Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Birmingham Alabama
1157 am CST Sat Dec 3 2016
Atmosphere is slowly moistening as system moves in but taking a
little time to precipitate down to the ground initially as mid
level cloud heights lower and surface dew points are slowly rise.
Only a few tweaks were made to today's pops as they are well
covered with highest chances northwest half. Did have to make some
adjustments upward on the highs especially southeast counties as
driest air highest cloud decks are there and no rain just yet and
we are warming nicely considering we are overcast. Rain will
eventually make its way eastward as the afternoon progresses with
heating slowing down.
18z taf discussion.
Cloudy skies with increasing coverage of largely stratiform rain
showers expected through this cycle. -Ra already observed at tcl,
expected to begin at bhm/eet within 2 hours and anticipated at
asn/anb by mid afternoon. Mgm/toi expected to see -ra tonight. No
ts expected due to lack of instability. Winds will remain out of
the northeast through the period. Ceilings and visible may drop early
Sunday morning in some spots but confidence too low to include in
Light rain will spread from west to east today. Heavier rainfall
and a few thunderstorms will occur tonight through early Tuesday.
Forecast rainfall amounts will average 2.5 to 3.5 inches through
/issued 335 am CST Sat Dec 3 2016/
today and tonight.
A classic isentropic lift rain event is in the process of developing
for today into tonight as southwesterly warm advection occurs above
cool easterly low-level flow. Have trended faster with the onset of
precipitation through the daylight hours based on current radar
trends. The highest rain chances and heaviest rain through 12z
Sunday should occur generally along and north of Interstate 20.
Temperatures have been lowered closer to raw model numbers for highs
today in anticipation of the faster onset of precip and widespread
Sunday through Friday.
Central Alabama will experience of prolonged period of showers and
thunderstorms Sunday through Tuesday, which will go a long way to
alleviate the severe drought conditions. Forecast rainfall amounts
are in the 2.5 to 3.5 inch range through Tuesday. The models are
in fairly good agreement showing the heavier rainfall occurring
during the day Sunday and again Monday night. The uptick in
rainfall intensity on Sunday is associated with a northern stream
short wave trof, while a strong short wave trof moving out of
Texas will bring a threat of severe weather and heavier rainfall
Monday night. Easterly low level flow Sunday through through the
day Monday will restrict northward advancement of more unstable
Gulf moisture, but model cross sections indicate some elevated
instability, and there will likely be some elevated storms. By
Monday afternoon a surface low will develop near the Upper Texas
coast and track rapidly northeast in response to short wave trof
becoming negatively tilted. The warm sector along the Alabama
coast will push northward Monday evening. 0-6km bulk shear and
favorable low level hodographs will support the formation of
supercells with tornadoes in the warm sector. Main limiting
factor across central Alabama will be the amount of destabilization
within the boundary layer due to widespread rainfall north of
warm front. A low confidence tornado threat will be added to the
hazardous weather outlook for Monday night for areas areas south
of Highway 80 and I-85.
The rain will push east of the area during the day Tuesday as the
main short wave trof lifts into the Ohio Valley region. The
exiting system may leave enough residual moisture Tuesday night
and Wednesday for skies to remain mostly cloudy, but dry aloft
will keep rain out of the area. A rapidly advancing northern
stream trof will push a strong cold front through Alabama on
Thursday. Moisture looks somewhat limited ahead of the front, and
kept rain chances below 40 percent. The coldest air mass of the
winter season will move into Alabama Thursday and Friday, with
highs on Friday in the upper 30s north to middle 40s south.
Preliminary point temps/pops...
Gadsden 54 43 49 47 58 / 70 100 90 70 80
Anniston 54 44 51 48 59 / 60 100 90 70 80
Birmingham 55 44 52 49 61 / 90 100 90 70 80
Tuscaloosa 54 46 53 50 62 / 90 100 90 70 80
Calera 57 45 53 51 62 / 80 100 90 70 80
Auburn 60 45 52 51 62 / 30 80 90 70 80
Montgomery 62 47 57 55 65 / 50 80 80 70 80
Troy 62 49 61 57 66 / 30 50 80 70 80