Area forecast discussion...aviation update
National Weather Service Mobile Alabama
1140 PM CDT Monday may 20 2013
Aviation (21.06z issuance)...MVFR ceiling and visbys expected to
develop again overnight and continue through early Tuesday morning
before improving. VFR conditions will then prevail through the
remainder of the period. /13
&&
Short term (tonight and tuesday)...as a lobe of energy swings
around the base of an upper low over the northern plains...it pushes
a piece of energy over the southeastern Continental U.S. East of the forecast area off.
This piece of energy pushed a weak boundary across northeastern
sections of the forecast area...but nothing in the way of precipitation has resulted
for the forecast area. What has developed by the time of this writing is well
to the east of the forecast area. With low level winds light and variable...am
not expecting any organized systems to move towards the forecast area for the
evening.
For the forecast...have went with a dry forecast forecast. For
skies...have went with stratus moving inland over the western
quarter of the forecast area...closer to the more organized onshore flow. The
rest of the forecast area...am expecting clearing skies and fog development.
With guidance pretty consistent in the transition zone being along
the miss/Alabama state line. Have used that as a general
boundary...though have not kept all the stratus west of the state
line. Am not quite buying the GFS/mav temperatures...with fog/dew
development limiting overnight cooling above what the mav was
advertising. Have leaned towards the warmer NAM/met overnight temperatures
for the forecast.
For Tuesday...the upper ridge moves east of the area...but am still
expecting temperatures to be above seasonal. /16
For Tuesday night through Thursday night...ridging over the forecast
area breaks down Tuesday night as a vigorous shortwave moves through
the base of a plains longwave trough. The shortwave continues
eastward and moves mostly across the interior portion of
Mississippi/Alabama on Wednesday. A surface ridge remains near the
coast meanwhile with an onshore flow continuing over the forecast
area and another afternoon sea breeze expected to develop.
Model soundings show lingering effects of ridging previously over
the area will be sufficient to continue with a dry forecast Tuesday
night. The environment becomes more favorable for convection on
Wednesday...more so west of the I-65 corridor. Surface based convective available potential energy
increase to 1500-2000 j/kg west of I-65 Wednesday afternoon and
1000-1500 east of I-65. Will have probability of precipitation increasing during the day to
chance generally west of I-65 with slight chance probability of precipitation east of I-65
where comparatively less favorable conditions exist. Will have
chance probability of precipitation continuing over much of the interior portion of the area
Wednesday night with slight chance probability of precipitation elsewhere for both lingering
convection and as another...albeit weaker...shortwave approaches the
forecast area overnight.
The longwave trough continues eastward into the eastern states through
Thursday night while a longwave ridge amplifies over the central
Continental U.S.. a surface low near the Great Lakes region moves off to the
northeast and sends a weak trailing front deep into the southeast
states...which moves into the central portion of the forecast area
on Thursday...then continues southward into the coastal waters
Thursday night. Model soundings show better moisture in the 800-900
mb layer although with somewhat unfavorable lapse rates in the
700-800 mb layer. Surface based convective available potential energy will increase to around 2000
j/kg and with both a sea breeze developing during the day and the
weak frontal boundary moving into the area...chance probability of precipitation are
supported. With model soundings also showing middle level drier air
beginning to move into the region...may see a few strong pulse
storms develop. Temperatures will be near seasonable values except
for several degrees above normal over inland areas during the
afternoon. /29
&&
Long term (friday through monday)...the longwave trough moves off
into the Atlantic through Saturday with the longwave ridge gradually
building eastward into the eastern states through Monday. A large
surface ridge builds into the eastern states through Saturday with a
surface ridge becoming established over the southeast states Sunday
into Monday. Daytime highs will be a few to up to several degrees
above seasonable levels Friday through Monday. A northerly flow
prevails Friday and Saturday but expect the sea breeze to be confined
to near the coast with the sea breeze making progressively more
headway inland Sunday into Monday.
Progressively drier deep layer air flows into the area on Friday and
generally persists through Monday with precipitable water values as
low as 60 percent of normal. Have continued with slight chance probability of precipitation
near the coast on Friday with a dry forecast otherwise through
Sunday. Although deep layer moisture will be below seasonable
values...with the sea breeze becoming more active on Monday...will
have slight chance probability of precipitation Monday. /29
&&
Marine...a surface ridge stretching west over the northern Gulf
Coast will begin to break down Wednesday as an upper trough swings
east over the plains/miss River Valley middle to late week. Until
then...light to at times moderate onshore flow will dominate area
coastal waters.
As the surface ridge begins to break down...with part shifting west
to over the northwest-eastern Gulf of mex...offshore flow returns to the area.
As the upper system creating the trough moves to over...then east of
the eastern Seaboard...a weak to moderate trailing front moves over
the area Thursday night into Friday. A surface ridge builds east
over the eastern Continental U.S. Into the coming weekend...with the offshore
flow becoming easterly by Sunday. /16
&&
Preliminary point temps/pops...
Mobile 67 87 67 86 67 / 00 05 05 30 20
Pensacola 69 87 70 85 69 / 00 05 05 20 20
Destin 70 84 72 83 71 / 00 10 05 20 20
Evergreen 66 91 65 90 65 / 00 10 05 30 30
Waynesboro 66 90 66 86 65 / 00 10 10 40 30
Camden 66 90 65 88 65 / 00 10 10 30 30
Crestview 66 92 65 91 65 / 00 10 10 20 20
&&
Mob watches/warnings/advisories...
Alabama...none.
Florida...none.
MS...none.
GM...none.
&&
$$
