Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Nashville Tennessee
325 PM CST Sat Feb 28 2015
well folks...we are in line at the amusement park...ready to hop
on the roller coaster ride that will be middle Tennessee's
weather this coming week. That will be addressed in the ext
portion of the discussion.
Currently...high pressure is located along the Atlantic coast. A
weak surface boundary...which is located upstream...will move our way
overnight. Moisture in the form of light showers will attempt to
make a run at US tonight and into Sunday. The boundary will stall to
our south and then lift northward as a warm front by Monday night.
Prior to that time... some overrunning light rainfall will be
possible into Sunday night as well.
All of the precipitation will be liquid through Monday night. In
fact...we will see a rather impressive stretch of above freezing
temperatures which will last from tonight all the way through Wednesday
morning. Not bad...considering that this February ranks somewhere
around #7 or #8 in terms of the coldest februarys on record.
In the ext forecast...
as mentioned before...the warm front lifts northward Monday night.
Then a strong Arctic front will be on approach and will push through
Tuesday night. Along and ahead of this feature...mild and wet
weather is expected. High temperatures on Tuesday will reach into the 60s.
Showers and thunderstorms are expected with rainfall amounts through Tuesday
and Tuesday nt of 1 to 2 inches. We are currently not outlooked for
severe as instabilities look marginal. Some rises of creeks and
streams will have to be monitored of course. Overall flood potential
at this point however...looks minor.
Behind the front...much colder air will build in.
Meanwhile...phasing of the polar and subtropical jets is expected.
Within the Post frontal sector...the middle south and portions of the
deep south will be located under the right rear quadrant of a very
strong 180 knots phased jet. The Arctic boundary to our south will slow
down as it will be oriented parallel to the upper flow. Pieces of
surface energy will then ride northeastward along the boundary. Moisture
will spread northward and back up into the cold air. On
Wednesday...rain will change to sleet and then snow across middle Tennessee.
The southward plunge of the 0c 850 mb isotherm looks impressive
enough...at this time...to create an all snow event. The way it
looks right now is that a sleet snow mix would be confined to far
southern areas. The surface trough inversion...or placement of the
Arctic front is oriented more WSW-ENE.
One thing to point out is that during historical major southern
winter storm events...you generally see a stronger surface low and/or
well defined upper level system. We really dont see either at this
point. But with the upper jet being that strong...strengthening of
the synoptic setup may occur going forward. Until we see that happen
though...it will be better to slowly ramp this situation up as the
For temperatures in the ext...GFS obviously has a built in snow pack
algorithm and is going very very low with its temperature graphics. Mex
numbers make a bit more sense. Consall does suggest that the GFS
and mex are a little too quick with the Arctic frontal passage. At
any rate...well below normal temperatures during the extended after Tuesday but
we do see 40s for highs by the tail end of the period.
Preliminary point temps/pops...
Nashville 41 49 33 45 / 20 30 70 10
Clarksville 36 48 32 42 / 30 60 70 10
Crossville 37 46 33 43 / 20 40 70 20
Columbia 40 50 35 46 / 20 40 70 20
Lawrenceburg 39 50 36 46 / 20 40 70 20
Waverly 37 49 33 44 / 30 60 70 10