Forecast Discussion
000
FXUS63 KLMK 230809
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
307 AM EST THU FEB 23 2012
.Short Term (Today through Friday)...
Updated at 307 AM EST Feb 23 2012
...Severe Weather Possible Late This Afternoon and Early This
Evening...
Low pressure along the Kansas/Missouri border at 12Z will deepen as
it moves east to the Wabash Valley by this evening. A warm front
will reach to the east from the low, along the length of Kentucky
just south of the Ohio River. The morning and early afternoon hours
should be fairly quiet, with scattered shower and thunderstorm
activity confined to the northernmost sections of the LMK CWA in
southern Indiana. Severe storms are not expected with this morning
and early afternoon activity.
As the low approaches our winds will increase out of the south
today. We may approach Wind Advisory criteria along and south of a
line from Hartford to Hodgenville to Stanford. Will handle this
with an SPS for now, with afternoon gusts of 30 to 35 mph possible.
Winds will be slightly less over northern Kentucky, but still brisk,
and less still in southern Indiana.
It will take until this afternoon for sufficient moisture to arrive
in the region to fuel storms. Mesoscale models bring surface dew
points to 60 in western Kentucky this afternoon, while the GFS only
has mid 50s. Looking at how the models are verifying at 06Z, it
appears that the truth lies somewhere in between these two extremes.
Storms will finally begin to erupt by mid afternoon to our west,
with initiation likely occurring over southern Illinois and the
lower Wabash River basin.
The degree of severity of these storms is still in question. Shear
will be plenty strong enough to support rotating updrafts, and by
mid afternoon precipitable water values will finally rise slightly
above an inch, which is quite a bit above normal for this time of
year. There will plenty of dynamics with a strengthening surface
low coming in, with most of the LMK CWA in the warm sector by late
afternoon, plus a robust low level jet and strong upper level vort
max. The big question mark is how much instability will be
available. Looking at forecast atmospheric moisture profiles and
recent satellite animations, there should be quite a bit of
cloudiness around today. This should help to keep instability in
check and, indeed, model progs show only modest surface-based
instability this afternoon and evening.
Nevertheless, it does appear that storms will fire and that severe
weather is a distinct possibility. With strong 0-3km and deep layer
shear isolated tornadoes will be something to watch out for. There
is a dry layer aloft in model sounding progs, suggesting the
possibility of those strong winds above the surface mixing down.
Hail appears to be something less of a threat looking at wet bulb
zero heights, but even last evening`s small thunderstorms were able
to put down some hail to the size of golf balls. As of this writing
it appears that the region that will be the most under the gun will
be along the I-64 corridor in far southern Indiana and northern
Kentucky, including the Louisville metro in the afternoon and the
Lexington area in the evening. The best timing for severe weather
appears to begin in the west around 3pm CST and end in the east by
10pm EST. This is not to say that southern Kentucky is entirely in
the clear -- just that the best chances are in the north. We
encourage all residents of southern Indiana and central Kentucky to
review and practice their severe weather action plans this morning.
Behind the front the rest of the nighttime hours should be dry,
cool, and breezy.
Friday will be an unpleasant day as the base of the larger upper
trof swings in, giving us a low overcast with patchy light rain.
Temperatures will be much chillier than what we saw Wednesday and
Thursday, and west winds will be in the 15 to 25 mph range.
High temperatures today will range from the middle 60s across the
northern fringe of the LMK CWA north of the warm front to the lower
70s in southern Kentucky. Low temperatures tonight will be from the
upper 30s in Hoosier National Forest to the middle 40s at Lake
Cumberland. Highs on Friday will struggle into the middle and upper
40s to around 50 in the south.
.Long Term (Friday night through Wednesday)...
Updated at 307 AM EST Feb 23 2012
The trough axis will slide through the area and to the east Friday
night with northwest flow commencing. Will continue the chance of a
rain/snow shower mix Friday night, as lingering low level moisture,
waves in the mean flow, and steepening low-mid level lapse rates
combine. Still not expecting any real problems with the potential
for snow, although soundings continue to hint that the profile could
be near convective instability and a few of the mesoscale models are
beginning to pick up on the potential convective nature of the
showers. So, any snow shower could be briefly heavy at times. Lows
will drop into the upper 20s.
High pressure will build across the forecast area for the weekend.
Expect mostly clear skies and dry conditions Saturday through
Sunday night. High temperatures will warm from the 40s on Saturday
to the 50s Sunday. High pressure will continue to shift east of the
area as the next low pressure system develops east of the Rockies.
This means the warming trend will continue into Monday on southerly
winds, with highs in the mid and upper 50s expected.
Models have come in line better with the moisture starved frontal
passage on Monday. It appears there will be very little moisture to
work with. So, have trimmed back PoPs to slight chance. May even
have to remove rain chances if these trends continue. The area will
remain dry Monday night into Tuesday before our next weather system
arrives. The latest ECMWF is starting to agree with the GFS. This
means rain chances will increase Tuesday afternoon as a low pressure
system approaches from the west. Of course there remain timing
differences amongst models, but rain and thunderstorm chances appear
greatest with the frontal passage late Tuesday and Wednesday as the
surface low is projected to track across Missouri, Illinois, and
into the Great Lakes. Given the ECMWF has been shifting toward the
GFS over the last few model runs, I have trended temperatures a
little warmer for next week and added thunder to the forecast.
Currently have highs in the low and mid 50s for Tuesday and
Wednesday, but these may be too low. At this time, there remains
enough ensemble spread, noted in the NAEFS data, that keeps me from
going too warm next week.
&&
.Aviation (06Z TAF Issuance)...
Updated at 1204 AM EST Feb 23 2012
A complex TAF period. A wave of showers and storms moved through
the northern terminals earlier this evening. The thunder with this
activity is over, but there will still be some lingering showers for
a few more hours. Also, the storms sent out a sharp gust front,
making winds chaotic across the region. By the time this TAF period
starts, the gust front will have passed SDF/LEX and will be
approaching BWG. SDF/LEX can expect northwest winds for a couple of
hours before becoming lighter and variable. BWG should see the gust
front come through within the first 30 minutes of the TAF, switching
winds abruptly to the northwest or NNW.
A new area of storms popped up over southern Illinois late in the
evening, and is heading to the southeast. The storms are expected
to weaken as they enter central Kentucky, however BWG may still be
affected by them, and they are included in the BWG TAF.
Some patchy MVFR BR may form by dawn thanks to the earlier rains,
though clouds will remain widespread enough and winds mixy enough to
prevent widespread significant fog.
For the daylight hours today, low pressure will move from Kansas
City to Terre Haute, with a warm front extending to its east.
Showers and thunderstorms will be found along the warm front today,
but should stay mostly north of the terminals.
Tonight the low will proceed to Lake Erie, dragging its cold front
through central Kentucky this evening. Showers and thunderstorms
will develop ahead of the front, threatening primarily SDF/LEX
during the 21Z-03z time period.
South and southwest winds ahead of the front today will switch to
the west tonight behind the front. Winds will be gusty today, and
will remain brisk tonight.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
KY...NONE.
$$
Short Term.......13
Long Term........MJP
Aviation.........13
NWS LMK Office Area Forecast Discussion
