033mb high pressure centered over Ontario and another 1022mb center
over ArkLaTx.

Ridging aloft will begin to weaken a bit as an upper low moves from
the Four Corners eastward toward the Lower MS Valley, filling as it
goes and eventually becoming enveloped within the upper flow. As a
result, southern KY will see increased mid and high cloud cover
Friday afternoon through evening. Otherwise, expect slightly cooler
temperatures Friday with morning mins in the mid 20s across the
Bluegrass and in the low 30s across southern KY. Highs Friday will
reach into the upper 40s to low 50s.

.Long Term...(Friday night through Thursday)
Issued at 250 PM EST Thu Mar 4 2021

...COOLER WEATHER THIS WEEKEND WITH A WARM UP NEXT WEEK...
...HEAVY RAINFALL THREAT DEVELOPING BY LATE NEXT WEEK...

========================================
Synoptic Overview
========================================

Amplified upper level pattern is expected at the beginning of the
forecast period (Friday night) with a broad/deep trough axis over
the eastern third of the US with ridging over the Rockies.  The
eastern US trough axis will slowly move off to the east by early
next week.  The upper level pattern will undergo significant changes
next by early-mid next week as a large and powerful trough pushes
into the western US.  As this occurs, downstream ridging will build
over the central and eastern US which will allow temperatures to
moderate and become quite mild across the central and eastern US. As
the western US trough heads eastward into the Plains, a large
synoptic scale cyclone is expected to develop with widespread
showers and storms expected across the Plains.  The shower and
thunderstorm activity will then shift into the Ohio and Tennessee
Valleys toward in the later half of the week and linger into next
weekend.  The set up may bring a renewed threat of heavy rainfall to
the Ohio Valley late next week.

========================================
Model Discussion and Sensible Weather
========================================

Overall, the global models are in decent agreement throughout the
upcoming long term period.  Model continuity has been fairly good
and the ensembles are generally good agreement.  There is some
spread in the Wed/Thu time frame, but nothing out of the ordinary
when talking about spread in the day 6/7 forecast period.

The guidance suggests a rather cool weekend across the area with
lows Friday night in the mid-upper 20s with highs on Saturday
remaining in the lower 40s across the Bluegrass with 45-50 across
the I-65 corridor and points west.  Temperatures look to moderate
slightly on Sunday with highs in the upper 40s in the Bluegrass with
lower 50s elsewhere.  Southerly flow should start to kick in on
Monday with highs warming into the lower 60s along and west of I-65
with mainly mid-upper 50s out in the I-75 corridor.  Overnight lows
still look to average out in the upper 20s to the lower 30s.

As heights build aloft on Tuesday/Wednesday we should start to see
much milder weather develop  Highs look to hit the 60-65 degree mark
by Tuesday and may get into the 65-70 range by Wednesday.  The
guidance through this period is probably too cool as the global
models always under estimate high temperatures under deep
southwesterly flow.  So I suspect that if the current forecast
pattern holds, then highs will likely trend warmer in subsequent
forecasts.

By mid-week a large Plains cyclone should develop and shift into the
Great Lakes.  The trailing cold front will likely spark a corridor
of strong to possibly severe storms over the central Plains.  This
activity will spread eastward into the Ohio Valley by late Wednesday
and into the day on Thursday.  Temperatures will probably remain
pretty mild here with highs in the 60s.

Looking past Thursday we have some concerns about how the pattern
may evolve by late week.  There are signals within the data that a
new upper trough axis may move into the western US resulting in the
upper level flow remaining more west-southwesterly across the OH/TN
Valleys by late week.  Should this scenario unfold, the late week
cold front may stall out across the Ohio Valley and serve as focus
for renewed convective development as additional waves translate
eastward within the flow regime aloft.  This could result in another
period of excessive rainfall and possible flooding and river
flooding by late next weekend and into week two.

========================================
Societal Impacts
========================================

No real societal impacts are expected this weekend and into next
week.  However, ongoing flooding along the Kentucky, Ohio, and
portions of the Green River will continue into next week.

Warmer temperatures will be noted during the mid-week time frame.
Record high temperatures do not look to be hit during this period.
However, there is a risk that we could tie or break some overnight
warm minimum temperatures by mid-late week in our southern forecast
area.

Moderate to heavy rainfall may lead to hydrologic issues by late
week and into the weekend if significant rainfall develops.   Given
wet antecedent soil conditions, runoff could be rather quick with
possible quick rises on area creeks and streams.  Residents in low-
lying and flood prone areas should keep an eye on forecasts next
week and be prepared for another round of flooding as early as next
weekend.

========================================
Forecast Confidence
========================================

Weekend Temperatures            : Moderate-High
Expected Warmup Next Week       : Moderate
Possibility of late hydro issues: Low-Moderate

&&

.Aviation...(00Z TAF Issuance)
Issued at 540 PM EST Thu Mar 4 2021

Surface high pressure spilling southward from the Canadian
Archipelago to the Ohio Valley will keep our weather quiet during
this TAF period with light NW-NE breezes. A weakening 5H low
traveling from DEN to LIT will bring high clouds to the region on
Friday.


&&

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

$$

Update...13
Short Term...CG
Long Term...MJ
Aviation...13