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

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FXUS63 KEAX 192043
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
343 PM CDT Thu Oct 19 2017

.Discussion...
Issued at 343 PM CDT THU OCT 19 2017

Focus of today`s forecast remains squarely on Saturday and the
potential for severe weather. Satellite imagery this afternoon
shows, what was, a rather flat zonal pattern beginning to amplify as
a significant shortwave trough makes landfall over the West Coast
today. Leading the large West Coast trough is a smaller trough,
currently swinging through the Desert Southwest into the Plains
States. This leading wave will help keep our pleasant run of well
above normal temperatures persisting through the end of the work
week --Friday highs in the 70s again--, but will also help set the
stage for the larger trough over the weekend by advecting
moisture north from the western Gulf.

For late Friday night into Saturday, the West Coast trough will be
swinging across the mountainous Western States; which will result in
a sharp front stretching from the Eastern Dakotas south into Central
Kansas by 18Z Saturday. Moisture ahead of the front will rapidly
increase thanks to the leading trough Friday and the 40-60 knot
850mb jet early Saturday morning, resulting in precipitable water
values around 1.5 inches by the time we get to daylight hours of
Saturday. The jet is also expected to help cap off the environment
ahead of the front as models soundings from both the GFS and NAM
indicate there will be a bit of a dry cap around 5000ft ahead of
the front. Thus, given the fight between the preceding isentropic
lift and the cap we expect some cloud cover and some scattered
showers or thunderstorms ahead of the front, with early morning
storm activity expected mostly across far northeast Kansas into
northwest Missouri where isentropic lift my be strongest.

Models in the short range have really come into agreement on
Saturday, as both the NAM and GFS have strongly trended to a
compromise solution, compared to the previous few days. As a
result, current expectations are that surface CAPE values in
excess of 1000 J/KG (MUCAPE values possible > 2000 J/KG) are
expected to advect into the pre-frontal environment across eastern
Kansas and western Missouri Saturday afternoon, which will be
coincident with increasing shear values; with 0-3KM values
starting the day in the 30 to 40 knot range, and increasing to 60+
knots along the front as it moves through during the late
afternoon and evening hours. Given all of the above to conceder,
expect morning to afternoon storm activity to plague areas north
of Kansas, which should be non-severe, but as the front pushes
across eastern Kansas that afternoon expect more robust
convection to go up starting between 4 and 7 PM, which is when the
front will be stating to cross the Missouri border. Isolated
strong to severe storms that go up along the front are expected to
develop into a strong and progressive squall line that will make
its way east Saturday evening. Strong bowing line segments
resulting in strong and damaging winds are seen as the primary
hazard at this time, but large hail and an isolated tornado or two
can not be ruled out given the number of ingredients present to
induce a QLCS type event. Primary areas of greatest threat look
to be from from Kansas City southwest into southeastern Kansas and
points south. Additionally, with precipitable water values so
high, expectations are that there will likely be a fair amount of
overrunning rain as the front pushes farther to the southeast.
Thus, while storms might move quickly enough to not induce flash
flooding, flooding along area rivers, creeks and low water
crossing may be an issue late Saturday night into Sunday morning,
particularly in areas south of the Missouri River.

Once the front pushes through early Sunday morning cooler air will
begin to filter in across Kansas and Missouri, knocking temperatures
down to something a bit closer to normal. However, even cooler
temperatures --highs around 60, lows in the 40-- will arrive next
Tuesday as a secondary cold front sweeps through the region.


&&

.Aviation...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 610 AM CDT THU OCT 19 2017

VFR conditions are expected through the period, outside of shallow
river fog slated to impact STJ for the next few hours. Southerly
winds will prevail, with some concern for LLWS overnight.


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&

$$

Discussion...Cutter
Aviation...Blair


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