Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 khun 290543 

Area forecast discussion
National Weather Service Huntsville Alabama
1243 am CDT Sat Apr 29 2017

for 06z tafs.


Near term...(tonight)
issued at 901 PM CDT Fri Apr 28 2017

Surface high pressure off of the East Coast near Bermuda was
providing a southerly flow across the southeastern states. A frontal
boundary was draped in a west-southwest to east-northeast orientation from the OK/Texas Red
River valley to just north of the Ohio/Kentucky border. Scattered to numerous
showers/thunderstorms were in progress along and north of this
boundary from eastern Oklahoma to Ohio/KY/WV region.

With an exception of cloud cover increasing during the overnight, no
weather of consequence is expected across the Tennessee Valley. South
to southwest winds will remain in the 5-15 mph range, with some gusts
above 20 mph mainly in the higher elevations. Warm for late April
warmth will continue, with lows in the mid/upper 60s.

Short term...(saturday through Sunday night)
issued at 335 am CDT Fri Apr 28 2017

The mid level ridge continues hold strong off the southeastern coast
on Saturday. Models continue to rotate upper level energy around the
backside of the upper level ridge as far north as northern Alabama
Saturday afternoon. Models do show a strong cap in place initially
around daybreak on Saturday, but weaken it as the forcing moves north
into the area. Forcing will still have to modify this cap during the
day on Saturday. However, with a more significant shortwave moving
north and very strong instability in place (2000-4000 j/kg) short-
lived pulse severe storms may be possible producing damaging winds or
large hail. Winds will remain breezy (sustained 10-15 mph with gusts
to around 20 mph) and highs look to rise into the lower 90s west of
I-65, where less cloud cover will be prevalent. This isolated to
widely scattered activity could last into the early evening hours
before dissipating.

The main show begins ahead of a cold front starting to produce a
line of thunderstorms somewhere between East Texas up through SW
Illinois Saturday night. Mid to upper level winds will be south-
southwesterly, so storms will be moving quickly in that direction
but given the slowly departing surface high pressure the line will be
overall slow to build east. Guidance continues bring this line into
northwest al by 00z, with the GFS being the faster outlier. The low level jet will be
kicking in around this time as well and there will be no lack of
shear/helicity with the line. Once we break through the cap Sunday,
there will enough instability ahead of the line to produce strong to
severe storms as it moves into our northwest counties. The threat will
lessen as it moves east and instability wanes, but a few severe
storms will still be possible east of I-65 until midnight. It is also
noted with model guidance, that the upper lift with the low is
lagging behind the initial line.

Timing will be everything with this line so we will continue to
monitor that in terms of possible hazards. Damaging winds and large
hail are both possibilities and a tornado or two cannot ruled out,
especially in the NW, if the line can arrive early enough to tap into
the better severe parameters.

The line will continue to move through overnight bringing slightly
cooler lows, in the middle to upper 50s. Although the line will be
slow on Sunday, with the upper jet dynamics moving in overnight, it
will likely pick up some speed.

Long term...(monday through thursday)
issued at 335 am CDT Fri Apr 28 2017

The previously mentioned system should be exiting between 12-18z on
Monday with timing differences still evident in the global models.
The GFS is the quicker solution although individual ensemble members
are lagging slightly behind the operational GFS so would imagine how
quickly the front exits may match closer to the European model (ecmwf). This would
leave lingering thunderstorms, mostly in the east, through the
morning with front moving through by 18z. Relief in the temps will
come Monday with highs in the lower 70s.

The upper low moves northeast into the Great Lakes by Tuesday with
near zonal flow aloft and weak surface high pressure building in
from the south over the local area. The return of southerly flow
will push highs back into the mid to upper 70s.

Another potent system will be tracking through the area Wednesday
into Friday with the timing and overall syntopic set up still
uncertain. Overall, it looks like more of a rain producer with any
stronger storms confined to the coast but it's too far out for many
more details than that. Will leave the blended pops for now which
does bring likely pops in on Wednesday. It looks like it will get
cooler after this system with highs Thu/Fri possibly down to the
upper 60s.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1240 am CDT Sat Apr 29 2017

Low clouds observed in multi-spectral satellite imagery are moving
northward from the Gulf coastal plain region and will overspread the
area later tonight. Forecast data in conjunction with latest
satellite imagery suggests ceilings may become broken at least as
early as 10z at kmsl and perhaps 12z at khsv. Although, some
uncertainty in timing remains. Obs to our south and model data also
indicate ceilings will likely be in MVFR range. However, ceilings are
likely to disperse with clouds becoming scattered by ~14-15z. Again,
the usual uncertainty remains in specific timing. Winds will become
gusty with the onset of deep mixing once again by 14-15z.


Hun watches/warnings/advisories...


Near term...rsb
short term...ktw
long term...ktw

National Weather Service Glossary of Abbreviations