Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 131116

Area Forecast Discussion
National Weather Service Topeka KS
516 AM CST Fri Dec 13 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 340 AM CST Fri Dec 13 2019

Currently at 09Z, the upper air pattern over the CONUS is
characterized by a fairly low amplitude trough axis extending from
the upper MS Valley into portions of the southern Plains and lower
MS Valley region.  Northwest flow pattern extends all the way back
to the Pacific Northwest region with Pacific moisture streaming into
the western CONUS via the "Pineapple Express" around the northern
periphery of a broad high pressure ridge making up its residence
over the Pacific Ocean to the west of the Baja region.  A weak
surface ridge is set up into portions of the area with calm winds at
most sites.  Due to higher clouds aloft, fog potential has been
limited.  But, there is some radiational cooling time left for the
overnight period, so can`t rule out some areas do develop some
patchy shallow areas of fog through sunrise.

Dry for the daytime hours today across the area with a southerly
breeze helping temperatures push into the 50s in some areas.
Tonight, a weak shortwave slides into the region.  Most models keep
the low levels too dry to see any meaningful amount of precipitation
make the trip to the surface.  But, saturation does look deep enough
that I have kept some slight POPs over the area into the evening
hours late this afternoon.  Look for most precip to remain in liquid
form with possible flurries if the wave is slower to move into the
region and thus more BL cooling effects would support flurries at
the surface or light snow if deep enough saturation is maintained.
Again, this wave looks like it weakens as it moves into the area, so
not expecting any significant precip amounts.

.LONG TERM...(Saturday through Thursday)
Issued at 340 AM CST Fri Dec 13 2019

The attention for the mid to long range forecast then turns to the
latter part of the weekend and the beginning of the work week.
Uncertainty is still a product of this forecast, so unfortunately
not many solid answers can be discerned as of yet.

What does appear to be coming together is that a slight focus on the
idea of a southern track of the low pressure trough and developing
surface low as the upper level southern stream trough digs into the
Desert Southwest region.  Essentially, this track of the upper level
and surface features, should yield mainly an isentropic ascent
forcing pattern for Sunday.  There is some better agreement in the
positioning overall of the possible main snow band setting up which
would be along and north of the I-70 corridor reinforced by the
mid level frontogenetical band into the overnight period Sunday
into Monday morning. Amounts are low confidence right now, but
several inches seem to be a reasonable possibility over this
general zone. Uncertainty in p-type comes into the forecast
further south of this general area as ice in the cloud and lack of
DGZ saturation could come into play more so. Right now, have gone
with mixed precip over this region for a longer period of time.
This has also increased potential ice accumulations over east
central KS. Amounts would still be considered to be light ice
accumulations. Again, still uncertain in system orientation and
upper level features, which give way to how lift and saturation
will play out in working together to produce precipitation over a
given area that results in the forecast accumulations. This
uncertainty is further complicated by the more amplified nature
overall of the ECMWF and thus slow system movement to the east.
Hopefully, some of this can begin to be resolved as higher
resolution models come into play and more upper air samples help
get a handle on the upper level features.

The rest of the week should see dry conditions with overall heights
rising as a broad ridge sets up over the central portions of the
CONUS.  Depending on snow cover lingering on the ground -- and for
how long -- high temperatures will likely be impacted.  But,
currently, the forecast calls for near normal temperatures with
highs reaching back to the 40s into the end of the week.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 450 AM CST Fri Dec 13 2019

some areas of ground fog have been able to form, so have
maintained that in the TAFs through sunrise. VFR conditions
outside of that today with any small chances for showers later
tonight which are currently too low to include. Winds
progressively veer to west and northwest as a weak front passes
through the area today.




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