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Area forecast discussion
National Weather Service Birmingham Alabama
1056 PM CST Mon Nov 18 2019

for 06z aviation.


Short term...
/updated at 0943 PM CST Mon Nov 18 2019/

An upper trough will move over central Alabama overnight. The
latest satellite imagery has plenty of mid and upper level cloud
cover approaching from the west. The local radars off to the north
and west were also indicating some returns. The local area raobs
displayed a very dry layer from around 850mb to almost 500mb.
Looking upstream in Arkansas and Missouri, this dry layer moistens
up significantly, but still dry below around 7k ft. The upward
motion and lift remain mainly north of I-20 into early Tuesday. It
appears that most of this activity will be virga or perhaps some
sprinkles. If more substantial reflectivities shows up, it will
not amount to much in the way of rain. At this time, will keep the
rain chances below 15 percent north and not mention.

The temperatures were dropping like a rock again this evening.
Therefore, the trend has been altered for this current trend. But
the trend will not last. As the clouds move in, the temperatures
should level off or slow the downward trend. Made some changes in
the lows and have a few spots in the 30s while most everyone stays
in the 40s. The last challenge was fog development. Due to the
cloud cover and the slow down of the temperature drop, fog
formation north appears iffy at best and removed from mention.
Farther south where lesser clouds will be, there could be some
patchy fog especially in the cooler valleys and near water bodies.
The upper system exits east early Tuesday and drying commences


Previous short-term discussion:
/updated at 0254 PM CST Mon Nov 18 2019/
through tonight.

A weak front has moved through the area today, with an increase
in high level clouds. Low level cool advection and added clouds
have kept temperatures 8-10 degrees cooler across much of the area
today. The exception being the southeast, which warmed into the
low 60s ahead of the front. Tonight, passing mid and high level
clouds are possible as a second upper level trough axis crosses
the deep south. Surface winds however diminish as surface high
pressure builds across the area. With light winds, localized
valley fog will again be possible overnight. Lows tonight will
fall into the mid 30s to around 40 degrees.


Made some updates to the extended forecast for days 5-7 based on
improvements in the model guidance with the latest run. A low-level
shortwave trough will eject northeastward from the Central Plains to
the Great Lakes region on Thursday. At the surface, an associated
cold front will initially extend through the Tennessee Valley where
it will slow across portions of western Tennessee and northern
Mississippi. Pops were raised to around 60-70 percent in our
northwestern counties on Friday where showers are more likely to
develop. Meanwhile, a secondary upper low will move across the
Midwest late Friday and induce low-level cyclogenesis along the slow
moving front. The newly developed low will finally push the cold
front through central Alabama by Saturday night. Guidance is in better
agreement on the timing of the front, although some spread remains.
Made some minor raises to the pops with most rainfall expected
generally Friday night through Saturday afternoon. Also trended
temperatures a few degrees lower on Sunday as breezy northwesterly
winds and cold air advection encompass the region.


Long term...
/updated at 0241 am CST Mon Nov 18 2019/
Tuesday through Sunday.

Northwest flow aloft will be present on Tuesday as a trough
departs to the east, and ridging builds over the plains downstream
of a digging trough over the northwest Continental U.S. And a cutoff low off
the coast of Baja California. Southwest winds at low-levels
associated with a weak surface trough will advect in a warmer air
mass from the Southern Plains, allowing temperatures to rise into
the mid to upper 60s except in the northeast counties where clouds
may linger the longest. Winds will go calm overnight Tuesday night
as a surface ridge axis moves overhead. The mid-level ridge axis
moves overhead on Wednesday as the baja cutoff low ejects over the
Central Plains as an open wave, and induces Lee cyclogenesis at
the surface. Meanwhile, another upper low will close off over
Southern California. Westerly flow aloft and a dry air mass will
favor a continued warming trend, and favored the warmest
mav/met/hex guidance for highs. Southerly winds over all but the
far eastern counties will result in somewhat milder overnight lows
Wednesday night.

The shortwave trough and associated surface low will lift up into
the Great Lakes region Thursday. The trailing cold front will
stall across the mid-south by Friday morning as it becomes
parallel to the flow aloft, and as the southwest Continental U.S. Upper low
begins to eject eastward towards the southern High Plains,
beginning to cause a wave of low pressure to develop along the
front over the Southern Plains. Weak waves in the southwest flow
aloft and increasing mid-level moisture could trigger a couple
showers in the northwest Thursday afternoon. Otherwise, pleasant
conditions are expected with highs in the low 70s. The front and
associated pre-frontal moisture axis will serve as a potential
trigger for shower development Thursday night. Deterministic
models have trended much drier for this period, but with a fair
amount of ensemble members being wetter, only made gradual changes
to the pops. There still continues to be model/ensemble member
spread for the Friday/Saturday timeframe regarding the shortwave
trough/upper low moving eastward from the Southern Plains and
possible phasing with the northern stream. This has associated
impacts on surface low development along the front and the
eventual cold frontal passage. Generally leaned towards the
European ensemble mean and wpc guidance through this period, with
highest rain chances appearing to be in the Friday night to
Saturday morning timeframe. Further refinement will be necessary
in later updates. Instability within the narrow warm sector
continues to be very limited, so will continue to leave out a
mention of thunder, but will continue to monitor. Dry conditions
will eventually move in behind the front ahead of another trough
moving into the western Continental U.S..



06z taf discussion.

General trend of the terminal forecast where held onto this
period, but the fog mention was reduced. Mid level clouds
associated with an upper trough will produce ceilings in the
090-110 range and this will hold off the fog development at all
the northern sites. It appears that mostly clear conditions will
last longer at mgm/toi before some clouds make it southward. Added
a tempo MVFR fog for these two sites for a few hours before
temperatures level off and clouds are around the area. If lesser
clouds move southward, fog potential could develop and last a
little longer. Otherwise, the mid level clouds move west to east
into Tuesday morning and exit the area. No ceilings at most
terminals by 15-16z. Winds will start off light southwest and
swing southwest and west at 6-9kts g14-18kts. Winds go light after



Fire weather...

Dry conditions continue through much of this week with relative
humidity values near or above 40 percent each afternoon.
Localized valley fog will lift quickly Tuesday after sunrise.
Although relatively light, winds will become westerly Tuesday and
then southerly Wednesday, ahead of the next weather system. Rain
chances increase Thursday, remaining elevated through the end of
the week.


Preliminary point temps/pops...
Gadsden 38 62 36 66 40 / 10 10 0 0 0
Anniston 38 63 38 68 43 / 10 10 0 0 0
Birmingham 39 64 40 70 45 / 10 10 0 0 0
Tuscaloosa 39 67 40 70 45 / 0 0 0 0 0
Calera 38 64 39 70 44 / 0 0 0 0 0
Auburn 41 62 41 68 44 / 0 0 0 0 0
Montgomery 40 67 41 72 45 / 0 0 0 0 0
Troy 39 66 41 71 45 / 0 0 0 0 0


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