Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO
FXUS63 KEAX 111149
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
649 AM 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
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 12Z TAFS through 12Z Wednesday Morning)
Issued at 646 AM CDT TUE MAR 11 2014
Latest KEAX Doppler Radar output still showing robust southwesterly
winds just off the surface so will maintain LLWS for the first couple
of hours of the forecast until boundary layer mixing commences.
Will delay the cold frontal passage from the north by a few hours.
Winds will increase substantially from the north with the passage of
the front. Expect widely scattered mid to late afternoon convection
to form over west central MO just east of the Kansas City terminals.
Some of the storms could become rather strong and produce small hail
and strong winds. Rain will also spread southward this evening and
mix with snow before changing over completely to snow for a few
hours. Low-end MVFR cigs will accompany the precipitation.