Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Morristown Tennessee
306 PM EST Tue Feb 21 2017
Short term...(today thorugh Wednesday night)...
clouds continue to push across the area. Though overcast, clouds
were thin enough across the north to allow some sunshine to filter
through and warm locations to around 70 degrees, with some spots
climbing into the low 70s. Some light rain showers this afternoon
will slowly give way to steadier rain across southern portions of
the forecast area as the atmosphere slowly becomes more
saturated. Short term models continue to want to keep areas north
of I-40 dry through at least midnight tonight. For Wednesday,
conditions should slowly dry out across the south as the closed
low slides east and cuts off the moisture transport to our area.
In contrast, this looks to be the better setup for rain across SW
Virginia and NE TN, and models indicate some rain through Wednesday
evening over the northern half of the forecast area. Overall,
rainfall amounts should be light, but south to southeast winds
could lead to some areas of downsloping. With overcast skies, lows
tonight will remain mild, holding in the 50s across much of the
area. Cloud cover tomorrow will keep lower, especially across the
north. Highs will range from the lower 60s there to the upper 60s
in the southern valley where some sunshine may be able to work in
by late afternoon.
Long term...(thursday through tuesday)...
a 700-500 mb shortwave trough is expected to cross the area on
Thursday. Forcing with it is weak, and forecast soundings show weak
instability across northern sections while southern sections
remained capped. Will have just a slight chance pop north on
Thursday. Temperatures will continue their upward trend Thursday and
Friday as the southerly 850 mb flow strengthens ahead of a Midwest
low. Highs in the Tennessee Valley will be in the lower 70s Thursday, and
mid 70s Friday.
Models have been consistent and in good agreement on the timing of a
cold frontal passage late Friday night. Convection ahead of the
front is expected to develop in middle Tennessee in the evening, and move
into east Tennessee around midnight. The overnight timing means instability
should be weak, but strong shear and favorable positioning of the
upper jet exit region could result in some strong to marginally
severe storms. Likely pops with a chance of thunderstorms will be
continued. With fropa expected around 12z, Saturday should have
lowering rain chances with clearing skies through the afternoon.
Cooler temperatures build in over the weekend, but still only close
to normal for late February - highs in the 50s and lows in the 30s.
The GFS shows a fast-moving shortwave trough bringing some precip to
northern areas Sunday night, but the European model (ecmwf) shows nothing. Will keep
this period fry for now. We return to a mild SW flow pattern on
Monday as the pattern becomes more amplified with a deepening trough
over The Rockies, which will also bring a return of rain chances on
Preliminary point temps/pops...
Chattanooga Airport, Tennessee 57 70 55 74 / 70 40 10 10
Knoxville McGhee Tyson Airport, Tennessee 55 67 52 73 / 70 60 20 20
Oak Ridge, Tennessee 54 66 52 73 / 70 60 20 20
Tri Cities Airport, Tennessee 51 62 48 72 / 70 80 30 20