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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 201143

Area Forecast Discussion
National Weather Service Topeka KS
543 AM CST Wed Feb 20 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 342 AM CST Wed Feb 20 2019

Upper trough axis on water vapor imagery this morning continues to 
lift northeast over the western high plains. Bands of light snow 
mixed with freezing drizzle continues to develop, lifting north and 
east at the current hour with an embedded vorticity max noted within 
the 500 mb flow from southern KS through central and eastern Kansas. 
An additional half to inch of snow is possible through 12Z this 
morning with precipitation exiting the CWA after 8 AM. 

Much drier air surges northward today, eroding cloud cover by the 
afternoon. Sided with consraw guidance for highs today given the 
gusty westerly winds coming off the snow covered ground. Readings in 
the low 30s are common with perhaps middle 30s southeast of 
Interstate 35 where they did not receive as much snow.

Surface high pressure shifts into the Missouri valley tonight with 
clear skies and light winds. Latest NAM and SREF are hinting at the 
potential for shallow fog to develop, however given the potential 
for mid and high clouds to increase northward by 12Z have not 
mentioned it in the forecast for now.

The active upper flow pattern persists with another stout upper low 
developing across the Intermountain West on Thursday. Inverted sfc 
trough deepens in response to the southwest with qpf developing on 
the GFS/Canadian/ECMWF in vicinity of a front. Uncertainty varies on 
the available moisture at the time with forecast soundings showing 
ample dry air below 700 mb. The GFS solution is also above freezing 
in the afternoon so precip type could transition to a light rain and 
snow mix. Little to accumulations are expected as the better forcing 
quickly exits the area aft 00Z. Elsewhere, mid clouds increase with 
a gradual warmup into the upper 30s and lower 40s.

.LONG TERM...(Thursday through Tuesday)
Issued at 342 AM CST Wed Feb 20 2019

The long range forecast continues to be dominated by a diverse 
weather pattern.  A mix of winter and spring type weather looks 
possible for the Saturday time frame with the Saturday afternoon and 
evening period shaping up to be quite diverse in terms of weather 
types from northwest to southeast.

A digging western CONUS high amplitude trough will advance east on 
Friday with main trough axis from the northern Rockies through the 
Desert Southwest vicinity.  A lead wave works out of the Rockies on 
Friday afternoon enhancing a WAA regime over the region.  Thus, 
expecting widespread showers and rain to develop over the forecast 
area into Friday afternoon.  Temperatures and dewpoints should 
generally be on the rise along with PWATs.  This sets up and 
increasingly unstable environment that should support mostly rain 
over much of the area with MUCAPE on the rise as well.  

This should foster an environment into Saturday where thunderstorm 
potential will be on the rise especially over east central KS as 
dewpoints increase to the upper 40s and possibly low 50s.  Saturday 
will see a potent shortwave lift into the area with strong PVA and 
ascent ahead of the main axis.  Increasing lapse rates ahead of 
strong height falls will foster quick deep cyclogenesis as the wave 
takes on a negatively tilted aspect.  There is a degree of 
variability on the actual position of the surface and upper low 
feature as well as the overall strength.  But, regardless of the 
solution, the timing looks to be consistent.  The differences come 
in to play with regards as to how much instability can develop over 
the region on Saturday.  Best chance for thunderstorms looks to be 
over the east central areas of KS as 0-6km shear will be very 
impressive.  Instability actually looks a bit more impressive than 
previous model runs as well, so can't rule out thunderstorms for a 
period of time until the axis of instability and the warm sector 
advance east of the region.  Perhaps the biggest question at this 
point comes on the backside of the system and developing deformation 
zone.  CAA is stronger in the low levels with the ECMWF which 
suggests a quicker transition to a freezing rain setup before full 
transition to all snow with cold enough temperatures through the 
column to support snow.  The deepening nature of the system suggests 
that strong kinematic responses will be in play as well.  This means 
very strong winds, especially with CAA component.  This could mean 
that Saturday night would see not only snow but blowing snow work 
across north central areas and counties along the KS/NE border 
region before the system finally exits the region overnight and 
early Sunday morning.  

Overall colder temperatures work into the area before the upper flow 
begins to transition to a more progressive zonal flow pattern with 
another quick shot of mixed precipitation and transition to snow 
late Monday into Tuesday time frame. 


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 538 AM CST Wed Feb 20 2019

Despite surrounding observations and short term forecasts showing
IFR conditions, KTOP/KFOE manages to remain in mostly VFR 
ceilings. While MVFR visibility lingers through sunrise, 
increasing westerly winds should help to lift sites to VFR as 
skies clear out aft 14Z. KMHK remains near MVFR at 12Z with 
similar trends for skies to clear to VFR aft 15Z as gusty west 
winds average 10 to 15 kts sustained. There is low confidence for 
shallow fog late tonight, given the increasing high clouds. 


Winter Weather Advisory until 9 AM CST this morning for 

Winter Storm Warning until 9 AM CST this morning for KSZ008>012-