Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 271123 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
623 AM CDT Thu Oct 27 2016

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 355 AM CDT Thu Oct 27 2016

Latest water vapor imagery shows an upper level trough over the
Great Lakes, stretching southward into the lower Mississippi Valley,
while a strong upper level ridge was in place over much of the
western CONUS. At the surface, a fairly weak low was slowly moving
east across Indiana, with a weak front draped to the southwest.
Light showers were continuing to move over portions of TN and N MS,
however very little precip was reaching the ground. Meanwhile,
temperatures were still rather warm across the TN Valley, as most
locations were still in the upper 60s, as of 3 am. Given the
extensive cloud cover and weak southerly flow, there may not be much
change in temps before sunrise, with lows likely remaining in the
lower to mid 60s. The first shot of precip is right on the doorstep
of NW AL, however fairly dry air in place will hinder the amount of
precip that will reach the ground and therefore will keep the slight
chance wording in the forecast.

The axis of the mid/upper level trough will reach the TN Valley
around sunrise. Meanwhile, the cold front will continue to weaken as
it slowly moves to the east and all but wash out before it reaches
the area. Moisture will continue to increase ahead of the trough, as
PW values rise to around 1.2 inch this morning, which is right
around the 75th percentile for this time of year. Isolated light
showers will continue to develop ahead of the boundary, as indicated
in hi-res guidance. Given the weakening trend of the upper trough
and associated surface boundary, not anticipating much coverage with
the precip activity. Forecast soundings indicate that instability
across the area will rise to between 500 and 1000 j/kg, however a
mid level inversion will limit the thunderstorm chances. An isolated
thunderstorm is certainly possible, however given the low coverage
expected, have removed the thunder wording from the forecast. If the
surface boundary does move through slower than currently forecast,
the coverage of thunderstorms may increase, however this will be
confined to the eastern portion of the forecast area. Even if
thunderstorms do develop, do not expect much organization due to the
wind shear remaining very weak. The precip is expected to exit the
area around mid day, as the trough axis pushes to the east of the

As stated above, the upper level trough will move to the east of the
area during the afternoon, bringing an end to what little precip
chances we had. Cloud cover will linger behind the front, though
high temps are still expected to rise to above normal temps given
our warm start to the day and the southerly flow remaining through
much of the morning.

.SHORT TERM...(Tonight through Saturday)
Issued at 355 AM CDT Thu Oct 27 2016

The upper level ridge to our west will quickly build into the region
during the overnight hours. Southerly flow will quickly return
during the day on Friday, meaning little relief from the above
normal temperatures. The upper ridge will persist through the
remainder of the short term period, as we move into the weekend.
Overnight lows will be fairly warm, with temps only dropping into
the mid to upper 50s. Highs will warm each day, and a few spots will
approach 90 degrees by Saturday, roughly 15 degrees above normal in
some locations.

.LONG TERM...(Saturday night through Wednesday)
Issued at 428 AM CDT Thu Oct 27 2016

A zonally oriented 500-mb ridge will likely extend from the Big Bend
region of west TX into southeastern Atlantic coast, providing a
moderate westerly flow aloft across the TN valley at the beginning of
the extended forecast period. However, mid-level flow is forecast to
strengthen and veer to the northwest throughout the day on Sunday as
the southern end of a shortwave trough impacting the Great Lakes
brushes the region. Due to the weak nature of lift associated with
this feature, only an increase in high-level cloudiness is expected
Sunday morning. Light southwest flow at the surface beneath a
strengthening low-level jet should translate to warm temperatures
both Saturday night and Sunday.

Models suggest that the subtropical ridge will become centered
across southern GA/northern FL and expand northward during the period
from Sunday night-Tuesday, downstream from a mid-level trough
predicted to eject east-northeastward from the Great Basin into the
northern Great Lakes. This will allow deep-layer southwesterly flow
to gradually strengthen across the local area, resulting in even
warmer afternoon temperatures Monday and Tuesday. Although highs
should rise into the mid/upper 80s for most of the region both
afternoons, diurnal mixing of what little moisture exists in the
boundary layer will maintain lows in the lower/mid 50s. Most NWP
guidance suggests that several lower amplitude waves will begin to
eject northeastward across the TN valley Tuesday night/Wednesday, as
the center of the subtropical high slowly retrogrades into the
eastern Gulf. However, these features will encounter very dry air
across our region and for this reason we will not include any
precipitation in the forecast at this time.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 623 AM CDT Thu Oct 27 2016

VFR conditions will persist through the forecast period. Light
showers are possible, however given the minimal coverage, have left
mention out of the TAFs. The greatest chance for rain will be
through 18Z, and if a shower does move over the terminals, flight
conditions will likely remain VFR. Winds out of the south will shift
to the west by the afternoon and become light and variable overnight.
Conditions will be favorable for fog development early Friday
morning, as winds become calm and skies clear, however given the dry
ground conditions and lower confidence, will not include fog in this
TAF issuance.





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