Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 231553 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1053 AM CDT Tue May 23 2017

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

&&

.UPDATE...The threat of flash flooding has diminished across areas
along and north and west of the I-65 corridor, so we have
cancelled the Flash Flood Watch for those areas. We are
maintaining it at this time for areas further south and east as
mesoscale models are showing the orientation of the shower and
thunderstorm activity becoming more west to east oriented, which
could result in higher totals due to training. This is the result
of the surface low currently over Monroe/Conecuh Counties moving
northeast and leaving a trailing boundary to the south. The
greatest risk of localized flooding through this afternoon may set
up closer to the I-10 corridor based on current radar trends.
34/JFB

&&

.PREV DISCUSSION... /issued 934 AM CDT Tue May 23 2017/

DISCUSSION...Updated for latest marine discussion below.

MARINE...Expanded the Small Craft Advisory to include all inland
bays as observations show widespread 20-30 kt winds occurring.
These strong winds will persist through at least early afternoon
across the AL bays and through late afternoon over the FL bays.
34/JFB

PREV DISCUSSION... /issued 912 AM CDT Tue May 23 2017/

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

UPDATE...Frontal boundary located from Covington County southwest
into central Baldwin County is providing a zone of enhanced low
level shear with 0-1km SRH of 200-300 m2/s2 and MLCAPE along and
to the south of boundary increasing to near 1000 J/kg. This has
already resulted in one strongly rotating storm to move through
Covington County and the threat for additional isolated severe
storms will persist from near Covington/Escambia AL southwest to
coastal AL, including the NW FL Panhandle through early afternoon.
Localized damaging wind gusts are possible, along with a brief
tornado, especially as storms track close to the frontal boundary
in Covington and the inland NW FL panhandle. Tornado potential
likely lower further south in the warm sector as winds begin to
veer to the southwest.

Any potential flooding threat for the rest of the today will be
confined south and east of I-65, particularly if convection along
the coast continues to develop. Conditions will improve west of
I-65 as the day progresses. Some changes/cancellations to the
Flash Flood Watch will likely be made later this morning/early
afternoon. We do expect another round of storms with the actual
cold front late tonight, but its quick movement may limit any
additional flooding potential. Will look at new data this morning
before making final decisions. 34/JFB

PREV DISCUSSION... /issued 646 AM CDT Tue May 23 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
12Z issuance...MVFR to low-end VFR ceilings and visibilities
expected through the forecast period. Widespread showers and
thunderstorms continue through this morning before tapering off
from west to east this afternoon. Showers/storms then redevelop
from west to east late tonight into early Wednesday morning ahead
of an approaching cold front. Expect lower vis/cigs in and around
showers and storms. Southwest winds around 10 to 15 knots gusting
to 15 to 20 knots today become more westerly around 5 to 10 knots
tonight. /49

PREV DISCUSSION... /issued 448 AM CDT Tue May 23 2017/

NEAR TERM /Now Through Tuesday night/...The upper level shortwave and its
attendant weak surface low lift northeast of the area late this
morning. With the removal of this lifting mechanism, expect the
heaviest and most widespread shower and thunderstorm activity to
wane off from west to east going into this afternoon. However, at
least some activity is expected to linger through the afternoon
and evening given the abundance of deep layer moisture and weak
stationary front remaining draped across the area. With upper
forcing and deep layer shear remaining favorable for organized
convection, the primary limiting factor for severe weather
potential during the near term will be the lacking instability.
This is noticeable in observations early this morning, with even
the strongest/heaviest convective bands and clusters containing
little to no lightning activity. As such, there is only a marginal
risk for severe weather through the near term, generally limited
to areas along and southeast of I-65, where the best chance exists
for at least modest instability to develop. Isolated damaging
wind gusts will be the primary threat. A second shortwave is then
expected to passes through later tonight, bringing with it another
bump in shower/storm coverage and intensity ahead of a trailing
cold front. Taking into consideration the continuous convective
activity and PWAT`s remaining in the 1.5 to 2.0 inch range through
the near term, have decided to continue the Flash Flood Watch at
this time, which runs through late tonight. Showers and
thunderstorms finally begin to taper off in the wake of the front
as it enters the local area from the west late tonight into early
tomorrow morning.

