Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Goodland Kansas
451 PM MST Sat Dec 7 2013
Short term...(this evening through sunday)
issued at 233 PM MST Sat Dec 7 2013
Latest satellite and upper air data shows areas of clouds over much
of the Great Basin and plains with an upper level short wave trough
moving over the central rockies. Ahead of the short wave trough
light snow/flurries have begun to fall during the afternoon across
most of the tri-state area.
Tonight the light snow will continue over most of the area as low
level frontogenesis develops over the area. The snowfall rate may
increase slightly but still remain light as the frontogenesis
strengthens. Overnight the left exit of the 500-300mb jet will move
over the area from the south. With increased lift over the area
have chances for snow increasing over the northeast half of the area
where the better frontogenesis will also be. As the left exit of
the upper level jet moves in drier air will also move in over the
southern part of the area causing the snowfall chances to end. On a
side note wind chill values around -15f will develop over parts of
east central Colorado where temperatures will be the coldest. Due
to the small areal extent and the uncertainty that wind chills will
fall below -15f will not be issuing an advisory.
Sunday morning the left exit of the upper level jet will move
northeast of the area ahead of the upper level short wave trough.
As the upper level trough moves through low level frontogenesis
strengthens so will have some lingering snowfall chances over the
southeast part of the area...with declining chances behind the
trough where isentropic downglide will develop. Snowfall chances
will end during the afternoon as the upper level trough moves
through the rest of the area.
Long term...(sunday night through saturday)
issued at 233 PM MST Sat Dec 7 2013
Forecast problems will be how cold to keep temperatures through
Monday night and then how much to warm up temperatures after that.
Satellite continuing to show an amplified pattern from the Pacific
into North America. Flow was slightly retrogressive in the Pacific
with upper ridge along the West Coast remaining highly amplified.
Per 850 mb temperature analysis there has been some modification in
the cold low level air mass now in place although today has been much
colder because of cloud cover and snowfall.
Models were starting out fine at middle and upper levels and were not
too far apart. At middle levels the GFS was doing a little better than
the other output. The European model (ecmwf) was doing best on the surface wind and
pressure field. The Canadian and European model (ecmwf) were doing best on the low
level thermal field.
Sunday night...precipitation will be done by this period. Area will
not only be in subsidence from exiting shortwave but also from strong
upper jet to our south. Low dew points will be in place as surface
ridge noses into the area by late in the night. So conditions seem to
be in place especially for the west and north for a very cold night.
Winds will be light but the cold temperatures in place it could be
close...as been the case the last few nights...to another Wind Chill
Monday/Monday night...area will continue to be in subsidence behind
southern upper jet. Strong jet to our north will remain well to our
north. So during the night strong subsidence will be in place.
Models do show a little bit of middle and upper level cloud cover
moving through during the day which could be possible in the fast
flow aloft but really hard to tell. Surface ridge that is in place at
the beginning of the day moves east through the day. 18z NAM is even
slower than the 12z NAM and the latest European model (ecmwf) in moving this through.
This does not Bode well for a Big Warm up and another much below
normal temperature day due to light and variable or light westerly
winds or recycled cold air. So went below the warmer guidance and
near to slightly above the cooler guidance for the maxes.
Somewhat tricky mins. There will be even less cloud cover in place
than the night before. However...most of the models are showing the
westerly winds picking up a little which could hold up temperatures
more than the previous night. However...dew points will still be
rather low plus any short term/brief letup of the winds would allow
the mins to plummet. So tended to go near to slightly below the
Tuesday...some differences as to how much to warm up the maxes. Area
is still in a fast west to northwest flow aloft which could still
allow or push a surface trough through. The differences in the warm
up are tied to drastically different surface depictions despite
very similar solutions aloft. It varies from southerly...lack of
downslope...to stronger west to northwest winds and better mixing
and downslope. Normally would say models are scouring out cold air
too fast. However...models recently have been not getting out of
here fast enough. Also models may be thinking there is a snow on
the ground when there is not. So at this time tended to go between
the warmest and coolest guidance. If warmer guidance verifies most
locations should get near or above freezing for the first time
since the previous Wednesday.
Tuesday night through Saturday...new model output has either westerly
flow aloft or ridging moving in through the period. That makes for a
dry forecast which is what the crh_init grids gave ME. So it comes
down to a temperature forecast. Another front comes through Tuesday
night which drops maxes on Wednesday temporarily back below freezing.
A developing Lee trough and developing middle and upper level ridge to
the west will allow for much milder temperatures to return for the
end of the week. If models correct...entire area should be well above
freezing on Thursday. A weak cold front or two will move through
Friday and especially Friday night into Saturday. Temperatures will
only be slightly cooler on Friday and Saturday when compared to
thursdays. So also accepted the init temperatures given ME since
they were reasonable per the pattern aloft. However...it is possible
that temperatures may be slightly warmer than what is in there now.
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 451 PM MST Sat Dec 7 2013
For kgld...MVFR conditions will continue this evening and then are
expected to deteriorate to IFR later tonight. Light snow has
brought visibility down to IFR temporarily earlier this afternoon
but radar and ob trends indicate improvement of visibility in the
last hour or two. Light snow may end for a period later this
evening with chances once again later tonight. Ceilings are
expected to lower to IFR through early morning before improving to
MVFR by middle day.
For kmck...light snow is currently located to the southwest and
should reach the terminal after 03z and lasting through the early
morning hours. MVFR ceilings are likely by around 03z followed by
a decrease to IFR later tonight lasting into the morning hours.
Improvement to MVFR ceilings should occur by later morning or middle