Scientific Forecaster Discussion
fxus64 kbmx 200029
Area forecast discussion
National Weather Service Birmingham Alabama
729 PM CDT sun Aug 19 2018
evening update and 00z aviation.
Extremely difficult to Pin Point the specific locations where
rain will fall as a rather chaotic setup continues. The latest
satellite imagery has the upper low spinning over the Central
Plains states with a short wave ridge just north of central
Alabama. The overall flow has not changed significantly the past
24 hours with a well defined moisture axis between northern and
southern areas, just north of Birmingham. This axis is also where
the instability axis exist. The overall low level moisture
convergence is limited and mesoscale driven. Where a brief bit of
sunshine peeked through and where meso scale boundary can aide
enough to kick off storms will be the best chance the next few
hours. Therefore, changed pops to include this instability axis
and where storms are in the southwest. Still expect a decrease in
coverage through the evening hours with the loss of daytime
heating and little low level forcing.
A band of thunderstorms will develop across northeast Texas and
Arkansas this evening ahead of a digging upper low over the
Midwest states. A decaying line of thunderstorms will likely move
across north Mississippi later tonight and could impact the
northwest counties of Alabama. Kept higher rain chances in this
area after midnight. Low clouds will likely form after midnight in
moist south to southwest flow. Boundary layer winds will stay in
the 10-15 range overnight, limiting any fog formation.
Monday through Saturday.
Models continue to indicate a well-organized system moving from
the Central Plains toward the Great Lakes on Monday into Tuesday.
A wide warm sector should be characterized by very high moisture
content, resulting in numerous showers and storms across the
forecast area on Monday. Models have been trending somewhat faster
with the upper-level shortwave and surface cold front for Tuesday,
and high rain chances should be focused along and southeast of
Interstate 59. During the Monday-Tuesday timeframe, deep-layer
shear appears to be insufficient for organized severe storms.
Wednesday has trended much drier with a more forceful frontal
passage, and rain has been removed from the forecast beginning at
12z Wednesday. Drier air and high pressure should remain in place
Wednesday night through early Friday, and temperatures may fall
well into the 60s each morning.
Easterly low-level flow may cause a moistening trend and increasing
rain chances from east to west on Friday afternoon into Saturday.
00z taf discussion.
Not a great deal of change to the main theme of the terminal
forecast the next 24 hours. Not a great deal of change to the
atmosphere and expect MVFR/IFR ceilings at all sites at some point
overnight into Monday morning.
Boundary layer winds will remain around 10kts overnight and this
should keep winds above calm in most spots. Therefore fog should
not be a widespread issue overnight. Low level winds remain south
to southwest and isentropic lift continues. This lift and
subsequent saturation will keep IFR clouds developing here and
there. The problem is when and how long these clouds are around,
similar to the previous few evenings. There are already clouds
below 010 and it will be another tough call. Went with the idea
that showers/storms will dissipate through the evening hours with
MVFR/IFR ceilings increasing in likelihood through 07z. Mention
mostly IFR from 07-13z. Thereafter, a mix of MVFR/VFR ceilings
before showers/storms redevelop. Winds south southwest 5kts or so
overnight increasing to 6-10kts after 16z.
Rain chances remain high through Tuesday as a cold front slowly
approaches the forecast area and the airmass remains unseasonably
wet. Low stratus and patchy fog will be possible, with conditions
improving with sunrise each morning. Drier conditions expected
after Wednesday through the end of the week. There are no fire
weather concerns at this time.
Preliminary point temps/pops...
Gadsden 70 86 72 86 68 / 30 70 50 70 10
Anniston 70 87 73 87 69 / 40 70 30 70 20
Birmingham 72 88 74 87 70 / 40 70 40 70 10
Tuscaloosa 72 89 74 90 70 / 50 70 50 50 10
Calera 71 87 73 87 70 / 50 60 30 70 20
Auburn 71 86 72 87 71 / 40 60 30 70 30
Montgomery 73 89 74 90 72 / 40 60 30 70 30
Troy 72 88 73 89 72 / 40 60 30 70 30