Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO
FXUS63 KEAX 181145
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
645 AM CDT Sat Apr 18 2015
Issued at 411 AM CDT SAT APR 18 2015
Overview: Closed and cut-off upper low now over central CO will be
the primary weather driver for the weekend. Feature will open up by
Sunday and move east in response to a shortwave trough digging
southeast through the Northern Rockies. Expect to see a several
rounds of active convection Saturday and Sunday.
Today - Sunday:
While eyes have been fixated on the closed upper low now over CO/NM
the real weather makers will be periodic vorticity lobes and
associated layered frontogenesis that rotate northeast out from
under the upper low. Little going on over the CWA early this morning
as we`re lacking any discernible feature to initiate any convection.
But we are finally seeing the long awaited next round of convection.
Regional radars have recently lit up from OK northward through
central KS albeit further west than we`ve been expecting. Favor
following the HRRR reflectivity trends, which have slowed down the
arrival of the KS/OK convection and latest NAM mass fields/h7
vorticity prog. Thus have pared back PoPs significantly for first
part of morning and slowed the eastward expansion of precipitation.
Even still this is a forecast which will need adjusting throughout
the day as the convection tied to the upper low has had repeated
false starts as well as expanding too fast to the east.
Thickening cloud cover and rain-cooled air will affect temperatures
over the western half of the CWA more so than the eastern half where
precipitation will move in later in the day. Precipitable water
values around two standard deviations above normal suggest potential
for 1"+ rains through tonight. Weak shear and MUCAPEs under 1000J/kg
favor convection remaining below severe limits.
Should see a lull in the rain later tonight and first part of Sunday
before the next wave of convection moves in. The upper low will have
opened up by then and will accelerate eastward. Anticipate convection
increasing as it moves east through the CWA in response to improving
upper level dynamics and low-level convergence associated with a
cold front. However, once again the 0-6km shear of 20-25kts and
modest MUCAPEs favor convection being sub-severe.
Monday - Tuesday:
A fairly deep upper trough stretching from MN through the Mid MS
Valley will influence our weather with widespread subsidence on the
backside of the trough. Abundant solar insolation will help offset
cold air advection but still result in below average temperatures.
Wednesday - Friday:
As the upper trough shifts east through the Great Lakes an upper
ridge will build eastward through the Rockies and into the
Central/Southern Plains. Medium range models are in agreement that a
cold front will surge through the region on Wednesday. However, they
disagree on whether or not convection will be generated. Moisture
fields look minimal and believe any shower activity will be widely
As we get into Thursday and Friday the ECMWF and GFS both lift a
shortwave out of the southwestern U.S. but the GFS appears
unrealistic in deepening a surface over the Central High Plains and
spreading warm advection convection too far downstream. Will use a
blended forecast but overall confidence low for Thursday`s PoPs but
timing looks better for the PoPs on Friday.
.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
Issued at 641 AM CDT SAT APR 18 2015
A large area of showers and thunderstorms will evolve and lift north
through eastern KS and western MO during the morning and afternoon
hours. Generally VFR conditions with occasional MVFR cig/vsby
restrictions with the stronger storms. Should see the rain
temporarily end from west to east during the evening hours.
Another band of showers and isolated storms may reach eastern KS and
west central MO by the pre-dawn hours of Sunday morning with
generally VFR conditions.