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Area Forecast Discussion (AFD)

Issued by Mobile/Pensacola (MOB)

FXUS64 KMOB 191602 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1102 AM CDT Wed Jun 19 2019

.DISCUSSION...See updated information below.


.UPDATE...Have decided to increase rain chances mostly over 
northern and western sections of our forecast area this afternoon
and this evening. Current visible satellite loops continue to 
show a well defined outflow boundary to our west likely reaching 
our western zones later this afternoon. With decent surface based 
instability, capes running above 2k for most inland areas 
already, sufficient moisture up to 5 kft combined with continued 
mid level forcing due to another weak mid level impulse 
approaching from the west also we will likely see better coverage 
than earlier anticipated. With these conditions along with plenty
of dry aloft a few strong thunderstorms will also be possible 
leading to gusty straight line winds, frequent cloud to ground 
lightning along with short durations of very heavy rain. Stay 
tuned to local media outlets or NOAA weather radio if threatening 
weather is approaching your area. 32/ee 


.MARINE...A moderate to occasionaly strong southwest wind flow 
will persist over the marine area through Thursday evening in 
response to a weak upper level system slowly tracking eastward over 
the north central Gulf states, combined with a strong surface ridge 
of high pressure building west over the eastern and north central 
Gulf. Winds and seas will slowly diminish Friday through early next 
week as the ridge of high pressure to the east continues to build 
west. Scattered showers and thunderstorms will continue over the 
marine area through Friday with less coverage over the weekend and 
early next week. Gusty straight line winds, frequent cloud to ground 
lightning and isolated waterspouts will be possible with some of the 
stronger thunderstorms through Friday. Small Craft Should Exercise
Caution for most marine locations through this evening. 32/ee 


18Z issuance...Expect mostly VFR conditions through 20.18z. Could
see short periods of MVFR to IFR cigs mainly in heavy rain from
scattered showers and thunderstoms later today and this evening
tapering off overnight. Showers and thunderstorms will be moving 
from west to east through the forecast period with a few strong 
storms possible this afternoon and evening. Gusty straight line 
winds, frequent lightning and heavy rain will be the main threats 
with the stronger storms. Winds will be mostly southwest at 10 to
15 knots with slightly higher gusts through this evening 
diminishing to 5 to 10 knots overnight through early Thu morning.


.PREV DISCUSSION... /issued 636 AM CDT Wed Jun 19 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

12Z issuance...Radar shows an eastward advance of isolated AM  
coastal shra/tsra. CIGs are mostly at high levels but occasional 
lower bases at upper end MVFR categories possible with passage of 
isolated to scattered shra/tsra today. Occasional MVFR vsby with 
passage of convection as well. Thru the day, a gradual increase in
southwest winds could become gusty at times. /10

PREV DISCUSSION... /issued 414 AM CDT Wed Jun 19 2019/ 

NEAR TERM /Now Through Wednesday night/...Radar data shows 
isolated to scattered showers and storms confined to the Northwest
FL Panhandle Gulf coast this morning and offshore. Repeated storm
motions over the same area resulted in isolated pockets of 3 to 6
inch rain accumulations near the Gulf Breeze FL area earlier in 
the forecast shift. This prompted short-fused Flood 
Statements/Warnings for increased potential of flooded roads. 
Fortunately, a gradual eastward shift in the precipitation is 
occurring as an upper level short-wave trof over western AL also 
migrates east. Latest mesoscale analysis also indicates a west to 
east zone from the MS Sound to the near shore northwest FL 
Panhandle coastal waters of an elevated potential of morning 
waterspout formation. For today, the mid level short-wave advances
east to over the southeast US with mid level flow flattening over
the area. Deep layer moisture is reduced somewhat but values 
between 1.5 and 1.7 inches will remain sufficient for the 
development of isolated to scattered showers and storms with the 
heat and instability of the day. Similar to Tuesday, although the 
risk of widespread severe storms is low today, forecasters can't 
completely rule out an isolated occurrence with the main threat 
being localized damaging wind gusts. Locally heavy rain and 
frequent lightning will also pose a significant hazard with the 
stronger storms. 

