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Area forecast discussion 
National Weather Service Mobile Alabama
403 PM CST sun Dec 21 2014

Short term [tonight through Monday night]...a weak area of surface
low pressure continues to drift southward across the north central
Gulf of Mexico this afternoon...while a ridge of surface high
pressure extended from the northeastern states to the Tennessee
Valley/northern portions of GA/al/MS. Looking aloft...a middle level
trough was amplifying over the northern rockies and adjacent plains
states...while a southwest flow aloft was present over the central
Gulf Coast region ahead of this developing feature. An axis of deeper
moisture was located along a stalled frontal boundary situated from
southwest to northeast across the north central Gulf of Mexico this
afternoon...where regional radar imagery indicated scattered showers
and thunderstorms developing well to our south. Our forecast area has
remained rain free for the most part today...but extensive cloud
cover has once again kept temperatures cooler than expected across
our region. Readings at 3 PM CST mostly ranged from the middle 50s to
around 60.

The middle level pattern will continue to amplify tonight into Monday
as the aforementioned trough continues to deepen...with short range
guidance in agreement with developing a bonafide deep upper level
low over the Central Plains and upper midwestern states by Monday
afternoon. Southwest flow aloft will continue to spread across our
forecast area ahead of this deepening feature into Monday. The
stationary boundary over the north central Gulf should slowly
retreat northward as a warm front through Monday afternoon...
becoming oriented just south of or near the coast by late Monday
afternoon. The axis of deeper moisture should also gradually lift
northward through Monday afternoon. An embedded shortwave trough in
the southwest flow should aid in the development of scattered to
numerous showers and perhaps isolated thunderstorms over the
northern Gulf tonight. There is potential that a few showers could
develop inland late tonight...and have left a low chance of rain
showers in the forecast...mainly southeast of I-65. Lift will
continue to spread across inland areas into Monday...with scattered
showers remaining a possibility over a good portion of the County warning forecast area.
Weak elevated instability and MLCAPE values generally less than 500
j/kg does support including mention of isolated thunderstorms by
Monday afternoon. The temperature forecast remains a challenge. Have
trended toward a blend of guidance tonight...and generally toward
cooler guidance Monday. /21

High level trough sharpens over the central US Monday night as a
strong h30 jet streak (140 to 150 knots) dives southward over the
western US. The lower Mississippi River valley sees an active
southwest flow aloft with a series of middle level impulses/weaker jet
energy translating northeast. At the surface...stalled front which
has been draped over the northern Gulf the past couple days...transitions
to a warm front and will ease closer to the coast through the night
Monday night. Considering the warm front near by and the jet streak
dynamics in place...isentropic lifting processes support a good chance
of measurable rain. For the most appears any convection
will be elevated north of the warm front and with low level 850
millibar winds remaining fairly weak...risk of severe weather looks
to be low over the land areas heading through the night. Exception
could be right along the coast and over the Gulf waters closer to and
south of the warm front. Storms approaching and moving across the
warm front...could exhibit some rotation but will quickly become
elevated north of the warm frontal zone. At this time...predominant
weather Mode will be showers with embedded storms mixed in for Monday
night. With light southerly flow in place...Monday night's lows to be
mild with numbers ranging from 59 to 64. /10

Long term [tuesday through sunday]...Tuesday still looks to be
potentially the most active weather day. In response to approaching
stronger upper level dynamics and cold front...low level jet is
forecast to increase with low level shear supportive of severe
storms/isolated tornadoes. There is considerable uncertainty to amount of instability that will be present. Increased
coverage of showers could very well act to limit boundary layer
instability. Also...if a more organized convective complex of storms
forms on coastal warm front as some models suggest...this could also act to
cut off northward transport of instability and thus limit severe convection.
Out of respect for increasing low level wind shear...but also
considering uncertainty to available instability...will maintain a
slight chance of severe storms for Tuesday and Tuesday evening. The main
risk in severe storms look to be damaging winds/isolated tornadoes.
In addition to any severe storms...locally heavy rains are also
possible which could lead to nuisance type flooding in areas subject
to poor drainage. The progressive eastward movement of storms and the
lengthy period of dry weather we have experienced of late...looks to
mitigate widespread flash flooding potential.

Wind shift with cold front is forecast late Tuesday night/early
Wednesday morning...bringing an end to the severe weather risk.
A small chance of Post frontal rains linger Wednesday morning before
tapering off further into the afternoon. Will be dry and cool on
Christmas day. Next cold front advances across the plains and is
expected to move across the forecast area on Saturday. Will maintain small
chances of shower this weekend for this feature. Highs in
the middle 60s for Friday...trend cooler Saturday/Sunday with highs in the
upper 50s northwest zones and lower to middle 60s southeast zones
Saturday to lower to middle 50s on Sunday as cool surface high
pressure moves across the deep south late next weekend. Although nights
will be not see freezing temperatures at this time during
the outlook. /10


21.18z terminal forecast discussion...
IFR to MVFR ceilings and occasional reductions in visibility to MVFR
levels should continue near the coast...while MVFR ceilings should be
the rule further inland. Ceilings should deteriorate to IFR to LIFR
levels late this evening through early Monday morning...with
additional potential for MVFR to IFR visibility reductions. Isolated
to scattered rain showers may develop near the coast late tonight and
early Monday morning before developing inland during the day Monday.
Northeast to east winds around 5 knots should otherwise prevail. /21


Marine...a weak area of low pressure will continue to drift across
the north central Gulf and weaken through tonight. A moderate to
occasionally strong northeast wind will diminish early tonight as the
surface low gradually weakens. Southerly winds and seas will develop
on Monday and build through early Tuesday night ahead of a strong
cold front approaching from the northwest. Scattered to numerous
showers and thunderstorms are expected ahead of the front Tuesday and
Tuesday night with some storms becoming strong to possibly severe.
The cold front is expected to move across the marine area by early
Wednesday leading to a strong west to northwest flow over the marine
area late Tuesday night through early Thursday. Seas may build to 7
to as high as 10 feet well offshore Tuesday night and Wednesday.
Small craft advisories will be likely ahead and in the wake of the
cold front by midweek. 32/21


Preliminary point temps/pops...
Mobile 52 69 62 70 54 / 30 30 50 90 90
Pensacola 54 68 63 70 61 / 40 40 50 90 90
Destin 56 68 64 70 63 / 50 40 50 90 90
Evergreen 49 68 60 70 57 / 30 40 50 90 90
Waynesboro 47 67 60 69 48 / 10 30 50 90 90
Camden 48 67 59 71 53 / 20 30 40 90 90
Crestview 51 68 60 70 61 / 40 40 50 90 90


Mob watches/warnings/advisories...


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