Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 030526

Area Forecast Discussion
National Weather Service Birmingham AL
1126 PM CST Fri Dec 2 2016

For 06Z Aviation.


Tonight through Saturday Night.

We have ample sunshine once again this afternoon with only some
scattered cirrus to note on satellite. We are looking at one more
rain free night across Central Alabama before rain returns. During
late tonight into Saturday, we will see a shift in the overall
pattern as the surface ridge center shifts to the Upper Midwest
and flattens some yielding a meager east southeast onshore flow.
Low level onshore flow will increase as we head into late
Saturday/Saturday night as a surface low develops on the Texas

At the same time, in the upper levels on Saturday, an upper low
develops and digs into the Southwest U.S. and into Northern
Mexico. This will in turn shift our upper zonal flow to a more
southwest flow regime and allow for shortwaves to be ejected from
the closed low and then across Alabama. Thus, we should see rain
chances return beginning in the west part of the state during the
middle to late morning Saturday and then spread eastward across
the area to become more widespread by Saturday evening. I only
have rain showers in the forecast and no thunder for Saturday and
Saturday night at this time as we have a long way for dew points
to recover with values only in the 30s generally and a couple of
40s expected during the day on Saturday and then more widespread
40s overnight.


Sunday through Thursday.

No changes to previous forecast thought from earlier this morning.

/Issued 308 AM CST Fri Dec 2 2016/

An active southern stream will continue into next week with several
upper level impulses bringing copious amounts of rainfall to
central Alabama. The time periods which look to contain the
heaviest rainfall are during the day Sunday and Monday afternoon
into Monday night. There will likely be a relative lull in the
shower activity Sunday night as a northern stream short wave trof
passes east of the area. Low level easterly flow Sunday and Sunday
night should keep the air mass too stable for thunderstorms. A
surface low will likely form near the upper Texas coast on Monday
and shift rapidly northeast as the main short wave trof ejects out
of northern Mexico. A low level jet will develop across the
central Gulf coast states with 60+ surface dewpoints pushing into
south Alabama Monday afternoon. The GFS model is more aggressive
with the inland surge of higher dewpoints than the ECMWF, and its
convective parameters are higher with regards to CAPE and lifted
indices. The GFS model would produce a minimal threat of severe
storms to the far southern counties Monday afternoon and evening,
but will hold off mentioning severe wording in any of our hazard
products due to more stable ECMWF model. The final push of
showers and storms will be Monday night with the rain exiting east
Alabama Tuesday morning. Because this system originated so far
south, there is no big change in air mass and highs Tuesday and
Wednesday will be in the 60s.

A strong cold front will arrive on Thursday accompanied by a pre-
frontal band of showers. The ECMWF model is much slower with the
passage of the cold front, so confidence is low regarding best
chance of rain and temperatures on Thursday, but the coldest air
of the season will arrive Thursday night and Friday.



06Z TAF Discussion.

High clouds overspreading the area should become mid-level around
daybreak and persist as VFR through the remainder of the TAF
period. Dry air will initially prevent rain from reaching the
ground, but light rain seems likely to affect the northern sites
beginning in the mid to late afternoon and continuing through the
end of the period. VIS and CIGs should not be an issue until after
the TAF period.




Rain free conditions are expected through tonight. Widespread
showers will return to the area this weekend and remain in the
forecast for the first half of next week. A few thunderstorms will
be possible as well for Monday.





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