Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Birmingham Alabama
1010 am CDT Tue Oct 16 2018
Updated for dense fog advisory expiration.
A slow moving cold front was positioned across central Alabama
this morning with temperatures falling into the 50's across our
far northern counties while readings are remaining in the low 70's
ahead of the front in our southeast counties.
An upper level disturbance will move east over the area later
today and will promote additional shower activity. Isentropic
processes will favor the highest chance of rain near and north of
the surface front.
Temperatures will range from the 60's to the north of the front
with readings in the 70's near the front and temperatures will
climb into the upper 70's to the low 80's south of the front.
The front is expected to stall later today between the I-20 and
I-85 corridors with best rain chances remaining near and north of
the surface front. Temperatures will again range considerably
overnight with lows in the upper 40's to low 50's north compared
to readings in the lower to mid 60's south of the front.
Wednesday and Thursday.
Lingering effects from frontal passage (fropa) will be felt on
Wednesday in the form of light rainfall scattered across the
forecast area through the evening. Northerly winds will continue to
provide cold air advection and decreasing tropospheric moisture
through Thursday as the center of high pressure in the plains moves
eastward to our north near the Ohio Valley. For now have placed 20-
30% pops in the forecast for Wednesday afternoon with decreasing
coverage & southward progression through the evening as low-level
confluent flow & isentropic ascent weakens. Temperature wise, 60s
and 70s are expected for daytime highs with a few counties in the
far southeast reaching the low 80s. Cool low temperatures Wed
night/Thu morning where mid to upper 40s are likely across the
north, increasing to upper 50s in the south under partly cloudy
skies. Dry on Thursday with pleasant conditions & temperatures,
highs in the mid 60s/upper 70s overall with a shift to easterly
winds as high pressure to our north slides towards the East Coast.
Friday through Sunday.
After a brief break in the weather, another approaching trough &
frontal boundary will enter the picture by Friday evening. A digging
trough and cold air mass will move from south-central Canada and
spill into the northern plains/Midwest before eventually moving
southward into our region Saturday. With easterly flow in place,
surface/low-level pre-frontal winds will veer with time giving a
small window of warm air advection and increasing moisture.
Frontogenetic forcing up through ~700mb will be in place across
field of higher moisture availability (pws ~1.6") and will likely
develop areas of light to moderate rain Saturday afternoon.
Instability looks to remain low, so have left thunder out of grids
at this time though wouldn't be surprised to see areas in the
southeast hear a few rumbles in heavier showers. Though isentropic
ascent keeps a slight chance of light rain across the south, this
system should move along fairly quickly with frontal passage expected by
Saturday evening. Subsidence will improve conditions thereafter with
drier air and sunny skies on Sunday. Highs in the low 60s/low 70s
expected by then.
Monday and Tuesday.
High pressure dominates weather conditions through the end of the
forecast period. After drying out on Sunday, the beginning of the
next work week appears to remain calm and pleasant as the jet stream
pattern remains under a period of transition. Split flow is
suggested in the extended with the polar jet amplifying back up into
Canada by Tuesday. A persistent upper-level low near the Desert
Southwest has been aiding in this configuration for the past several
days. Marginal flow aloft will remain in place here with westerly 300 mb
sub-tropical jet stream winds ~50 kts. Pre-dominant easterly winds
at the surface should keep daily our weather pleasant and dry
overall with temperatures in the upper 60s/lower 70s under mostly
12z taf discussion.
IFR ceiling pretty much across the north behind the cold front and
IFR visibility in the south as they remain south of the front.
Most of the fog in the south should dissipate by 9 or 10 am, while
the low clouds may have hang out until 15 to 16z. On and off
showers with a high chance at rain in the north to isolated to
scattered in the south. More IFR ceilings and visibility
overnight and into the morning hours.
Rain chances will increase today as a front slowly moves through
the region. Cooler readings return by mid week with a rain break
for late Wednesday into Thursday. However, rain chances return
again for late Friday into the weekend as another frontal system
moves into the area. No fire weather concerns are expected.
Preliminary point temps/pops...
Gadsden 72 55 67 48 71 / 90 70 30 10 0
Anniston 75 58 70 50 73 / 50 50 30 10 0
Birmingham 71 56 67 51 71 / 80 70 30 10 0
Tuscaloosa 71 57 69 51 72 / 80 60 30 10 10
Calera 74 58 69 51 72 / 50 30 30 10 10
Auburn 82 63 74 55 73 / 40 30 20 10 10
Montgomery 85 64 77 56 77 / 40 40 20 10 10
Troy 86 66 80 56 77 / 30 40 20 0 10