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Area forecast discussion 
National Weather Service Huntsville Alabama
521 am CST sun Nov 29 2015

for 12z tafs


/issued 151 am CST sun Nov 29 2015/
synoptic picture indicates an upper ridge implanted over the Gulf of
Mexico into the eastern Gulf states. Mostly upper level southwesterly
flow was being directed as a result through the Southern Plains and
then eastward through the Ohio/Tennessee valleys. This flow contained multiple
weak shortwaves. An upper level low was cutoff across the Great
Basin extending into the Dakotas. At the sfc, a cold front has become
nearly stationary from the Middle Atlantic States through middle Tennessee and S
along the MS river into the western Gulf of Mexico. A surface wave was
taking shape along the front in northern MS. Radar mosaic shows clusters
of rain showers have crossed the Tennessee Valley with additional development
upstream in northern/northwestern MS. The rain showers have tended to weaken or die off as
they hit drier air further east in Alabama and Georgia. These initial rains are
at the nose of increasing moisture transport and precipitable water values of 1.5+

The synoptics during the next couple of days favor moderate to
potentially heavy rains in some areas despite limited instability
along and north of the surface boundary. Showalter indices will be running
near 0 to -2 within the 800 mb Theta-E ridge, so we can't rule out an
embedded storm or two. But thus far, no lightning has been detected,
so will leave out for now given very limited coverage expected. The
surface wave is prognosticated by short term models to track into middle Tennessee
today. As this occurs, the cold front may sneak just into far northwest Alabama
this afternoon, then stall out across Tennessee through northwest Alabama into northern MS. This
boundary will likely be the focus for multiple rounds of rain showers through
tonight and Monday. The latest NAM is a bit further south of the axis
of persistent rain showers across Tennessee and far northern Alabama. It appears that each
successive cluster of showers will reinforce the boundary as another
round moves in. The greatest chance of rain through Monday will be in Tennessee
and far northern al, with probability of precipitation dropping off further south of the
boundary/shortwave axis. There is some indication of a break between
rain systems Monday afternoon and evening, so probability of precipitation attempt to address
this with somewhat lower values. The NAM shows a sharp cutoff in our
southern counties, so we may need to make further pop adjustments as
this becomes more clear. The next round of rain will be along and
immediately behind the cold front late Monday night and Tuesday.
Slightly more potential for thunderstorms exists due to frontal
convergence and weak elevated instability noted in forecast
soundings. The front will slowly progress east by Tuesday night with
lingering rain showers possible.

Rainfall amounts of 2-3 inches are forecast, with some spots near 4
inches in our Tennessee counties. The lessor amounts at this time would be in our
southern counties in north Alabama. The threat of flash flooding appears
low at this time given that the heavier rain will be spread out over several
hours. But, will certainly monitor these trends during the periods
of heaviest rain which will be tonight into Monday and again late
Monday night into Tuesday with the cold front. Thanks to
mrx... wpc for their coordination on this.

Will stick with the dry forecast in blended guidance for the
balance of the week into the weekend.The surface boundary and moisture
pushes southeast of our area as secondary southern stream upper trough passes through
the region late next week. Nevertheless, will need to monitor future
model trends to see if this system can back low level winds and
increase overrunning potential further north.


for 12z tafs...ceilings will continue to lower through the morning and
should settle around 600-800ft by 14-16z. There is a chance they
could dip lower briefly but not expecting them to settle to 400-500ft
until 02-03z Monday. However...amendments may be needed today as ceilings
may drop lower than forecast and quicker than expected. Light to
occasionally moderate rain will persist through the taf period. There
may be a break or two in the rain but cannot pinpoint the timing well
enough to include a break in the tafs.



Hun watches/warnings/advisories...


For more information please visit our website
at weather.Gov/Huntsville.

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