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Area forecast discussion...updated 
National Weather Service Mobile Alabama
723 am CST Sat Dec 20 2014

Marine...had to update the current marine forecast mainly for early
morning drainage along the coast. This offshore flow is likely
enhanced this morning due to the position of the broad surface low
south of the Alabama..MS and nwfl coast. The northerly flow is expected to
gradually diminish today and continue through early next week as the
area of low pressure continues to weaken and drift mostly southward.
32/ee

&&

Previous discussion... /issued 410 am CST Sat Dec 20 2014/

Short term (today through Monday night)...for today and
tonight...dampening short wave trough moving east over the central
Gulf states this morning will continue to shift east reaching the
Atlantic Seaboard by early this afternoon. To the south broad
surface low along a stalled frontal weakens as upper energy moves
east. Both the low center and frontal boundary look to maintain
continuity over the northern Gulf through tonight drifting further
southward from the coast through 12z sun. As this system drifts
southward the better coverage of rain shifts south and east late
this morning and this afternoon with isolated coverage continuing
over the adjacent Gulf waters through tonight. Further west a
deepening upper trough moves eastward over much of Texas by 12z sun
setting the stage for another round of measurable precipitation late sun
into Monday. For now will continue to keep mostly cloudy skies in the
forecast through tonight with rain chances decreasing generally from
the north to south through tonight. As for temperatures a big discrepancy
between the current MOS guidance continues through tonight with the
current mav guidance probably to warm due to the position of the
stalled frontal boundary to the south combined with mostly cloudy
conditions continuing through tonight. Latest thickness values from
both the physical GFS and European model (ecmwf) also support this reasoning. For now
will keep high temperatures mostly in the middle 50s for most of the County warning forecast area with
the exception of the upper 50s over most areas in nwfl. As for low
temperatures tonight due to the persistent cloud cover over the region will
lean towards the warmer mav guidance for lows tonight going a degree
or two higher for most areas, as a result lows will range from the
lower to middle 40s for most of the northern half of the County warning forecast area and
the upper 40s to lower 50s further south. 32/ee

For Sunday through Monday night...an upper trough over the plains
amplifies significantly into a longwave trough Monday into Monday
night while a series of shortwaves are ejected downstream across the
forecast area. An associated surface low moves across the northern
plains to the Great Lakes region and brings a trailing cold front
towards the lower Mississippi River valley late Monday night. There
is increased confidence now on a surface low developing over Texas
on the frontal boundary on Monday which will be a significant
feature for Tuesday in the long term period. A surface ridge
remains in place over the southeast states on Sunday then weakens
Monday into Monday night with the approach of the cold front/Texas
surface low. The series of shortwaves in the southwest flow over
the region interact with a preexisting inverted surface trough over the
northeastern Gulf and the southeast states surface ridge to produce
moderate isentropic lift seen in the 290-300k layer Sunday which
strengthens somewhat Sunday night. Based on condensation pressure
deficits in the 290-300k layer...the best probability of precipitation will be over the
southeastern portion of the area Sunday into Sunday night. With
improving deep layer moisture in this portion and the increasing
isentropic lift...will have chance to good chance probability of precipitation on Sunday for
most of the southeastern portion of the area tapering to slight
chance over the northwest portion...then for Sunday night will have
likely probability of precipitation over the southeastern portion and chance to good chance
probability of precipitation for the remaining portion.

The isentropic lift weakens on Monday with both the weakening of the
southeast states surface ridge and the breakdown of the northern
Gulf inverted surface trough...and will have chance probability of precipitation for the
eastern portion tapering to slight chance probability of precipitation over the western
third. Isentropic lift increases again Monday night while deep
layer moisture increases further across the area and will have
chance to good chance probability of precipitation with the highest probability of precipitation near the coast
where the best deep layer moisture will be present. The land
portion of the area remains stable and have kept thunder out of the
forecast through Monday night...although expect isolated embedded
thunderstorms to develop over the marine area Monday night. Highs
on Sunday will range from near 60 inland to lower 60s closer to the
coast then warmer temperatures follow for Monday with highs in the
middle 60s inland ranging to upper 60s closer to the coast. Lows
Sunday night will range from the upper 40s inland to lower 50s
closer to the coast...then in the middle to upper 50s Monday night. /29

Long term (tuesday through friday)...the plains longwave trough
advances slowly eastward through Tuesday night then takes on a
negative tilt while advancing into the eastern states on Wednesday.
The surface low will be located near the Sabine River valley or
extreme eastern Texas early Tuesday morning and advances
northeastward through Tuesday night with the cold front moving
through the forecast area Tuesday night. The 850 mb jet increases
to 35-45 knots on Tuesday and a line of storms is expected to move
through the forecast area ahead of the cold front...exiting to the
east possibly as late as Tuesday evening. Confidence has increased
with timing for this system and have gone with likely probability of precipitation across
the area on Tuesday with likely probability of precipitation for the eastern portion Tuesday
night. It looks probable that 0-3 km MUCAPES of 500 j/kg will be
present with the passage of this line of storms in an environment of
0-1 km helicity of 150 m2/s2...sufficient to add mention of
potential for some severe storms for Tuesday to the hazardous weather
outlook. Dry conditions follow in the wake of the cold frontal
passage then small probability of precipitation return for Friday as another cold front
advances from the plains. /29

Marine...a weakly organized low pressure system over the north
central Gulf will continue to drift east and south over the weekend.
As a result a moderate northeast to easterly wind flow will continue
over the marine area through Sunday morning. Winds and seas will then
diminish late Sunday into early next week as the surface low to the
south continues to weaken. Southerly winds and seas will build on
Tuesday in response to a stronger cold front approaching from the
northwest. The cold front is expected to move across the marine area
by late Tuesday night leading to a strong west to northwest flow over
the marine area early Wednesday through midday Thursday. Small craft
advisories will be likely in the wake of the cold front by midweek.
32/ee

Aviation...
12z issuance...mostly LIFR to IFR ceilings through 20.15z followed by
IFR to MVFR ceilings through 21.12z. Low clouds and light rain will
shift east and south late this morning and this afternoon. Lowering
ceilings with light drizzle possible redevelops overnight and early Sun
morning. Winds will continue from the northeast at 8 to 10 knots
with higher gusts through 21.12z. 32/ee

&&

Preliminary point temps/pops...
Mobile 55 48 63 53 69 / 40 10 30 50 20
Pensacola 58 50 63 55 69 / 40 20 50 70 40
Destin 59 53 62 57 68 / 30 20 60 70 40
Evergreen 56 44 60 49 67 / 40 10 30 50 30
Waynesboro 55 40 60 47 66 / 30 10 20 30 20
Camden 56 41 60 47 65 / 30 10 20 40 30
Crestview 58 48 63 52 69 / 50 20 50 70 40

&&

Mob watches/warnings/advisories...
Alabama...none.
Florida...none.
MS...none.
GM...none.
&&

$$

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