Scientific Forecaster Discussion
fxus63 keax 171110
Area forecast discussion
National Weather Service Kansas City/Pleasant Hill MO
610 am CDT Sat Mar 17 2018
issued at 250 am CDT Sat Mar 17 2018
Satellite imagery and surface observations show the nearly
vertically stacked storm system tracking over the area early this
morning. Low clouds are spilling into the region on the backside of
the low across eastern Kansas and western MO. There may be some
lingering light precipitation across northern to northeastern MO
this morning, but other than that, it looks dry and cool today with
highs climbing into the 40s north and the 50s in our southwest.
Temperatures will moderate into the 50s and low 60s on Sunday ahead
of the next storm system that should impact the area beginning Sunday
night and persisting through the day Monday. There are some
significant differences in the models for this system, despite them
being in agreement with taking the surface low to our south. The NAM
is a clear outlier here. It has a little bowling Ball of a pv
anomaly move over the area and is much deeper with the upper low.
This strong forcing seems to feed back into the intense band of snow
it produces across northern MO. Forecast soundings in this band show
very steep lapse rates develop with some instability noted. In
essence, there is dynamic cooling of the column due to the strong
upward vertical motions. This results in a narrow swath of a foot+
of snow. At this point, this seems very unlikely given the cutoff or
closing off of the upper low. The GFS, Canadian, and the European model (ecmwf) all
seem much more reasonable and don't produce the dynamic cooling that
results in a narrow swath of heavy snow. Rather, they present a much
more reasonable widespread rain event where the area could see half
an inch to three quarters of an inch of much needed rain. So have
basically discounted the NAM at this point for this time frame.
Through the rest of the forecast, there should be a general warming
trend as temperatures warm from the 40s on Tuesday to the 50s and
60s by Thursday and Friday. There may also be several chances for
precipitation. These look less widespread than the Monday system and
models are in less agreement with the timing and areas of
precipitation. Most of these chances seem to come from the GFS
which moves several small systems through the area through Friday.
Given the lack of agreement on these smaller systems, would not be
surprised to see subsequent forecasts lower/remove these pops.
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 611 am CDT Sat Mar 17 2018
Low MVFR ceilings are expected to persist through the morning
hours before lifting to MVFR by the afternoon. Ceilings should
become VFR by late in the afternoon. Winds will be from the
northwest this morning but will gradually weaken and become
variable as high pressure tracks to the north and to the east.