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

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FXUS63 KEAX 250338

938 PM CST Tue Feb 24 2015

Issued at 933 PM CST TUE FEB 24 2015

After much deliberation and collaboration with adjacent offices agree
on the need to slow down the arrival of precipitation into the CWA.
The 00Z NAM is considerably slower than it`s previous runs and is
actually in closer agreement with the 12z GFS and latest SREF. Looks
like there will be two precipitation waves with the warm air
advection driving the first batch that is expected to slide southeast
through northern and central IA very late tonight and tomorrow
morning...and affect the far north central and northeastern counties.
Second wave starting tomorrow afternoon will be aligned with the
increasing frontogenetic forcing.

Going dry overnight and no longer see the need to carry any PoPs
over northwest MO through 18z Wednesday. Have also adjusted rest of the
morning PoPs to affect only the far northeast and north central CWA.
Mainly snow although a rain/snow mix is likely on the southwest
fringe. Looking more and more likely that most of the precipitation
will be post-frontal and the risk of rain within the warm sector is
decreasing. The mid-shift and Wednesday`s day shifts may need to make
adjustments for towards this. For now, don`t want to paint them into
a corner with the GFS, ECMWF, SREF and the local WRFs yet to look at.
Interestingly, even with all the changes there were only minor
changes to the overall snow totals.

Also make adjustments to the hourly temperatures.


.SHORT TERM...(This Evening through Wednesday)
Issued at 342 PM CST TUE FEB 24 2015

Warm temperatures, approaching daily normals adorn the forecast area
for today, as good insolation and a westerly surface wind component
combine to bring temperatures back into the 40s for Tuesday.
Although winds have shifted from the west to northwest the warm
temperatures across southern and central Nebraska suggest that we
have nothing to worry about regarding cold air moving in behind the
northwest winds. By tonight, a surface low will form over western
Nebraska and move generally E/SE into SE Nebraska and eventually
into NE Kansas. The effect of this surface low will be to bring the
winds around to the SE for the bulk of Wednesday. This will aid in
keeping the temperatures seasonal for Wednesday - again in the lower
to middle 40s. The surface low will be associated with an upstream
mid level trough, which will move through the area Wednesday night,
bringing with it a chance for accumulating snow, especially across
far northern and central Missouri.

Within the northwest mid level flow there water vapor imagery
suggests an embedded shortwave trough, located roughly over the
Montana Rocky Mountains. Models agree that this wave will continue
along a southeast track into the Northern Plains, then eventually
into northern Missouri. Cold air will generally be in place across
far northern Missouri, prior to the system`s arrival. This will be
more aided by the thick snow pack that has been located across NE
Missouri. Farther south the SE winds will keep the area warm through
a majority of the day. For areas where the cold air will be more
prevalent - namely far N/NE Missouri the initial precipitation with
this wave will be snow, and will likely remain snow for the duration
of the event. expect the first bits of precipitation to form around
12z-15z as the atmospheric column saturates. Expect full saturation
and accumulating precipitation no later than 18z Wednesday
afternoon. As the better lift continues to drift southeastward
through the day on Wednesday precipitation will become more
widespread and snow rates will increase. Forecast soundings indicate
saturation through the -10C to -16C dendritic growth layer through
Wednesday night and into Thursday morning, perhaps through 18z
Thursday across central Missouri. The best snow rates will likely
occur during the overnight period. Regarding the individual elements
of this system, it appears that the majority of the ascent
associated with the precipitation production will be attributed to
the mid level ascent with the shortwave trough, as well as some good
low level frontogenesis. In other words there does not appear to be
a long lasting or deep isentropic component to this system, nor does
there appear to be much in the way of instability enhancing the
ascent. All told, omega values over the areas with best snow
production potential range from -5 to -10 ubars/sec, which is
formidable, but not incredibly impressive. That being said,
generally expect a light to perhaps moderate at times snow fall over
several hours on Wednesday night across northern and central
Missouri. With QPF amounts ranging in the quarter to half inch range
and with snow ratios starting around 12-14:1 eventually rising to
18-20:1 by the end of the event have gone with a general 3 to 6
inches across N/C Missouri, with perhaps a few isolated locations
perhaps reaching 6+ inches. As a result of expected snow amounts
below 6 inches have gone with a Winter Weather Advisory, starting
around noon (18z) Wed afternoon, going through 6am (12z) Thursday
morning. The area within the advisory at this point reflects the
area with the highest confidence of getting 3+ inches of snow. Given
that there is more time between now and when snow will begin south
and west of the current advisory will let the next shift assess the
fringes of the advisory.

