Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Goodland Kansas
858 PM MDT Tuesday Sep 2 2014
issued at 858 PM MDT Tuesday Sep 2 2014
Updated forecast to refine fog/stratus chances tonight. Inserted
areas/widespread fog mention as boundary layer moisture continues
to increase. With mostly clear skies expected and radiational
cooling...stratus/fog should develop similar to last night and
move in. Stratus development has already been observed over
central Kansas so these trends should continue. In addition...
forecast guidance winds may go calm across portions of northwest
Kansas and southwest Nebraska...heightening the threat of fog.
Was not confident enough to mention dense fog or issue an advisory
but it is possible one may be needed.
Also watching elevated thunderstorm development over south
central Kansas. Latest Storm Prediction Center mesoanalysis indicates up to 2000 j/kg
MUCAPE over eastern portions of the forecast area. Thinking most
of the activity remains to the southeast but will need to watch
Short term...(this evening through wednesday)
issued at 1240 PM MDT Tuesday Sep 2 2014
Dry and warm through tonight and Wednesday.
Upper level westerly flow tonight transitions to southwesterly on
Wednesday as the high pressure area over the southern United
States moves over the southeast United States and the trough
sweeps through the Pacific northwest.
The Lee surface trough deepens along the eastern Colorado border
tonight and Wednesday with south to southeast near surface flow
turning more southwesterly as the trough expands over the Central
High plains. This will help transport additional low level
moisture into the region with dewpoints increasing into the middle
60s with the boundary layer nearing saturation around sunrise.
Expect any low ceilings and fog that end up forming between 10-13z
to be short lived and dissipate quickly after 14z...especially as
the surface winds turn to the southwest. With dryer southwest
winds expected during the afternoon and a very dry airmass
aloft...expect high temperatures well into the 90s and approaching
the century mark.
Long term...(wednesday night through tuesday)
issued at 203 PM MDT Tuesday Sep 2 2014
Wednesday night through Thursday night the upper level ridge will
gradually move east across the southern Continental U.S. While an upper level
long wave trough along the US/Canadian border will also move
eastward. Between the two features minor short wave troughs will
move across the tri-state area Wednesday night through Thursday
night. Due to the weak upper level troughs moving across the area
and the dry environment shown by the soundings...will continue with
a dry forecast Wednesday night and Thursday.
On Thursday a cold front will move through the area ahead of a
stronger short wave trough. Behind the front north winds will be
breezy to gusty in the morning primarily north of I-70. During the
afternoon the winds will decline as the pressure gradient relaxes
while front continues to move south.
Thursday night a weak right entrance to the 500-300mb jet develops
over the area. Over the southeast counties 700-500mb frontogenesis
develops. Meanwhile a couple stronger upper level short wave
troughs move across the area...one during the evening and one
overnight. As the first short wave trough moves through higher
mixing ratios move in from the southeast along with nose of the
750mb jet. Along this nose isentropic lift develops with elevated
cape values of 1000-2500j/kg possible and little cinh. With deep
layer shear of 30kts severe storms are very likely if elevated
convection develops. Mean storm motion will be parallel to the nose
of the 750mb jet so training storms will likely occur. Contemplated
raising probability of precipitation along the nose of the 750mb jet...however based on past
elevated convection events this season the models tend to jump
around with the location of the convection which usually are
oriented in a fairly narrow line.
The most likely window for severe storms will be the evening when
deep layer shear is strongest and mixing ratios are highest.
Current cape profiles of soundings along/behind the 750mb jet nose
suggest a potential for 2 inch diameter hail or larger. However the
high mixing ratios in the 700-500mb layer of 6-8j/kg and the deep
saturated layer from 700mb to 300mb in the soundings may support
more of a high precipitation super cell structure which would tend
to support much smaller hail production. In addition the training
storms may serve to seed storms upstream with more ice nuclei which
would create beneficial competition for super cooled water droplets
and lead to smaller hail stones. With these uncertainties in mind
will hold off forecasting a specific hail size...but will add a
mention of severe T-storms in the forecast for the southeast part of
the area where the strongest storms are most likely.
Overnight Thursday a second more compact upper level short wave
trough moves through. By this time models suggest the elevated
instability will be waning as winds behind the first short wave
trough turn to the west...cutting off the southeast part of the area
from the higher mixing ratios and allowing the environment to become
more stable with elevated cape above 750mb less than 1000j/kg.
Friday through Tuesday an active weather pattern will return to the
tri-state area as multiple upper level short wave troughs move
across the area. Meanwhile the cold front will remain stationary
just south of the area from Friday through the weekend before
heading back north across the area. With somewhat weak upper level
troughs moving across the area during this time...the southern part
of the area will have a better shot at receiving rainfall due to the
front lingering nearby. Monday the front moves north allowing near
normal temperatures to return to the area. There will continue to
be some chances for rainfall Monday and Tuesday as upper level short
wave troughs continue to move across the area.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 532 PM MDT Tuesday Sep 2 2014
Main aviation concern for next 24 hours is stratus/fog tonight.
Many high resolution models suggesting stratus/fog at both kgld
and kmck. With rich boundary layer moisture advecting in from the
southeast...do not find any reason to disagree. Stratus/fog
dissipates shortly after sunrise...similar to what occurred at
kgld this morning. A low level jet persists through overnight
hours and with elevated instability in place...its possible there
may be a storm or two in the region. Most guidance suggests any
storms remain east of taf sites so will not include ts mention.