Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kmob 221159 

Area forecast discussion
National Weather Service Mobile Alabama
559 am CST Mon Jan 22 2018

Discussion...updated for latest aviation discussion below.


22/12z issuance...MVFR to occasional LIFR conditions due to low
clouds and patchy fog early this morning, then generally MVFR due
to clouds and rain showers/thunderstorms and rain late morning through early evening
although brief periods of IFR possible in and near tsra's. Surface
winds southeast to south today into this evening, becoming west
and northwest overnight.Higher gusts will be likely in and around
showers and thunderstorms from late morning through early evening.


Previous discussion... /issued 439 am CST Mon Jan 22 2018/

Near term /now through Monday night/...upper low pressure situated
over the Central Plains states early this morning will lift
northeast to the Great Lakes by late tonight. Meanwhile, the
accompanying large upper trough axis over Texas this morning will
move east into the southeast. Associated surface cold front now
moving east into Lousiana should be just to the west of our forecast
area by around midday, and move east across our forecast area this
afternoon and early evening. In advance of the front, look for areas
of fog, dense in a few coastal locations, early this morning
followed by an increase in showers and thunderstorms across the area
from late morning through early evening as the front moves across
the area. Upper jet dynamics look to be well north of the forecast
area today as the upper low lifts away, but a low level 850mb jet
initially up to 45 knots this morning over northwestern zones,
although weakening slightly to 30 to 40 knots during the course of
the day. Mid level lift seems to split across the area today as the
system moves east, with best lift being to the north of the forecast
area, and also to the south out over the Gulf. As such, most of the
mesoscale models decrease the coverage of convection along the front
as it moves east, keeping storms most numerous near the coast and
offshore. This being said, will continue to advertise likely pops
across the area today. Storm Prediction Center continues to have most of our area
outlooked with a marginal risk of strong to severe storms, and with
the factors noted above, plus with Max mixed layer cape values today
ahead of the front possibly as high as 500 to 700 j/kg and with mid
level lapse rates ranging from 5 to 6 c/km. As a result, any of the
storms that do hold together as the system moves east across our
area could be strong to briefly severe, with damaging wind gusts
being the primary threat. Wind profiles indicate that a brief, weak
tornado or two could be possible, but this threat is very low. One
limiting factor is a marine layer of more stable air that could
extend inland from the Gulf as the onshore flow increases. This
possibility is already noted with the areas of advective fog that has
developed across the area this morning. This potential could lower
the already low threat of strong to severe storms and we will
monitor throughout the day. Showers and storms ending with a
windshift from the west and northwest after the front moves through
our area late this afternoon and early this evening. Highs today in
the lower 70s, except upper 60s at the coast. Lows tonight a little
cooler once again in the wake of the front, ranging from the lower
40s well inland to the upper 40s and lower 50s at the coast. 12/ds

Short term /Tuesday through Wednesday night/...the upper system
that pushed a front across the area in the near term continues to
move east as more energy moves southeast over the northern
plains/Ohio River valley/mid Atlantic region. This second round of
energy pushes a second front southeast across the eastern conus.
The southeasterly push of his second front slows down the eastward
movement of Post-frontal high pressure, along with placing its
southerly push of cooler air well to the east of the forecast
area. Result for the forecast area is cooler and drier air moving
over the area Tuesday into Wednesday as the surface high moves
over the area, but any secondary push of cooler air is west of the
area. The cooler air mass drops daytime highs to around seasonal
levels whilst the drier airmass helps to drop to below seasonal
Tuesday and Wednesday nights. A light freeze is possible Wednesday
night over parts of the inland counties.


Long term /Thursday through Sunday/...more shortwave energy moves
east over the western conus Thursday to over the plains into
Friday night. In combination with a shortwave being pushed from
over the Southern Plains, the surface high over the forecast area
gets pushed off the East Coast and onshore flow off the Gulf is
restored over the Southern Plains and lower Mississippi River
valley. Best moisture flux inland remains generally west of the
forecast area through Friday, but a few shra are possible over
western portions of the forecast area. Temps moderate upward to
above seasonal levels with the return of east to southeasterly
flow over most of the area.

Friday night through the weekend, the models have diverged in
their solutions from previous runs. Both the European model (ecmwf) and GFS are
advertising shortwave energy moving across the Southern Plains in
addition to the energy moving east from the northern plains. This
southern energy develops a surface low over the northern Gulf
Saturday night, then takes it northeast over northern FL. Instead
of a front being pushed across the forecast area Saturday into
Sunday, this leads to more of an over-running precip situation
over land portions of the forecast area. This is a big departure
from previous runs, so am continuing to lean towards previous
solutions until guidance is more consistent. Result is a front
moving across the area Saturday night into Sunday, with best rain
coverage being Saturday ahead of the front. Temps remain a bit
above seasonal for daytime highs, much above for overnight lows.


Marine...a moderate onshore wind flow will continue today and
early this evening as a cold front approaches from the west. Areas
of sea fog over inland bays and sounds and the near shore Gulf
waters early this morning as the warmer and moist onshore flow lifts
north across the cool near shore waters. Showers and a few
thunderstorms developing later today as the front approaches, moving
west to east across the coastal waters later today and early this
evening. The front moves east across the marine area tonight,
bringing a moderate to occasionally strong offshore wind flow mid to
late week. Winds and seas generally near exercise caution through
most of the week, possibly increasing to small craft conditions late
in the week. 12/ds


Mob watches/warnings/advisories...

National Weather Service Glossary of Abbreviations