Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 271347
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
947 AM EDT Wed May 27 2015
Updated 945 AM EDT Wed May 27 2015
Storm complex to our west is fluctuating. At times it looks like it
is declining then new cells are forming along the line. A few of the
mesoscale models had this activity, but most did not. Following
those models that did have the activity, some weaken it and some
maintain it movinng northeast. Given the clear airmass ahead of the
activity, will lean the direction of maintaining it and possibly
allowing new storms to form along the gust front later this
afternoon. SPC mesoanalysis has forecast CAPES to around 2000 this
afternoon, and this is somewhat in line with GFS/NAM/RUC soundings.
The main threats still look to be damaging winds and quarter-sized
.SHORT TERM (Now through Thursday)...
Issued at 310 AM EDT Wed May 27 2015
...Strong to Severe Storms Possible this Afternoon/Evening...
A few sprinkles were moving east over east central KY early this
morning. Other than this very light/isld precip, the rest of the
area was dry with skies becoming mostly clear to partly cloudy west
of I-65. Expect that we`ll continue to see sky cover slowly
decrease through the morning hours especially after sunrise. Before
sunrise low stratus and light patchy fog will be possible over
portions of south central and east central KY.
The next chance for showers/storms will arrive this afternoon as an
upper level shortwave trough passes through the Midwest. The latest
NAM/GFS indicate the wave will be stronger and better organized to
our north, but we`ll still see modest forcing and decent low to mid
level flow resulting in around 30-35 kts 0-6km bulk shear. If skies
go mostly sunny to partly cloudy for a good portion of the morning
and early afternoon as predicted, we`ll likely see a good amount of
sfc based instability build up...around 2000+ j/kg. Steep low and
mid level lapse rates will exist too. For these reasons, think that
damaging winds will certainly pose a threat today in storms that get
going in our area especially along and north of I-64 close to the
best forcing from the upper level shortwave. Hail up to around 1
inch will also be possible. Boundaries from storms that initiate to
our NNW may also provide a trigger for storms in our area this
Storm clusters should wane and move east of the area by late evening
with only small storm chances for the rest of tonight.
Thursday small chances for showers/storms will continue as we remain
in a moist, unstable environment. However, an upper level ridge
moving through the area will certainly work to suppress convection
somewhat. With a weaker flow, would expect isld to sct pulse-like
storms to bubble up in the late afternoon/evening hours Thurs
although some short range models keep us mostly dry Thurs.
Temperatures should be a tad warmer today than yesterday with highs
in the 82-86 degree range. Lows tonight will remain mild in the
lower 60s. Highs Thurs will warm into the 84-88 degree range.
.LONG TERM (Thursday night through Tuesday)...
Issued at 250 AM EDT Wed May 27 2015
The main focus in the long term is on precipitation chances as a
moist and seasonably warm air mass holds over the lower Ohio Valley.
Thursday night into Friday the synoptic pattern is expected to
feature a longwave trough from the southern Plains through the Great
Lakes while a ridge remains across the Southeast US. The local area
will be on the periphery of both of these features. Models remain
consistent showing that the ridge will build slightly and in the
absence of any shortwave trough, this period is our `driest` with
only slight chances for afternoon and early evening showers/storms.
More synoptic influence and dynamics are expected Saturday into
early Sunday as a shortwave trough, seen currently in water vapor
imagery off the coast of California, treks through the southwest US
and southern Plains. This system will brush our northwest Saturday
afternoon, enhancing mid/upper level lift. Closer to the surface, a
slow moving front will approach as well. Moisture pool and PWATs
climb along/ahead of the front and with the greater lift, expecting
more widespread showers and thunderstorms. 60 to 70 percent POPs
look good at this time.
Model uncertainties and differences arise Sunday into early next
week as to how progressive this boundary pushes south. 27.00z GFS
was the most aggressive, clearing the front through the entire
forecast area Sunday into Monday, while the GEM and ECMWF held it up
right through central KY. Where the front clears through,
north/northeast flow could bring much drier and somewhat cooler air
in its wake, while to the south, the moist/warm air mass will
remain. By Monday night, guidance pulls this front back north,
bringing back the warmer and more moist conditions.
Temperatures through Saturday are expected to be relatively
persistent with highs in the low 80s and lows in the mid/upper 60s.
Sunday onward is less certain, but if/where the front comes through
then cooler temperatures may prevail. For now, a model consensus of
highs in the upper 70s and lows in the 60s seem reasonable.
.AVIATION (12Z TAF Update)...
Updated 650 AM EDT Wed May 27 2015
Low clouds and light br may affect LEX/BWG for a few more hours this
morning before conditions return to VFR.
Another upper level disturbance will bring showers/storms this
afternoon/evening. MVFR/IFR flight restrictions will be possible in
any storm that hits a TAF site. Did not include in the TAF attm
since t-storm coverage is expected to be scattered this
afternoon/evening. Will continue VCTS in the TAFs and better time
convection out with a coming TAF issuance.
Winds will be light SSW early this morning and more SW for the
daylight hours today. Winds may gust up to around 15-18 kts today.
Higher gusts will be possible in convection.