155 
FXUS64 KMOB 221159
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
659 AM CDT Sun Aug 22 2021

.AVIATION...
12Z issuance...VFR conditions were observed across the area early
this morning. These conditions are expected to persist through 
the period with the exception of temporary MVFR to IFR ceilings 
and/or visibilities in and around the heavier convection that may 
develop. Generally expecting scattered showers and thunderstorms 
to develop this afternoon, with the greatest coverage occurring
along the coast. By mid to late evening, showers and storms 
should decrease to more isolated coverage. Winds will remain 
southwesterly to westerly. /14


&&

.PREV DISCUSSION... /issued 503 AM CDT Sun Aug 22 2021/ 

NEAR TERM UPDATE /Now Through Monday/...An upper level low 
resides over the Mid-Atlantic states and will slowly Fujiwara with
Hurricane Henri along the northeastern coastline of the U.S. 
today. This interaction will pull Henri inland over the 
northeastern U.S. and pivot the trough axis (associated with the 
upper level low) to the east through Sunday evening. The upper 
level ridge over the ArkLaTex region seizes this moment to build 
in further east over the region gradually transitioning flow aloft
from northerly to more northeasterly by Monday. Weak disturbances
within the flow between the trough/ridge pair continue to 
percolate across the southeastern U.S., with a transient mid to 
upper level disturbance coming through Sunday afternoon and 
evening. A broad and very weak surface high meanders around the 
northern Gulf of Mexico through the period while a weak surface 
trough over central Alabama and Georgia slowly sags south on 
Monday. 

It sounds like a broken record, but we are once again expecting 
scattered showers and thunderstorms across the area today. With the 
trough axis shifting east and more ridging over our area, it stands 
to reason that the best coverage will be mainly over the eastern and 
southern portions of the CWA, with more isolated to scattered 
convection over northwestern portions. SBCAPE values upwards of 
2,500j/kg with MLCAPE values towards 1,500j/kg will aid in 
thunderstorm development in the afternoon. Some slight drying in the 
mid levels may promote stronger downdraft production, reflected in 
higher DCAPE values of 750 to 1,000j/kg. Although 2+ inch PWATs are 
still maintained across southern portions of the CWA, these values 
do come down slightly in our northern counties, generally in the 1.9 
to 2.1 inch range. This is still more than enough to foster heavy 
rainfall potential in thunderstorms, and minor nuisance flooding 
will be of concern where stronger storms develop on Sunday. Model 
guidance suggests convection may linger into the late evening hours 
Sunday, remaining isolated to scattered in coverage. Sundays highs 
will top out in the lower to middle 90's. Sunday night will see lows 
in the lower to middle 70's. Heat indices will range between 100 to 
106. 

Convective activity looks to be slightly less on compared to what
we've seen the last few days. Mid level dry air continues to 
filter in to the area, and PWATs start to come down a good bit in 
the 1.5 to 1.8 inch range. At the moment, opted to maintain 
scattered to likely PoPs, mainly across coastal counties where the
seabreeze will act as a source of forcing. PWAT's in these 
coastal areas are still around 1.8-2 inches, but if models 
guidance starts to bring the drier air further south, these may 
have to be adjusted down in future updates. Any storm that does 
manage to get going will have strong wind gust potential, with 
DCAPE values generally 1,000 to 1,300j/kg. With less cloud cover 
and convective coverage, Monday will be a fairly hot day with mid 
90's for highs, and some isolated spots reaching the upper 90's. 
Heat indices will range between 103 and 108. If confidence 
increases on heat indices reaching the upper end of this range 
over a larger area, a heat advisory may become necessary for 
Monday. 

