Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO
FXUS63 KEAX 111738
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1232 PM CDT TUE MAR 11 2014
Issued at 408 AM CDT TUE MAR 11 2014
Today - Tonight: Have several forecast concerns covering a number of
elements. First is the abnormally warm temperatures. Second is the
the risk of a few strong thunderstorms popping up during the late
afternoon and early evening hours. Third is the return of wintry
weather with some minor snow accumulations likely.
A fairly pronounced upper trough is noted in water vapor imagery
from MT through UT. Models have been consistent over the past few
days in handling this feature as they break off a piece of energy
and track it east through the Central Plains. Downstream height
falls will induce falling surface pressures resulting in a deepening
of the surface low currently over northwest KS. While the NAM has
the most northern track of this feature the more southern route
taken by the GFS and ECMWF has shown a gradual northward shift over
the past couple of model runs. In addition, a closer inspection of
the GFS and ECMWF surface elements notes the low pressure center
being stamped well south of where the actual circulation is
generated by the surface winds. So, am inclined to favor a more
northern track of the surface low through the CWA this afternoon and
early evening. This allows most of the CWA to reside within the warm
sector. And with the same airmass in place have raised high
temperatures across the board. The only negating parameter will be
an increase in high clouds this afternoon. If we had full sun we`d
be knocking on 80 degrees.
Concerns for more than just general thunder this afternoon entails
impressive 0-6km bulk shears in the 60-80kt range, MLCAPEs between
500-700 J/kg, 30-40kt southwesterly low level jet and a
west-southwesterly 90kt speed max at 250mb nosing through the CWA
and juxtaposed over the south-southwest low-level jet. While quality
of moisture leading to marginal MLCAPE values will be a limiting
factor believe the extremely strong shear will help balance the
scale to allow for a few strong storms approaching severe levels
to form from near the surface low southward along a pseudo dry-line
and possibly near the east-west frontal boundary. High winds and
sub-severe hail are possible.
As the Central Plains shortwave continues east this evening another
upper trough will be diving south-southeast through the central
Canadian plains and into the Upper MS Valley and accelerate the cold
front through the CWA as well as pour much colder and drier air
southward. While the models are similar in evolving a post-frontal
deformation zone there are differences in timing with the GFS/ECMWF
more progressive. Inspection of the vertical thermal profile yields
a north-south phase transition from all rain this evening over the
entire CWA to a changeover to snow. The ground will lag in cooling
due to the recent very warm temperatures so then the precipitation
changes over to snow much of it will melt upon contact. Best bet for
any meaningful accumulations will be over northeast MO.
Northerly winds will ramp up with the passage of the cold front as
the pressure gradient tightens in response to a deepening shortwave.
Will hold off on issuing a wind advisory as they should remain just
Wednesday - Friday: Cold air advection all day Wednesday looks like
it will result in slightly cooler temperatures than the previous
forecast so have lowered them some. Have also added some flurries as
a h7 vorticity max dives south-southeast through the eastern portion
of the CWA.
Thursday and Friday look uneventful with temperatures quickly
rebounding back above normal.
Saturday - Sunday: Medium range models still advertising a
moderately strong shortwave zipping through the central U.S.
Saturday night and Sunday with another surge of cold air. This could
produce rain and snow Saturday night/early Sunday. Too early to
include any snow amounts.
Monday: Another quick recovery with temperatures bouncing back to
.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1238 PM CDT TUE MAR 11 2014
Dramatic changes coming to the terminals over the next 6 hours.
Surface low pressure located near MHK at 17Z will advance eastward
this afternoon. Attendant strong cold front will sweep across STJ by
21Z and across KC terminals toward 00Z. Southwest surface winds will
become light and variable for a couple hours as the sfc low slides
across, then abruptly become strong north-northeast as sharply
colder air surges southward. TAF wind forecast could even be a bit
conservative with some potential to see sustained speeds at 30 knots
with gusts to near 40 knots for a period this evening before
gradually subsiding after 06Z with a slight shift to the
north-northwest. Strongest winds appear to be 23-04Z at STJ and 01
to 06Z at the Kansas City terminals.
Precipitation is likely to develop across the terminals around 00Z,
although much variability in intensity and coverage exists along the
western extent (across the terminals). It should generally be light
in nature and start as rain, but as the colder air surges in,
precipitation will change over to snow this evening. Generally do
not expect worse than MVFR conditions in light snow, for a couple
hours mid-late evening before ending 06-07Z.
VFR conditions expected from early morning through remainder of TAF
period with gusty north-northwest winds continuing at 15 to 25