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Area forecast discussion 
National Weather Service Jackson MS
436 PM CST sun Dec 21 2014

short term (tonight through Tuesday night)...low clouds have held on
throughout the day across much of east and southeast Mississippi...
holding temperatures down in the lower 50s. Elsewhere better
insolation and the beginnings of return flow has allowed
temperatures to warm into the lower 60s. Big changes are on the way
with increasing rain chances over the next few days.

Latest upper air analysis places upper troughing over the central
US...with an impressive upper jet streak (170-180 kts) entering the
Pacific northwest. At the surface...lingering ridging over the
eastern states is losing influence over our area as pressures lower
across the plains in advance of the approaching storm system. Surface
pressures will also fall over the northern Gulf as improving jet
dynamics interact with an old frontal boundary currently located
offshore. Tonight this front will begin to lift northward as a warm
front...with surface winds becoming southerly across the area.
Considerable low cloudiness will develop tonight as isentropic lift
increases in this warm advection regime. Given this setup and the
likelihood of a persistent breeze overnight...opted to trend min
temperatures toward raw guidance.

On Monday the upper jet streak will begin to round the base of the
trough as a surface low develops over the Dakotas with a trailing
front extending southward into the Red River valley. Strong warm
advection will continue over our region...with isolated to scattered
showers possible through the day. With 60s dewpoints beginning to
nose northward into the southern half of the area...there will be
some surface based instability along with ample shear thus thunder is
also possible. Mesoscale and high-res models suggest linear or
quasi-linear convection developing after sunset ahead of the front
near the MS river...pushing eastward overnight. While much of this
convection will be elevated...prognosticated sbcapes up to 500 j/kg are
depicted as far north as the Delta. Overnight as the warm sector
continues to advance into the forecast area...additional convection
will be possible farther east. With shear remaining more than
sufficient...some severe storms cannot be ruled out.

By Tuesday morning the strong jet streak will be lifting into the
Ohio Valley leaving the lower Mississippi Valley under the strongly
divergent right entrance region. This will spur on surface low
development along the Gulf Coast during the day. While there has been
considerable spread in potential track of this surface low over
previous model runs...there seemed to be a growing consensus among
12z guidance in a track generally from near Natchez to near Jackson
to near Tuscaloosa by the late evening. While the Euro and GFS
indicate a more well-defined surface low...the NAM depicts a weaker
low/broad troughing. Nevertheless persistent warm/moist advection will
continue over the eastern two thirds of the County Warning Area...with middle 60s
dewpoint potentially reaching the I-20 corridor by the late
afternoon/evening hours. Across the warm sector showers and
thunderstorms will be likely through the day and into much of the
evening. With regards to severe potential...questions remain over
whether convection either along the Gulf Coast or farther north
throughout the warm sector will prohibitively stabilize the
environment. If these potential negative factors fail to
materialize...a more substantial severe weather threat could be
realized across south and east portions of the area. Due to the
uncertainty...a limited threat will be maintained in severe weather potential statement/graphical
products...though this may need to be adjusted as confidence
increases in the way things will evolve on Tuesday. Barring a change
in the forecast track of the low...there will be no substantial threat
for strong/severe storms in areas farther west...including most of
the Delta on Tuesday. Heaviest rainfall potential will also be mainly
east of the east of the surface low track. Any potential
for severe weather will end later on Tuesday night as the low and
surface front move eastward out of the state...though Post frontal
showers will continue overnight. /Dl/

Long term (wednesday through next weekend)...lighter rain
showers...drizzle...and clouds may take until later Wednesday to
entirely clear out of the region. If the 00z op Euro model is right
the improvement of conditions may happen a little quicker than this
although the op GFS (with its closed trailing upper low) can not yet
be discounted. This GFS solution may even hold some wet Snowflake
potential for some of our neighbors to our north...but that really
looks to be out of the realm of possibility for our neck of the

In fact...seasonably chilly conditions in the wake of the system
look to really only last through Christmas day with temperatures
warming by the day after. But this weather pattern has gotten a
little active again and we should only have to wait until later next
Friday or Saturday for another frontal passage and at least minor rain
chances. At this time this scheduled front holds more potential to
usher in a change to colder regime that lasts for a while. /Bb/


Aviation...clouds have cleared most locations except for along and
southeast of the Natchez trace. MVFR ceiling restrictions continue
to plague kgtr/kmei/kpib/khbg this afternoon. Ceilings will
eventually lower again tonight ahead of an approaching storm system.
MVFR to IFR ceilings are expected. Some fog will be possible before
daybreak. /28/


Preliminary point temps/pops...
Jackson 47 68 61 72 / 5 21 57 85
Meridian 47 66 60 69 / 11 23 58 86
Vicksburg 46 69 58 69 / 4 23 50 82
Hattiesburg 49 71 62 71 / 13 27 57 81
Natchez 48 70 60 71 / 5 23 47 87
Greenville 44 63 54 61 / 4 33 53 65
Greenwood 45 64 56 68 / 5 26 62 71


Jan watches/warnings/advisories...



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