Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 212306
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
706 PM EDT Mon Apr 21 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Tuesday)...
Issued at 315 PM EDT Mon Apr 21 2014
A cold front will approach the area tonight. Ahead of it, showers
and isolated t-storms will be possible. We`ve had light radar
returns over the area throughout the afternoon, but most of the
precip has been virga with maybe a lucky sprinkle reaching the
ground under the best radar returns. Most precip has remained aloft
due to very dry low levels. However, as we get into the late
afternoon/evening hours, low level moisture will increase allowing
showers to reach the ground. Rain showers will continue on and off
throughout the night with most places seeing at least a sprinkle or
shower. Thunderstorm chances are in question as we`re not seeing a
whole lot of lightning activity downstream. However, most model
soundings do indicate some elevated instability overnight so will
continue an isld t-storm mention. Due to such a dry airmass in
place already, overnight temps will likely fall into the low-mid 60s
as the atmosphere saturates with overall night time lows bottoming
out in the upper 50s and lower 60s.
For Tuesday, the cold front will pass through the region early in
the morning with showers and isld t-storms gradually pushing east of
the area through the morning hours. Skies will turn sunny from NW
to SE during the afternoon hours. Expect cooler afternoon high
temps in the mid 60s to around 70. Also, NW winds will be a bit
gusty (up to 25 mph gusts) in a tight pressure gradient behind the
frontal passage Tues afternoon.
Tuesday night expect clear skies with high pressure sinking south
into the Ohio Valley. The cold airmass and decent rad cooling
conditions will likely result in temps dropping into the mid 30s to
lower 40s across the area. Although low level moisture is in
question, some locations over the Bluegrass that drop into the mid
30s may experience patchy frost. Sheltered locations would stand
the best chance at any frost formation.
.LONG TERM (Tuesday Night through Sunday)...
Issued at 315 PM EDT Mon Apr 21 2014
Wednesday - Thursday...
Ridging from a surface high centered over the Great Lakes will be in
place over the Ohio Valley Wednesday, sliding east of the area
through Thursday. Meanwhile, a progressive upper ridge will build
over the area, then slide east by Thursday evening. This pattern
will result in dry conditions, with temperatures making a recovery
from Tuesday`s cold front. Highs on Wednesday look to range from 63
to 68, with the warmer temps being across the west closer to the
building upper ridge/increasing thicknesses. Wednesday night should
be slightly milder than Tuesday night, with lows mostly in the low
and mid 40s. A few of the cooler eastern valleys might drop into the
upper 30s closer to the surface high. A few of the models try and
depict some very light rain associated with isentropic lift over a
warm front across southeastern IN, but will not bite on these very
small chances attm. Thursday will see a nice increase in
temperatures as thicknesses rise and a steady southerly flow takes
hold. Mainly upper 70s above guidance looks like a good call under
this pattern, as has been the case recently.
A progressive shortwave and its associated surface low will cut
across the upper Midwest and into the Great Lakes Thursday night.
Meanwhile, the trailing cold front will approach our region. Look
for pretty solid coverage of showers and scattered thunderstorms
Thursday night ahead of this feature. Have continued mention of
likely Pops. Looks like the best dynamics will scoot to our north so
not concerned about severe potential at this time. A few of the
stronger storms may be able to produce some gusty winds, brief heavy
rain, and cloud to ground lightning.
Friday - Saturday...
The cold front passes through quickly and have all of the
precipitation chances east of our area by dawn on Friday morning. We
look to go into a fairly benign zonal flow, gradually transitioning
to shallow northwest flow by Saturday morning. Will go dry through
this period, although very small chances of a shower or storm can`t
be ruled out as a moisture starved front drops south toward the Ohio
Valley. Look for highs in the low and mid 70s on the warm side of
this boundary as we head into the weekend.
Saturday Night - Monday...
Complicated forecast to end the weekend and start the new week as
forecast models diverge in solutions. The problem appears to lie in
how amplified an omega block gets over the central CONUS and its
impact on the resulting downstream flow over our region. The latest
ECMWF seems to have some support from the GFS ensemble mean in less
amplified flow, which would allow the frontal boundary to stall out
near our region as it becomes nearly parrallel to the upper flow.
The GFS is much more amplified with the omega block and the
downstream flow, allowing the front to progress through our area and
well south. The ECMWF solution would be much warmer/wetter, while
Pretty much have to pick a path at this point. Will side with the
warmer/wetter ECMWF and its supporting cast. This will lead to
gradually increasing shower and storm chances late Saturday night
along and north of the Ohio River, with several waves riding along
this boundary through at least Monday. As the front hangs out or
very slowly slides south across our area, expect temperatures to
become slighly cooler each day. Highs Sunday should generally be in
the mid/upper 60s, with Monday in the low to mid 60s.
Please note that if it becomes more clear that the more amplified
solution will work out. Look for big changes to the forecast in the
direction of cooler/drier during this time.
.AVIATION (00Z TAF Update)...
Issued at 705 PM EDT Mon Apr 21 2014
A cold front will push towards the area tonight bringing scattered
showers and a few rumbles of thunder. Initial batch of scattered
showers is moving into the area now and will affect KBWG and KSDF in
the next couple of hours. Current thinking is that we will continue
to see VFR conditions this evening and into the overnight hours.
Conditions will probably deteriorate later tonight as the actual
frontal boundary approaches. MVFR conditions are expected develop
around 22/09-10Z and continue until the front passes through the
region. Current data suggests that the front will pass through in
the 22/12-14Z time frame with an end to the showers and a shift in
winds from the west to the northwest. Skies will begin to clear out
towards mid-morning with a stronger pressure gradient developing.
We should see winds pick up into the 8-12kt range with gusts up to
20kts being possible. Winds are expected to subside by 23/00Z.