Scientific Forecaster Discussion
fxus64 kbmx 181708
Area forecast discussion
National Weather Service Birmingham Alabama
1208 PM CDT Fri Oct 18 2019
for 18z aviation.
/updated at 0417 am CDT Fri Oct 18 2019/
Today and tomorrow.
A high pressure over the Midwest has resulted in cooler and drier
easterly flow for central Alabama this morning. I would expect some
gradual warming as the day progresses with highs reaching in the
upper 60s to low 70s.
The main story is the tropical disturbance currently in the western
Gulf of Mexico. Some uncertainty continues on whether it will become
tropical or extratropical as it develops today. Regardless of the
system categorization, it is a low pressure system that will bring
increased winds to our area due to the increased pressure gradient.
A stationary boundary is draped through the northern Gulf, keeping
the best "tropical" environment on the south side of that boundary.
The forecast track for the system takes it into the Florida
Panhandle early Saturday morning.
The greatest impact for central Alabama will be the increased
winds. There will be a very sharp gradient in wind speeds on the
west side of the track. For now, wind gusts up to 30-40mph are
possible for Barbour County Saturday morning. The rest of central Alabama
will see noticeably gustier winds due to the pressure gradient, but
impacts will be far less with wind gusts in the 10-20mph range. The
strongest winds for Barbour County should diminish by the afternoon
as the system moves into southern Georgia.
Based on the current track, rain chances gradually increase south of
I-85 late this evening with rain becoming highly likely after
midnight. I can't rule out an isolated thunderstorm, but I don't
think the chances are very high due to the lack of significant
instability. As we go through Saturday, the eastern half of central
Alabama will see the best chances of rain, gradually decreasing from west
to east in the afternoon. Guidance has trended downward in total
rainfall estimates. This is due partially to the quick forward
motion and because of the more southeasterly track away from central
Alabama. We also don't quite see the deep tropical moisture flow that
would be necessary for the typical heavy tropical rainfall events in
this area. Latest forecast has 1-2 inches of rain generally south of
I-85 and in the far eastern counties with less than half an inch of
rain for the rest of central Alabama.
/updated at 0417 am CDT Fri Oct 18 2019/
Sunday through Friday.
Between weather systems, height rises will take place on Sunday as
a significant trough digs toward the Southern Plains. A dry and
warm afternoon is expected under the influence of southerly flow.
Temperatures should reach the upper 70s in the north with lower
80s across the south.
Rapid surface pressure falls will take place Sunday night into
Monday across the span of the Mississippi River valley as a
powerful jet carves out a deep trough centered over the upper
Midwest. A strong low-level jet is expected to be located along
the MS river at 12z Monday with upper 60s to lower 70s dewpoints
advecting northward across the arklamiss and Alabama. Much of our
forecast area should remain dry through noon, but a band of
showers and storms should move in from the west during the
afternoon and evening. Models generally agree that pressure falls
will be minimal across Alabama as the system becomes occluded.
However, our northwestern counties may be clipped by a 35-45 kt
low-level jet around 18-21z Monday. With SBCAPE of 500-1000 j/kg,
there may be a non-zero threat for isolated damaging winds and
perhaps a brief tornado. Farther east, there is good agreement
regarding weakening low-level jet as the low over the upper
Midwest becomes more vertically stacked. Though low-level shear
does not appear to support a tornado threat, 700-500 mb flow of
40-50 kt may be sufficient for an isolated damaging wind threat to
continue eastward across the forecast area. For now, a marginal
risk of severe storms will be introduce for areas north of I-20/59
and west of I-65.
Cooler and much drier air will move into the region on Tuesday
behind a cold front. High pressure should remain in control
through Thursday. The next chance of rain may start come on Friday
as another trough develops to our northwest.
18z taf discussion.
A closed upper level low over southern Texas will slide east
across the northern Gulf Coast tonight through Saturday. This
system will interact with a potential tropical cyclone and
associated surface low pressure located over the western Gulf of
Mexico later today.
Expect cloud cover to continue to overspread the forecast area
with gradually lowering bases this afternoon and tonight. Rain
showers are expected at mgm/toi toward midnight tonight, becoming
heavier further into the morning hours on Saturday and persisting
beyond the end of this cycle. For the northern terminal locations
expect rain showers to be possible toward daybreak Saturday and
will linger through the end of this cycle with highest potential
east and lower chances west.
Low-level winds across the northern locations will generally be
from the east through this cycle from 6-12 kts. At mgm/toi the
low-level wind field will gradually strengthen overnight with
general easterly winds around 10 kts tonight potentially
increasing up to 15 kts toward midnight tonight and reaching up to
20 kts at times before daybreak Saturday. Winds look to remain in
the 10-20 kt range into midday Saturday at mgm/toi with a
northerly flow developing as the heaviest activity moves further
east into Georgia and into the Carolinas.
Rain should remain to the south of our area through this afternoon
as a low pressure system becomes more organized across the Gulf
of Mexico. Minimum relative humidity values are expected to range from 35 to 45
percent with light easterly winds. Moisture and rain chances will
increase for tonight and Saturday especially across the eastern
half of Alabama. Dry and warm conditions will return for Sunday
with afternoon relative humidity values around 50 percent.
The Alabama forestry commission continues to have a fire alert in
effect that includes all of central Alabama. For more information
about restrictions, visit their web site at forestry.Alabama.Gov.
Preliminary point temps/pops...
Gadsden 72 52 65 51 77 / 0 20 60 20 0
Anniston 72 55 66 53 78 / 0 40 60 20 0
Birmingham 72 57 68 55 79 / 0 20 50 10 0
Tuscaloosa 71 55 71 55 81 / 0 20 40 10 0
Calera 71 55 69 54 79 / 0 30 50 10 0
Auburn 69 57 67 55 78 / 0 70 80 20 0
Montgomery 69 58 71 55 81 / 10 60 60 10 0
Troy 69 56 72 55 80 / 10 80 70 20 0