204 
FXUS64 KMOB 092336 
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
636 PM CDT Sun May 9 2021

.AVIATION...
00Z issuance...VFR conditions prevail through the evening hours. 
Clouds increase overnight, maintaining at VFR ceilings, while rain
showers and thunderstorms begin to move in late tonight into 
Monday morning. Local reductions in ceilings and visibility are 
possible in any storms. /13

&&

.PREV DISCUSSION... /issued 354 PM CDT Sun May 9 2021/ 

NEAR TERM UPDATE /Now Through Monday/...A complicated and messy 
pattern will set up across our forecast area late tonight into 
Monday as a rather noisy looking series of upper shortwaves and 
impulses over the ArkLaTex region will translate eastward in the 
zonal flow across the Lower MS Valley into early this evening, 
then across MS and into AL later this evening into late tonight. 
The high-resolution Convection Allowing Models (CAMs) are not in 
agreement at all with the development and subsequent movement of 
the anticipated convection due to their differences in handling 
the noisy pattern aloft, so will rely mainly on the short-term and
spectral models (NAM, GFS, and ECMWF). With this said, will need 
to monitor the convection to our west this afternoon for a 
potential mesoscale convective system (MCS) to develop and 
eventually determine a speed of motion eastward this evening.

For now, we are still forecasting the leading edge of an MCS to
move into interior portions of southeast MS and southwest AL 
sometime around midnight tonight, give or take a couple of hours 
on either side dependent on the strength of cold pools allowing 
for propagation of the system toward our area. Low level wind 
fields should gradually weaken over MS/AL by late this evening as 
the stronger dynamics associated with the low pressure system 
quickly lift northeast toward the Appalachians and Eastern 
Seaboard. This will probably result in a weakening trend with 
convection approaching our northwest zones late this evening. 
However, plentiful moisture and instability will be available and 
there is a high chance that convection will arrive in these 
northwest zones late this evening or shortly after midnight, so 
will have POPs increasing to likely coverage over these areas
starting at 06Z. Will need to watch for a couple of strong to 
marginally severe storms embedded within the line as it approaches
our NW counties. The main concern would be strong/gusty winds and
possibly some small hail.

Precipitable water values trend up to near 1.9 to 2 inches over 
this portion of our forecast area overnight, while MLCAPE values 
also trend up to around 1000-1500 J/KG late tonight into Monday
morning per the latest RAP and NAM. The GFS and ECMWF hold off
with the MLCAPE values of 1000-1500 J/KG until early Monday
afternoon. The very moist/unstable airmass and available ascent 
will support the development of numerous showers and thunderstorms
northwest of a line from Greenville AL to Mobile AL late tonight,
and a few could be strong with gusty winds, small hail, and very 
heavy rainfall. This line of convection should continue to weaken 
as it shifts southeast of I-65 through mid morning. There could be
a brief lull in convection late Monday morning before yet another
additional round of showers and storms develops Monday afternoon 
in association with another mid level perturbation arriving within
the zonal flow. Instability with MLCAPE inching upward to between
1200-2000 J/KG across the western 2/3rds of the forecast mid 
afternoon along 40 to 50 knots of deep layer shear. This should be
more than sufficient for few strong to marginally severe storms 
capable of producing strong to locally damaging gusts, small hail,
and pockets of locally heavy rainfall Monday afternoon.

The latest QPF/rainfall forecast in the near term has trended
downward about one-half inch area-wide. While we still expect
widespread rainfall amounts between 1 to 2.5", localized higher 
amounts have dropped slightly to between 2.5 to 3.5". We will 
however still need to watch for localized flooding concerns late 
tonight through Monday. /22

SHORT TERM /Monday night Through Wednesday night/...The active
pattern remains as the shortwave train keeps on trucking. Westerly
to slightly southwesterly flow aloft will continue through
Wednesday night. Several weak shortwaves will progress through the
flow each day bringing the potential for several rounds of 
showers and thunderstorms. At the surface, rain chances will be 
focused along a slow moving boundary that will drift south each 
day. Cape values will range in the 1500 to 2500 J/kg each day and 
shear will range in the 30 to 40 knot range which would certainly 
support at least some organization to the convection. This will 
likely bring at least the chance for a few strong storms with a 
damaging wind threat. Lapse rates are rather pathetic and mostly 
moist adiabatic which could inhibit more widespread stronger 
storms. The bigger threat will likely by the potential for heavy 
rainfall. PWATS will be in the 1.5 to 1.8 range and even some 2 
inch PWATS will be possible along the surface boundary. With 
westerly flow aloft running parallel to the west to east oriented
boundary this could lead to training storms. Additional rainfall 
amounts could range in the 2 to 4 inches with locally higher 
amounts where training occurs. All of this on top of the already 
soggy antecedent conditions leads me to believe that I would not 
be shocked to see a flash flood warning or two. 

Temperatures will remain mild through the period with highs
ranging in the upper 70s to low 80s. Rain and cloud cover will
probably be the main thing keeping temperatures down from getting
too warm. Lows will be on the muggy side as low level moisture
continues to funnel into the area. Lows will range from the upper
60s to near 70 along the coast and mid to low 60s inland. BB/03

EXTENDED TERM /Thursday Through Sunday/...The active pattern will
come to an end on Thursday and into Thursday night as a large
upper trough/low centered over the Great lakes will progress
eastward into the northeastern US. This will break the zonal flow
and bring a more northwesterly component allowing for drier air to
move into the area and the surface boundary to push offshore. Rain
will linger through Thursday as the remaining dynamics move
through but by Friday skies and remain clear through Sunday as
high pressure builds over the central US. Once we get through
Thursday, conditions will be about as perfect as you can get for a
beach weekend as highs will be in the low 80s to begin the period
and eventually warming into the mid 80s by Sunday. Lows will also
be a little more manageable as the drier air moves in leading to
lows in the mid to upper 50s. The best part will be the dewpoints
in the 50s leading to much more comfortable conditions. BB/03 

MARINE...A light to moderate southerly flow will prevail through 
Tuesday ahead of a weak cold front approaching from the north. 
Southerly winds will be elevated enough that small craft will need to
exercise caution at times this morning. Light easterly to variable 
winds are expected midweek as the cold front stalls near the coast, 
followed by light to moderate northeasterly winds Thursday as the 
front moves further offshore. Showers and thunderstorms will increase
in coverage starting late tonight and will continue into Thursday.
/22

&&

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

$$

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