Area forecast discussion...updated
National Weather Service Huntsville Alabama
1001 PM CDT Tuesday Jun 18 2013
Update...
evening forecast update
&&
Discussion...
as the weak frontal boundary continued to slide south of the
Tennessee Valley this evening...showers along the boundary quickly
dissipated following sunset. The wind shift that followed behind the
boundary has brought slightly drier air to the Tennessee Valley but
low to middle 60s dewpoints remain across much of the County Warning Area. While
temperatures have cooled across the forecast area...it seems to be
more attributed to diurnal cooling than any strong cold advection
behind the front. 9pm temperatures still ranged from the upper 60s (at
Tullahoma/Winchester and vinemont) to the middle 70s (khsv)...which are
not significantly different from surrounding cwas on both sides of
the boundary.
The going forecast was modified slightly to account for the effects
from some lingering high level cloud cover streaming our way ahead of
the next middle level trough axis. Scattered to bkn250 clouds should continue to
track across the southeast through the overnight period and help
dampen the expected diurnal cooling...and therefore help prevent
dense fog development. Am still leaving fog wording in the grids for
overnight though since there should be enough cooling to at least
produce some patchy fog (helped by all the ground moisture remaining
from recent rains). Have otherwise updated products to remove mention
of rain chances through 06z as all the precipitation has dissipated and
increased overnight lows by a degree or two due to the high clouds.
Ccc
&&
Aviation...
/issued 629 PM CDT Tuesday Jun 18 2013/
for 00z tafs...with the exception of potential fog development
overnight...VFR conditions should be predominant at both terminals
for the period. Due to recent rainfall and expected clearing of cloud
cover overnight...MVFR fog should begin to develop by around 08z and
continue to drop visible through the early morning. At this time am expecting kmsl
to see the lower visbys (to IFR/2sm at times) but if more of the high
clouds dissipate...fog could become much thicker at both terminals.
Will be monitoring evening trends closely for updates.
Ccc
&&
Previous discussion...
/issued 340 PM CDT Tuesday Jun 18 2013/
Tennessee Valley weather has been relatively quiet today, all things
considered, because a fairly deep shortwave trough passed through
overnight. There are three surface boundaries of note this afternoon:
an initial front now along/south of I-20, a secondary boundary
draped from ktup to Vinemont/3a1 to between Winchester/bgf and kcha,
and a third more robust boundary draped across Iowa to the Ohio
Valley. A weakening band of showers is focused along the 2nd boundary
in north Alabama, but there is little else now in the hun County warning forecast area. Not
surprisingly, the off-and-on rain and clouds has kept temperatures
from getting out of the lower 80s.
While the wettest and most unstable period is coming to an end, we
are not going to be totally dry for the next 7 days.
First, the shortwave trough over Texas should stay mostly south of
the area. Once showers clear out of the area this evening, we will
need to watch for fog formation late tonight, especially if there is
any decent clearing. However, a shortwave trough currently over the
Missouri Valley will drive the 3rd boundary noted above southward
into the Tennessee Valley tomorrow. The trough and boundary will get
hung up, and some additional forcing could arrive Thursday. While
forcing will not be terribly robust either day, there should be
sufficient moisture, convergence, and heating to drive a few showers
and storms during the afternoons--no more than a 15 to 20 percent
pop, but just enough to mention in the forecast. The increased
sunshine should easily push temperatures into the 90s.
The synoptic scale pattern becomes increasingly murky by the weekend.
Energy from the Wednesday/Thursday trough gets caught up/trapped on the eastern
flank of a building ridge. Medium-range models disagree on the
location and amplitude of the resulting trough, but agree on its
presence and persistence. The European model (ecmwf) model maintains some sort of weak
troughing or upper low over the southeast for the entire remainder
of the forecast, and the GFS and GFS ensembles solutions are similar.
Unless more robust subsidence or drier air pushes into the region, it
is tough to go with a dry forecast during this time of year, so will
maintain the 20-pop parade through the entire forecast. There will be
days with higher coverage and those with lower coverage, but those
details are too mesoscale to resolve at this kind of time range.
Temperatures offered by the European model (ecmwf) and GFS are largely climatology-based,
with highs around 90 and lows in the upper 60s (and little variation
among the various ensemble members). These are acceptable with the
expected pattern, since the troughing should keep the high-amplitude
ridge (and hotter conditions) at Bay.
Bcc
&&
Hun watches/warnings/advisories...
Alabama...none.
Tennessee...none.
&&
$$
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