Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Birmingham Alabama
538 am CST Thursday Dec 18 2014
for 12z aviation.
This morning...a surface ridge extends from south central Canada
into the Mississippi and Ohio valleys to the Gulf. At the same
time...an upper level trough digs over the Desert Southwest
ejecting weak disturbances and upper moisture across the Gulf
Coast states/southeast U.S.. an area of showers is moving across
northern Mississippi/western Tennessee and the northwest fringe of
Alabama. A few of these showers this am may scrape our northwest
County Warning Area counties. Most of the activity is expected to skirt to the
The upper trough digging is helping to develop a Lee side surface
system which will interact with low pressure along the Texas coast
on Friday as the upper trough swings eastward across the central
U.S.. this will bring a decent chance for mainly shower activity
as the surface low is expected to stay along the Gulf Coast with
very limited instability. Will leave in a token slight chance of
thunder along the southern fringe tier of counties. However...with
highly positive lifted indice's/little cape/meager tt/S think the strikes
will be few and far between if the low continues on the current
forecast track. Could see one half to an inch of rain across
portions of the south in the better cells.
The upper trough flattens out as it progresses across the country
Saturday. This will allow the surface low to linger across the
northeast Gulf and weaken. It will also allow for some lingering
low probability of precipitation (best chances southeast half) for the latter part of the
weekend. By late Sunday into Monday another upper trough makes its
way across the country and helps to nudge the surface feature
across Florida into the Atlantic and usher in our next surface
front as well across the Central Plains.
By Tuesday/Tuesday night...rain chances pick up once again ahead
of/along the next surface front. Some wrap around moisture will be
possible as the colder air gets ushered in as well...but there is
normally a fine line between the lingering moisture and the
arrival of the cold air (enough for anything frosty that is) and
they normally are not quite in time together. So across the
extreme northern counties Wednesday morning could see a flurry or
two mixed in with the exiting rain showers but more than likely
just rain and with temperatures above freezing the more important
thing is that we are not expecting any impacts from this.
For now it looks like all moisture will have exited before
Christmas evening night and Christmas day...which are expected to be
dry with near normal temperatures.
12z taf discussion.
VFR conditions will prevail through the period. Middle/high clouds will
continue to stream across the forecast area as a shortwave slides
eastward. There are light showers ongoing across Tennessee and MS...and
these will move east-northeast across portions of north Alabama today. At this
time...still expect the majority of the rain to stay north of the
terminals. Winds will be light and generally out of the north.
Preliminary point temps/pops...
Gadsden 52 34 51 41 50 / 20 10 30 90 60
Anniston 54 36 53 44 52 / 10 10 20 90 70
Birmingham 52 37 52 44 53 / 20 10 40 90 50
Tuscaloosa 53 39 52 45 54 / 20 10 60 90 50
Calera 54 39 53 45 54 / 10 10 40 100 50
Auburn 59 41 56 47 55 / 0 10 30 80 80
Montgomery 60 41 57 48 57 / 10 10 50 90 60
Troy 61 42 57 48 58 / 0 10 40 80 60