Regarding areas south and west of the current advisory, we are still
expecting some light snow fall over just about all of the forecast
area, including the KC Metro on Wednesday night. However, since that
area will be in the lower to middle 40s on Wednesday it will take
longer to cool the thermal column, and perhaps eat into snow totals,
since the early precip could be rain, gradually transitioning
through a rain/snow mix and eventually snow by Wednesday night.
Perhaps .10"-.20" of QPF is expected over these areas, which would
translate to around and inch or two of snow in the areas not listed
in the current advisory. Farther to the south and west - namely in
the Kansas counties and far southern Missouri zones, anticipating
only a dusting to perhaps an inch, as models continue to show the
system weakening fairly quickly upon arrival into northern Missouri.

Expect some light lingering snow to remain through the morning hours
on Thursday, but by then the bulk of the precipitation will have
fallen. Thereafter another very cold air mass will move into the
area, bringing temperatures back into the teens and lower 20s for
Thursday and Friday. Wind chill values for Thursday morning will
droop to around zero for the I-70 corridor, with WC values
approaching -10 toward the IA/MO border. For Friday morning wind
chill values will be well below zero across the entire area, with
the IA/MO border area reaching -10 to -20.

.LONG TERM...(Friday Night through Tuesday) Issued at 342 PM CST TUE FEB
24 2015

The later half of the forecast continues to advertise a very active
pattern for our section of the country starting this weekend and
persisting into next work week.

Overall pattern towards the end of the work week will be adjusting
form a northwest flow, which helped bring our recent bout of cold
temperatures, to more of a locally zonal flow as energy tumbles
over the peak of the east Pacific ridge, ultimately developing a
large sheared trough over the west coast this weekend. This pattern
is similar to one that brought some 36 hours worth of stormy weather
back on January 31st into the beginning of February, as a shearing
wave to our west spit out bits of vorticity into and through a
convergent flow in the Central Plains. Specific confidence on the
forecast for anyone day this weekend into next week is rather low
owing to uncertainties in thermal profile, small temperature
difference means big precipitation type differences, but there is a
sufficient single to warrant keeping our POPs fairly high as we
transit through Saturday and into Sunday.

Moisture return will get going Friday as a cold dry surface high
slides off to the east. This will keep conditions precipitation free
for Friday, but also rather cold as the advertised surface high will
have a pressure of 1040mb. Precipitation will likely spread into our
region during the day Saturday, with current temperatures making
p-types look like snow. However, as the weekend progresses the warm
air advection that is inducing much of the advertised precipitation
will modify the thermal profile sufficiently Sunday morning through
Sunday afternoon enough to induce a precipitation changes. This cold
mean we start Sunday with snow, only to have it transit through
sleet and freezing rain to just rain for a bit in the afternoon,
before temperatures cool back down that night. Precipitation type
issues will likely persist into Monday as the flow will remain
relatively flat into the beginning of next week.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 528 PM CST TUE FEB 24 2015

Clouds will begin to increase in coverage overnight as the next storm
system begins to impact the region. Winds will become light overnight,
becoming more southeasterly by tomorrow morning and then southerly
the remainder of the period. Precip chances will also increase
towards the later half of the prevailing period with rain showers
beginning to develop during the late morning and early afternoon hours.


MO...WINTER WEATHER ADVISORY from Noon Wednesday to 6 AM CST Thursday
     FOR MOZ002>008-014>017-023>025-032-033.



SHORT TERM...Leighton
LONG TERM...Cutter
AVIATION...PMM is the U.S. government's official web portal to all federal, state and local government web resources and services.