Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 221646
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1245 PM EDT WED MAY 22 2013
...Updated Aviation Discussion...
.Short Term (Today through Thursday)...
Issued at 310 AM EDT Wed May 22 2013
Areas of low pressure will move from Iowa to lower Michigan today,
with surface trofs dropping to the south. One such trof, combined
with an upper shortwave, should help to spark renewed showers and
thunderstorms today. A few stronger storms could develop, with
marginally severe wind gusts as the main threat and marginally
severe hail as a secondary concern. Any tornadic activity would be
confined to just a brief spin-up where local convective boundaries
High temperatures today will be highly dependent on cloud and shower
coverage. Will go for highs around 80, which is consistent with
current guidance, the inherited forecast, and surrounding offices.
The warmest temperatures should be in the east.
Shower and thunderstorm activity should wane this evening, with a
fairly quiet overnight period. The mercury will drop to around the
60 degree mark.
On Thursday the upper trof axis will finally swing through and give
us one last chance of showers and thunderstorms with this system.
Moisture will be more shallow and instability not as great, so
severe weather is not expected. Some small hail could fall from the
taller storms, though, as the upper trof moves in and wet bulb zero
heights drop. High temperatures will be in the lower to middle 70s.
.Long Term (Thursday Night - Tuesday)...
Issued at 300 AM EDT Wed May 22 2013
An amplified 500mb pattern continues late Thursday with a deep
stationary closed low forecast over the Pacific Northwest. A narrow
ridge is expected to extend north into the Canadian Front Range.
Closer to home, a very deep, cold and yet progressive trough is
expected to extend southward from Hudson`s Bay through the Great
Lakes. It is this feature that will usher in a very pleasant weekend
with cool temperatures for late May.
A relatively sharp cold front will move southeast of the Ohio River
late in the afternoon on Thursday. Much drier air will move south
overnight all the way through Tennessee as strong high pressure of
Canadian origin builds southward along the Mississippi River valley.
Brisk northwest winds late Thursday afternoon will become northerly
and continue at 10 to 15 mph through the evening hours.
Residual cloudiness Thursday evening will clear by dawn Friday.
Temperatures will cool off rapidly and bottom out in the upper 40s.
Expect mostly clear skies and cool temperatures Friday through late
Saturday. With high pressure building right over Indiana on Friday,
winds will become light from the northeast during the afternoon and
will become nearly calm by early Saturday. Despite nearly cloud-free
skies Friday afternoon, highs will struggle to reach 70, with upper
60s likely across the Bluegrass. After another cool night with lows
in the upper 40s, Saturday will warm a couple of degrees into the
500mb heights will begin to build over the southern Plains by
Sunday. Eventually, ridging is forecast to expand across the Plains
and eventually into the Lower Ohio Valley from Tuesday through the
rest of the upcoming work week. This will eventually bring
mid-summer heat to much of the mid-section of the CONUS.
During this period of transition, Sunday through Tuesday, northwest
flow aloft will persist over the Lower Ohio Valley. A boundary will
develop by late Sunday across the region, separating cool dry air
and easterly winds over Ohio from more humid air advancing north
along the Mississippi River. In general, this front may lie over
northern Kentucky late Sunday, slowly moving north of the
Commonwealth through Tuesday. Moisture pooling along this boundary
coupled with occasional disturbances sliding southeastward may bring
occasional rounds of convection. The ECMWF is the farthest south
with precipitation of any of the long-term guidance, developing
widespread showers during the day Sunday right over Kentucky. Prefer
the slightly farther north GFS, which presents greater chances of
occasional convection across southern Indiana and the Bluegrass
Despite increasing clouds, low dewpoints will keep Sunday quite mild
with highs in the mid to upper 70s. Both temperatures and humidities
will rise towards Tuesday with highs in the lower to mid 80s
.Aviation (18Z TAF Issuance)...
Issued at 1245 PM EDT Wed May 22 2013
SW winds are well established over Kentucky, and mixing has picked
up just enough to support gusts near 20 kt at SDF. Speeds increasing
just enough at BWG and LEX, and we expect to see gusts by the valid
time of the TAFs. Mid-level clouds have been the limiting factor in
convection thus far, but we are starting to see some Cu and expect
that will continue to increase with heating.
POPs are quite high but it is still difficult to pin down when and
whether any storms will impact each terminal. At this point, will
carry VCTS from 20Z until 00Z Thursday, with prevailing VFR.
However, once storms do develop an update will likely be required to
get a better handle on actual impacts. If any storms directly affect
any of the airports, conditions will likely drop to MVFR if not IFR,
but only for a brief period.
Storms and winds will diminish this evening, but a VFR ceiling will
remain through the night. Broad frontal wind shift will give us SW
flow through the night, and then due west on Thursday with a VFR
ceiling. Upper-level impulse and associated cold pool aloft will
move ESE through the Ohio Valley on Thursday, and will likely
trigger scattered showers and even a few thunderstorms. However, the
better chances are in SDF and LEX, and will be late enough in the
day to be mainly limited to the 24-30 hour planning period in the