Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Mobile Alabama
1212 am CDT sun Apr 26 2015
updated for the latest aviation discussion below.
except for some areas of cirrus/cs closer to the coast...p6sm sky clear
conditions were generally noted across terminals across the forecast
area late this evening. The problem for the 26/0600 UTC taf package
remains centered around boundary layer conditions...and possible
flight category reductions due to low ceilings and reduced visibilities.
Latest available forecast soundings continue to develop the
subsidence inversion overnight...as well as maintaining boundary
layer wind speeds of 10-15 kts. However...it doesn't appear the layer
between the surface and base of the inversion will be quite as moist.
As such...lower ceilings will likely be slower to develop and associated
timing in the latest terminals has been adjusted accordingly. /Butts/
Previous discussion... /issued 710 PM CDT Sat Apr 25 2015/
updated for the latest aviation discussion below.
in wake of this afternoon's shra/tsra...with only a few spotty -shra
remained S of the ih-10 corridor early this evening. Considering the
low probability of getting precipitation at any of the major coastal
terminals over the next 2-3 hours...there will be no mention of
precipitation in the 0000 UTC taf package.
Problem for this taf package will involve the boundary layer...and
IFR flight categories due to low ceilings and patchy fog. Forecast
soundings develop a subsidence inversion overnight...but maintain
boundary layer winds of 10-15 knots. Given ample ground moisture...I
feel we will see some patchy fog even with the elevated boundary
layer winds. However...low cloud development should be more abundant
overnight. Probabilistic guidance suggests the greatest odds of
seeing IFR ceiling development between 26/0600-0900 UTC. As such...I have
adjusted the timing with the latest taf package. The inversion should
lift shortly after sunrise...allowing VFR flight categories to return
by middle-morning Sunday. /Butts/
Previous discussion... /issued 525 PM CDT Sat Apr 25 2015/
area radars show the line of strong/severe storms has moved east of
our region early this evening. Clusters of strong storms continue
moving eastward across the offshore Gulf of Mexico waters...but
should remain over the marine area into this evening. Based on
this...we have cancelled the Severe Thunderstorm Watch for the
remainder of our forecast area. No other significant changes have
been made to the forecast at this time.
Isc grids have been sent and should be posted to the internet.
Updated text products will be issued shortly. /Butts/
Previous discussion... /issued 424 PM CDT Sat Apr 25 2015/
Short term [tonight through Sunday afternoon]...breaks in the cloud
cover have allowed temperatures to warm into the low/middle 80s. This has
created moderate instability with MLCAPE values around 1500 j/kg.
The instability combined with deep layer shear around 50 knots will
lead to the potential for strong to severe thunderstorms through the
remainder of the afternoon and early evening. A Severe Thunderstorm
Watch remains in effect for most of the area through this evening.
The driving upper shortwave will move east tonight taking the
thunderstorms with it. A weak cold front will move into the area on
Sunday. A drier atmosphere along with weak upper dynamics will keep
precipitation chances low with only an isolated shower or thunderstorm
possible near the coast. Lows tonight will fall into the upper 60s
inland to low 70s along the coast. Highs on Sunday will climb into
the middle and upper 80s. /13
[sunday night through Monday night]...weak upper ridging will remain
across the region as a closed upper low pressure area over New
Mexico moves slowly eastward over the Texas Panhandle and Oklahoma.
A dry cold front approaching the region from the north on Sunday
will move through the area Sunday night and then stall just south of
the coast through the remainder of the short term. The northern
portions of the forecast area will remain dry through Monday
evening...with isolated to scattered showers and a few storms
lingering along the coastal sections close to the stalled front. A
developing surface low across the western Gulf of Mexico on Monday
will move east-northeast bringing numerous rain showers and
thunderstorms back into the area by late Monday night...mainly
across the southwestern portion of the forecast area.
Lows Sunday night will range from 60 to 65 degrees inland areas...
and from 65 to 70 degrees across the coastal sections. High
temperatures on Monday will range from 78 to 84 degrees. Lows Monday
night will be cooler ranging from 53 to 58 degrees across the
northern half of the forecast area...and from 59 to 65 degrees
across our southern areas. /22
Long term [tuesday through saturday]...the upper system over the
plains moves east...opening as more energy dives south over the
southeastern Continental U.S.. a surface low organizes further over the north
central Gulf of Mexico on Tuesday and moves east along the northern
Gulf Coast through Wednesday morning. With the slow eastward
movement of the upper dynamics and surface low...an extended period
of rain showers and thunderstorms moving back into the area through
Wednesday night through Thursday night...the medium range guidance
diverges. The European model (ecmwf) takes the former southwestern Continental U.S. Energy and
the energy diving south over the eastern Continental U.S....merges them and
organizes another upper low over the Carolinas and takes it east
over the open Atlantic. The result for the forecast area is stronger...cooler
northerly air move over the forecast area. The GFS is advertising a piece of
the upper energy breaking off and forming an upper low over the
Southern Plains...weakening the northerly push. Both are advertising
temperatures dropping below seasonal levels. The GFS ensemble mean is on
the higher side of group...so went in the middle...with numbers
close to the operational GFS. 50s return to the overnight temperatures and
daytime highs in the 70s expected.
Friday through Saturday...the differences continue...with the European model (ecmwf)
advertising a cool...Post system surface high moving east over the
southeastern Continental U.S. And the GFS advertising the upper low that
organized over the plains moves over the forecast area. Fortunately...both are
advertising temperatures around or a bit below seasonal...with rain not
25.18z kmob/kbfm and kpns taf cycle...
a line of thunderstorms will move across the area through middle and
late afternoon. MVFR/IFR conditions are possible in and near
scattered to numerous showers and thunderstorms. The strong storms
could also produce large hail and strong winds. Conditions will
improve this evening with patchy IFR/MVFR fog developing late
Marine...a moderate southwest flow tonight will decrease on Sunday
as a cold front approaches the marine area. The front will stall
offshore Sunday night. A light to moderate east to southeast flow
develops Monday into Tuesday as an area of low pressure develops
over the northern Gulf and moves eastward through middle week. An
offshore flow will develop in the wake of this system on Thursday
and continue through the end of the week. /13
Preliminary point temps/pops...
Mobile 70 87 65 81 63 / 05 05 20 40 60
Pensacola 72 85 69 81 66 / 05 20 20 40 50
Destin 73 81 70 82 65 / 05 20 20 30 50
Evergreen 68 88 61 83 56 / 05 05 05 05 20
Waynesboro 67 88 63 80 58 / 05 05 05 20 30
Camden 67 88 61 80 54 / 05 05 05 05 20
Crestview 70 88 64 85 61 / 05 05 20 20 40