Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 231032
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
631 AM EDT THU MAY 23 2013
...Updated Aviation Discussion...
.Short Term (Today through Friday)...
Issued at 310 AM EDT Thu May 23 2013
An amplified 500mb upper air pattern is in place with a deep closed
low over the Pacific Northwest, ridging over the Canadian Front
Range, and a deep trough over the Great Lakes.
A thin line of light showers or sprinkles developed earlier this
morning across southwestern Indiana along a weak cold front. These
will continue to diminish during the pre-dawn hours, bringing just a
light rain shower or some sprinkles along the Ohio River before 5am.
Expect mostly sunny skies across our southern counties this morning
with variably cloudy skies along and north of Interstate 64 through
mid-morning. As the base of a sharp upper trough approaches this
afternoon, steepening lapse rates will lead to increasing cloudiness
by late morning or early afternoon, with mostly cloudy skies through
early evening. Surface based instability is weak, however, some
scattered showers and isolated thunderstorms are likely once again
this afternoon and early evening.
A sharp cold front will move south of the Ohio River this evening.
High pressure of Canadian origin will then quickly build south along
the Mississippi River by early Friday. Winds will turn northerly by
late evening and temperatures will fall quickly into the upper 40s
to around 50 by Friday morning. Skies will clear during the pre-dawn
Unseasonably cool temperatures will continue Friday through late
Saturday. Despite almost unlimited sun on Friday, temperatures will
remain in the upper 60s, maybe reaching 70 next to Tennessee. High
pressure will build directly overhead by early Saturday. Clear skies
and light winds will bring another chilly morning for Saturday, with
lows bottoming out in the mid 40s across our Bluegrass and southern
Expect mostly sunny skies Saturday with light southeasterly winds
and highs ranging from the upper 60s across the northern Bluegrass
to the lower to mid 70s near Bowling Green.
.Long Term (Friday Night - Wednesday)...
Issued at 340 AM EDT Thu May 23 2013
Friday Night through Sunday Night...
Cooler and much drier air will filter into the region in the early
part of the extended as cool upper trough swings through the Great
Lakes and into the northeastern US. Friday night looks to be rather
cold across the region as clear skies and light winds will allow a
decent shot of radiational cooling. While individual model guidance
datasets have been showing some 30s being possible, the multi-model
consensus is not that cold at this point. With this forecast
package, we did trend things colder for Friday night with upper 30s
in the Bluegrass region and lower 40s elsewhere. If the radiational
cooldown continues to look favorable, future downward adjustments
may be required.
High pressure looks to remain in control of the weather for Saturday
with sunny conditions with highs in the upper 60s in the Bluegrass
to the lower-middle 70s in the I-65 corridor and into our
southwestern sections. With the high heading off to the east on
Saturday night, we`re likely to see a shift back to a southerly
flow, so temperatures do not look to cool as much on Saturday
night. For now, plan on going with lower 50s based on the consensus.
Model spread begins to increase rapidly by Sunday as the models show
the region going into a northwesterly flow pattern. A mid-level
wave looks to ride over the ridge in the Plains and then head
southeastward into our area. For now, have kept the low chance PoPs
in the forecast and will continue to monitor over the next few
days. Overall, it does not appear Sunday will be a washout.
Temperatures look to remain a little below seasonal normals here
with highs in the lower-middle 70s and overnight lows in the middle
Monday through Wednesday...
Forecast confidence drops off dramatically during this portion of
the forecast period as model agreement goes out the window. In
tonight`s data sets, the GFS solutions take a quasi-stationary
boundary from our region and send it northward into the Great Lakes
through the period. On the other hand, the latest 23/00Z Euro run
is much slow and keeps the NW-SE oriented boundary right across the
forecast area through much of the period and finally pushing it off
to th east by Thursday. Given the model spread, have opted to go
closer to a blend of the model data along with climatology here.
Thus will keep a diurnal chance of PoPs in the forecast for each
afternoon with lesser chances during the overnight hours.
Temperatures will moderate once the boundary passes through the
region. Highs Monday/Tuesday will be in the upper 70s to the lower
80s and then rise into the middle 80s by Wednesday and into Thursday.
.Aviation (12Z TAF Issuance)...
Issued at 630 AM EDT Thu May 23 2013
A surface trough will move across eastern Kentucky this morning. A
few sprinkles and broken...but still VFR ceilings will continue at
SDF and LEX through around 13z.
Partly cloudy skies will continue through the middle morning hours
at LEX and SDF while mostly clear skies will continue at BWG.
Partly cloudy and dry conditions are expected through the early
afternoon hours today. Skies will likely become broken to overcast
at some point during the afternoon. However cloud bases will stay
above the MVFR threshold. Scattered showers are expected Thursday
afternoon with perhaps around 30% coverage.
Winds will stay from the west around 5kt through 14z, then veer
to the west by mid to late morning as they increase to around 7 to
10kt. By early afternoon, west winds will increase to 12 to 16kt
with some gusts up to 20kt. Winds will rapidly shift to the
northwest at around 10 to 15 mph by early evening as a cold front
moves through. Cloudy skies this evening will clear after midnight.
North winds around 8 to 10kt will continue through 12z Friday.