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

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000
FXUS63 KEAX 121711
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
1111 AM CST Thu Jan 12 2017

.Discussion...
Issued at 358 AM CST THU JAN 12 2017

...Ice Storm Expected this Weekend...

Today - Tonight

Today is the calm before the storm. Thanks to the cold front that
passed yesterday and the arctic surface high pressure settling into
the area, high temperatures will be below normal; the mid 20s for
northern MO and mid 30s south of I-70. In addition, an upper level
short wave is currently moving east through southern IA. As it exits
the region, the clouds should clear some, temporarily, allowing the
sun to make one more appearance before the weekend. As for tonight,
the clouds will fill in again and temperatures will drop to the
teens and upper 20s.

Friday - Monday

The main focus of the forecast period is of course the impending
ice storm this weekend. Have enough confidence now to issue a
Winter Storm Watch for the entire forecast area starting at noon
Friday. We split the ending times up based on when we expect the
freezing rain to change over to rain. Models are still in good
agreement regarding the broader features at play. A positively
tilted, closed upper level low will be over the southwestern US,
providing the upper level moisture and energy for this event. As
the weekend progresses the upper level low will become negatively
tilted and begin moving northeast through the TX and OK panhandles
by Sunday. At the surface, the previous mentioned cold front will
stall in northern AR, and will begin to retreat north as a warm
front early Sunday. There are two surface highs stalling the
front; the previously mentioned arctic high and a surface high
over the southeastern US. The arctic high will provide the below
freezing surface temperatures, while the southern high will advect
warm, moist air that will override the colder surface
temperatures creating the elevated warm layer between 3-9 kft.
This setup means freezing rain will be the dominant precipitation
type. Right now, the freezing rain should move into the southern
portion of the forecast area around 18Z Friday. By Friday night,
the entire CWA should see freezing rain. The freezing rain will
continue into Saturday but some models, such as the
ECMWF/NAM/Canadian, suggest during the afternoon most of the
precipitation will be in the southern forecast area with some
scattered activity around I-70 and northward. This would be short-
lived though as these models bring the more widespread freezing
rain back up north covering all of the forecast area Saturday
evening. The GFS is the outlier in that it shows this break in
freezing rain later in the day Saturday. There is also the
possibility counties along our southern forecast area border will
see a transition to rain for a brief time Saturday afternoon. The
NAM/Canadian/GFS all bring the surface freezing line north of
those counties, whereas, the ECMWF keeps the freezing line just
south of the forecast area meaning this area would continue to see
freezing drizzle. Have more confidence in the ECMWF and its
cooler surface temperatures because of the strong arctic surface
high, the northerly winds, and cloud cover; therefore have kept
freezing rain in the forecast all day Saturday. Saturday night
into Sunday, the closed low in the southwestern US will eject
pulses of energy over the area providing additional lift. This
will increase precipitation chances and is the best timeframe for
significant ice accumulation for the entire forecast area.

Sunday, everyone will see a transition to rain, the question that
remains is timing. As previously stated the ECMWF is the coolest
solution and it does not move the freezing line north of the area
until Monday morning. On the other hand, the GFS, the warmest
solution, has the surface freezing line north of the area by Sunday
evening. Have gone with a blend in the forecast. Right now, the
Winter Storm Watch ends in segments based on the timing of the
transition to rain. Total ice accumulation for the weekend right now
will be between one quarter to three quarters of an inch with.

By Monday, the surface will be warm enough for everyone to see
rain. Moderate to heavy rain will be possible for most of the area.
We can expect the entire system to exit the area by Tuesday
afternoon.

Keep in mind there is still some variability among models so the
forecast may change some. In addition, total accumulations are
subject to change depending on when the surface freezing line
retreats north.

Tuesday - Thursday

Once the weekend system moves out of the area, dry conditions are
expected with temperatures in the 40s for highs and and upper
20s/low 30s for low.

&&

.Aviation...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1111 AM CST THU JAN 12 2017

MVFR cigs have pushed east of the terminals and VFR conds with
sct-bkn high cirrus are expected thru the duration of the TAF pd.
Towards the end of the TAF pd ovc cigs around 4kft will move into
the terminals with pcpn holding off until after 18Z tomorrow.
Winds will veer from the north today to the NE tonight and ENE
tomorrow morning while remaining btn 8-15kts.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Winter Storm Watch from Friday afternoon through Sunday
     afternoon for KSZ025-102>105.

     Winter Storm Watch from Friday afternoon through late Saturday
     night for KSZ057-060.

MO...Winter Storm Watch from Friday afternoon through Sunday
     afternoon for MOZ020>025-028>033-037>040.

     Winter Storm Watch from Friday afternoon through late Saturday
     night for MOZ043>046-053-054.

     Winter Storm Watch from Friday afternoon through Sunday evening
     for MOZ001>008-011>017.

&&

$$

Discussion...Grana
Aviation...73



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