Scientific Forecaster Discussion
fxus64 kbmx 291211
Area forecast discussion
National Weather Service Birmingham Alabama
711 am CDT Mon may 29 2017
for 12z aviation.
today and tonight.
Models including cams continue to perform poorly in this mesoscale convective system-driven
pattern, and the short term forecast continues to be a lower
confidence Nowcast. An mesoscale convective system tracked eastward out of Texas last night
into Mississippi. It has since weakened considerably, but
stratiform rain with embedded lightning strikes associated with
the remnant mesoscale convective vortex is currently entering West Alabama. This weakening
occurred as it encountered the air mass over Alabama which is
still stable from last night's convection, with Storm Prediction Center mesoanalysis
indicating nil MLCAPE across central Alabama currently. A large
cold pool was left in the wake of the mesoscale convective system over Louisiana and
Mississippi with low 60s dewpoints and northerly winds down to New
Orleans. On the western side, the cold pool is reinforced by
another mesoscale convective system over the Gulf south of Lake Charles. An outflow
boundary currently extends southward from the mesoscale convective vortex along the MS/Alabama
line, helping trigger additional storms near Mobile. And up near
Memphis, thunderstorms have developed near the slow-moving cold
front without much movement.
The hrrr is the closest to handling the current situation, but
even it is too slow. Extrapolating the precipitation associated
with the mesoscale convective vortex takes it across the northern counties this morning,
exiting into Georgia by 15z. This early exit time should prevent
any destabilization and stronger storm threat ahead of it. The
hrrr does indicate the cluster of storms near Mobile may lift
northeastward across southeast central Alabama this morning ahead of
the trailing outflow boundary, and a strong storm or two would be
possible but instability/shear do not look strong enough for a
severe threat in this area this morning. The mesoscale convective vortex precipitation may
also stabilize the northwest counties before the northern MS
The morning activity and subsidence/the cold pool behind the mesoscale convective vortex
makes afternoon diurnally enhanced coverage questionable. Made some
adjustments to the pops to indicate higher coverage during the
morning and more scattered coverage in the afternoon. Later forecast
updates may need to drop parts of the area to isolated afternoon
coverage. However, there will be a moisture axis across the area
with cyclonic flow aloft south of an upper low over Lake Superior
and the front off to the northwest, which will aid some re-
development. Overall, no need to cancel outdoor plans this
afternoon, but be prepared to move indoors just in case. Looking at
severe parameters, 0-6 km shear is marginal at 25-30 kts, mid-level
lapse rates look weak, and there isn't much dry air aloft to support
downdrafts. So, severe chances are too slim to mention in the severe weather potential statement
but stronger storms may be possible if the atmosphere can recover.
Tonight, activity will generally decrease through the evening with
the loss of heating, but some isolated to scattered activity will
linger with the moisture axis along the front. Very late tonight,
rain chances may start to increase in the southwest counties ahead
of an approaching southern stream shortwave.
Tuesday through Sunday.
A second front will dig south/southeast across the U.S. Toward
Alabama and meet up with our lingering stalled frontal boundary on
Tuesday. However, front number two is not expected to swing
through the state either as the low associated with it is expected
to pull further northward across Ontario. So, it should stall too
and weaken before making it through to the coast. Also, the upper
flow will start as southwest on Tuesday and then become zonal, so
we will not see much help with upper support. This is not
surprising being that it is late may. However, we should see
elevated rain chances for Tuesday with several shortwave impulses
going through the southwest/zonal flow ahead of/along the fronts
across c Alabama. With increased cloud cover and rain chances, we are
looking at high temperatures a few degrees milder than expected
for today, but again still very humid.
Temperatures moderate back for the latter half of the week. We
should see continued upper shortwaves shooting through the mainly
zonal flow with weak ridging at the surface across the southeast U.S.
With a hot and humid airmass in place this week, we should see
somewhat diurnally enhanced convection Wednesday through Friday.
As we head into next weekend, rain chances should be slightly
higher as better upper shortwave activity swings across Texas and
the mid Mississippi Valley toward Alabama ahead of yet another
approaching front to keep things wet for next weekend.
12z taf discussion.
Computer models have not been handling the forecast well with the
mesoscale convective vortex precipitation this am. Latest hrrr is the closest to reality
but still off some. Have tried to time progression north/northeast
of the Gulf Coast convection and timing possible of more
development for rain showers/ts across the area, with west/S first and
lasting through early evening. With the uncertainty, and more
likely afternoon activity, keeping cigs VFR for now.
Scattered to numerous showers and storms will be possible each
day as we remain in an unsettled pattern across the area. Critical
fire weather conditions are not expected due to abundant low
Preliminary point temps/pops...
Gadsden 80 65 78 62 83 / 50 50 50 20 30
Anniston 81 65 77 63 83 / 50 50 60 20 30
Birmingham 81 68 79 64 84 / 50 50 60 20 30
Tuscaloosa 83 68 79 65 84 / 50 50 60 20 40
Calera 81 67 77 64 83 / 50 50 60 20 30
Auburn 83 68 79 65 83 / 60 50 50 30 30
Montgomery 84 69 81 67 85 / 60 50 60 30 40
Troy 85 69 82 66 85 / 50 40 50 30 40