Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson MS
358 PM CST Sat Dec 20 2014
Discussion...it has been a rather nice day after yesterdays
raw...rainy day. Morning clouds have been dissipating through the
day but some locations in the south have been shrouded in clouds
through the day. Dry weather will continue for the rest of the day
and Sunday. There could be a small chance for some light rain for
the Pine belt/southeast Mississippi Sunday evening as a low pressure
system moves across the northern Gulf. However I did leave this out
of the forecast as it appears this will remain out of the County Warning Area.
The main forecast concern continues to be the next weather system
that will affect the region starting Monday night through Tuesday.
Early on Monday an upper trough and surface low will drop south out
of Canada toward the Ohio Valley. This will drop a cold front toward
our region. By early Tuesday another surface low will develop across
Texas/Arkansas and track northeast across generally the southern states. The
track of this surface low is still not being handle consistently between
the GFS/ECMWF/NAM. The GFS and European model (ecmwf) bring the surface low across
northwest Mississippi and the Delta Region. If this is the
case...this isnt an optimal place for severe weather across our
area. However the NAM shows the low tracking across Arkansas which
would be much better placement for severe weather to occur over our
region. Models...particularly the NAM which has been a little more
bullish though other models are trending toward that...show the
atmosphere destabilizing Monday night. 35-40kts of 850mb flow will
be pumping moisture into the region by Monday night. Models are
showing that at 06z Tuesday there will be plenty of wind shear(30kts
0-1km and 50-55kts 0-6km) and surface based and most unstable cape
will be increasing across the area. By 12z...models show near
1000j/kg of mu cape. In addition...vertical totals from Monday night
through Tuesday will be 27-29c given -15 to -16c 500mb temperatures.
This will imply some better organized storms and potential for hail.
All of this indicates some potential for severe storms to be
possible even Monday night. Therefore we have gone ahead and
included Monday night in our graphics and severe weather potential statement as well as Tuesday.
Helicity values are not exceptionally high but are sufficient and
maximized Monday night. This indicates that this actually may be the
better time window for tornadoes. By Tuesday...helicity values
decrease and this may indicate that the higher risk on Tuesday would
be from damaging winds. Will continue to include mention of
tornadoes...wind and hail through Tuesday. One negative factor in
all of this is that heights appear a little lower than what would be
optimal for this time of year. Nevertheless will continue to monitor
later model runs.
The deepening surface low will track off into the Ohio Valley region
through Tuesday into early Wednesday. This will drag a cold front
through the region and rain will exit late Tuesday and early
Wednesday. The 531dm upper low will move across the lower Ohio
Valley and some wrap around moisture will affect our northeastern
counties. This cold core may allow for some light snow mixing with
light rain but have kept this out of the forecast for now and no
accumulation would occur. Surface high will move in along with upper
ridging for Christmas evening night and Christmas day. Dry weather but
cooler/mild temperatures will prevail.
Our next round of rain will come late Friday night into Saturday.
Both the European model (ecmwf) and the GFS arent terribly impressive with the trough
and swing it through fairly quickly Saturday before ridging resumes
Sunday into Monday. /28/
Aviation...mainly VFR conditions expected all taf sites expect for
kmei and khbg. MVFR ceilings expected to hang tough at khbg through the
forecast period. Partial clearing was leading to improved ceiling
categories at kmei but expect clouds to redevelop tonight there.
Some light fog possible late tonight at all sites. /SW/
Preliminary point temps/pops...
Jackson 35 60 44 66 / 3 5 9 9
Meridian 35 59 43 65 / 5 5 9 9
Vicksburg 34 59 42 67 / 3 5 9 9
Hattiesburg 41 64 46 69 / 5 7 10 14
Natchez 37 59 46 67 / 3 5 9 9
Greenville 34 54 43 65 / 3 5 8 8
Greenwood 32 59 43 64 / 3 5 9 8