Area Forecast Discussion
Issued by NWS Huntsville, AL

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105
FXUS64 KHUN 290201
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
901 PM CDT Fri Apr 28 2017

.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 WSW to ENE orientation from the OK/TX Red
River Valley to just north of the OH/KY border. Scattered to numerous
showers/thunderstorms were in progress along and north of this
boundary from eastern Oklahoma to OH/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 E 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
NW Al by 00z, with the GFS being the faster outlier. The LLJ 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 NW 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 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 00Z TAFS through 00Z Saturday evening)
Issued at 621 PM CDT Fri Apr 28 2017

VFR conditions will prevail at the KMSL and KHSV through the first 6
to 10 hours of the forecast period. Southerly winds will remain
sustained between 10 and 15 kts, with gusts as high as 20 kts though
03Z. Gusts may linger a little past 03Z, however confidence is not
high. Winds will then shift to the southeast and remain between 10
and 15 kts through much of the overnight period. Skies will become
overcast over the next hour or so, but cloud bases will remain above
3000 ft. MVFR cigs will filter into the terminals around 10Z
Saturday, as low level moisture increase. These clouds will lift and
erode by 14Z, leaving VFR conditions for the remainder of the
period. Additionally, winds will become gusty once again after 14Z,
with gusts up to 22 kts. There may be an isolated thunderstorm
during the afternoon on Saturday, however confidence and coverage are
too low to add to the forecast at this time.


&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...RSB
SHORT TERM...KTW
LONG TERM...KTW
AVIATION...73


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