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

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000
FXUS63 KEAX 310949
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
349 AM CST Sat Jan 31 2015

.SHORT TERM...(Today through Sunday Night)
Issued at 334 AM CST SAT JAN 31 2015

Short-term forecast remains focused on accumulating snowfall expected
over Northern Missouri tonight into Sunday. Winter Storm Warnings and
Advisories have been issued for portions of the forecast area.

Overview: Regional radar composite this morning shows an expansive
area of light to moderate precipitation stretching from the Texas
Panhandle to eastern Kansas. The large majority of this activity is
in the form of rain as strong warm air advection continues across
the Southern and Central Plains. Model guidance is in strong
agreement to bring and keep areas of precipitation in the forecast
area through much of the day. Based on high-res model solutions and
current upstream observations, this seems quite reasonable. Forecast
soundings suggest rain as the primary precipitation type during the
daylight hours for the entire area. By this evening into the
overnight hours, the approach of the shortwave trough will provide a
broad area of strong ascent with periods of moderate precipitation
possible. With the position/track of the system and through dynamic
cooling, precipitation should slowly changeover from rain to snow
with southern extent over time. Prior to midnight, snowfall should
mainly be confined to areas north of Highway 36. The changeover will
eventually take place over the remaining portions of the CWA during
the day on Sunday, but with temperatures near freezing and
precipitation rates notably decreased, lesser amounts of snowfall for
areas south of Interstate 70 is expected. Areas of light accumulating
snowfall may continue through early Sunday evening as a second
vorticity maximum dives across the region before all precipitation
exits the CWA by midnight Monday. FWIW, this system has a non-trivial
amount of moisture to work with, with precipitable water values
roughly two standard deviations above normal for this time of year.
Additionally, much of the forecast area is expected to receive
precipitation totaling one inch or more of liquid equivalent; a
welcome sight.

Forecast uncertainty: Models have kept good run-to-run consistency,
so there are no substantial changes to the forecast. The biggest
uncertainty remains with how well the models are resolving the
near-surface temperature layer. While dynamic cooling will help cool
this layer, concern remains to the strength of warm air advection in
advance of the system. The sensitivity to simply a degree in the
lowest 2kft will make a notable difference to the forecast
precipitation type. Additionally, 2m air temperatures will hover at
or above freezing for a large majority of the snowfall duration,
owing to some melting. Relatively warm ground temperatures will also
effectively melt some of the initial snowfall before moderate rates
can overcome warm surface. These variables make this forecast
particularly challenging, and physically explains the reduction in
snowfall amounts compared to model-derived snowfall amounts.

Snow amounts and impacts: One important aspect of this event is the
potential for a very sharp snowfall gradient on the southern
periphery (our forecast area). Forecasting the southern extension of
the highest snow amounts is further exacerbated by the synoptic
setup and mesoscale challenges mentioned above. Currently, the
highest snowfall totals look to reside over far northern Missouri,
generally extending along and north of a line from Worth to Adair
Counties. Six inches or greater is forecast for this area from this
evening into Sunday afternoon, making for potentially dangerous
travel conditions, and a Winter Storm Warning has been issued for
these areas. South of this area, a Winter Weather Advisory has been
issued from Oregon to Moberly, where two inches or more of snowfall
will be possible. The Kansas City metro is expected to see less than
one inch of snow, with decreasing snowfall amounts with southward
extent. There is some low potential for blowing and drifting snow on
Sunday afternoon as strong northerly winds develop behind a cold
front. While much of the snow is expected to be wet in nature, snow
that falls with the approach of the colder air may tend to be more
powdery and be lofted easier, potentially reducing visibility.

Side note to changes made on highs/lows...raised high temperatures
today south of Interstate 70 into the middle 40s. FWIW, the latest
HRRR tries to bring in lower 50s by afternoon over central Missouri
outside of the precipitation areas. Otherwise, raised overnight low
temperatures to above freezing along/south of Interstate 70. Look
for steady/falling temperatures during the day on Sunday.


.LONG TERM...(Monday through Friday)
Issued at 334 AM CST SAT JAN 31 2015

After this weekend`s winter storm passes, the prevailing northwest
flow will keep conditions cool going into the work week, but a
shortwave trough moving through during the week will keep temperatures
jumping around a bit.

A cold air mass will follow the weekend winter storm system into the
central Plains. This should keep any snow that falls Sunday sticking
around at least through Monday as temperatures will not reach above
freezing till Tuesday. Speaking of Tuesday, warm air advection will
kick in Monday night through Tuesday ahead of a moderately sized
trough that will be rotating under the Hudson Bay low through
Wednesday. This will give us a quick warm up Tuesday with 40s
likely. However, the warmer temperatures won`t last long as the
trough swinging under the Hudson Bay low brings more cold Canadian
air south across the Plains. Forcing along the leading edge of this
cold pool might be able to squeeze out some light precipitation
Wednesday and Wednesday night. This will also leave Wednesday and
Thursday cool as the Canadian high oozes through the region, though
temperatures may warm back above normal by Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1123 PM CST FRI JAN 30 2015

VFR conditions are prevailing currently at all four terminals and
will continue to prevail for the next few hours. However, as the
rain and lowering ceilings migrate in from the west, MVFR and IFR
conditions will take over. For much of Saturday, expect overcast
skies and periods of rain to affect the terminals. By later
Saturday, better rain chances move into the region with much
colder air beginning to filter down from the north. This colder
air will force a changeover from rain to snow with STJ being the
first terminal to see a mix in the evening hours to snow
overnight. The transition at STJ currently looks to occur sometime
after around 23Z or so but have left out the mention at this time
given the uncertainty in how quickly or slowly the colder
temperatures moves in. The remaining three terminals likely won`t
see a changeover until beyond this TAF period.


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...WINTER WEATHER ADVISORY from 8 PM this evening to 9 PM CST
     Sunday FOR MOZ001-002-004-011>015-023>025-032-033.

     WINTER STORM WARNING from 8 PM this evening to 9 PM CST Sunday
     FOR MOZ003-005>008-016-017.

&&

$$

SHORT TERM...Blair
LONG TERM...Cutter
AVIATION...lg





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