Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
FXUS64 KMRX 241913
Area Forecast Discussion
National Weather Service Morristown TN
213 PM EST Tue Jan 24 2017
.Short Term (Tonight through Wednesday Night)...
Quiet night tonight as our low clouds erode this afternoon.
Ridging aloft moves in tonight...and cold front will move through
TN from west to east during the day Wednesday...keeping our area in
the warm sector all day...so expect high temps in the TN valley to
generally reach the 60s. Chances of rain move in from the west
after lunch...peaking with likely category pops or higher Wednesday
evening. Front will begin to clear precip from the area from west
to east after midnight Wednesday night...with only isolated to
scattered showers left east of I-81 by sunrise Thursday. H5 flow
will be wsw`erly by sunrise Thurs and temps will not quite get to
freezing at most places...so not expecting any issues when the
cold air moves in behind the tapering precip.
.Long Term (Thursday through Tuesday)...
A cold front will be approaching the Atlantic Seaboard to start
the extended portion of the forecast with cold air advecting in
behind the departing front. A long-wave trough across the Eastern
CONUS will prevail throughout much of the long-term forecast.
Several shortwave troughs will rotate through the area during this
portion of the forecast. The challenge will be the amount of lift
and moisture with each passing system. The GFS continues to be the
most bullish with each passing wave producing at least some
measurable precipitation across the region. Cooler air will be in
place with a reinforcing shot of cold air with each passing system.
Thursday night into Friday it appears the best chances for
precipitation will be in the higher elevations and locations north
of I-40. The much more conservative ECMWF even shows some light QPF
during this timeframe as well. For now, have mentioned 20-30 PoPs
due to the uncertainty and low amounts forecast. Due to the cold
air would expect much of this to be snow with any accumulations
mostly limited to the higher elevations with light amounts expected
there as well. Saturday looks to be a dry day as there is a brief
break between system.
Large discrepancies exists in the models on Sunday into Monday with
the strongest of the upper level troughs forecast. The GFS and
Canadian both indicate a phase between a northern trough diving
southward out of the Northern Plains into the Tennessee River Valley
and a southern wave moving across the Central Plains into the
Northern Gulf. This phases allows the trough to dig across the
region brining the heart of the cold air across the area. In
addition, light precipitation will spread across the region. The GFS
is the most bullish with QPF amounts of around 0.1-0.3 inches across
the area with the Canadian being around half of that. Meanwhile, the
ECMWF does not indicate this phase and the trough doesn`t dig as far
south. The southern extent of the trough occurs Monday morning
across the Mid-Atlantic. This puts the forecast area on the western
periphery of the cold air advection with the moisture remaining
well to the north and east. This latest run of the ECMWF is much
different than the last run which was more in line with the current
GFS. For the forecast, have included around 30-40 PoPs Sunday into
Sunday night with mostly snow expected with 850 mb temps well below
zero Celsius even on the warmer ECMWF. Again, there is still a good
bit of model uncertainty and the forecast is likely to change over
the next several days. Monday and Tuesday morning will be the
coldest mornings throughout the forecast period with widespread
upper teens and lower 20s. A moderating temperature trend is
forecast on Tuesday as a ridge builds in from the southwest.
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 39 65 42 47 / 0 30 70 10
Knoxville McGhee Tyson Airport, TN 37 64 42 45 / 0 20 70 20
Oak Ridge, TN 38 61 41 45 / 0 30 70 20
Tri Cities Airport, TN 33 62 42 44 / 0 10 60 20