Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 141750 AAA

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1150 AM CST Thu Dec 14 2017

Updated for 18Z aviation discussion


18Z TAF discussion:
Mid and high level clouds will continue over the region through
Friday but VFR conds wl prevail. A cold front will move across the
southern half of the area this aftn and bring a wind shift to the
north but wind speeds wl remain less than 10kts. /22/


Satellite imagery showed mid and high level clouds across our area
south of Highway 82. These clouds will continue today. Mid morning
surface analysis had a cold front across our Delta region that
will continue shifting south today. This will be a dry cold front
that will reinforce the cool dry airmass over our area behind the
wind shift to the north associated with it. No changes to the
current forecast were needed with it. /22/

Prior discussion below:

Today through tonight: Expect a quiet period in the short term
through tonight. Latest RAP analysis and satellite imagery show a
split flow pattern with westerly flow aloft across the southern
stream. Mid to upper clouds were tracking east across our southern
counties due to weak isentropic lift. On the surface a cold front
was approaching the forecast area from the northwest. For today a
dry cold front will cross the region. Mid to upper level clouds
will continue to cross the forecast area due to isentropic lift.
Minimum RH values will be above 40 percent for any fire weather
issues. Highs today will be from the lower 50s north and lower 60s
south. An upper level disturbance will be approaching from the
Southern Plains for tonight. It will be a colder night with lows
from the middle 20s north to around 40 south. Precipitable water
will increase in the south to around 0.80 inches. /17/

Friday through Wednesday: A seasonably cool continental polar
airmass associated with a progressive thermal trough crossing the
area will combine with considerable cirrus and northerly breezes
to bring uncomfortably chilly conditions Friday. The weather
should stay dry over the ArkLaMiss with strong mid/upper level
convergent flow helping to suppress deeper moisture to well south
of the area, however would not rule out very light precipitation
along/south of the Hwy 84 corridor Friday afternoon. If skies
clear out enough Friday night, temperatures could dip well into
the 20s. As the CP air retreats and warm advection develops,
temperatures will warm up Saturday with developing warm advection.

Going from the weekend into early next week, a major weather pattern
change will take place for the ArkLaMiss. The eastern CONUS longwave
trough that has been in place for weeks now will be replaced by a
ridge, and this will promote moist southwest flow aloft over the
region as we go later into early next week. Many locations have not
observed a daily rainfall amount of 1+ inch since early August, but
this could change given the forecasted pattern favoring persistent
convective rainfall and precipitable water values > 1.5 inches.
Initially, the primary shortwave trough of interest will be passing
through the area Sunday. Strong wind shear would be supportive of
organized deep convection, but high pressures and limited
destabilization due to the limited duration of boundary layer
moisture transport into an initially dry airmass will limit
convective intensity. Nonetheless, it will be a good idea to monitor
this system for strong/severe storm potential should warm advection
manage to over-achieve.

Following this system, expect upstream shortwave energy to bring
additional rounds of convective rainfall and perhaps increasing
heavy rainfall potential as we go from early into mid week per
guidance consensus. /EC/


Jackson       60  35  51  31 /   0   0   4   3
Meridian      61  34  49  30 /   0   0   4   3
Vicksburg     60  32  52  31 /   0   0   4   2
Hattiesburg   62  40  50  32 /   0   2   7   4
Natchez       61  36  51  31 /   0   2   5   3
Greenville    56  31  50  31 /   0   0   3   1
Greenwood     56  29  49  30 /   0   0   3   2





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