Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Huntsville Alabama
843 PM CST Wednesday Dec 4 2013
no changes to forecast.
the Arctic cold front is now stretching from the Great Lakes through southeastern MO
and into NE Texas. As the cold front slowly approaches the Tennessee Valley tonight
the chance of a few rain showers will develop especially after midnight. New NAM
data coming in also shows this as well. With cloud cover and southeast
winds 5 to 10 miles per hour...temperatures will only drop into the low/middle 60s...very
mild for this time of the year. It was also a warm day today as mean sea level
tied the old record high temperature (back in 1998) by hitting 76 degrees.
Otherwise current forecast looks on track...no changes are planned at this time.
/issued 522 PM CST Wednesday Dec 4 2013/
for 00z tafs...an Arctic cold front extends from the northern plains through MO
and into southern OK. At this time the only precipitation close to the Tennessee Valley was over
southeast Alabama...this band of precipitation will not effect the taf sites. However as
the cold front approaches the County Warning Area by Thursday afternoon...rain showers and a few thunderstorms and rain
will be possible especially after 18z. The cold front is prognosticated to stall
out across northern Alabama which will keep the chance of rain showers for both taf sites
through the end of the forecast period. VFR conditions are expected through 05z
tonight...after 05z expect mainly MVFR with occasional IFR conditions
for both kmsl and khsv for the remainder of the forecast period.
/issued 353 PM CST Wednesday Dec 4 2013/
an increasingly amplified upper pattern is becoming apparent
across the North American domain...as a storm forms across the
US/Canadian border west of the Great Lakes. Along with this storm...
an Arctic front continued moving south across the lower-48. As of
the middle afternoon...that boundary was draped from near Green
Bay...to central Texas and the Colorado Front Range...then to SW
Arizona. This system was causing a variety of wintry weather near
and west of it...especially over Great Lakes and The Rockies...
along with dramatic temperature falls. That boundary and moisture
upglide will produce a generally wet period for the late week and
early next week.
Locally...broad high pressure off of the East Coast continued to
bring a warm southerly flow across the Tennessee Valley. Highs so
far in many spots locally have warmed into the low/middle 70s. The
Muscle Shoals site in fact has at least tied their old record for
today of 76...last set in 1998. Huntsville record of 79 will be
harder to break. Despite the copious lower level moisture flowing
north and upper level clouds headed in from the west...some sun
managed to break through today.
With deeper moisture and the front nearing from the northwest...rain
chances will go up on Thursday across the Tennessee Valley.
Forecast soundings from the NAM/GFS continue to show minimal cape
and shear...so will keep a mention of thunder going with higher
probability of precipitation. Have scaled back the timing of when rains will arrive in
earnest till Thursday afternoon. The above mentioned cold front should
reach far northwest Alabama...then very slowly progress to the southeast during
the night time. Despite its slow movement...much colder air will
filter in from the north. For northwest Alabama...after highs nearing 70
for a last time tomorrow...they will fall into the middle 40s by
daybreak Friday...and remain more/less unchanged into the evening...
before tumbling more late Friday. For the central/eastern areas...
for a short while...a dramatic west-east temperature gradient will
be realized. The front will take its time moving across this
portion of the Tennessee Valley...finally positioned southeast of this
area around noon on Friday.
Long with colder temperatures...rain chances will increase as weak
disturbances and 'overrunning' of the colder air at the surface by
the warmer air forced aloft. Precipitation timing wise...have left the
evening dry...then introduced low rain chances and patchy fog.
Along with showers...a few thunderstorms are also possible during
Thursday...especially the afternoon. Some of the storms could
become strong...with gusty winds the primary threat. Colder air and
more stable conditions should end the thunder risk Thursday night...but
the rains will continue. Rainfall totals through Sat should range
in the 1-2 inch range...with higher amounts possible if cells
repeat over the same area.
To add to our weather woes...sufficient cold air moving in to a
moist atmosphere will cause a wintry mix to develop. At this
time...the soundings support freezing rain/sleet early...then
becoming freezing rain late Friday night/early Sat morning. At this
time...think that elevated surfaces such as tree branches...power
lines...and may be those Road surfaces that are elevated could be
impacted. The main roads given the recent warm conditions of late
should probability stay ice free this go around.
The precipitation should end during Sat afternoon for a very brief spell.
We say brief...as more rain is forecast to form/move across the
area Sat night through Monday...with the best rainy period Sat night
through late sun. Runoff from this next rain event...on top of
already wet soils could result in rises in area streams/rivers
early next week. The models this go around were a tad drier than
yesterday...so have held off on a hydrologic outlook this issuance.
The rain should end as snow late Monday to early Tuesday.
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