109 
FXUS64 KMOB 202326 AAA
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
626 PM CDT Fri Apr 20 2018

.DISCUSSION...Updated for latest aviation discussion below.

&&

.AVIATION...
00Z issuance...Surface high pressure well north of of the forecast
area will shift to over the East Coast overnight, bringing a shift
in low level flow from northeasterly to easterly overnight, then
southeast by the end of the forecast. With the shift in winds to
easterly, guidance is advertising a slug of low level moisture
(centered around 950mb) moving over the area beginning around 
sunrise. This will bring a drop in CIGs from general VFR to mid 
MVFR beginning around sunrise, the a rise back to VFR by 18z as 
the boundary layer deepens and the moisture layer mixes out. Am 
not anticipating any low end MVFR/IFR CIGs/VISBYs affecting
operations with this package.

/16

&&

.PREV DISCUSSION... /issued 353 PM CDT Fri Apr 20 2018/ 

NEAR TERM /Now Through Saturday/...A shortwave upper ridge will 
move eastward across the central Gulf Coast through Saturday. This 
will allow for a slight increase in high temps Saturday, while 
maintaining dry conditions. Meanwhile, southeasterly low level flow 
will increase through the day as a cold front begins to approach 
from the west. Moisture levels are expected to increase enough near 
the coast for the possibility of a few light showers by the 
afternoon. Lows tonight will range from the upper 40s and low 50s 
inland to upper 50s along the coast. Highs on Saturday will climb 
into the low to mid 70s. /13

SHORT TERM /Saturday night Through Monday night/...An upper level
low over the south Plains pushes east into the lower Mississippi
River Valley and Mid South Saturday night into Sunday. Upper 
level height falls ahead of this system, in conjunction with upper
diffluence associated with the left exit region of a jet max 
rotating through the base of the trough, will serve to increase 
deep-layer ascent along and ahead of an attendant surface front. A
quickly moistening warm sector ahead of this front should see 
enough destabilization (~500 J/kg MLCAPE) to support showers and 
thunderstorms, with the best potential for thunder coincident with
the greatest forcing and instability along the front and near the
coast. Veering deep layer wind profiles and effective bulk shear 
magnitudes at or above 40 knots could allow any stronger cells to 
become better organized and capable of producing severe weather. 
Given the uncertainty in available instability, however, only a 
marginal threat is in place at this time. Generally expecting 
rainfall amounts of up to 2 inches with this system, with local 
amounts up to 3 to 4 inches not out of the question. These totals 
may not appear heavy at first glance, but it should be noted that 
those who received significant rainfall with the previous system 
(i.e., interior southeast Mississippi and southwest Alabama) are 
likely to be more vulnerable to flooding than normal, as this 
additional rainfall only exacerbates the already elevated rivers 
and streams.

The cold front pushes through Sunday night into early Monday as
the upper low weakens and pushes off to the east, eventually
settling over the southeastern states Monday and Monday night.
The passage of this front should mark the end of precip for most,
particularly near the coast. Farther inland, could see some light 
showers continue throughout the day Monday in the wraparound
region of the surface low. /49

LONG TERM /Tuesday Through Friday/...The upper low stalls over 
the southeastern states as another quick-hitting shortwave rotates
through the region to start the long term period. Lingering 
wraparound moisture over inland and western portions of the area 
should be enough to squeeze out some showers as this shortwave 
passes through Tuesday.

The first in a series of troughs digs from central Canada 
southeast into the upper Mississippi River Valley and Midwest on 
Wednesday, helping to finally push that stalled upper system over 
the southeastern states east and away from the area. As the former 
trough continues to dig into the eastern CONUS, it pushes another 
cold front southeast towards the Gulf coast. We see a bump in rain
chances along and ahead of that front Wednesday night before it 
passes through and brings dry conditions Thursday. Dry weather 
will be short lived, as the next in the series of upper troughs 
digs into the upper Midwest Thursday night. This pushes yet 
another front towards the area, with moisture quickly returning 
and rain chances increasing Friday ahead of the front. /49

MARINE...A moderate easterly flow tonight will increase on Saturday 
as a cold front approaches from the west. A moderate to sometimes 
strong southeast to south flow develops Saturday night ahead of the 
front. Winds become westerly in the wake of the front by Monday, 
with a light to moderate west to northwest flow then continuing into 
the middle part of mid next week. /13

&&

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

$$

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