In terms of temperatures, expect clouds and showers/storms to keep
high temps today in the upper 70`s to low 80`s across the area. Lows
tonight will range from the mid 60`s inland to low 70`s at the
beaches. /49

SHORT TERM /Wednesday Through Thursday night/...Wednesday, a
lobe of energy swinging around an upper low over the Central
Plains pushes a front east of the forecast area Wednesday, and any
residual rain Wednesday afternoon at the latest. With the close
proximity of the upper low and wrap-around stratus possible over
northern parts of the forecast area Wednesday, am expecting this
area to see the greatest chance of precip hanging on into
Wednesday afternoon. With cooler air moving over the forecast area
beginning early Wednesday, a below seasonal day with respect to
temperatures is expected. Highs ranging from mid 70s north to
around 80 east expected.

Wednesday night through Thursday, cooler, drier air continues to
push over the forecast area, but with surface high pressure moving
over the area quickly behind the front, am expecting the push to
be limited. the push is strong enough to bring lows ranging from
the low 50s northwest to around 60 along the coast Wednesday
night (well below seasonal) and highs in the low 80s Thursday (a
bit below seasonal).

Thursday night, an upper ridge of high pressure moves east to over
the Mississippi River, as upper level high pressure over the Gulf
of Mexico builds north. The surface high than had moved over the
forecast area shifts well east, becoming a surface ridge
stretching west over the northern Gulf Coast. With a return of
warming southerly flow returning with the surface ridge and
bringing an increase in warming southerly flow off the Gulf along
with an increase in warming subsidence as the upper ridge shifts
close (but mainly later in the period), a warm-up is expected,
with coastal areas seeing the biggest warm up. Lows ranging from
mid 50s north to mid 60s along the coast expected.

/16

LONG TERM /Friday Through Monday/...Friday through Saturday night,
an upper low digging south over the Plains quickly pushes the
Mississippi River upper ridge over and well east of the forecast
area (to near the East Coast), while allowing the Gulf of Mexico
upper ridge to build north. This will re-enforce the northern
Gulf Coast surface ridge, and help to maintain the onshore flow.
With increasing subsidence from the Gulf ridge and warming flow
off the Gulf, temps rise back to above seasonal levels. Highs in
the upper 80s to around 90 expected Friday and Saturday. Lows
Friday night in the upper 60s to low 70s, low to mid 70s Saturday
night.

Sunday through Monday, the upper low over the Plains meanders east
to over the Great Lakes, opening as it moves. This swirling mass
of energy pushes a surface front south of I20, and in combination
with the continued southerly flow, a chance of rain. Isolated to
scattered afternoon/evening shra/tsra becomes possible, but with
coverage limited enough to allow for decent incoming heating
along with the Gulf ridge maintaining its present, temps above
seasonal continue. Highs in the upper 80s to around 90 each day,
lows ranging from around 70 to the mid 70s along the coast Sunday
night.

/16

MARINE...Shower and thunderstorm activity continues through Tuesday
night as a low pressure system interacts with a remnant frontal
boundary stalled across the local area. Expect increasing winds and
building seas through that period, followed by moderate to strong
northwest flow in the wake of a frontal passage Wednesday into
Thursday. A light to moderate onshore flow then returns to finish
off the week as high pressure builds east of the area. /49

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Flash Flood Watch through late tonight for ALZ059-060-261>266.

     High Rip Current Risk through Wednesday evening for ALZ265-266.

FL...Flash Flood Watch through late tonight for FLZ201>206.

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

MS...None.
GM...Small Craft Advisory until 7 PM CDT Wednesday for GMZ650-655-670-
     675.

     Small Craft Advisory until 7 PM CDT this evening for GMZ630>635.

&&

$$

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