Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 100540
Area Forecast Discussion
National Weather Service Birmingham AL
1140 PM CST Fri Dec 9 2016
For 06Z Aviation.
Tonight and Saturday
Cold surface high pressure slowly moves eastward tonight and
Saturday. The main center of the ridge remains just north, but
good radiational cooling expected tonight and the winds becoming
light after sunset. A few of the cooler locations dropped into the
upper teens last night, and tonight will be colder area wide.
Generally have 20 to 25 degrees for lows but certainly some
temperatures of around 15 in outlying areas. No Hard Freeze
Warning will be issued due to the lack of coverage. Otherwise,
very little in the way of cloud cover.
850 temps do rebound from what they are today and advection
becomes neutral in the boundary layer by afternoon. Therefore,
temperatures will increase on Saturday and top out 2 to 5 degrees
warmer. Dry conditions continue on Saturday.
Saturday night through Thursday
Models are in fairly good agreement through Monday, before some
placement and timing differences occur regarding a frontal
boundary that will be stalled across the region during the first
half of the workweek before moving out late in the week. These
differences are due to the low-amplitude, quasi-zonal progressive
upper level pattern in place at this latitude, south of a deep cold
upper low moving across Canada.
Low temperatures will not be as cold Saturday night under light
southeast winds, but still make it into the upper 20s to low 30s.
A low stratus deck may approach the southeast counties by Sunday
morning as low-level moisture begins to return to the area.
Strengthening southerly flow will bring milder temperatures on
Sunday but also an increase in cloud cover due to moist isentropic
lift. Precipitation with the approaching system will remain west of
the area through the day on Sunday, but wouldn`t be surprised if
isentropic lift squeezes out a stray shower in the southeast Sunday
Low temperatures Sunday night will probably occur in the early
evening before temperatures gradually rise through the night as dew
points increase. A shortwave trough will move through the Midwest
and Great Lakes Sunday night into Monday as a surface low moves from
Kansas to Ontario. Meanwhile a trailing cold front will reach the
area by Monday morning. The main upper-level forcing will remain
north of the area, but there should be enough moisture pooling along
the front courtesy of a 45 kt LLJ, as well as isentropic lift and
glancing influence from the right entrance region of an upper-level
jet streak, for showers to be likely across the north late Sunday
night into Monday. Amounts will not be heavy, however. With
dewpoints remaining in the 50s instability looks to be negligible
through Monday morning. Models do indicate some instability
developing across the southern counties south of the front by Monday
afternoon which could allow for a few thunderstorms. The LLJ and the
upper-level dynamics will have left the area by then, so am not
concerned with severe weather at this time.
The front will stall near the southern counties by late Monday
afternoon. The ECMWF develops a surface wave and lifts the front a
bit further north Monday night before pushing back to the south
Tuesday night, while the GFS waits until Tuesday night into
Wednesday to lift it back north before pushing it back to the south
Wednesday night. These differences would be expected given the low-
amplitude pattern with spread present in the ensembles as well. Some
adjustments will need to be made to rain chances and temperatures
when models come into better agreement. Another shot of cold air
will move in behind the front Wednesday night, but should lag behind
any remaining moisture. Lows will probably need to be lowered either
Wednesday night or Thursday night when models come into agreement on
timing of the coldest air. Another rain-maker will arrive just
beyond the end of this forecast cycle.
06Z TAF Discussion.
Surface high pressure slowly builds into Central Alabama this
period with generally light winds and VFR conditions.
Relative humidity values will drop into 20 to 30 percent range on
Saturday afternoon. But, winds will be rather light. Moisture
begins to increase Sunday with rain chances returning late Sunday
night into Monday. While the best chances will be late Sunday
night into Monday, rain chances will remain a possibility through
the middle of next week as a front stalls over the area.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 17 46 25 54 47 / 0 0 0 0 50
Anniston 21 48 28 55 48 / 0 0 0 0 40
Birmingham 23 48 31 58 50 / 0 0 0 0 40
Tuscaloosa 21 49 29 59 53 / 0 0 0 10 50
Calera 22 49 30 57 51 / 0 0 0 0 40
Auburn 26 49 32 56 50 / 0 0 0 10 30
Montgomery 24 52 30 60 53 / 0 0 0 10 30
Troy 21 51 30 61 54 / 0 0 0 10 30