Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kmob 251739 aac 

Area forecast discussion...updated
National Weather Service Mobile Alabama
1239 PM CDT Sat Mar 25 2017

Discussion...updated for latest aviation discussion below.


18z issuance...MVFR cigs forecast into much of the afternoon
along with moderate to at times gusty southeast to south winds.
Increased impacts, that being lowering cigs, erratic strong wind
gusts and vsby reducing (lifr categories) heavy rains from
eastward moving line of convection looks to move across mob/bfm
terminals between 25.21 to 26.01z and eastward into pns between
26.00 to 26.03z. /10


Previous discussion... /issued 1027 am CDT Sat Mar 25 2017/

Discussion...see updated information for land areas below.

Update...vigorous upper level storm system centered over eastern
Kansas/eastern OK begins to lift northeast up across central MO
thru the afternoon. This allows a diffluent high level southwest
flow and larger scale ascent to progress eastward over the
central Gulf Coast today. An assessment of deep layer moisture
from 25.12z weather balloon releases show best moisture (pwats
~1.2 inches) generally from southern half of MS westward to
southern la. Aligned within the larger scale high level flow/better
moisture and resulting enhanced lift, forecasters see colder
cloud tops/clusters of lightning mostly confined to MS
southwestward to the Upper Texas coast. Latest mesoscale analysis
shows best instability residing from southern MS westward to the
Upper Texas coast. A complex eastward evolution in the convective
line is expected thru the remainder of the day. Initially, the
northeast extent of the line is ragged but expect more development
to be organizing from southwest Alabama to off the la coast thru the
remainder of the day as a wave of better instability, ahead of an
eastward moving surface front, pivots over the central Gulf
Coast. No major changes made to the timing of the eastward moving
convective line with interior northwest zones seeing ongoing
activity spreading eastward thru The Heart of the forecast area
during the mid and late afternoon hours. Some to become strong to
briefly severe, with damaging wind gusts the primary threat.
Marginally severe hail (around a quarter size or so) will also be
possible with the strongest storm updrafts given latest weather
models showing a slight uptick in mid level lapse rates between
6.3-6.8 c/km and lowest wbz heights 9 to 9.5 kft above ground level. /10

Previous discussion... /issued 645 am CDT Sat Mar 25 2017/

Discussion...updated for latest aviation discussion below.

12z issuance...other than some very localized MVFR cigs near the
immediate coast, VFR conditions are prevalent across the region
early this morning, with broken mid-high decks spreading
overhead. Primary aviation impact today will be numerous to
widespread thunderstorms and rain that are expected to develop and spread across the
region. This activity initially develops into southeast MS after
25.14-15z, develops toward the I-65 corridor through around
25.21z, then east of I-65 through 26.03-04z. A few storms will be
capable of producing locally strong wind gusts, IFR or lower
cigs/visibility, and heavy rainfall. /21

Previous discussion... /issued 525 am CDT Sat Mar 25 2017/

A few severe thunderstorms and locally heavy rainfall possible
across much of the region today...

Near term /now through Saturday night/...water vapor satellite
animation shows a potent upper level low slowly lifting across
eastern OK early this morning. Large scale ascent within diffluent
mid level flow ahead of this feature was spreading from far
southeast Texas and southwestern la and northeastward across the lower
Mississippi Valley region early this morning, where regional radar
imagery shows an organized squall line of thunderstorms slowly
advancing eastward. Radar is currently quiet across our forecast
area as of 4 a.M., Aside from some very isolated light rain showers
developing across portions of southeast MS and southwest Alabama. A warm
and moist southeasterly low level flow persists between the surface
ridge of high pressure over the eastern Seaboard and the area of low
pressure over the plains.

The upper level low over northeastern OK early this morning is
forecast to lift northeastward toward MO through this afternoon,
while the associated region of large scale ascent gradually advances
eastward toward our forecast area through this afternoon and
evening. High resolution guidance, including the past few runs of
the hrrr along with the 26.00z WRF-arw lends confidence that showers
and thunderstorms will increase in coverage over our southeast MS
counties especially around and after 10 am, before convection
gradually develops eastward over southwest al, generally west of I-
65 through the early to mid afternoon hours. Convection should then
continue to develop/spread eastward along and east of the I-65
corridor from mid-afternoon into the early evening hours. We expect
there to be opportunity for decent de-stabilization of the airmass
with daytime heating today, with MLCAPE values generally increasing
to 500-1000 j/kg ahead of the approaching convection. Low level wind
fields and deep layer shear is not overly impressive, but the
available instability in conjunction with 25-35 knots of 850 mb flow
and up to 200 m2/s2 of 0-1km storm relative helicity could enable
a few storms to become strong to severe late this morning into
this afternoon, with damaging wind gusts the primary threat.
Marginally severe hail will also be possible with the stronger
storms given mid level lapse rates between 6-6.5 c/km and wbz
heights around 9 kft above ground level. Locally heavy rainfall also looks
possible as storms spread east. We mentioned locally heavy
rainfall especially over central and western portions of the area
this afternoon, where between 1-2" of rainfall with locally higher
amounts will be possible. Highs today should range in the mid 70s
to around 80 inland, with lower to mid 70s along the beaches.

