FXUS64 KHUN 120453 AAC

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
1053 PM CST Tue Dec 11 2018

For 06Z TAFS.


.NEAR TERM...(Tonight)
Issued at 855 AM CST Tue Dec 11 2018

A quiet evening across the Tennessee Valley, with high pressure at
the surface promoting a dry air mass and mostly clear sky. The result
as been some good radiational cooling after sunset as 02z
temperatures have fallen into the low to mid 30s. The one saving
grace on temperatures will be that some broken to dense cirrus is
quickly filtering in from the northwest which will help to limit
additional cooling, especially after midnight. Still, am expecting
lows will bottom out in the upper 20s to lower 30s in most locations,
just below the freezing mark. There's a bit less boundary layer
moisture to work with tonight (as seen by dewpoint depressions of
greater than 5 degrees at many observing sites). Still, the mostly
clear and calm conditions earlier in the night could result in some
localized patchy fog development along the rivers and lakes of
Northeast Alabama. With temperatures slipping below the freezing mark
later tonight, localized, patchy freezing fog will be possible across
this portion of the CWA once again. However, unlike last night, do
not think dense fog is as likely, and thus a frost/light icing along
the tree tops and other elevated surfaces will be the rule. Still,
current obs/trends will need to be monitored closely overnight to see
how widespread this fog may become.

.SHORT TERM...(Wednesday through Saturday)
Issued at 252 PM CST Tue Dec 11 2018

The shortwave moving into the Great Lakes tonight into Wednesday will
flatten the subtle ridge that developed during the day today. We'll
continue to see moisture streaming in aloft and likely have a mix of
high clouds and sun tomorrow. Warm air advection starts to increase
through the day and temps shouldn't have any problems reaching into
the 50s for highs Wednesday. Models are all showing that as the WAA
increases, winds around 850mb shift to the SW, which will allow for
better moisture to stream in and could see a midlevel stratus deck
arrive shortly before sunset. The clouds hold through the night and
help to keep in the upper 30s to lower 40s for lows.

The cut-off low over the desert SW kicks east during the day
Wednesday. At the same time a trough digging SE from the PacNW could
intercept this cut-off feature and end up phasing over TX/OK on
Thursday into a closed low. It looks like there might be enough jet
energy that get pulled southward with the digging trough that as the
two systems phase we'll see a stronger jet round the base of the
closed low and move N/NE into the TN Valley during the Thu/Fri
timeframe. As the feature moves over the area the deep layer shear
increases and due to the slower motion of the system stays between 40
to 60kts for the Thursday through Saturday period. However, because
the system digs so far south with the center of the low over central
LA, surface winds out ahead stay easterly. Even though we'll see good
WAA aloft, the easterly flow at the surface may limit warming a bit
and could keep slightly drier air in place. Models have slowed the
onset of precip until later Thursday and have adjusted PoPs to
reflect this slower timing. Although, it's probably not out of the
question to see a few showers develop Thursday morning as WAA
increases aloft. The heavier rain arrives Friday morning as the jet
energy mentioned above pivots into the area and coincided with the
better moisture advection. As we go through the day Friday, this axis
of heavy rain shifts east and we could end up getting a dry slot to
move over the area, which may briefly lower rain chances Friday
afternoon/evening. But as this bowling ball of a low continues to
move east, we get into the colder core aloft and rain chances should
pick back up Friday night into Saturday.

In terms of thunderstorm potential, think that the storm may be a bit
too far south, which could really enhance the coverage of storms
along the Gulf coast where instability is better. The steeper lapse
rates aloft never seem to align with the better forcing until during
the day Saturday, when the core of the system is over the area. But
those chances will be pretty limited and have kept thunder out of the

Rainfall totals have continued to fluctuate over the past few days
due to poor handling of this system by the models. However, the
guidance is starting to converge on a solution and totals should
range from about three quarters of an inch to an inch and a half.
While these lower totals aren't overly impressive, the still
saturated ground conditions could allow much of this to be runoff.
So, some additional river flooding is possible over the weekend.

Temperatures through the period range from the mid to upper 50s for
highs and fall into the mid to upper 40s for lows.

.LONG TERM...(Saturday night through Monday)
Issued at 252 PM CST Tue Dec 11 2018

The system shifts east of the area Saturday night into Sunday with
precip chances decreasing from west to east. Based on the latest
forecast it looks like the CAA occurring on the back side of the low
won't be that strong and any lingering precip should likely remain
liquid. Model solutions diverge significantly as this system
continues to move east, with the GFS developing a broad trough across
the entire eastern US, while the ECMWF drops an almost clipper like
system into the area Sunday into early next week. But even if the
ECMWF solution were to be accurate it looks like limited moisture
will prevent any precip from falling and the forecast is dry after
Sunday. Due to the uncertainty have gone with a blend of guidance and
highs may hover in the lower 50s with lows in the falling into the
lower 30s.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1053 PM CST Tue Dec 11 2018

VFR conditions will prevail through the period at both terminals.
Cloud cover will gradually increase overnight into Wednesday morning,
as ceilings lower to around 5 kft by late afternoon/evening. Winds
will generally be 10 kt or less, and from the south.




LONG TERM...Stumpf

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