Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Morristown Tennessee
311 PM EDT Tuesday Jul 22 2014
Short term...(tonight and wednesday)...upper low over southern
Alabama still the dominant feature for our area...although the upper
ridge off the fla coast is actually gaining more influence over our
northern sections. This may explain why it has been relatively
quiet over the northern parts of our region. Will have lower probability of precipitation
tonight as this system for the last 24 hours has looked diurnal with
respect to convection. Still going with decent probability of precipitation for
Wednesday...as front gets closer would expect increasing
organization with wind structure as well as the start of some
cooling aloft. GFS MOS guidance looks very good overall for these
two periods...only went about 1 degree cooler for Wednesday maximum temperature.
Long term (wednesday night through tuesday)...
models continue to trend faster with the approach of a middle/upper
level shortwave trough and surface cold front...with the best qg
forcing coming Wednesday night. With plenty of moisture in
place...precipitable water values will be around 1.75 inches...will have likely
probability of precipitation for that period. The NAM and GFS agree on some precipitation lingering
in eastern sections Thursday morning as the surface front moves
through...but we should have the Post-frontal air mass building in
by the evening. Will remove all probability of precipitation from Thursday night.
Surface high pressure originating from central Canada and a northwest flow
aloft will provide an unseasonably dry and cool air mass for Friday.
Lows will be in the upper 50s to middle 60s...with highs Friday
between 80 and 85 in most spots. Some moderation will occur Saturday
when the high moves east...with highs closer to normal but below the
GFS MOS numbers...which seem way too warm.
A closed low drops into the Great Lakes region for
Sunday...producing falling heights aloft and pushing another front
toward the area from the northwest. GFS and European model (ecmwf) agree fairly well with
the general pattern...so will have chance probability of precipitation Sunday and Monday.
The trough axis should be east of our area Tuesday...with yet
another cool and dry high dropping out of Canada providing below
Preliminary point temps/pops...
Chattanooga Airport, Tennessee 70 89 71 86 / 20 50 60 50
Knoxville McGhee Tyson Airport, Tennessee 70 88 70 84 / 10 50 60 50
Oak Ridge, Tennessee 70 88 70 84 / 10 50 70 40
Tri Cities Airport, Tennessee 66 87 66 81 / 10 50 70 50