Next in a series of mid level trof features advances into the Mid
South late tonight and brings with it and eastward spread of 
organized convection into the OH River Valley southwest to 
northern AL/MS down thru AR. Appears the bulk of this activity 
will stay to the north of the local area through tonight. 

Daytime highs recover mostly into the upper 80s to lower 90s. 
Overnight lows remain muggy. Risk of dangerous to potentially
deadly rip currents at the beaches remains high. /10

SHORT TERM /Thursday Through Friday night/...An upper trof located
near the Mississippi river valley advances eastward across the 
eastern states and begins to move into the western Atlantic late 
Thursday night. An amplifying upper ridge builds into the eastern 
states during the remainder of the period while the upper trof 
continues off into the western Atlantic. A surface ridge oriented 
east-west over the northern Gulf meanwhile maintains a light, 
moist southwest flow over the forecast area with surface dewpoints
ranging from the lower 70s inland to the mid 70s near the coast. 
For Thursday, MLCAPE values near 2500 J/kg are still indicated, 
possibly reaching 3000, although model soundings also continue to 
show a warm layer centered near 800 mb which will need to be 
overcome by daytime heating in order for deep convection to 
develop. With afternoon highs in the lower 90s, this should be 
sufficient to overcome the cap/warm layer, although the issue now 
is how much coverage can be expected in response to a weak sea 
breeze and modest shortwaves moving across the area. Have opted to
continue with chance pops for now, but it's possible lower pops
could be utilized on subsequent shifts. Bulk shear values (0-6 
km) will be higher Thursday morning, around 25-35 knots, then 
trend lower to 20-30 knots in the afternoon when potential deep 
convection develops (overcomes the warm layer near 800 mb). Given 
the fairly high instability and also mid level dry air, will still
maintain the possibility of a severe storm or two for Thursday 
despite weakening environmental shear. For Friday, subsidence 
associated with the upper ridge building into the region will 
start to suppress convective development and coverage should be 
mostly isolated. Although shear values will be very low on Friday,
MLCAPE values around 2500 J/kg will be present in the afternoon, 
and with mid level dry air still see some potential for a possible
severe storm or two. Heat Index values around 105 are expected 
Thursday afternoon over the southern portion of the area, then 
most of the area on Friday. These values should remain below Heat 
Advisory criteria of 108 but will need to be monitored. Overnight 
lows will be about 5 degrees above normal, ranging from the mid 
70s inland to the upper 70s near the coast. A high risk of rip
currents continues along area beaches through Friday evening. /29

LONG TERM /Saturday Through Tuesday/...The upper ridge over the
eastern states weakens and moves off into the western Atlantic as
an upper trof advances across the Plains then moves across the 
Great Lakes region. A surface ridge remains in place over the
northern Gulf and maintains a moist southerly flow over the
forecast area through the period. Subsidence associated with the
upper ridge is expected to suppress convective development and
have continued with a dry forecast for Saturday and Sunday
although it's possible a storm or two could develop. Slight chance
to chance pops return to the forecast for Monday and Tuesday with
the departure of the upper ridge. Highs each day typically range
from 90 to 95 and lows range from the lower 70s inland to the mid
70s at the coast. /29

MARINE...Main threats in the near term will be potential of
waterspouts. Remember, waterspouts can also form even under rain 
free cumulus. High pressure over the southwest Atlantic noses 
westward into the Gulf and maintains a southwest wind component. 
Meanwhile, a frontal wave of low pressure moves out of the 
central plains and up across the OH River Valley through Thursday.
This results in a strengthening southwest flow and building seas.
Small craft should exercise caution over the open Gulf waters the
next couple days. Winds, waves and seas locally higher in and 
near showers and storms. /10


AL...High Rip Current Risk through Friday evening for ALZ265-266.

FL...High Rip Current Risk through Friday evening for FLZ202-204-206.



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