Area forecast discussion
National Weather Service Memphis Tennessee
304 PM CDT Tuesday may 21 2013
Discussion...
very active radar this afternoon. Overnight/early morning
convection may have US from a much more significant severe
weather outbreak today...although severe potential still
exists...especially across north Mississippi. Farther north the
airmass has been worked over...and abundant cloud cover has kept
temperatures quite a bit cooler. Instability is highest in north
Mississippi where temperatures have been able to climb into the
middle and upper 80s. Dew points are in the upper 60s to lower 70s
resulting in convective available potential energy in excess of 2500 j/kg and lifted indice's below -6c. Just
across the state line in most of Tennessee...the Missouri bootheel and
northeast Arkansas...convective available potential energy are generally below 1500 j/kg with lifted indice's
-4c or greater. Dew points are also slightly higher. In the past
couple of hours storms have developed in north Mississippi and
have shown some signs of rotation. 0-3km helicity is generally
50-90m^2/s^2 which would certainly support rotating storms. Upper
level support is not currently as favorable for severe
thunderstorms...although better support is expected to move in
tonight.
Another round of storms can be seen over North Texas into
Oklahoma. This line will bring additional showers and
thunderstorms to the midsouth overnight. Numerous outflow
boundaries will only help support focus updrafts and maintain a
severe threat.
A shortwave trough currently over the Texas and Oklahoma
panhandles will shift to the east this evening and approach the
Mississippi River by sunrise. A surface low has developed over
North Texas and should track northeast across central Arkansas
during the night. We will see a 40-45kt low level jet develop by midnight
and much of the midsouth will be in the right entrance region of a
70-80kt upper level jet. This additional dynamic support will move
in just as we lose daytime thermodynamic support. Thus feel like
the threat for severe weather will remain about the same during
the night...marginal but certainly not zero.
Researchers at Mississippi State University launched a weather
balloon midday about 30 miles southwest of Greenwood Mississippi.
It shows a bit of a cap at 10kft...but cape in excess of 3500
j/kg. Farther north at Little Rock a midday sounding was
indicative of a worked over environment...featuring only 343
joules of cape. Any threats from storms in west Tennessee and east
Arkansas would be primarily hail.
A cold front will sweep across the midsouth tomorrow bringing an
end to the precipitation. The front should move into east Arkansas
by 10 am...cross the Mississippi River midday and exit into
central Tennessee/north Alabama during the middle afternoon hours.
Rain will likely limit temperatures again tomorrow but as rain
ends...we could see temperatures surge into the low 80s during the
afternoon hours. The diurnal temperature profile will likely be
tricky tomorrow due the rainfall and front.
Thursday through the weekend look mostly dry. Temperatures Thursday
will be near normal...with coolish Friday...then trending
gradually warmer through the weekend. Friday through the weekend
our weather should be primarily influenced by a weak ridge aloft
and surface high pressure resulting in dry conditions.
&&
Aviation...
18z taf cycle
Complex weather pattern for this afternoon and evening. Ongoing
convection..mainly over north Mississippi at this time..will
continue to develop and briefly affect terminals this afternoon.
Winds out of the south at around 10kts are expected at all sites
this afternoon...with some brief gusty winds generated by nearby
ts. Overnight..expect thunderstorms to increase in coverage and
move from west to east with strong wind gusts to 20kt possible.
Thunderstorms will move east of the midsouth between 10-12utc
with additional showers expected through the morning.
Sak
&&
Preliminary point temps/pops...
mem 69 83 61 82 / 80 60 10 10
mkl 67 81 58 81 / 70 60 10 10
jbr 65 82 57 80 / 90 40 10 10
tup 67 83 60 86 / 70 70 10 10
&&
Meg watches/warnings/advisories...
Arkansas...none.
MO...none.
MS...none.
Tennessee...none.
&&
$$
