Scientific Forecaster Discussion
fxus64 kbmx 190557
Area forecast discussion
National Weather Service Birmingham Alabama
1157 PM CST Tue Dec 18 2018
for 06z aviation.
A longwave ridge is positioned over the southeastern states with a
shortwave trough moving northeast over the Tennessee Valley and
into central Tennessee. An upper low was located over southeast
New Mexico with longwave ridging further west from Utah southwest
into Southern California.
Toward the surface sprawling high pressure extended from the Great
Lakes region through the Ohio Valley south into the Tennessee
Valley and down into the central Gulf Coast. A weak cold front
extended from southwest Kansas southwest into New Mexico and
tonight through Wednesday.
Gradual increasing clouds and not as cold tonight, rain showers
arrive during the day Wednesday from the southwest.
High clouds will arrive this evening from the southwest as the
closed low well to our west continues to slide slowly eastward.
Temperatures will not be as cold tonight due to the high clouds.
Clouds will continue to increase from the west during the day
Wednesday but dry conditions will give way to a few rain showers
through the mid to late morning hours from the southwest into our
central counties toward midday. Rain showers will become scattered
in coverage tomorrow afternoon and evening across the forecast
area with a few rumbles of thunder possible across our far
southern counties from midday tomorrow through tomorrow night as
modest instability across the Gulf Coast region makes some
Temperatures tonight will range from the upper 30's north to the
low 40's south. Expect highs Wednesday to range from the upper
50's northeast to the low 60's south. Lows Wednesday night will be
milder due to clouds and rain with readings ranging from the mid
40's far north to around 50 degrees south.
Thursday through Friday.
Have placed highest pops (70-90%) from 00z Thursday through 12z
Friday as the low pressure strengthens & continues eastward across
our area and pws approach ~1.2", particularly across the south.
During this time, mid/upper-level dynamics continue a rather
impressive southward trend as the trough undergoes amplification.
500 mb height anomalies may approach ~40 decameters below average when
the trough passes over the area Friday morning, indicative of
very cold temperatures aloft and a lowered tropopause. However,
pops & quantitative precipitation forecast continue a downward trend by then, though cloud cover &
light rain showers along a deformation axis are expected to stick
around Friday afternoon as the upper-level low moves into
Georgia. A tight pressure gradient and cold-air advection on the
western side of the surface low will provide gusty northwesterly
winds & chilly conditions Friday afternoon as well. Overall,
forecast rainfall totals are expected to be in the 0.7-1.1" range
across central Alabama.
Saturday through Tuesday.
A stable Continental airmass and surface high pressure will make its
way into the southeastern Continental U.S. Behind the mid-latitude cyclone
exiting our area as we head into the weekend. Upper-level split flow
makes its return as well as we await the next significant rossby wave
in the long-term. For now, a brief opportunity exists for isolated
light rain showers early next week as a shortwave passes to our
north Monday, but moisture will be limited and lift likely stays out
of our area so have kept pops <20% for now. Thereafter, more quiet
and mild weather remains in place as we look ahead towards
Christmas. Generally expecting highs to rebound to the 50s/60s
Sunday-Tuesday with corresponding overnight lows in the 30s/40s.
06z taf discussion.
VFR forecast is expected for the next 24 hours. We have
considerable high cloudiness tonight which will aide in keeping
the fog to a minimum, maybe only right near rivers/valleys if any.
Cigs will lower as we move through Wednesday as our overall column
moistens and our next system approaches. I have added areas of
-ra moving in from the southwest after 00z. However, at the onset
I have cigs around 5kft.
Clouds will gradually increase from the west tonight and tomorrow
with increasing rain chances through the day. Rain showers will
become likely Wednesday afternoon and through the overnight hours
with a few thunderstorms possible over our far southern counties. Relative humidity
values will remain above critical values and there are no fire
weather concerns at this time.
Preliminary point temps/pops...
Gadsden 36 57 45 54 41 / 0 0 70 80 80
Anniston 40 59 47 56 41 / 0 0 80 80 80
Birmingham 40 60 49 57 41 / 0 0 80 80 80
Tuscaloosa 41 62 49 58 40 / 0 20 80 70 70
Calera 40 60 47 58 40 / 0 0 80 80 80
Auburn 42 59 48 57 42 / 0 0 80 80 80
Montgomery 42 62 51 61 42 / 0 10 80 80 80
Troy 42 62 50 62 43 / 0 10 80 80 70