The overall severe potential should decrease by early this evening
as instability and shear wanes. However, will keep pops likely
across the eastern zones during the early evening as forcing
continues to push eastward. Lingering scattered convection may
continue into the overnight hours as the shortwave trough axis moves
overhead. Lows tonight will range from around 60 to the mid 60s.

Short term /Sunday through Monday night/...the active weather
pattern will continue into the extended period with the potential
for a few distinct trough passages over the work week.

Lingering deeper moisture and lift will continue moving east at
the start of the short term period Sunday. A few scattered showers
and storms remain possible in our eastern counties but this
potential will diminish through the day. In its wake, somewhat
drier air aloft will filter into the region leading to a mostly
dry forecast for the remainder of the area Sunday. Southerly winds
will continue to allow for a robust low level moisture feed into
the region and partially clearing skies will allow temperatures to
warm into the mid 70s near the coast with low to mid 80s
prevalent through the interior zones during the afternoon Sunday.
Accordingly, lows on Sunday night and into early Monday will be
rather warm as well with low 60s interior to upper 60s along the
immediate beaches.

Zonal flow aloft will transition to southwesterly once again as
the next trough nears the area from the west beginning late Sunday
night and into Monday morning. Increasing deep layer moisture and
lift will accompany the approaching trough and will include
likely pops in the far northwestern zones with chance to slight
chance pops for the remainder after 12z Monday morning. The
dynamics with monday's system appear to be weaker than what we
will be dealing with this afternoon and evening. However, a few
strong storms will be possible Monday afternoon and into the early
evening owing to modestly steep mid level lapse rates and 30 to
35 knots of 0-6km shear. Nickel to marginally severe hail and
gusty winds appear to be the most likely severe hazards with this
activity. Expect the northwestern portions of our area to have the
greatest chance for storms as the better dynamics and shear are
centered to our north and west. Showers and storms should be on
the wane with the loss of daytime heating Monday evening but
isolated showers could linger across the north towards midnight as
the axis of the mid level trough crosses the area. High
temperatures Monday will reach the upper 70s to perhaps the low
80s across inland areas with low to mid 70s expected at coastal
locations. Overnight low temperatures will be in the low to mid
60s. 05/rr

Long term /Tuesday through Friday/...a lingering surface boundary
could lead to widely scattered showers with perhaps a rumble or
two of thunder across the region on Tuesday. Large scale support
for precipitation will be lacking with weak ridging building in
temporarily in the mid levels. Wednesday looks to be dry as the
next system takes shape across the Texas Panhandle leading to
modest amplification of the downstream ridge over our area.
Temperatures will be warm Tuesday with highs the low 80s inland
and mid 70s along the coast. Wednesday will be a touch warmer
with mid 80s possible inland and upper 70s south of I-10, a bit
cooler along the immediate coast.

Our next potential weather maker looks to arrive Thursday and
into early Friday and will bring yet another chance for showers
and thunderstorms to the area. Early indications are that this
system may have a more favorable configuration of surface and
upper level features for strong storms but won't get overly
focused on the details at this time range. Temperatures on
Thursday and Friday will be a little cooler than previous days
with upper 70s to low 80s inland and mid 70s at the beaches. 05/rr

Marine...a strong southerly flow with elevated seas between 5-7
feet will continue over the coastal waters today between a ridge of
high pressure over the eastern Seaboard and low pressure lifting
toward the Mississippi Valley. Will maintain a Small Craft Advisory
for the coastal waters, also including lower Mobile Bay and the MS
sound through this evening. Showers and thunderstorms will increase
in coverage over the marine area this afternoon and evening ahead of
the approaching storm system. Some storms could be strong to severe,
with locally high winds and seas, frequent lightning and heavy
rainfall this afternoon and evening. A southerly flow will otherwise
continue through the middle of next week. /21


Mob watches/warnings/advisories...
Alabama...high rip current risk through late tonight for alz265-266.

Florida...high rip current risk through late tonight for flz202-204-206.

GM...Small Craft Advisory until 7 PM CDT this evening for gmz631-632-


National Weather Service Glossary of Abbreviations