Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 181934

Area Forecast Discussion
National Weather Service Birmingham AL
234 PM CDT Wed Oct 18 2017

Through Thursday.

Little change in the low-level pattern/sensible weather is
expected through the short term period, with fairly wide diurnal
temperature ranges. Skies are crystal clear this afternoon with
temperatures in the low to mid 70s. Surface high pressure centered
along the Mid-Atlantic coast remains in control over much of the
eastern CONUS. The center of the surface high will retrograde
westward towards the southern Appalachians tonight and tomorrow.
Good radiational cooling conditions will be present again tonight,
allowing lows to again fall back into the 40s, with temperatures
near 40 in the typically cooler sheltered locations. Tomorrow, 500
mb heights will rise as a mid-level ridge axis moves into the
Lower Mississippi Valley, but continued east-northeast winds will
keep highs in check with only about a 3 degree increase expected.


Friday through Wednesday.

Latest GFS and ECMWF seem to be coming into better agreement on
the evolution and timing of the system affecting the area Sunday
into Monday, with the southern portion of the trough at least
partially closing off. Introduced some likely PoPs during the
Sunday night to Monday timeframe due to the better agreement,
and adjusted PoPs to indicate a slightly quicker exit Monday
night into Tuesday. Otherwise, the previous long term discussion
remains valid.


Previous long term discussion:

High pressure remains in place across the Southeast US Thursday
and Friday as an upper level ridge slides eastward across the
area. This could result in a little more efficient daytime warming
across Central AL by Friday afternoon allowing temperatures to
increase slightly above normal. By Friday night, a trough begins
to dig into the Western US, shifting the previously mentioned high
pressure eastward. This will shift our winds more southeasterly
to southerly beginning Friday night into Saturday, increasing
moisture across Central AL. The high amplitude trough continues to
deepen as it propagates eastward through the Central Plains and
into the Mississippi River Valley Saturday into Saturday night.

It`s at this point (Saturday night into Sunday morning) that models
begin to diverge significantly on the evolution of the trough. The
ECMWF has remained somewhat consistent the past few runs in bringing
the the associated cold front through Central AL as part of a phased
trough, increasing rain chances for Sunday and moving out by the
early part of next week. However, the 00z GFS has now returned to a
previous solution and is developing a cutoff low at the base of the
trough, which then hangs around the Gulf States for an extra day or
two, increasing rain chances through at least mid-week before it
gets picked up by the next trough. I have very little confidence in
the cutoff low solution, so have trended PoPs closer to the Euro at
this time. It should be noted, however, that models keep coming back
to this closed low development, so I don`t want to ignore that
solution completely just yet. For now, have increased PoPs to around
55% as the front moves through. As we get a better handle on the
timing, I could see these rain chances increasing.



18Z TAF Discussion.

VFR conditions will continue for the duration of the forecast
period with clear skies. Winds will remain under 10 knots this
afternoon generally from the east and northeast. Light and
variable or calm winds can be expected overnight tonight.




Cool and drier air will continue through the rest of this week.
Relative humidity values will remain above critical thresholds.
There are no fire weather concerns.


Gadsden     41  75  44  76  50 /   0   0   0   0   0
Anniston    44  76  47  77  52 /   0   0   0   0   0
Birmingham  47  77  50  79  56 /   0   0   0   0   0
Tuscaloosa  46  79  51  81  57 /   0   0   0   0   0
Calera      47  77  50  78  55 /   0   0   0   0   0
Auburn      47  76  52  78  56 /   0   0   0   0   0
Montgomery  49  80  52  81  57 /   0   0   0   0   0
Troy        48  79  53  80  58 /   0   0   0   0   0




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