Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 280516
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
116 AM EDT Thu May 28 2015
...Updated Aviation Discussion...
Updated 845 PM EDT Wed May 27 2015
Last of the convection has exited the Bluegrass. To our north and
west, isolated to scattered storms along the cold front in central
Indiana are not organizing and do not appear able to push any
boundaries south. Therefore have continued the trend of backing off
overnight POPs. Most of the area will remain dry, with south central
and east central Kentucky having the best chance for a stray shower
Updated 615 PM EDT Wed May 27 2015
Complex of storms that formed this afternoon, and produced isolated
strong to severe winds, has pushed south and east. Trailing
stratiform rain still lingers across the Bluegrass. Models had
advertised convection developing along the cold front but between
the front hanging farther north than expected, and the atmosphere
being worked over, that has not happened. Updating the forecast to
cut back on POPs for tonight. Believe most of the night will be dry,
but with the juicy air mass still in place it`s hard to rule out a
stray shower. Will also include patchy fog after midnight, mainly
east of I-65, given wet ground and small T/Td spreads.
.SHORT TERM (Now through Thursday Night)...
Issued at 245 PM EDT Wed May 27 2015
Have line of storms along the I-65 corridor this hour. The northern
part of the line has been the strongest at this point, with the
southern more widespread and less organized. Thinking at this point,
after collaboration with SPC, is that most of the storms the rest of
the afternoon will be below severe limits, so holding off on issuing
a watch at this time. DCAPE`s are not as impressive over the eastern
part of the area.
The next round of storms for the day will depend on how quickly we
recover from this first round. Areas along and north of the I-64
corridor will have the best chance to fire again before sunset, but
looking upstream there is a dearth of low clouds over southern
Illinois. Will limit late afternoon chances to under 40% for now.
Should these late storms fire up, we could additionally see some fog
form overnight, thanks to lighter winds and the extra influx of
For Thursday, there will be a little less moisture in place across
the region, but more importantly there should be less of a trigger.
Thus storms that develop should not become organized, though an
isolated wind/hail threat isn`t out of the question. Have gone with
40% or less coverage mainly across south central KY, in the area
with best moisture and isolated coverage in the north. Highs
Thursday should be a touch warmer than today, given the less
coverage of storms. For lows, went pretty much with persistence.
.LONG TERM (Friday through Wednesday)...
Issued at 300 AM EDT Thu May 28 2015
Latest 00z model runs are in reasonable agreement with overall
synoptic weather pattern in extended forecast, indicating a
generally unsettled period with off and on showers and
thunderstorms. General mid-level troughing over the central Plains
on Friday is forecast to evolve into a slow-moving cutoff low over
the mid-to-lower Mississippi Valley late this weekend and through
the early-to-mid parts of next week. Ahead of this feature will be a
persistent feed of low-level moist southerly flow over much of the
Ohio and Tennessee Valleys, including central Kentucky and south-
As the mid-level low closes off to our west, it will induce a weak
surface low to our west along a cold front which will sag slowly
southeast into the lower Ohio Valley over the weekend and early next
week. Scattered showers Friday night will become more numerous
Saturday through Sunday, with a diurnal maximum and a relative
nocturnal minimum (but still scattered) in convective activity
expected in general. Difficult to pinpoint where greatest coverage
of rainfall will be over the weekend, but along and just north of
the front at night, and along and south of the front during the day
within greater low-level instability.
At this time, wind fields/system dynamics do not support much severe
weather, but some strong pulse storms are possible from time to time
especially over central Kentucky south of the front during the
afternoons. However, persistent precipitable water values of 1.5-1.8
inches, deep warm cloud depths, moist model soundings, and moisture
replenishment courtesy of continued low-level southerly inflow
suggest periods of heavy rainfall over the weekend.
.AVIATION (06Z TAF Update)...
Updated 115 AM EDT Thu May 28 2015
The main TAF challenges for this issuance will include low cigs/fog
early this morning and timing the next round of showers/storms
through the region later today. Currently a sfc front was
approaching from the NW with an upper level impulse pushing north
from TN. Our region remains in between these features attm, but
each will infringe upon the area throughout the TAF period. With
plentiful moisture from rains early today and sfc winds expected to
turn light or calm during the pre-dawn hours, fog and low stratus is
expected to drop flight conditions to at least MVFR/IFR and possibly
lower. Flight restrictions will be most severe between 10-13Z this
morning. Conditions should improve after sunrise, but convection
looks to fire along the aforementioned synoptic features and result
in isld-sct coverage of showers/storms mainly from just after
sunrise through late afternoon. It`s a little difficult to pinpoint
an exact window of opportunity for the TAF sites to receive a
t-storm today so will stick with VCTS and see how convection evolves
throughout the day. Although flight conditions could be reduced to
MVFR/IFR in any t-storm, prevailing flight conditions should
generally return to VFR after sunrise this morning. Winds will be
ENE at BWG/SDF and more SSE at LEX during the daylight hours today.