Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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FXUS63 KEAX 241016

416 AM CST Tue Feb 24 2015

.SHORT TERM...(Today through Thursday)
Issued at 415 AM CST TUE FEB 24 2015

...Accumulating snow likely Wednesday afternoon through early

To start off the short-term period, benign weather will continue
through overnight tonight with warming temperatures being the only
thing of note. However, as a well-advertised low pressure system
crosses Nebraska, making a beeline for this forecast area,
accumulating snow late Wednesday through early Thursday looks
increasingly likely. There are still some model discrepancies on
where precisely the low will track as well as some relatively minor
differences in timing. Looking up higher in the atmosphere, cutoff
low initially ejecting out of the southern Rockies today/tonight
phases with the overall upper-level pattern, transitioning into an
open wave near the ARK-LA-TEX-OK borders by tomorrow afternoon,
simultaneously as longwave trough swings through the upper Plains
and into the Midwest by tomorrow night. Translating this back down,
aforementioned surface low riding out ahead of the primary trough
axis briefly strengthens over NE before quickly losing its punch as
it tracks southeastward, washing out by early Thursday. Where the
models diverge is with respect to how the low weakens, with them
struggling to determine its track once it essentially reaches the
MO-NE-IA borders. The GEM seems to be the only one that keeps the
low a bit more together through the overnight period tomorrow night,
taking it more ESE across this forecast area. Both the ECMWF and GEM
keep the bulk of the precip along the MO-IA border, whereas the GFS
and NAM brings more of it diagonally from NW to SE right through
this forecast area.

Highest confidence at this time of what to expect regarding PoPs and
snow amounts resides primarily across northern Missouri. Expect
tweaks to the forecast as the system fully comes within the high-res
models views and as coarser models grab a better grip on its
anticipated evolution. That said, continues to look like 2" to 3"
(with locally higher amounts possible) can be anticipated through
midnight Thursday across the northern third of the forecast area
with widespread 1" to 2" amounts elsewhere. Model soundings are
indicating the potential for some moderate snow to occur, which is
where those higher amounts could be seen. Snow ratios are expected
to increase as colder air comes crashing into the region so tweaks
to expected ratios could also impact the forecast, but not expected
to be by very much. Other questions with respect to amounts include
where the freezing line sets up on Wednesday (rain south/west of the
freezing line, rain/snow mix along, snow north/east - see below) and
how long the snow lingers on through Thursday morning. The 00Z GFS
holds onto light snow possible for longer than other guidance, which
could contribute slightly to these amounts, potentially bumping up
storm total snow amounts, but currently doesn`t look to be more than
about another half to one inch. Definitely stay tuned.

Brief window of weak ridging aloft and southerly to westerly winds
closer to the surface will allow for a warm up today through
tomorrow. Highs today will reach into the upper 30s across the
northeastern portions of the forecast area to lower 40s elsewhere,
especially along the KS/MO border. For tonight, lows will be warmer
than this morning, ranging from the upper teens to mid 20s, again
with those higher temps near and along the KS/MO border. By
Wednesday, high temp gradient will likely setup with upper 20s
across northeastern MO to lower 40s around and south of the KC
metro. Wrench for those highs will be based on the discussed track
of the low and how far north [south] the warmer [colder] air gets
pulled into the area. Vertical thermal profiles support either
simply rain, snow, or a mix so no concerns on any other precip types
joining this particular event; just a matter of where the alluded to
freezing line sets up, which is currently forecast to run a NW to SE
diagonal line from the northwestern corner of MO through somewhere
in between Moberly and Sedalia. Temps will certainly drop back off
by Thursday morning, ranging from around 10 degrees or so across
northern MO to around 20 in the far southern portions of the
forecast area. Highs Thursday will struggle to get out of the teens
and 20s and will likely dip into the single digits on either side of
the zero degree mark, keeping temps especially cooler wherever a
decent snowpack lays out.

.LONG TERM...(Friday through Monday)
Issued at 415 AM CST TUE FEB 24 2015

Name of the game early on in the period will be well below normal
temperatures as Arctic high pressure of 1040+ mb drifts over the area
on Friday. This should result in high temps only reaching into the
middle to upper teens north of the Missouri River...with lower 20s
to the south. High pressure will continue tracking east through the
early weekend which will result in developing return flow from the
Gulf as southerly flow increases across the lower Miss Vly and
southern Plains. As this is occurring...strong Pacific energy
digging along the West Coast will lead to the creation of longwave
trough extending well south into the Desert Southwest and Baja
California region by mid-weekend. The combination of return flow
from the Gulf along with additional moisture arriving from the
eastern Pacific in strengthening southwest flow aloft...will will
lead to an extended period of unsettled weather beginning this
weekend and persisting into early next week.

Based on latest model runs...have held off mentionable pops until
Saturday when both the GFS and ECMWF show enough low-level
saturation to allow precip to reach the ground. Considering the
amount of expected cloud cover along with dynamical cooling from
developing precip...have trended high temps down below regional
guidance on Saturday. Meanwhile...fcst models show strengthening
warm air advection on Sunday as main sfc low approaches and is
accompanied by a LLJ on the order of 45-50 kts. Despite the thermal
advection...enough precip and cloud cover will be in place to limit
the affects of the jet and temps on Sunday were also trimmed
slightly after extensive collaboration with adjacent offices. With
cooler temps now expected...this morning/s fcst calls for a bit more
snow and less mixed precip than yesterday/s package called for.

As for precip timing....initial warm air advection snows to begin
impacting the area on Saturday with precip only increasing in
intensity by Sunday as main sfc low tracks to our south and high
pressure arriving from the northwest increases frontogenetical forcing
over the area. Fcst soundings suggest a small warm nose developing
Sunday morning/afternoon as warm air advection increases ahead of
main sfc reflection. Warm nose with this morning/s guidance looks a
less impressive than in previous days which supports the backing off
of FZRA mention in favor of a RA/SN/PL mix across the area. Across
the far southern zones...temps warming above freezing may even
support pure RA during the afternoon hrs on Sunday. All
told...several inches of snow still still looks possible by event/s
end as lingering snow showers should persist into early next week as
frontal boundary stalls to our south. Stay tuned!


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 1127 PM CST MON FEB 23 2015

VFR conditions will persist through the TAF period. SW winds will
veer through the forecast while becoming gusty from the morning hours
until Tuesday evening. Low-level moisture will develop in the morning
hours and increase throughout the afternoon. There is a possibility
of MVFR ceilings toward the end of the period, though for now will
maintain VFR conditions.




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