Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 210600

Area Forecast Discussion
National Weather Service Jackson MS
100 AM CDT Mon Aug 21 2017

Updated for 06Z aviation discussion


06Z TAF discussion:
Other than brief MVFR visibilities around dawn with ground fog,
VFR conditions will prevail through the period./26/


Shower and thunderstorm activity has diminished this evening, with
mostly clear skies expected overnight. Lows will be in the low to
mid 70s, with some patchy fog possible towards daybreak. No
changes were needed to the current forecast. /27/

Prior discussion below:

Expect another muggy night tonight after the evening stray
showers and storms diminish by a few hours after sunset. Lows will
be in the low to mid 70s with only a few patches of light fog
around at daybreak.

Tomorrow, the subtropical ridge aloft over the Lower MS Valley
will start lessening its grip a bit, but certainly not in a
dramatic way. Convective suppression will not be as much as today
and we should see a little better coverage of afternoon showers
and storms in at least southern and western zones. Of course the
biggest story in the sky tomorrow will be the partial eclipse
overhead starting in the late morning and ending in the mid
afternoon. The partial insolation blockage in our region will
peak shortly after 2 pm and we actually anticipate enough shade to
cause at least a little temperature decrease during the time of
day usually reserved for peak heating. This shade will certainly
be welcome because otherwise the continued hot regime would be
unabated and more heat advisories would likely be necessary.
However, since we are taking the eclipse into account, our current
thoughts are that heat indices will remain too marginal for
another heat advisory (but of course the next shifts will be
examining that aspect of the forecast closely). Also, keep in
mind the shade and somewhat reduced associated instability during
peak heating will probably mean computer models (which don`t take
the eclipse into account) will probably overdo afternoon
convection here. That potential bias was kept in mind when doing
the forecast. /BB/

Monday night through Saturday: Come Monday night the eclipse will be
over but a 594dam ridge axis will continue along the Highway 82
corridor while a TUTT axis pokes up over our northeast Louisiana
parishes from the northern Gulf. Both of these features will weaken
Tuesday as mid level troughing develops over the eastern CONUS and
the TUTT shifts farther west over the Texas coast. Afternoon
temperatures in the low to mid 90s Tuesday will combine with high
relative humidity in our west for peak heat index values to range
from 101-104. A Heat Advisory is not currently anticipated for
Tuesday but, cooler temperatures and lower relative humidity look to
mitigate heat stress related concerns the remainder of the week.

A closed low swinging across Ontario and into Quebec Tuesday night
into Wednesday will send a cold front into the region Wednesday.
Although there appears to be very little convergence across our CWA
when the cold front drops in, 2 inch PWATs look to pool across our
CWA ahead of it. Lower heights aloft and daytime heating should
contribute to a good coverage of convection Wednesday afternoon into
the early evening hours. By Thursday morning the cold front is
expected to be near our Highway 84 corridor with dew points in the
60s north of Interstate 20. Continued northwest flow aloft Thursday
will support a >1020mb high dropping over the Great Lakes region and
nudging the The front south of our CWA. By Friday morning, a much
drier airmass will have filtered into our whole CWA with dewpoints
in the 60s areawide. Although mid level ridging will strengthen over
the region Saturday, the surface high will shift east slowly through
the weekend. This will keep the Gulf closed over our area and hold
deep moister at bay while temperatures warm. Cooler than normal
afternoon highs are expected Thursday and Friday; mainly in the
upper 80s. Afternoon highs will top out closer to normal Saturday
and Sunday but due to the drier airmass remaining over the region,
peak heat index values will not reach critical values. /22/


Jackson       74  93  74  91 /   9  24  14  56
Meridian      74  92  74  91 /   9  30  21  60
Vicksburg     74  94  74  91 /   8  23   7  56
Hattiesburg   74  92  73  92 /  15  41  19  52
Natchez       74  91  73  92 /   9  27  10  56
Greenville    75  94  74  89 /   6  18  11  56
Greenwood     74  93  74  88 /   7  24   9  64




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