Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 241051 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
551 AM CDT Mon Apr 24 2017

For 12Z TAFS.


.NEAR TERM...(Today and Tonight)
Issued at 247 AM CDT Mon Apr 24 2017

Water vapor imagery depicts the upper low was curling slowly
southeast through northern AL. Low ceilings remained prevalent over
the area with patchy drizzle still being reported. Clouds will be
slow to depart until very late this afternoon or early this evening
as the low drops into southern GA. As a result, temperatures will
remain on the cool side today, with partial clearing late this
afternoon possibly allowing highs back into the upper 60s in some
areas. However, updates may be needed depending on cloud trends.
Clearing tonight and the very moist boundary layer with light flow
should result in at least patchy fog development.

.SHORT TERM...(Tuesday through Wednesday Night)
Issued at 247 AM CDT Mon Apr 24 2017

As the upper low pivots northeast through the Carolinas on Tuesday, a
shortwave ridge axis will shift east through the TN valley and
central Gulf states. Temperatures should warm nicely back into the
70s to around 80 degrees. The warmup will continue in earnest on
Wednesday as south-southwest flow develops in low levels with an
impressive 8h thermal axis of 16-19C advecting into middle TN and
north AL on Wednesday morning. The airmass will be too dry to
support any elevated convection. High temperatures should easily
reach the middle 80s in several locations Wednesday afternoon.

.LONG TERM...(Thursday through Sunday)
Issued at 247 AM CDT Mon Apr 24 2017

The extended portion of the forecast is fairly active with a pair of
troughs expected to impact the TN Valley.

The first one is a progressive mid-level shortwave trough moving
along the Plains on Wednesday and approaching the MS River Valley on
Wednesday night. Prior to its arrival, a building ridge over the
western Atlantic will act to slow its trajectory. As a result, the
models are showing a negative tilt and a narrow moisture tongue
extending northward over the MS River Valley. There is the potential
for severe weather with this system. However, current forecast
soundings show a rather substantial layer of dry air in the mid-
upper levels prior to the primary lifting mechanism (cold front)
arrival on late Wednesday night/early Thursday morning. The GFS
seems to be the most robust in developing a QLCS feature initially,
but it appears to collapse upon arrival over the TN Valley. Re-
development could occur later in the afternoon, but the same
question mark with antecedent dry air could limit convective
initiation. Another limitation is the potential for a MCS or
convective complex moving along the northern gulf of Mexico which
could actually indirectly inhibit development across the TN Valley.
So, at this point, with this many mitigating factors (even within the
highly sheared and modestly unstable environment), will highlight
the potential for strong to marginally severe thunderstorms. This
will be especially the case over northeast AL and southern Middle
Tennessee as the front moves over that part of the area during peak
daytime heating. Impacts would likely be small hail and gusty winds.

In the wake of this `cold` front, on Thursday evening the next
trough will be deepening over the Intermountain West while mid-level
shortwave troughs move within the amplifying flow aloft. One of
these shortwave troughs and ridge building may lift the cold front
north as a warm front, causing scattered storms on Friday, but
confidence is low on the storm potential. With the western Atlantic
ridge building west over the Southeast, daytime high temps will
likely be in the low to mid 80s on Friday.

The broad trough over the Intermountain West will gradually deepen
and move east towards Plains on Saturday and may affect the MS and
TN River Valleys late in Sunday night to Monday timeframe. However,
with the strengthening ridge over the western Atlantic could also
see this system`s velocity slowing/changing further. Because of
this, could see substantial changes in POPs on Sunday/Monday.
Another effect of this ridge, will be much warmer daytime highs
close to 90 degrees on Saturday and Sunday.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 551 AM CDT Mon Apr 24 2017

IFR ceilings of 008-010agl will persist this morning, then lift
slowly into the MVFR range of 010-020agl. Slow clearing will take
place late this afternoon with a clear sky possible by 23-01Z. If the
sky does clear, the potential for fog will go up substantially
tonight. Have included 3/4sm visibility by 07-09Z in BR.





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