Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Birmingham Alabama
212 PM CST Friday Nov 27 2015
Short term (tonight into saturday)...
Somewhat tight surface pressure gradients are present once again
across central Alabama. Some wind may continue to be present after
sunset but models do tend to relax the pressure gradients some.
Confidence is low in the cloud forecast for tonight. Models have
been overdoing the onshore flow/moisture return and thus overdoing
the late night stratus cloud cover...especially the NAM. GFS/Euro
are slower with retreat of the ridge and have verified better.
Thinking one more night of persistence before things change for
the wetter/cloudier. So...with that said...mid/upper level
moisture streaming from the Pacific tropical system Sandra will
continue to feed into the areas some...best west tonight so do
have them a tad higher for lows...but similar to last night in
some respects. With less low clouds possible for Saturday morning
do not see why our daytime temperatures would not be similar for
highs Saturday as they are today...especially in the southern
counties...warm and above guidance. For the most part...the deeper
moisture for rain showers should hold off until Saturday night
into Sunday as the front gets a closer. Have only a slight chance
of showers mentions in the far northwest for Saturday afternoon.
Long term (saturday night through friday)...
Models have trended flatter with the 500mb ridge for Saturday
night into Sunday...which should be more favorable for the front
to make more progress than previously indicated. Have increased
rain chances along and north of I-20 with an embedded impulse
expected to move across northern MS/al. The large trough out west
will begin to shift eastward but the focus for rain should remain
across the north and west through Tuesday...where enhanced
southwesterly flow will provide a fetch of deep moisture. Though
the main part of the trough will move across the Great Lakes on
Wednesday...decent height falls will occur farther south and
provide enough support for the front to finally push through the
forecast area. Model spread is quite high at the end of the period
regarding a southern stream shortwave and have kept slight chance
probability of precipitation in for Thursday and Friday as a hedge between the dry European model (ecmwf)
and wetter GFS.
Temperatures for Sunday through Tuesday will be quite warm ahead
of the front and swath of rain. Have increased afternoon highs
across the south based on a persistent flow pattern and observed
temperatures exceeding guidance the past few days.
18z taf discussion.
High cirrus clouds continue to stream in across the U.S. From the
Pacific tropical moisture associated with Sandra. Our low level
moisture continues to have trouble making it into central Alabama
as the return flow has been slow to change with no help from the
model guidance. Easterly winds continue for the most part across
the area today. Will go with VFR forecast for the next 24 hours
with only upper level moisture to continue. Tomorrow night we
might finally see a change ahead of our next system with more
model agreement of the shift a more onshore flow in the lower
Mild and dry conditions will continue for much of the area
through Saturday. Rain chances will arrive Saturday night in the
northwest part of the state...expanding slowly to near the I-20
corridor on Sunday and Monday. There are no fire weather concerns.
Preliminary point temps/pops...
Gadsden 52 72 54 66 57 / 0 10 20 60 60
Anniston 53 72 53 68 58 / 0 0 10 30 50
Birmingham 55 73 58 67 59 / 0 10 10 40 50
Tuscaloosa 56 75 57 70 61 / 0 10 10 40 50
Calera 55 73 56 70 59 / 0 0 10 30 40
Auburn 54 75 52 74 57 / 0 0 0 10 20
Montgomery 54 76 53 77 56 / 0 0 0 10 20
Troy 54 77 51 77 54 / 0 0 0 0 10