Area Forecast Discussion
Issued by NWS Jackson, MS

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000
FXUS64 KJAN 040613 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1213 AM CST Sun Dec 4 2016

.UPDATE...
Updated for 06Z aviation discussion

&&

.AVIATION...
06Z TAF discussion: A narrower channel of rain will continue over
the the majority of the TAF sites overnight. Meanwhile, the back edge
of the widespread rain shield will move into the GLH area by 04/11Z
and slowly traverse east through the TAF period, exiting MEI by
05/03Z. The rain looks to hang on at HBG throough the end of the
period. Once the rain does end there will be no change in flight
categories with low ceilings and visibilities reduced by fog
continuing to support IFR/LIFR./26/

&&

.DISCUSSION...
As of 03z, a sfc ridge is currently centered over OH with an
inverted sfc trough across south central LA into SW MS and a stalled
front/baroclinic zone along the Gulf Coast. Gusty easterly winds at
the surface in association with the pressure gradient between the
aforementioned high and inverted surface trough, combined with
overcast skies and rainfall helped to reinforce a cold sfc layer and
kept temps in the 40s across much of the area. Meanwhile, an elevated
boundary lifted north across the area this afternoon resulting in
veering of the mid level winds and thus inducing WAA and positive
ThetaE advection across the area. A significant warm nose was also
noted per the 00z JAN sounding. Enhanced frontogenetical forcing with
the boundary also helped to maintain a narrow band of higher rainfall
rates as the boundary moved through. Isentropic ascent ahead of and
behind the boundary resulted in widespread stratiform rain throughout
the day today across the majority of the area with most locations
receiving measurable rainfall. The highest totals were located in
our NW where upwards of 3" has fallen per latest dual-pol radar
analysis.

For the rest of the evening and into tomorrow morning, latest model
guidance is in agreement on the SW to NE oriented inverted surface
trough moving through south central MS. Enhanced frontogenesis and Fn
vector convergence along the trough axis in concert with 45-55kts of
mid level southerly flow partially influenced by a diabatically
enhanced internal PV anomaly will result in the highest rainfall
totals oriented along a line from HEZ to just NE of JAN with the max
shifting towards the HBG to MEI area into tomorrow morning as the
trough pushes east. Kept thunder mention as an area of MAUL will also
be present. The heaviest rainfall totals will be in the SW near HEZ
with lower totals across the NW where isentropic descent behind the
trough will limit more widespread rain and will gradually clear out
the remaining showers. Overnight temps will not moderate much and
stuck with a raw blend for min temps. /TW/

Prior discussion below:

Tonight through Sunday,

The new forecast generally carries over from the previous forecast
in the near term with broad isentropic ascent expected to continue
producing light to moderate rainfall over most of the ArkLaMiss this
weekend. Greater moisture flux and lift are occurring over
northeastern Louisiana into western Mississippi so far today, and
that is where rainfall totals are adding up to near two inches in
some cases. There is evidence of MAUL as suggested by localized
intense rainfall rates (dual pol instantaneous rates > two inches)
within strongly forced convective looking radar signatures, but
these heavier bands are progressive enough to keep hourly rainfall
rates well below flash flood guidance values.

Per coordination with WPC, rainfall rates overnight into Sunday
should not produce flash flooding, and will thus not include this
period in the flood graphic that has been issued for Monday`s
greater heavy rain concern. Otherwise, expect raw, rainy conditions
that have seemingly heralded in the start of winter to continue for
most of the forecast area. /EC/

Sunday night through early next weekend...

One of the most wet, active periods we`ve experienced in some time
will continue Sunday night through Monday night as moisture
overspreads the area ahead of a potent upper shortwave. Precip
coverage will begin to decrease areawide on Sunday night as the
first shortwave lifts out of the area. Lows Sunday night will only
fall a few degrees less than the high on Sunday due to ample
moisture and significant cloud coverage.

Monday: Models agree on a closed low with origins near the Baja
Peninsula crossing Northern Mexico and beginning to approach the
Lower Mississippi River Valley as its associated surface low rides
along the northern shore of the Gulf of Mexico. southwesterly flow
ahead of the approaching low will result in moisture increasing
throughout the area Monday morning. By late Monday, the once closed
upper low will begin to approach the region as a potent upper
shortwave. Th potential for severe weather will begin to increase as
the surface low begins to lift through the area and shear and
instability increase. Timing is still somewhat uncertain but there
was enough certainty in the severe potential remaining through
the early portions of Monday night to expand the limited mention in
the HWO for Monday into Monday night.

Flash flooding will also be a threat on Monday due to the increased
potential of convective storms producing higher rainfall rates than
what we`ve seen already today and what is expected on tomorrow.
These higher rainfall rates combined with an already saturated
ground resulted in the addition of a limited flood threat areawide
on Monday and Monday night. WPC has included the western and
northern portions of the ArkLaMiss in a slight risk area for the
threat of rainfall exceeding flash flood guidance.

Tuesday onward: Rain chances will begin to decrease early Tuesday as
the upper disturbance and surface low begin to lift out of the
region and surface high pressure begins to filter in. Temperatures
will be near their normal values on Tuesday and Wednesday. Moisture
will increase ahead on a reinforcing front that will track through
the region on Thursday. The Euro depicts the more bullish solution,
increasing precipitation chances area wide, while the GFS took the
more conservative, dry approach. Went with a blend of both.
Nonetheless, long term models agree on a cold, arctic airmass
filtering into the region behind the front. Some of the coldest
December temperatures the ArkLaMiss has seen in some time will exist
behind the front. Lows on Friday and Saturday mornings will dip into
the lower 20`s areawide with some upper teens not out of the
question for our northern most counties. Wind chills in the lower
teens on Friday morning will make for dangerous conditions. Highs on
Friday will struggle to reach 40 degrees. /JPM3/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       54  50  63  51 /  77  72  88  77
Meridian      57  51  64  54 /  90  71  87  82
Vicksburg     53  49  61  48 /  54  74  90  65
Hattiesburg   67  56  69  54 /  94  67  80  72
Natchez       55  49  62  49 /  63  78  90  56
Greenville    51  46  55  48 /  48  59  86  75
Greenwood     51  46  58  49 /  72  60  87  84

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.

&&


$$



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