Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 070527
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
127 AM EDT Thu May 7 2015
...Updated Aviation Discussion...
Updated 1008 PM EDT Wed May 6 2015
Forecast is on track this evening. The last of the very isolated
showers that popped up this afternoon diminished with the loss of
heating. Conditions will be mostly clear and calm overnight, and
this will lead to some patchy fog, mainly in the river valleys. Do
think we will see a few more patches than last morning as dew points
are running a few degrees higher, and radiational cooling is still
optimal. Crossover T`s also support patches of fog in some areas.
.SHORT TERM (Now through Thursday Night)...
Issued at 300 PM EDT Wed May 6 2015
Forecast question last couple of days seems to be answering itself
with popping of a few showers across the region this hour. Models
have been over advertising these showers the last couple of days,
but we now are finally seeing some development. Deeper development
still seems to be limited by a mid-level cap, but we are seeing
10-20% coverage. That cap should be weaker tomorrow, so a 15-25 pop
would seem better for the afternoon.
Other than that, above normal temps will continue with highs in the
low to mid 80s today and Thurs, and lows in the mid 50s to lower 60s
tonight. Some light patchy fog will be possible in typical fog prone
areas again tonight, right around daybreak.
.LONG TERM (Friday through Wednesday)...
Issued at 300 PM EDT Wed May 6 2015
The synoptic pattern at the start of the long term period will
feature a Rex block across the eastern seaboard, with a broad trough
across the southwestern CONUS. This regime will place the Ohio
Valley within ridging aloft for the beginning of the period, before
transitioning to a more zonal pattern by the end of the period as
the western trough deamplifies and ejects across the eastern half of
the United States.
The main story through the first part of the long term period will
be the building heat over the Ohio Valley. Given temperatures the
past few days have exceeded even the highest guidance, think
temperatures touching 90 are looking increasingly likely in the
typically warm spots Friday into Saturday. 850mb temperatures of
around 13C today will increase to 14-15C by Friday into Saturday.
While southwesterly surface flow will not be overly strong, daytime
mixing aided by the expected sunshine should be enough to get
temperatures into the upper 80s and lower 90s. Record high
temperatures are in the lower 90s on Friday and Saturday, so a few
locations may make a run at these records.
Otherwise, focus will shift to increasing thunderstorm chances this
weekend into early next week. The aforementioned western trough and
associated surface front will slowly approach the Ohio Valley.
Still feel the GFS is way overdone with precipitation coverage on
Friday (a known bias), so will not introduce pops until Saturday.
Forcing for ascent Saturday into Sunday will be limited to lingering
outflow boundaries from convection to the northwest and differential
heating boundaries, thus do not think coverage will be very high
(20-40%). By Monday, the trough and associated cold front should
push into the region increasing storm coverage. The exact evolution
will be ironed out in the coming days, but 1000+ J/kg of MLCAPE
coupled with 30-40 knots of 0-6km shear could support some stronger
storms with this fropa. Timing is still a bit in the air, so a
later arrival (overnight) would obviously lessen this threat.
Behind the front, temperatures will fall back into the 70s for the
middle of next week. Conditions will dry out as high pressure
builds into the region from the northwest.
.AVIATION (06Z TAF Update)...
Updated at 125 AM EDT Thu May 7 2015
High pressure at the surface and aloft will keep winds light and
variable at the TAF sites this morning. VFR conditions are expected
to prevail, but a short period of MVFR vsbys at KBWG and KLEX still
look possible between 07/09-13Z. Isolated convection may be
possible later today at KLEX. However, the expected sparse coverage
still precludes a mention in the TAF at this time.