Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Goodland Kansas
1118 PM MDT Tuesday Sep 1 2015
Short term...(this evening through wednesday)
issued at 200 PM MDT Tuesday Sep 1 2015
Strong surface heating along a surface boundary in eastern Colorado
has resulted in the formation of cumulus. There is weak support
aloft from a shortwave trough embedded in the southwesterly flow.
However moisture is meager/dew points in the upper 40s to lower 50s/
and storm motions are slow. Given those factors and the weak forcing
will carry only slight chance probability of precipitation through 06z for northeastern
Colorado and immediately adjacent areas of northwest Kansas. Storms
expected to dissipate with loss of daytime heating by middle/late
Little changes expected on Wednesday as upper ridge centered over
the Gulf Coast area continues to be the main upper feature. Possibly
another weak shortwave coming out of Colorado in the afternoon and
another day of strong surface heating may be enough for isolated
thunderstorms in the same areas as today. Temperatures will be much
above normal...with some triple digits possible in the usual hot
spots of eastern portions of the tri state area.
Long term...(wednesday night through tuesday)
issued at 205 PM MDT Tuesday Sep 1 2015
Forecast problem will be precipitation chances through the entire
period. Satellite continuing to show an amplified pattern from the
Pacific into the western Atlantic. Deep upper low is moving toward
the Pacific northwest as persistent upper ridge has moved a little
to the east. This leaves a southwest flow aloft over the area with
numerous shortwave troughs embedded within this flow. Rather strong
looking system in this flow approaching the Southern California
coast. Pacific and mostly monsoon moisture continues to be brought
into this area.
At jet level..the models were close with the Canadian a little
better. At middle levels...the GFS/Canadian/UKMET were doing a little
better than the ECMWF/NAM. The NAM/sref started out the best on the
surface wind/pressure field. The NAM/GFS were doing a little better
than the sref/Canadian on the low level thermal field.
Wednesday night...surface trough stays out to the west of the area
until late in the night when the nightly trend of it moving into the
western portion of the area occurs. Lift and instability aloft increases
after midnight. Not a whole lot of confidence in this but an isolated
storm may develop over the far western portion after midnight.
Depending on how much cloud cover is around...the west will probably
be the coolest due to the lightest winds.
Thursday/Thursday night...it will possible that some lingering
precipitation in the far west will occur in the morning. After that
..the surface boundary is over or near the western end of the area in
the afternoon. At the same time...a much stronger shortwave trough moves
across the western third of the area. Models differ
on the amount of moisture and instability that will be in place.
European model (ecmwf)...NAM and sref have the most and as a result...the most quantitative precipitation forecast.
The GFS has the least.
Models also differ on how far east to take this precipitation
through the entire period. Moisture...lift and mean flow go almost
straight south to north. So far the afternoon will keep a slight
chance to low chance in the western half or so with the greatest
chance along and west of the Colorado border. For the evening will
keep slight chance to low chance probability of precipitation as the lift and moisture
translates north northeast to northeast across the area. Lift looks
to be done by late evening.
Once again the mav/GFS is warmer than the remainder of the guidance.
Based on recent biases and better performing guidance...made little
if any changes to the current forecast. Again lightest winds and low
temperatures will be in the west.
Friday...not too much in the setup for this day. Stronger lift comes
across in the afternoon with the surface trough near the western
end. One difference is that we appear to have deeper moisture in
place. However once again there is a big difference in the amount of
instability. Whatever precipitation develops may not move too far
east once again due to the mean flow being from south to north. Once
again will keep slight chance to low chance probability of precipitation over most of the
area with the highest probability of precipitation in the far west.
Maximum guidance is very similar and much cooler. This makes sense due
to what looks like a lot more cloud cover. So went ahead and near
Friday night through Tuesday...not too much has changed in the
previous thinking. Through Saturday a deep/cold upper trough
develops over the western portion of the country with the middle level
ridge ridge to our east...slowly moving east. At the same time
periodic shortwave troughs move through in this flow.
Then that upper system starts moving toward the north central
portion of the country shifting the flow to a more west to southwest
flow aloft before getting into a Flat Ridge at the end of the
period. Models do this at different speeds/amplitudes. Once this
system kicks out causing the flow becoming more westerly...then the
moisture to work with decreases.
So available moisture and lift will be most favorable for rainfall
in the early portion of the extended.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1114 PM MDT Tuesday Sep 1 2015
VFR conditions are expected at kgld and kmck for the next 24 hours
as a ridge continues over the plains. At this time, no
thunderstorms should impact either site.