Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 091909
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
309 PM EDT Wed Jul 9 2014
.SHORT TERM (Now through Thursday Night)...
Issued at 252 PM EDT Wed Jul 9 2014
High pressure building over the Great Lakes and moving towards the
Northeast will provide us with pleasant and quiet weather in the
short term. Tonight will be mostly clear with light winds and lows
in the lower and middle 60s. Sheltered spots may slip into the 50s,
and patchy valley and field fog will be possible.
With mostly sunny skies and a north breeze on Thursday, afternoon
readings will peak in the 80s with comfortable dew points. The
mostly clear skies and light winds will continue into Thursday night
with lows similar to tonight`s.
.LONG TERM (Friday through Wednesday)...
Issued at 300 PM EDT Wed Jul 9 2014
Changeable weather conditions expected during the extended forecast
period. Dry weather and weak northwest flow aloft will be the rule
at the start of the period (Friday) as surface high pressure
prevails over the Ohio Valley. High temperatures Friday will be
seasonal in the mid and upper 80s, with humidity values remaining
Over the weekend, flow aloft across the Great Lakes area will
increase ahead of a very anomalous trough that models predict will
move south out of Canada into the Great Lakes early next week.
Return flow on the backside of the high pressure system will result
in upward moisture transport/isentropic lift into the central U.S.
to western Ohio Valley and Great Lakes area ahead of this trough.
Thus, scattered showers and thunderstorms should develop in those
areas on Saturday, north and west of central KY and southern IN.
However, a few stray showers could work into our northwest/northern
forecast area Saturday. But this should be more clouds than showers
as the rain moves away from the more unstable air mass to our north
and west, and into a more stable air mass over us. Highs Saturday
could reach 90 or lower 90s over southern half of central KY in the
afternoon, but clouds north should keep readings from 85-90 with
some breaks of sun in the afternoon.
On Saturday night and Sunday, models diverge on what will occur. The
general pattern of west to northwest flow aloft with at least an
embedded shortwave or two would suggest possibility of scattered
thunderstorms and perhaps an MCS to our north and/or west. If this
occurs, then movement could push some showers into our northern
forecast area late Saturday night or Sunday (GFS solution) or stay
to our north (ECMWF and GEM solution). Will lean toward a drier
solution Saturday night with precip north of area. On Sunday,
confidence is lower as to evolution of precip. Air mass will be more
unstable to our north and west again, but with some destabilization
over us. Any outflow boundaries or cloud boundaries from convection
to our north late Saturday night could focus isolated to scattered
showers and storms Sunday, especially over the northern half of
forecast area. At this time, south-central KY appears to have least
chance of showers during that time.
For Sunday night and Monday, models suggest a cold front will be
approaching from the northwest in advance of the deep trough over
the Great Lakes/southern Canada. High moisture values will be in
place (precipitable water values progged at 1.75-2 inches and K
index values in the mid-upper 30s). Westerly low-level flow of 25-30
kts along with a decent 300 mb jet for this time of year to our
north should be enough to spark scattered to perhaps numerous
showers and storms Sunday night and/or Monday, with heavy rain
likely in cells. Precip evolution Monday will be complicated by
potential convective boundaries.
The cold front should move through Monday night or Tuesday with
drier and cooler air moving in behind it. Models hint that at least
clouds and perhaps scattered showers could affect parts of
south-central KY north of the front by the end of the forecast
period (mid next week), but much of that precip should remain over
the TN Valley on south. Temperatures by mid next week will be below
.AVIATION (18Z TAF Update)...
Issued at 114 PM EDT Wed Jul 9 2014
High pressure developing over the Great Lakes will keep our weather
quiet for this TAF period. Winds this afternoon will come in from
the west around 7 to 10 knots...maybe a few gusts into the 13-18
knot range. Those winds will calm down as the sun sets.
Went ahead and put some temporary MVFR BR at BWG for a few hours
around sunrise. The other airports should have dry enough air to
preclude sub-VFR vsbys.
Tomorrow winds will switch to the north as the sun climbs in the
sky, at speeds a few knots below today`s.