120 
FXUS64 KMOB 042334 AAA
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
634 PM CDT Sun Apr 4 2021

.AVIATION...
00Z issuance...VFR conditions will prevail through the next 24
hours. /13

&&

.PREV DISCUSSION... /issued 337 PM CDT Sun Apr 4 2021/ 

NEAR TERM UPDATE /Now Through Monday/...A northwest upper flow pattern 
continues through Monday along with a large surface high pressure 
centered across the southeastern states. Clear skies and dry 
conditions will prevail, resulting in cool nighttime temperatures 
and warm daytime temperatures. Lows tonight will be in the mid and 
upper 40s inland to low 50s along the coast. Highs on Monday will be 
in the mid and upper 70s inland to low 70s along the coast. A 
MODERATE rip current risk continues through tonight, followed by a 
LOW risk on Monday. /22

SHORT TERM /Monday night Through Wednesday night/...Upper level
ridging and surface high pressure prevails Monday night into 
Wednesday morning before giving way to a rapidly approaching upper
level trough/upper level low from the west. This system ends up 
situated over the central Plains states by Wednesday afternoon and
begins to tilt negative, likely serving as a foci for severe 
weather over the ArkLaTex region. Thankfully for here we are not 
looking at that potential, at least in the short term. We will 
however have an uptick in rain shower and isolated thunderstorm 
activity Wednesday morning into afternoon as adequate moisture 
return occurs amidst a warm air advection regime Tuesday night 
into Wednesday. This will help bring PWATs back into the 1.0" to 
1.4" range by Wednesday evening. Semi-dry mid-levels and lack of 
forcing precludes more widespread convective coverage, but can't 
rule out some showers and thunderstorms particularly during peak 
heating. Rain and thunderstorm chances will continue to increase 
into the evening as a cold front begins to surge southeast over 
eastern AR, western MS, and eastern LA. The bulk of this activity 
will affect us during the extended period which will be discussed 
below in the extended term section. In the mean time, we continue
to see the warming trend in temperatures with daytime highs 
peaking in the upper 70's to lower 80's, with some mid 80's 
looking likely over south- central Alabama come Wednesday. Morning
temperatures Tuesday will be in the lower to middle 50's for 
most, with morning temps Wednesday in the upper 50's to lower 60's
along the coast. MM/25

EXTENDED TERM /Thursday Through Sunday/...A complicated/active 
extended term unfolds Thursday through Sunday. The period starts
off with a cold front/boundary associated with a convective line 
working its way southeast into the northwestern CWA Thursday 
morning as the parent surface low occludes in tandem with the 
upper level low over the Midwest states. Along and ahead of this 
boundary, meager to modest instability exists over the area at
daybreak around 500 to 1,000 J/kg SBCAPE and MLCAPE. 40kts of deep
layer shear is present across the area and given the forcing from
the front itself can't rule out some strong to marginally severe 
thunderstorms Thursday morning including a threat for isolated 
damaging winds and large hail. An isolated tornado can't be ruled 
out given decent low level speed/directional shear exhibited by 
modeled hodographs and resultant SRH values approaching 150 
m^2/s^2. This boundary does not make it very far into the CWA 
Thursday morning before lifting northward and diffusing over 
central Alabama through Friday.

Now the more complicated and uncertain part of the forecast comes.
Forecast models still differ on overall evolution of the upper 
levels, albeit to a lesser extent than the previous forecast 
packages. An upper level trough/cutoff upper level low from the 
prior system still resides over the western Great Lakes into 
northwestern Ohio Valley. An active subtropical jet continues to 
feed into the base of this as a shortwave tracks around the 
southern periphery of the trough base. This will likely serve as 
another trigger for convection over the region Thursday night into
Friday morning/afternoon. It's important to note that we continue
to have adequate instability (albeit elevated) and shear over the
area, and I would not be surprised if we maintain a threat for 
severe weather over the forecast area overnight Thursday into 
Friday, erring on the side of elevated convection with loss of 
surface heating and unfavorable period of the diurnal cycle. With 
this said, MLCAPE values exceeding 750 to 1,500 J/kg and MUCAPE 
values over 1,000 to 2,000 J/kg coupled with 40 to 50+kts of deep 
layer shear supports elevated strong to severe thunderstorm 
activity. Of greatest interest is the steep mid-level lapse rates 
present on the Euro which may support a more predominate large 
hail threat during the aforementioned period, although this threat
will need to be analyzed further once forecast models come into 
better agreement on the thermodynamic environment.

Friday afternoon into Saturday morning is where there is much 
larger divergence in the models, with the GFS remaining more 
progressive with an upper level trough/cutoff upper level low 
shifting east from the central Plains into the Great Lakes while 
during the same time frame Friday night the Euro holds this system
back in the Midwest states as another vigorous shortwave 
traverses the Gulf Coast states. GFS keeps this shortwave shunted
south in the northern Gulf of Mexico. This will have large 
implications on the forecast Friday night into Saturday. The GFS 
would imply a drier forecast with bulk of activity staying 
offshore. Euro would imply a setup favorable for severe 
thunderstorms over the CWA. It is important to note despite the 
differences in the upper levels, the overall trend on both 
forecast models has been to slow the upper level low progression 
and gradually increasing our threat for showers and thunderstorms 
over the area. With that said, have no problem keeping chance PoPs
in the forecast for Friday and Saturday leaning towards the Euro 
solution. The severe threat for Friday night into Saturday will 
have to be revisited in a later forecast package when models come 
into better agreement.

Saturday night into Sunday we get a decent FROPA associated with a
cold front surging southeast across the area. Behind it, weak 
high pressure quickly builds in providing for a slightly drier 
forecast by Sunday evening. Kept chance PoPs in the grids in the 
event the system slows down as has been the trend over the last 24
hours, and owing to some residual showers behind the front 
itself. Temperatures should remain steady state for highs and lows
during the extended period. Highs each day are being maintained 
in the upper 70's to lower 80's, with some middle 80's possible in
spots each day. Overnight lows will be generally in the lower to 
middle 60's, with only exception being Saturday night into Sunday 
morning with the frontal passage supporting middle to upper 50's 
inland and lower 60's along the coast. MM/25

MARINE...No immediate hazardous to marine operations until the 
middle of this week when increasing southerly winds along with a 
gradual building in seas may require Small Craft Exercise Caution 
headlines. Otherwise, light southerly winds will continue through 
this evening, becoming variable less than 8 knots from midnight 
through Monday morning. A more southerly flow will prevail 
throughout the week. /22

&&

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

$$

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