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Area Forecast Discussion (AFD)

Issued by Jackson, Mississippi (JAN)

FXUS64 KJAN 191751 AAA

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1251 PM CDT Wed Jun 19 2019

Updated for 18Z aviation discussion


18Z TAF discussion: 
Scattered TSRA wl affect TAF sites in the east this aftn as an
outflow boundary continues shifting east. TAF sites cntrl and west
may not see TSRA activity until around 06Z Thu provided another
outflow boundary moves into the area. Otherwise, VFR conds will
prevail until 11Z Thu when MVFR cigs are expected to develop and
take until after 16Z to scatter out. /22/


Local radars showed a band of thunderstorms just west of the
Mississippi River that are associated with a decaying MCS that has
pushed east this morning. Models are not handling the boundary 
well but, this boundary will remain a focus for additional 
thunderstorm development this afternoon as it drifts further into 
Mississippi. Some of the storms may become severe with damaging 
wind gusts and hail. The HWO has been updated to reflect a greater
area to the south under a "SLIGHT" and "Marginal" for this 
afternoon and tonight. Have increased pops in the west and lowered
afternoon highs several degrees to account for the early 
thunderstorm development. /22/ 

Prior discussion below: 

Today and Tonight: Impressive mid level shortwave moving through 
southern KS at the moment responsible for MCS moving across OK/north 
TX. CAM guidance is mixed on evolution of this convective system as 
it moves across AR and eventually toward our area later this 
afternoon. At present the system looks to decay before moving into 
the forecast area, but its outflow will be moving into a moist 
unstable airmass over the ArkLaMiss Delta region this afternoon. 
This should ignite scattered convection in these areas, but of 
greater concern will be the next convective cluster that develops 
over the ArkLaTex region during the late afternoon and eventually 
moves into the forecast area later in the evening. By this time, 
stronger shear and better lapse rates will have moved into the 
region with the mid level feature. Shear and instability look to be 
as such for rather robust convection mainly over the northern half 
of our area overnight and into early Thursday morning, with 
damaging wind and large hail as the primary threats. /GG/

Thursday through Tuesday:  The consensus of model guidance has 
backed off some on precip lingering into Thursday, but given the 
overnight activity, a Marginal threat for isolated strong to 
severe thunderstorms may continue into the morning hours. The 
ECMWF is more aggressive with spreading convection southward 
toward the Gulf Coast through the day on Thursday, however mid-
level capping may be too much to overcome farther south as deep 
layer shear eases and a shortwave ridge begins to move overhead. 
Showers and thunderstorms cannot be entirely ruled out for Friday,
especially if returning southerly flow can help any seabreeze 
convection to spread northward. Then it looks like the next best 
chance for more than a few isolated showers or storms will be next
Monday into Tuesday time frame as a low pressure system moving 
eastward across the country brings some height falls and increases
convection at least to our north and west. For now it appears the
associated frontal boundary will stall out before dipping into 
our forecast area, but we will continue to monitor the trends for 
this early week setup.

Now for the other summertime impact that will be felt this week - 
heat. With the convection looking to be a little less expansive on 
Thursday, the cap should allow for dangerous heat conditions to 
build into southwestern portions of our forecast area this Thursday 
afternoon. With dewpoints expected to remain in the low to mid 70s 
throughout the day and temps climbing into the low 90s, calculated 
heat index values in the 103 to 105 degree range look to be most 
likely from around Hattiesburg, MS extending north and west toward 
Bastrop, LA. A Limited Heat threat has been included for areas south 
of this line on Thursday. The heat will continue to build into 
Friday as mid-level ridging increases and onshore flow keeps 
dewpoints high. The Limited Heat threat area has been expanded on 
Friday to include all of northeast Louisiana, far southeast 
Arkansas, and areas in Mississippi southwest of a line from 
Greenville to Jackson to Hattiesburg. Peak heat index values of 
around 105 are expected to be more common, especially if convection 
looks to be limited for the day. A Heat Advisory may be needed for 
parts of the area on Friday if this setup looks to hold true. Better 
mixing on Saturday may allow for the heat to be lessened somewhat, 
so will hold off on advertising a heat threat over the weekend for 
now. Be sure to stay cool and hydrated as we end the week, and check 
on neighbors and the sick and elderly. /NF/


Jackson       90  73  91  74 /  70  31  34  16 
Meridian      91  73  92  74 /  50  25  35  24 
Vicksburg     89  74  91  76 /  22  34  29  14 
Hattiesburg   92  73  93  75 /  32  11  23  15 
Natchez       89  74  92  75 /  14  21  17  14 
Greenville    90  73  90  76 /  44  57  39  20 
Greenwood     90  72  89  76 /  50  59  50  24