Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 211219
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
819 AM EDT Thu May 21 2015

...Forecast Update...
Updated 818 AM EDT Thu May 21 2015

Patchy drizzle is being reported across the region this morning. Did
a quick update to expand the mention of drizzle in the forecast to
the entire forecast area. Otherwise the forecast is in good shape.

.SHORT TERM (Now through Friday)...
Issued at 253 AM EDT Thu May 21 2015

The synoptic pattern this morning features zonal to northwest flow
across the Ohio Valley.  This regime will continue through the short
term period, bringing continued seasonably cool conditions.

A weak surface low has pushed east into western North Carolina this
morning.  In its wake, northerly surface winds have brought much
cooler temperatures along with copious cloud cover to the region.
Temperatures this morning currently range from the 50s to lower 60s,
with lows by sunrise expected to drop into the upper 40s and 50s.

For today, a PV anomaly will slide southeast through the northwest
flow aloft, bringing large scale height falls across northeastern
portions of the CWA.  Many hi-res guidance members and ensembles
suggest this forcing may be enough to squeeze out some sprinkles or
a few light showers this afternoon in the northern Bluegrass
region.  However, an analysis of forecast soundings this afternoon
shows that the moisture profile will be rather shallow.  While we
cannot rule out a few sprinkles or even a light shower this
afternoon east of I-65, think the threat is too low to put in the
forecast.  Given the expected cloud cover and northerly surface
winds, temperatures today will be well below normal, with readings
expected to top out in the low and mid 60s.

For tonight, any lingering cloud cover should dissipate/push east by
the late evening hours.  If this occurs as forecast, we should be in
for a chilly night as surface ridging slides into the Ohio Valley.
The best radiational cooling conditions will be found across western
and southern KY, where the ridge axis looks to set up.  Temperatures
across the area will dip well into the 40s, with even some upper 30s
readings not out of the question in the typically cooler locations.
Some patchy fog will also be possible, mainly south of I-64 where
winds should be lightest.  This threat will likely be dependent on
dewpoints this afternoon, and if we are able to see any breaks in
the cloud cover which may help to mix them out.  The day shift will
monitor trends this afternoon and adjust as needed.

Friday is shaping up to be a rather nice day, but still seasonably
cool.  A good amount of sunshine should help us mix to near 800mb,
but 850mb temps will only be around 7-8C.  Therefore, highs will
only top out in the low to mid 70s, despite the sunshine and
expected deep mixing.  A weak front will approach from the north
later in the day, which may spread a few clouds into southern IN and
northern KY by later in the afternoon/evening.

.LONG TERM (Friday Night through Wednesday)...
Issued at 250 AM EDT Thu May 21 2015

The long term will be dominated by upper ridging developing over the
southeast U.S., peaking Monday-Tuesday. At the surface a large dome
of high pressure centered over Michigan (but covering much of the
eastern half of the country) will slide to the ESE Friday night and
Saturday.  It will then park off the Carolina coast as it meets up
with the westernmost extent of the Azores High.

The operational runs of the GFS, ECMWF, and CMC have all trended
significantly drier for Sunday and Sunday night in the Ohio and
Tennessee Valleys.  Most ensemble plume traces of the GFS are flat,
but there is still enough uncertainty that we`ll need to keep at
least low chance PoPs in the forecast.  The best chance for
convection will be in the afternoon as surface LI`s go slightly
negative and a weak wave comes up from the southwest.

For much of the rest of the long term we`ll be in deep, moist
southwesterly flow.  As waves move through this atmosphere
convection can be expected.  While the large scale models are likely
overdoing precipitation coverage Monday through Wednesday, chance
PoPs through that time period are well warranted.  Forecast
refinements will be made as individual triggers become more apparent.

The best instability and upper dynamics are expected to remain just
to our west from the southern Plains to the western Great Lakes. As
a result, widespread severe weather outbreaks are not expected at
this time across southern Indiana or central Kentucky through
midweek.

&&

.AVIATION (12Z TAF Update)...
Updated at 645 AM EDT Thu May 21 2015

A weak surface low has pushed to the east of the region this
morning, leaving low cigs in its wake.  The low cloud deck seems to
be rather sporadic, thus confidence in cigs over the next 4-6 hours
is low.  That said, have high confidence KBWG will continue in IFR
cigs for the next few hours.  Fuel-alternate MVFR cigs should affect
KSDF and KLEX, with even high-end IFR cigs not out of the question
at these locations.

Otherwise, cigs will slowly rise throughout the day with daytime
mixing.  Winds will continue out of the NNW around 10 knots this
afternoon.  By tonight, clouds should push off to the east, giving
way to a mostly clear night.  This could set the stage for some
light fog development at KBWG tonight.

&&

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

$$

Update.........EER
Short Term.....KJD
Long Term......13
Aviation.......KJD





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