Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 301210

Area Forecast Discussion
National Weather Service Birmingham AL
710 AM CDT Tue May 30 2017

For 12Z Aviation.


Today and Tonight.

A second front will dig south/southeast out of Missouri and Kentucky
and across Tennessee toward the stalled front across the northern
portions of Mississippi and Alabama today. The synoptic forecast
thinking has changed little, in that we are still expecting this
second front to make minimal headway into Alabama as the parent low
breaks away today as it moves northward across Ontario. So, this
front should stall too and weaken as it enters the state. The upper
flow remains unsupportive as we have a west southwest/zonal
configuration. Being generally south of this boundary, we will
continue to be in a rather moist environment. Rain chances for today
will consist of several shortwave impulses going through this upper
flow. While the main rain band now is across the south half of the
area, latest hires guidance are pointing toward a shift in this
during the morning to a band further northward across the I-20
corridor and then during the afternoon a second shift to one in the
southeast 1/3 of the area more toward the I-85 corridor by late
afternoon and early evening. These smaller scale features have been
difficult to pinpoint. In any case, many are likely to get rain
today, but it should not be constant for the whole day. With
increased cloud cover and rain chances, we are looking at mild high
temperatures, but again still very humid. Rain chances are expected
to taper off in the southeast by late evening as the shortwave exits
and with the loss of daytime heating.


Wednesday through Monday.

The upper-level trough and embedded closed upper low in the Great
lakes/Ontario region will be lifting northeastward away from the
forecast area Wednesday, resulting in weak height rises over
Central Alabama and a transition to westerly to west-northwesterly
upper-level flow. The lack of upper-level forcing should result in
convection following the typical diurnal cycle. PWATs and 1000-500
mb mean RH values indicate the best coverage of scattered
afternoon convection should be in southern Central Alabama where
PWATs will be in the 1.5 to 1.7 inch range. Further north, deep
layer moisture will be more limited, but some convection may
develop on a weak surface boundary moving in from the north.

The upper-level pattern across the country will be fairly blocky
through the rest of the week, with a high amplitude ridge
extending northward from the Plains through the Canadian Prairies
to the Arctic. The blocking pattern shows some characteristics of
a rex block with a southern stream trough located south of the
ridge and some characteristics of an omega block with troughs over
eastern Canada and the northeast Pacific. Central Alabama will be
in a weakly forced, moist/humid pattern, with the potential for
occasional southern stream disturbances to eject out of the
southern stream trough over northern Mexico. Elevated moisture
values indicate generally elevated chances of diurnal summertime
scattered showers and storms, though exactly how elevated will
depend on weak disturbances and remnant boundaries. Wednesday
night, a back door cold front may move into northeast Alabama and
temporarily bring in some drier air in northeast Alabama into
Thursday, while also potentially serving as a trigger for activity
on Thursday. Meanwhile, increasing moisture in southwest Central
Alabama ahead of a southern stream disturbance should result in
fairly good coverage of showers/storms Thursday afternoon there.

As we move into the upcoming weekend, a strong Pacific jet moving
into the West Coast should allow the blocky pattern to start
moving again. This may allow the main southern stream trough to
move into Central Alabama by Sunday and allow for enhanced rain
chances by then. However, the latest ECMWF has trended much weaker
and slower with this trough. Will maintain likely rain chances on
Sunday for now but these may need to be adjusted if this new trend
holds. A front may also approach the area towards the beginning of
next week. Overall, through the extended period temperatures will
be close to normal, with highs in the 80s, with the typical
summertime risk of a few strong storms.



12Z TAF Discussion.

Shortwave TSRA activity expected to continue today again with some
lower cig/vsbys at times for the terminals due to convection.
Activity is expected to taper off from west to east during the
late afternoon and evening hours as the shortwave exits to the




Scattered to numerous showers and storms will be possible each
day as we remain in a moist summer pattern across the area.
Critical fire weather conditions are not expected due to abundant
low level moisture.


Gadsden     79  62  83  63  83 /  60  20  30  10  20
Anniston    78  63  83  63  84 /  60  20  30  10  30
Birmingham  80  65  85  66  84 /  60  20  30  10  40
Tuscaloosa  80  65  87  65  86 /  60  20  30  10  40
Calera      79  65  83  65  85 /  60  30  40  10  40
Auburn      80  65  83  66  83 /  60  50  40  20  40
Montgomery  82  66  86  68  87 /  60  50  50  20  40
Troy        83  65  87  65  86 /  60  40  40  20  40





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