Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Mobile Alabama
1115 am CDT Sat Apr 25 2015
Update...the forecast has been updated to reflect newly issued
Severe Thunderstorm Watch 111 in effect for southeast Mississippi
through 6 PM this evening. Current satellite imagery indicated an
increasing area of thunderstorms over central Louisiana moving
eastward. Downstream...breaks in the clouds this morning have allowed
instability levels to increase with MLCAPE values of 1000-1500 j/kg
across the area. In addition...deep layer shear values around 50 kts
and steep middle level lapse rates will favor large hail in the stronger
storms this afternoon along with damaging straight line winds. The
tornado threat is minimal due to weak sunrise helicity as surface winds remain
southwest. Updates have already been sent. /13
Previous discussion... /issued 630 am CDT Sat Apr 25 2015/
Aviation... 12z issuance...currently...the eastern third of the
area will be dealing with two lines of thunderstorms and rain moving east over them.
Generally low end MVFR level ceilings will see drops well into IFR levels
as these lines pass. The rest of the area...and these areas after
the lines move out...will see a break...with more thunderstorms and rain expected to
develop this afternoon. Tonight...with winds settling as they become
more southwesterly...IFR level ceilings in Post system stratus are
Short term...(today through monday)...for today through tonight...
with rain ongoing...have to be brief. A passing upper system will
bring rain today. With upper support and pretty good wind
shear...some may become severe...especially over areas along and
north of Highway 84 this morning. As the day progresses...and this round
of rain ends...heating is expected to occur...upping the instability
available and creating a second chance of rain today. With backing of
the low levels winds to southwest...wind shear will decrease...but
the risk of strong to severe remains for this afternoon into the
For Sunday through Sunday night...a lobe of energy swings south
around the west side of an upper system meandering around off the New
England coast...driving a surface front towards the forecast area Sunday...and
to the coast by Monday morning. With upper ridging over the miss River
Valley as an upper low moves east over the southern rockies...pushing
against the aforementioned upper system off the New England coast.
The result for Sunday is temperatures well above seasonal...with some areas
seeing the first 90s of the year. Sunday night...a weak front moves
across the forecast area to near the coast...meeting a trailing front left by
today's system. This weak front does help to cool the northern half
of the forecast area....but overnight temperatures remain above seasonal.
Monday...the southwestern system moves over the Southern Plains...and
with a surface low trying to organize off the Texas coast...
southeasterly flow over the Gulf begins to strenghten the surface
boundary along the northern Gulf Coast. After a short dry spell...an
increase in cloud cover will help to limit heating and keep daytime
highs closer to seasonal...especially over western portions of the
forecast area...along with bringing the next chance of rain back to the area.
Long term...(monday night on)...Monday night through Wednesday...the
upper system over the plains moves east...opening as more energy
dives south over the northeastern Continental U.S.. a surface low organizes
Monday night off the Texas coast and moves east...south of the northern
Gulf Coast with this set of guidance. With the slow eastward movement
of the upper dynamics...an extended period of rain is expected.
Running from late Monday through Wednesday...this will help to limit
the diurnal temperature range and keep daytime highs well below seasonal and
overnight lows around seasonal for this sections of the forecast.
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
Marine...a moderate southeasterly flow will turn southwesterly
today as a warm front moves northward across the coastal waters. A
moderate southwesterly flow will then persist through Saturday night
before becoming light Sunday. Winds turn southeasterly Monday as
another frontal system approaches the area. A moderate northwesterly
flow then develops Tuesday night in the wake of a cold front.
Preliminary point temps/pops...
Mobile 84 70 89 67 83 / 70 10 10 05 20
Pensacola 83 72 87 70 83 / 70 20 10 05 20
Destin 80 74 82 70 81 / 60 20 20 10 20
Evergreen 84 68 89 62 83 / 70 10 10 05 10
Waynesboro 85 67 90 64 80 / 70 10 05 05 20
Camden 84 68 89 61 80 / 70 10 05 05 10
Crestview 84 70 90 65 86 / 70 20 10 05 20