Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
400 am EDT sun Mar 29 2015
Short term...(today through monday)
issued at 400 am EDT sun Mar 29 2015
Two issues to deal with...first being very low relative humidities
this afternoon. Second concerns the passage of a surface cold frontal
Short wave ridging aloft and surface high pressure moving off to the
east through the day will keep skies mostly clear through much of
the day as southerly return flow increases. Combined this will
allow very dry air to mix down into the boundary layer and
eventually to the surface...all while temperatures make a strong
rebound. As a result relative humidities will drop into the teens
by this afternoon...well below critical fire weather thresholds.
Short wave trough moving through the Great Lakes late today and
tonight will send a surface cold frontal boundary through the region.
Clouds will increase ahead of this system late this afternoon.
Models also develop a band of showers along and ahead of this
system. However...very dry boundary layer will eat away at some of
the model/S advertised quantitative precipitation forecast values. Consequently we are expecting
one of those relatively high pop...low quantitative precipitation forecast events. The frontal
boundary will be through eastern Kentucky by Monday morning.
Fortunately...considering that the origin of the air mass behind
this front is Pacific in nature...temperatures will turn out to be
warmer behind the system than ahead. Stayed fairly close to the
blend of model solutions and guidance for probability of precipitation and temperatures.
Long term...(monday through saturday)
issued at 245 PM EDT Sat Mar 28 2015
The forecast period will be active with several short waves moving
fairly quickly through zonal flow...with rain chances increasing
during the latter half of the week. The zonal flow will result in
mild temperatures...and as instability increases later in the week
thunderstorms will also become possible. There is good model
agreement to start the period...but significant differences develop
by late in the week.
At the start of the period surface high pressure will be nosing east
from the middle MS valley...while a short wave and associated surface
low move into the northern plains. This low will track into the
Great Lakes on Tuesday...bringing a warm front across the area that
will then be quickly followed by a cold front. However...moisture
looks to be limited and the model blend keeps the forecast dry for
Tuesday...with only a slight chance of rain Tuesday night. Will
follow neighboring weather forecast offices to North...East and west...and lower probabilties
slightly for Tuesday night...thus resulting in no mention of rain
for Tuesday night. Another short wave and surface low look to track
across Ontario on Thursday...with associated fronts moving across
our area and bringing better rain chances. The trailing cold front
with this system looks to stall somewhere from the Great Lakes or Ohio
Valley into the Southern Plains...with low pressure developing over
the Southern Plains Thursday night. It is at this point that the
models begin to show significant differences. The European model (ecmwf) is very
aggressive with phasing the northern and southern streams as we move
towards the weekend...with the Southern Plains surface low deepening
rapidly as it moves towards the Great Lakes on Friday. The GFS is
much weaker aloft and at the surface...with the surface low tracking
more eastward in flatter flow. Both scenarios result in shower and
thunderstorm chances for our region...but the European model (ecmwf) solution would
result in a severe weather threat as well. This will need to be
watched as wpc notes the Canadian and GFS are beginning to trend
towards more amplified solutions...but wpc and we are not yet
committed to the fully phased European model (ecmwf) solution.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 200 am EDT sun Mar 29 2015
Surface high pressure centered over Portsmouth Ohio will keep our
skies clear and winds light through tomorrow morning. As this high
pressure move eastward southerly gradient flow will increase
through the day Sunday ahead of approaching cold frontal system.
Winds should increase to around 10kts and become gusty later in
the day. Clouds will increase and scattered showers will begin to
develop Sunday evening...generally from around 03z and after.