Scientific Forecaster Discussion
fxus64 kbmx 230503
Area forecast discussion
National Weather Service Birmingham Alabama
1203 am CDT Thu Mar 23 2017
for 06z aviation.
Main front now south of the I-85 corridor and moving southward.
The shortwave that moved through earlier has just about diminished
and we will now be dry for the next 24 hours. A ridge will build
in behind the front tonight and continue to slide over the area
the area on Thursday. Overall cooler over the next 24 hours.
Thursday through Wednesday.
The surface high pressure slides east of our area on Thursday with
an upper level ridge building in over the southeaster US. This will
result in easterly flow moving across a cooler air mass, moderating
temperatures back to near-seasonable for Thursday. The high pressure
shifts further east by Friday ahead of a deepening trough in the
central US, which will veer winds to a more southeasterly to
southerly flow on Friday and Saturday, advecting warmer air into the
Models have come into better agreement on the timing of a low
pressure system as it moves northeastward through the Ozarks and
into Missouri on Saturday. Models show a 500mb impulse moving
through just ahead of the main frontal boundary. It's still a
little to early to mention exact timing of the frontal boundary
and the upper-level impulse, but i've been leaning closer to the
European model (ecmwf) in the forecast due to it being more consistent run to run
the last few days. Instability does appear to build in to portions
of central Alabama with some overlap of better deep layer shear. The
steeper mid- level lapse rates are still displaced somewhat, and
the upper- level and lower-level jets are on the weaker side,
which could limit the severe potential as the system moves through.
The best moisture axis seems to be in the western half of central
Alabama for now, but will continue to mention a low confidence severe
threat for entire region at this time. I would like to see some
more run to run consistency in the placement of this moisture
axis, and in the overlap areas of better instability and shear
before adding much higher confidence in the forecast.
Chances for rain/thunderstorms looks to linger into Sunday as the
departing low moves through the Great Lakes region and another low
pressure system digs into the Southern Plains. Elevated instability
across the area remains high enough to support mention of at least a
slight chance of thunderstorms with any storms that linger through
Sunday. The next low pressure system on Monday into Tuesday follows
a similar track as the Saturday system, which will again bring the
possibility for some stronger storms across central Alabama. For now,
will hold off on mentioning anything in the severe weather potential statement for Monday or
Tuesday until there is better model agreement. Upper level
ridging builds quickly in behind the Monday/Tuesday system, and
the amplified synoptic pattern appears to continue into the middle
of next week with another trough over the western US, though
details are still unknown due to significant model differences.
06z taf discussion.
The general weather idea remains the same this run, but have
lowered the ceilings some and some MVFR possible before 18z. Winds
have remained a bit higher in some locations late this evening.
So winds ranging from calm to around 7kts and north northeast to
east overnight with veering possible as we go through the night.
By sunrise, easterly flow really kicks in. Winds will be gusty at
most sites with low level winds to near 20kts. Therefore, the
09g20kts range looks applicable as we begin mixing. The moisture
will also increase with this easterly flow. Ceilings ranging from
035-060 should move east to west over much of central Alabama
through the day. These ceilings may briefly become MVFR around 025
for anb/asn and possible near toi/mgm. Ceilings will eventually
become VFR everywhere with wind gust diminishing by sunset.
The next significant chance of rain will not come until the
weekend along and ahead of a stronger frontal system, where some
locally heavy rain may be possible. Critical fire weather
conditions are not expected this week.
Preliminary point temps/pops...
Gadsden 45 64 49 70 54 / 10 10 10 10 10
Anniston 49 64 50 72 57 / 10 10 10 10 10
Birmingham 51 69 53 73 59 / 10 10 10 10 10
Tuscaloosa 51 74 55 74 59 / 10 10 10 10 20
Calera 50 69 53 73 58 / 10 10 10 10 10
Auburn 53 63 50 71 56 / 10 10 10 10 10
Montgomery 55 72 53 77 58 / 10 10 10 10 10
Troy 55 71 52 75 57 / 10 10 10 10 10