Severe Thunderstorm Warning 188, NWS Jackson, MS

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
121 PM CDT Sat May 26 2018

...THREAT FOR ALBERTO TO PRODUCE FLOODING IN EASTERN MISSISSIPPI IS
INCREASING...

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
Scattered to numerous TSRAs wl cont to develop across the area and
impact TAF sites this aftn into early evng. Away from TSRA
activity VFR conds wl prevail through this evng. A brief period
from 10Z-14Z MVFR Cigs wl be psbl over the se. Otherwise, VFR
conds wl prevail Sunday until TSRA activity dvlps again. /22/

&&

.DISCUSSION...
Mid morning water vapor imagery/RAP analysis showed circulation
around a weak low over our southeast Arkansas counties with a
shear axis extending south very near the Mississippi river. Local
wet microburst checklist and latest CAM guidance suggests storm
development in our southwest third could be vigorous this
afternoon including the potential for isolated pulse severe
storms. Damaging wind gusts will be the primary threat. Our PWAT
this morning was 1.78in and considering a relatively slow storm
motion to the east southeast locally heavy rainfall will also be
possible. Have updated our HWO to include a Marginal area
generally west of a line from Crossett Arkansas to Columbia
Mississippi. Temperatures were on track. /22/

Prior discussion below:

Today through Tonight: Summer thunderstorms expected around the
area again today. With abundant moisture remaining in place (PW
values of 1.7 to 1.9), storms will again be efficient rainfall
producers, and isolated flooding could be a concern in a few
spots. Analysis of water vapor satellite imagery reveals the axis
of a mid-level trough extends north to south over roughly the
LA/MS state line. Short- term guidance shows a vort max dropping
south from AR today through the base of the trough, and this could
excite convective activity in what will be a more convectively
unstable air mass over the Delta and surrounding areas this
afternoon. Forecast soundings show steeper low-level lapse rates
and a little better DCAPE through those areas, so there may be a
few isolated severe storms that develop by late afternoon.
Elsewhere, we will be watching for scattered strong storms
producing gusty winds and locally heavy rainfall. Storms will
linger into the evening hours and should generally die off by
later tonight. We could see some patchy fog develop again tonight.
/NF/

Sunday through next Friday: Expect an active period to be in
store with all focus on the eventual track of Subtropical Storm
Alberto. This morning Alberto is located just east of the Yucatan
Peninsula but is getting sheared from the west from mid-high level
jet stream winds. This is helping to keep the center of
circulation exposed all the while this large gyre will continue to
linger over the area. Expect this to be the main focus of the
long term forecast but just prior to the landfall and impacts
expect enough PWs for some convection to break out by Sunday
afternoon. Right now it doesn't look as though there should be
much of a severe potential as lapse rates are meager, flow is
light and and high moisture should limit overall downdraft and
hail potential. Couldn't rule out a few stronger storms due to
precipitation loading and some instability.

As Alberto lifts to the north and the upper jet that has been
shearing it begins to ventilate the system, expect some
redevelopment of the surface circulation to be possible closer to
the mid-level circulation. This will help the system become
somewhat better vertically stacked and a little more organized and
stronger. As the jet dives south and helps to continue ventilate
Alberto, expect it to begin a turn to the northwest towards the
area around Monday. Euro seems to have a good handle on the
system, which will keep most of the best upper lift and
ventilation along the eastern periphery of the circulation. Due to
that, expect the most intense convection along and east of the
circulation, which will focus the heaviest precipitation just east
of the area along Mobile Bay. Alberto is expected to make
landfall around late Monday into early Tuesday. Due to the upper
jet helping the storm to propagate to the northwest, definitely
feel there will be a sharp cutoff in overall QPF from west-to-
east. Sided towards the WPC QPF which shows a sharp cutoff in the
highest QPF in southeast Mississippi. For now, expect
deteriorating conditions on Memorial Day, especially along the
Gulf Coast and Pine Belt as it makes landfall near Mobile Bay.
After coordination with other offices and WPC, adjusted the QPF to
fit that area more. WPC has a "Moderate" for excessive rainfall
in the Gulf Coast and coastal Mississippi but due to a good amount
of uncertainty on center redevelopment, only kept "Elevated" and
"Significant" in the HWO/graphics in the east and especially in
the Pine Belt for decent rainfall totals of 3-5+ inches or so. Due
to high anomalous moisture and the overall setup, this could
bring some flash flooding to our area. In addition, Alberto could
bring some gusty winds upwards of 30+mph or so, especially along
the I- 59/Highway 45 corridors. Due to uncertainties on the
intensity and track, will hold off on any mention of wind in the
graphics but will have to maybe introduce this later. Stay tuned
and keep a close eye on future forecasts.

In the wake of Alberto by mid-week on Wednesday, expect it to
eject northeast and our region to be on the eastern periphery of a
strengthening mid-level ridge over northern Mexico and Texas.
This will help rain and storm chances to become more diurnal and
build to the east by late week. Due to strengthening ridge around
590-592DM at 500mb nosing in, expect highs to peak into the low-
mid 90s & heat stress could become a problem. There is some
potential we could get near heat advisory criteria by next
weekend. Main takeaway is warmer and more humid weather can be
expected by late next week. /DC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       85  68  86  69 /  76  31  25  23
Meridian      85  67  85  68 /  84  39  44  47
Vicksburg     86  69  88  69 /  63  31  36  11
Hattiesburg   85  67  84  69 /  84  39  53  50
Natchez       87  68  87  69 /  65  31  34  12
Greenville    87  70  88  70 /  55  31  35  12
Greenwood     85  69  88  69 /  65  31  35  18

&&

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

&&

NF/22/DC

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