Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 212122 CCA

Area Forecast Discussion
National Weather Service Jackson MS
417 PM CDT Sat Oct 21 2017


Tonight and Sunday:

Warm advection showers and a few thunderstorms continue to break
out over south and east central LA as deep moisture (dewpoints in
the mid 70s) pools along the Gulf Coast. All of this occurring
ahead of a storm system taking shape over the Plains which looks
to deepen as it approaches the MS valley. The scattered warm
advection showers will continue in the west overnight as a QLCS
gets going over OK/TX and approaches the westernmost parts of the
forecast area by sunrise Sunday.

By Sunday morning deep moisture will be in place as PWs approach
1.85 inches and surface dewpoints rise into the lower 70s. With such
moisture, very efficient rainfall will occur likely producing 2-3
inches before ending late Sunday night.

Also of concern will be a marginal risk of severe thunderstorms over
southeast portions Sunday afternoon. CAPEs of 1500-2500J/kg will
nudge northward into southeast MS while the deep shear increases to
30-40 knots. This may allow some of the more robust storms to
produce some damaging winds and/or hail. /26/

Sunday night through Friday:

By Sunday night, expect the deep longwave trough to be amplifying
& diving through the ArkLaTex & quickly towards & through the
ArkLaMiss. This will help cold front to quickly move through the
area overnight. There will likely be some anafrontal showers & a
few thunderstorms, with best PoPs & storms residing across eastern
Mississippi. This will be due to the fact of better lift & jet
dynamics/diffluence over that area. PWs will be just high enough
in the wake to help spark some shower & thunderstorm development
before midnight or so before drier air quickly filters in the
wake. Due to some lingering moisture in the +1.5-1.75 inch range
across eastern & southern zones (90th+ percentile), expect some
heavy downpours to still be possible. Kept the HWO going into the
night but likely will be earlier for any flooding threat across
the east.

As the trough ejects through & strong high pressure builds down
into western to southern Plains, this will help drive much drier &
cooler air into the region. This will help drive down PWs around
to half to three quarters of an inch. However, another deep &
anomalous trough will dig down even drier & colder environment in
the wake by mid-week. This trough is extremely anomalous, with
850mb temperatures & 500mb heights approaching only around the 1st
percentile or so. With only 1-4+ deg C at 850mb, this will bring
highs possibly some 8-10 degrees below normal by Wednesday
afternoon in the low-mid 60s. Went cooler for highs on Wednesday
due to that setup. Wet soils should limit some mixing but we will
be very dry with dewpoints falling into the mid 40s by Tuesday
with them falling into the mid-upper 30s by Thursday. Fire weather
concerns should be lower due to recent heavy rainfall but due to
humidity levels being below critical levels & strong pressure
gradient, this will have to be monitored around early-mid week.
Due to ~1025mb surface high over Texas & strong gradient on
Wednesday & developing low over the northern Plains Thursday
morning, winds will stay up enough in this environment to keep
lows from falling off too much. Went slightly cooler on lows
(still 5+ degrees below normals) but not too much due to factors
previously mentioned.

Another anomalous trough will dig down by mid-late week over the
western half of the nation, with the GFS & Canadian being slightly
faster & more progressive to move east. This is likely due to the
injection of a strong typhoon over the west Pacific, helping
buckle the pattern downstream. Similar to the upcoming cold front,
this has potential to be pretty chilly in the wake but likely in
store sometime next week. The Euro is slower with this cold
frontal passage & sided towards this slower solution due to
strong longwave amplification & strengthening high-latitude
blocking. Due to this slowed down PoPs moving in on Friday,
especially eastern half of the area until after the period. But it
could be even later into the weekend more rain & storms would be
possible if the new slower 12Z Euro solution pans out. /DC/


18Z TAF discussion:
Winds this afternoon will be out of the south/southeast at 10 to
15 knots with some gusts up to 25 knots, but should diminish
somewhat during the evening. VFR conditions will continue through
the afternoon and into the evening, but MVFR ceilings will begin
moving in from the west toward dawn. In the HBG vicinity, MVFR
conditions will be possible by 22/09Z as areas of fog develop.
After sunrise, showers and thunderstorms will increase from the
west through the end of the period. MVFR ceilings and visibilities
will accompany the convective activity./26/


Jackson       69  78  54  72 /  34  99  76  12
Meridian      65  79  59  73 /  17  84  92  19
Vicksburg     69  78  52  74 /  45  99  60   7
Hattiesburg   68  80  59  74 /   7  94  84  11
Natchez       70  78  52  72 /  45  99  54   6
Greenville    68  75  52  73 /  32 100  56  10
Greenwood     69  76  53  72 /  33  99  66  16





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