Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 271550 AAB
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1050 AM CDT Thu Jul 27 2017

.DISCUSSION...See updated information for land areas below.

&&

.UPDATE...27.12Z upper air analysis continues to show a deep layer
ridge positioned from New Mexico, eastward into the Mid-South. A
weakness in the geo-potential height field is more aligned over
the southeast, where a weak trof/cyclonic circulation was
generating cloud cover over the southeast US along the Georgia
and southern South Carolina coast. At the surface, weak high
pressure was analyzed over the central Gulf coast. An assessment
of deep moisture has shown a continued lowering of pwat values
over the past 24 hrs with values now 1.4 to 1.7 inches over the
forecast area. Deepest moisture (pwat`s 1.8 to 2.2 inches resides
over the northern Florida Peninsula closer to the trof position.

For today, little change in the forecast. Isolated to lower end
scattered coverages of storms is expected thru the course of the
afternoon along and east of the Tombigbee River. Drier conditions
look to persist west of the river which is dominated by the
eastern nose of the deep layer ridge/better compressional sinking
there. Considering instability, latest Mesoscale analysis shows
surface based capes having lifted to between 2000 to 4000 J/KG and
along with drier air aloft, the collapse of any stronger
afternoon thunderstorm cores will be efficient in producing brief
strong gusty surface winds up to near 50 mph and frequent
lightning. A very isolated severe storm cannot be ruled out, with
main threat in these be damaging winds in excess of 60 mph.

Away from storms, afternoon heat index values rise to a range of
102 to 107 degrees for many areas. Review heat safety tips at the
following link: www.nws.noaa.gov/om/heat/index.shtml

/10

&&

.PREV DISCUSSION... /issued 657 AM CDT Thu Jul 27 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
12Z issuance...Prevailing VFR conditions expected over the next 24
hours, with occasional MVFR conditions possible in and around late
afternoon showers and thunderstorms around PNS. /22

PREV DISCUSSION... /issued 440 AM CDT Thu Jul 27 2017/

NEAR TERM /Now Through Thursday night/...Abundant sunshine will
allow temperatures to rise quickly this morning into the upper 80s
by 10 am. Temperatures will continue to climb into the mid 90s
inland areas by early afternoon with lower 90s along the immediate
coast. These high temperatures when combined with surface
dewpoints in the low to mid 70s will allow the heat indices to
skyrocket to between 102 to 107 degrees by early afternoon. A few
pockets could see the heat index rise to near 109 degrees. The
surface heating will also result in a scattered cumulus field
developing throughout the day, with bases between 4-5 thousand
feet across the entire forecast area.

The eastern extent of an upper high pressure ridge across the south
will reside over the western half of the forecast area, while
upper level weakness remains over the eastern half. Meanwhile, a
very weak surface high pressure ridge across the northern Gulf of
Mexico will remain intact, keeping winds generally light and
variable.

Rainfree conditions will occur throughout the morning followed by
isolated to low-end scattered coverage this afternoon along and east
of the Tombigbee River. Dry conditions will persist west of the
river. With ML Capes expected to rise to between 1500 to 2000 J/KG
today and with dry air aloft, some of the thunderstorms could again
become strong enough to produce gusty surface winds to near 50 mph
and frequent lightning.

A few thunderstorms may persist along the Florida coast this
evening, while the activity inland areas dissipates with loss of
surface heating as sunset nears. Isolated coverage will then
redeveloping across the northern gulf overnight.

A Code Orange Air Quality Alert for Ozone has been issued for Mobile
and Baldwin counties again today. Ground level ozone concentrations
within the region may approach or exceed unhealthy standards, and
members of sensitive groups may experience health effects. Low
temperatures tonight will be in the mid 70s, except for the upper
70s along the beaches. /22

SHORT TERM /Friday Through Saturday night/...The short term
begins with continued hot and dry weather as upper ridging remains
over the area and subsidence keeps thunderstorm activity more
isolated in nature. Thus, expect to see only slight chance to
chance PoPs over inland areas where daytime heating could be
substantial enough to fire off a few storms. Any stronger storms
will be capable of producing frequent lightning, locally heavy
rain, and gusty winds. High temps once again reach the mid 90`s
across much of the area (low 90`s along the coast), with heat
indices once again getting up into the 102 to 107 degree range.
Lows Friday night remain muggy and in the mid 70`s areawide as
cloud cover and perhaps some shower activity increases from the
north, ahead of an approaching front.

Going into Saturday, the pattern changes quite dramatically as a
deepening eastern CONUS trough aloft helps push a weak front south
into our local area. Shower and thunderstorm activity ahead of
this front Saturday will be more scattered to numerous in nature,
with higher-end chance to likely PoPs shifting north to south
throughout the day. Given the amount of progged instability ahead
of this front, along with the enhanced lift and dry mid/upper
levels, a few storms could become strong to marginally severe
during the afternoon and evening hours. These stronger storms will
be capable of producing strong downburst winds on top of the
typical summertime frequent lightning and locally heavy rainfall
threats. The front is then progged to push just offshore (or if
you believe the GFS, all the way into the central Gulf) late
Saturday night, with relatively cooler and drier air moving in
behind it. Given the increased cloud cover from the showers and
storms Saturday afternoon, expect high temps to only reach the
upper 80`s. Lows Saturday night range from the upper 60`s inland
to mid 70`s along the coast as that drier air moves into the area
behind the front. /49

LONG TERM /Sunday Through Wednesday/...The GFS continues to be
the most bullish with Saturday night`s front, pushing it well
offshore and dropping PWATs in its wake to below 1.00 inch. While
this would feel fantastic (and the optimist in me would love to
believe it), not actually expecting that significant of a drop in
moisture at the surface, given the fact that we are still on the
Gulf coast in July and dewpoints will likely remain in the upper
60`s to low 70`s for much of the area. Still, a person can dream,
and it`s entirely possible Sunday turns out to be a beautiful day
with highs in the upper 80`s, dewpoints in the mid 60`s, and only
a slight chance for storms right along the coast.

Precip chances then increase and spread inland Monday through
midweek as weak surface low pressure sets up over the northern
Gulf and light easterly flow, coupled with a southerly influence
from daytime sea breeze circulations, returns moisture to the area
beneath a series of passing upper-level shortwaves. With this
gradual return of moisture, expect the best chances for showers
and storms to remain mostly limited to coastal areas early in the
week before gradually spreading inland by midweek, with much of
the area seeing chance PoPs by Wednesday. High temps through the
long term period reach the upper 80`s to lower 90`s each
afternoon, and lows range from upper 60`s to low 70`s inland and
mid 70`s along the coast each night. /49

MARINE...Weak high pressure over the north central gulf will
begin to shift south late in the week as a weak frontal boundary
moves south towards the north central gulf. Showers and
thunderstorms will increase in coverage late in the week and over
the weekend as the frontal boundary nears the coast and moves
offshore by early Sunday. Winds and seas will be higher near
showers and thunderstorms through the forecast period. /22

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

$$

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