A MODERATE risk of rip currents is in effect through Monday. Swell 
heights continue to trend downward to around 1 ft, although there 
appears to be a surge of long period swell around 10 seconds that 
approaches local beaches later this afternoon. For now, opted to 
keep MODERATE risk as this swell packet is not expected to linger 
for long. However, this is something we will continue to monitor 
throughout the day. 25/14

SHORT TERM /Monday night Through Tuesday night/...An expansive
upper level ridge of high pressure will remain centered over the
vicinity of the ArkLaTex Monday night into Tuesday and will 
slowly build east/northeast toward the Mid-Mississippi Valley 
region through Tuesday night. Our forecast area will remain 
positioned along the eastern and southeastern periphery of the 
upper level ridge through the short term period. Hot temperatures 
and rising heat indices will become an increasing concern early 
this week with the building ridge and this will be discussed a 
bit more in detail below. A weak surface trough of low pressure 
will meanwhile continue to extend from southern portions of 
southeast MS into interior southwest AL Monday night into Tuesday 
morning, but it does appear that this feature will gradually lift 
N/NW and become more diffuse Tuesday afternoon into Tuesday night.
Isolated to scattered convection may develop near the immediate 
coast and adjacent offshore waters Monday evening/night and will 
keep low POPs in the 20-30% range near the immediate coast through
the Monday night period. Precipitable water values will range 
between 1.7-2.0 inches across much of our forecast area by 
Tuesday afternoon across locations along and to the southeast of 
the surface trough axis. MLCAPE values also look to average 
between 1500-2500 J/KG across much of the region. The plentiful 
moisture and instability along with weak ascent provided by weak 
impulses in the northeasterly flow aloft and some low level 
convergence will aid in the development of scattered to locally 
numerous showers and thunderstorms across the region on Tuesday. 
The best convective coverage (50-60%) will be focused along 
southern portions of the CWA near the seabreeze, while slightly 
lower chances (20-40%) will be in place across interior southeast 
MS and southwest AL. A few storms will be capable of producing 
brief strong/gusty winds, frequent lightning, and locally heavy 
downpours. 

As mentioned above, heat concerns will increase early this week as
the ridge aloft expands eastward. High temperatures on Tuesday are
forecast to range between 93-98 degrees across most locations 
along and north of the I-10 corridor and slightly cooler between 
90-93 along the immediate coast and beaches. High afternoon dewpoints
between 70-75 inland and in the mid to upper 70s along the coast 
will likely result in maximum heat index readings between 105-110 
over much of the region. A Heat Advisory may become necessary over
a good portion of the forecast area Tuesday and we will need to 
monitor trends closely. Lows Monday night and Tuesday nights will 
continue to range in the lower to mid 70s inland and in the upper 
70s to around 80 degrees along the immediate coast and adjacent 
beaches. /21 

EXTENDED TERM /Wednesday Through Saturday/...A deep layer ridge is 
expected to be aligned from the Mid-Atlantic to Texas on Wednesday. 
The ridge is expected to weaken slightly late in the week as an 
inverted trough moves westward from the Atlantic into the 
southeastern states. The end result will be a continuation in the 
hot and muggy pattern with scattered to locally numerous showers and 
thunderstorms developing each afternoon. Rain chances may be 
slightly higher later in the period depending on how the 
aforementioned feature develops. High temperatures will begin in the 
lower to mid 90s but cool slightly to the lower 90s by late week. 
Hot and humid conditions will lead to heat indices in the 100-106 
degree range through at least Thursday. Lows in the low 70s inland 
to mid and upper 70s along the coast will continue. /13

MARINE...Light to occasionally moderate southwesterly to westerly 
flow will continue through Monday, becoming southerly on Tuesday.
Southeasterly flow will then take hold on Wednesday and will prevail 
through mid-week. Scattered to locally numerous showers and storms 
can be expected over the marine area each day. Frequent lightning in 
addition to higher seas and winds will be possible near any storms 
that develop. Seas will remain around 2 feet through Tuesday, 
building to 3 to 4 feet Wednesday and Thursday due to the 
southeasterly fetch. /14 

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk until 6 PM CDT this evening for ALZ265-266.

FL...High Rip Current Risk until 6 PM CDT this evening for FLZ202-204-
     206.

MS...None.
GM...None.
&&

$$

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