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Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO
1152 PM CST Wed Dec 17 2014

Discussion...
issued at 310 PM CST Wednesday Dec 17 2014

No major changes to the current forecast, which still calls for a
broad one to three inches of snow with the higher amounts near and
west of the kc Metro. This is in response to a weak upper wave that
is currently producing quite a bit of precipitation across OK and
southern Kansas. This activity is more widespread than models had
predicted, an indication that moisture may be a bit more readily
available than previously thought. Assuming convection down there
doesn't get too deep and rob our area of moisture, this should favor
at least an inch or two of snow overnight tonight into early Thursday
as the upper wave moves through. This wave will lose its definition
fairly quickly on Thursday, leading to a steady weakening of
precipitation as it spreads into north central and eastern Missouri
through the late morning and early afternoon. A slight loss of upper
level moisture on the back side of precipitation could favor some
patchy areas of freezing drizzle tomorrow, but without any good
source of low-level lift by this time, any ice accumulations would
be very minor if anything at all.

Several of today's model runs have been hinting at a small band of
3" to 6" snows that could set up anywhere from the kc Metro westward
into central or north central Kansas. This of course raises an Eyebrow to
the possibility that our forecast amounts could be too low for some
areas. Upon closer inspection of these models, they seem to be
producing bands of frontogenesis on the north edge of lower Theta-E
air that will punch into the 700-500 hpa layer later this evening.
This dry slot is also producing a bit of low static stability in
these models. While these dry slots do have the tendency to reduce
stability and potentially enhance snow rates, the frontogenetical
forcing one would typically like to see in banded snow cases is
questionable given the lack of a good temperature gradient or
converging wind fields. Rather, the frontogenesis in these models
seems to be in locations where diabatic cooling is taking place near
the dry slot. Can't totally say this won't happen, but it's too risky
to put much weight in such a random process that seems to be giving
models a hard time (evidenced by the inconsistencies in if/where such
a band occurs). Will therefore stay with our general 1" to 3"
forecast, but later shifts will keep an eye on trends in case such a
band begins to take shape upstream. If this occurs we would have to
boost snow amounts for a few locations.

Weather pattern behind thursday's system still looks fairly quiet,
especially now that models are taking friday's system well south of
our area. This will favor dry conditions until Monday and Monday
night when a broad wave will track to our north and send a weak front
into the area. Given the storm track, most precipitation should fall
as rain other than perhaps a few flakes on the back side. All eyes
will then be on how this system evolves to our east with signs of
significant cyclogenesis taking place across the Ohio Valley or Great
Lakes. This would keep any major impacts for the Dec 23-24 period
east and northeast of our area, but it bears watching in case it
were to drift further west with future model runs.




&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1114 PM CST Wednesday Dec 17 2014

Snow is currently impacting, or will impact the terminals in the next
hour. Main edge of snow currently along a line from kfnb
southeastward to kjef and is slowly spreading northeast. Main issue for the
prevailing taf period is periods of reduced visibility as heavier
bands move across the terminals. Visibility has been falling to LIFR
with these bands. Snow will begin to wind down between a 15-17z
period. As main area of lift moves out of the region, snow will come
to an end but there is a slight chance for some patchy freezing
drizzle to develop given saturated lower levels.

&&

Eax watches/warnings/advisories...
Kansas...Winter Weather Advisory until 9 am CST Thursday for ksz025-057-
060-103>105.

Winter Weather Advisory until noon CST Thursday for ksz102.

MO...Winter Weather Advisory until 9 am CST Thursday for moz028>031-
037>039-043>046-053-054.

Winter Weather Advisory until noon CST Thursday for moz011>014-
020>024-032-033-040.

&&

$$

Discussion...hawblitzel
aviation...pmm

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