Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Morristown Tennessee
312 PM EDT Wednesday Apr 23 2014

Short term (tonight and thursday)...surface high pressure ridging
into the area from the north will shift east of the area through
Thursday. A warm front will move north through the Tennessee Valley on
Thursday. Very dry air has mixed down to the surface especially
across NE Tennessee and SW Virginia. Good cooling conditions setting up for early
tonight. Some isolated patches of frost are possible but coverage
and duration appear too brief to meet advisory criteria. Some high
clouds riding between upper ridge to the west and trough to the NE
will stream across SW Virginia and NE Tennessee late tonight and early Thursday.
This will also hinder frost development. Temperatures warm to above
normal Thursday afternoon.

Long term /Thursday night through Wednesday/... a quick moving
shortwave Thursday night into Friday will bring some showers and
isolated thunderstorms to the region from 06-15z on Friday...before
rapidly clearing the region from west to east by the early
afternoon. Ridging will quickly build in for late Friday into the
weekend and result in a nice warm-up...along with ample sunshine as
highs return to the upper 70s and lower 80s. A few spots could even
reach the middle 80s by Sunday.

A deepening upper-level low pressure system will shift from the
Southern Plains into the lower Mississippi Valley and the Tennessee
Valley late Sunday into Monday. This will bring the potential for
showers and thunderstorms...with some severe weather possible Monday
evening and night. The latest run of the GFS has come nicely in line
with the European model (ecmwf) with the timing and track of the upper low. Given the
moisture and some instability in place during the afternoon and
evening /combined with some favorable shear/...severe thunderstorms
will certainly be possible. The latest guidance suggests a squall
line /with supercells ahead of it/ may develop well to the west
along the Mississippi Valley during the day. As these storms move
east into middle Tennessee they may congeal into more of a line of
storms...potentially moving into the plateau and forecast area late
Monday evening and night. Damaging thunderstorms winds appears to be
the primary threat...but a lot will hinge on the exact timing of the
storms and how much instability is available. Precipitation chances
will persist into Tuesday and the middle of next week as the upper
low gradually pushes into the Ohio Valley. This will also result in
much cooler temperatures to kick off may...with highs into the upper
50s to middle 60s.


Preliminary point temps/pops...
Chattanooga Airport, Tennessee 45 76 60 78 / 0 10 70 30
Knoxville McGhee Tyson Airport, Tennessee 42 75 57 75 / 0 0 70 40
Oak Ridge, Tennessee 42 75 57 76 / 0 10 70 30
Tri Cities Airport, Tennessee 36 74 50 72 / 0 0 70 50


Mrx watches/warnings/advisories...