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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 161001
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
401 AM CST Sat Feb 16 2019

.SHORT TERM...(Today and tonight)
Issued at 400 AM CST Sat Feb 16 2019

Yet another winter system is set to impact the forecast area this
afternoon into tonight. Unlike yesterday's system, there are 
concerns over the exact precipitation type.

A PV lobe currently rounding the base of a West Coast longwave 
trough ejects eastwards along the northern flank of a 170 kt 
subtropical jet and into the central CONUS by late this afternoon.
This negatively-tilted shortwave energy will fuel our next round 
of winter weather. Meridional surface ridging currently centered 
over the forecast area slides eastward over the course of the day,
with return east/southeasterly lower tropospheric flow setting in
by midday. Clouds have been steadily eroding across various parts
of the area overnight, but should build back across the area this
morning with increasing H900-H850 theta-e advection. Isentropic 
upglide along the 280-290K surfaces also increases over the 
forecast area as lee cyclogenesis takes place over the Front 
Range. 

Deeper kinematic lift associated with the mid- to upper-level 
wave overspreads the region shortly after midday. The degree of 
column saturation will play a key role in precipitation type over 
the area, and unfortunately we are flirting right on the threshold
between snow and freezing drizzle (possibly freezing rain in 
regions of deeper moisture and increasing collision coalescence 
processes). South of Highway 24 there may be a few hours in which 
the column saturates through the DGZ, but RAP/HRRR/NAM/GFS bufr 
soundings all indicate periods in which ice is lost within the 
column and moisture becomes limited to the lowest 200 mb of the 
sounding, though the lower tropospheric wet bulb values will be 
near the edge of the ice nucleation zone itself. Therefore, went 
with a mixture of snow and freezing drizzle for much of the event.
Deeper lift and moisture may prevail in far northeastern Kansas, 
where snow is more likely and accumulations of a few inches area 
possible. The bulk of the forcing departs between 06 and 12Z, 
though some CAM solutions linger light PoPs along the KS/NE/MO 
border region into Sunday morning.

Have issued a winter weather advisory for the entire forecast 
area starting this afternoon and ending early Sunday, driven 
mainly by the potential for a light glaze of ice. Impacts may be 
spotty, especially early on, but with very cold ground and surface
temps, any droplets will quickly freeze and create a potential 
travel hazard.

.LONG TERM...(Sunday through Friday)
Issued at 400 AM CST Sat Feb 16 2019

Not to be outdone, another winter event is looming on the horizon
for Tuesday into Wednesday.

Broad longwave troughing persists over the western 2/3rds of the 
CONUS through Sunday before amplifying late Monday as ridging 
encroaches from the northeast Pacific. The weather pattern leading
up to this event will be characterized by continued well-below 
average temperatures with highs in the 20s (near our normal low 
for this time of year) and lows in the teens/single digits under 
continuous northerly flow off a Canadian high pressure ridge. The 
characteristics of the Tuesday/Wednesday storm are still somewhat 
unclear at the present time. There is some concern that with the 
displacement of the surface baroclinic zone over the Lower 
Mississippi River Valley that there will be issues with the degree
of moisture return and possible undercutting of whatever moisture
does make it this far north. The EC surface features are the 
furthest north of the longer range guidance suite and would bring 
the most snowfall to the region, but it is too early to be 
advertising exact forecast amounts.

Model solution diversity slowly increases mid to late week as the
upper level wave along the west coast becomes reestablished and 
ejects at least one lobe of energy late in the week over the 
central CONUS.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1138 PM CST Fri Feb 15 2019

For the 06z TAFs, VFR conditions are expected overnight through
Saturday morning before the next round of wintry precipitation
enters the region. MVFR cigs are expected as cloud cover increases
ahead of this next system, with a mix of snow and freezing
rain/drizzle by mid-afternoon and likely persisting through the
end of the TAF period. As this wintry precipitation overspreads
the area, cigs/vis will continue to drop to IFR conditions and
possibly even to LIFR at KMHK by the end of the TAF period. 


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 PM this afternoon to 6 AM CST 
Sunday for KSZ010>012-023-024-026-038>040-054>056-058-059.

Winter Weather Advisory from noon today to 6 AM CST Sunday for 
KSZ008-009-020>022-034>037.

&&

$$

SHORT TERM...Skow
LONG TERM...Skow
AVIATION...Hennecke