230 
FXUS63 KTOP 151806
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1206 PM CST Tue Jan 15 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 423 AM CST Tue Jan 15 2019

Widespread fog and stratus continue to plague the CWA this morning. 
Visibilities have not quite reached a quarter of mile with the 
exception of a few areas in far eastern Kansas, given the sustained 
speeds over 10 mph towards EMP, MHK and CNK. Through 15Z, given the 
very low stratus and patchy freezing drizzle in place, it's 
conceivable many of the low lying areas may drop to a quarter mile 
so will leave the headline as is, expiring at 9 AM CST. Patchy fog 
may still linger through 18Z towards far eastern Kansas.

Main focus for the short term is cloud cover today as winds veer 
towards the southwest, advecting a warmer airmass from west to east. 
Stronger winds throughout the boundary layer, especially towards 
north central Kansas, lend towards better confidence in the stratus 
clearing as far east as EMP and MHK before halting in the late 
afternoon. Which means much of far eastern Kansas should remain 
mostly cloudy to overcast with cooler temps in the upper 30s. 
Further west, highs in the lower 40s with sunshine should help to 
melt some of the snow cover. 

Next forecast challenge is if and where stratus builds back in 
overnight as winds weaken and veer to the north as a weak cold front 
passes through. Most of the short term guidance is in line with 
patchy fog or freezing fog building back in. Towards the Topeka and 
Lawrence areas, a mix of stratus and fog is expected. Confidence at 
this point on extent of cloud cover is uncertain which may have an 
impact on temps currently forecast in the 20s.

.LONG TERM...(Wednesday through Monday)
Issued at 423 AM CST Tue Jan 15 2019

Lead upper trough ejects into the western high plains by Wednesday 
afternoon. Meanwhile aforementioned sfc boundary begins to lift back 
northward through the afternoon from southern Kansas. The associated 
warm, moist airmass aloft lifting over a shallow cold layer at the 
sfc results in a decent probability for drizzle across southeast 
Kansas Wednesday morning, lifting northwards towards the
Interstate 70 corridor by mid afternoon. Due to the drizzle and 
overcast skies, coordinated with surrounding offices to lower 
highs Wednesday into the lower and middle 30s. Upper trough is 
progged similarly between guidance to impact the CWA Wednesday 
evening through Thursday morning. Initial warm nose aloft and 
degree of saturation in dendritic growth layer lead to 
uncertainties on where the wintry mix switches over to all snow. 
The latest ECMWF is the coldest in respect to the warm nose layer 
while the GFS is the warmest and the NAM is in between. Current 
thinking based on forecast soundings is predominantly a light 
wintry mix overnight with perhaps light snow towards the end 
before exiting eastward. QPF amounts are generally around a tenth 
of an inch or less, with overall little to no accumulation. 

Main focus for the extended is the potential winter storm followed 
by the coldest airmass of the season from Friday into Sunday. Latest 
guidance still differs on precip onset with the ECMWF being faster 
and colder Friday afternoon compared to the warmer and slower GFS 
solution. There is however a gradual trend for the warm nose to 
advect southward, transitioning the area to all snow Friday night 
and Saturday. What is becoming more concerning are the winds Friday 
night through Sunday morning as the upper low is attempting to 
deepen and become closed off as it tracks overhead. This would 
translate to stronger northerly winds at the sfc between 20 and 30 
mph sustained with gusts over 40 mph. In addition for the
possibility of blowing snow, wind chill readings will quickly 
fall from 7 to 15 below zero early Saturday evening, bottoming out
in the 15 to 25 below zero range for the entire CWA Sunday 
morning as the strong 1040 mb sfc high sits directly overhead. 
Temps during this period continue to trend cooler so have adjusted
highs on Sunday to the single digits as the snow comes to an end.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1202 PM CST Tue Jan 15 2019

MVFR to IFR visibilities with BR/FG are expected through early this 
afternoon, followed by a temporary improvement in visibilities, with 
visibilities lowering again to MVFR to IFR around 04Z-06Z tonight. 
Confidence regarding visibility magnitudes and timing transitions are
limited, though the lowest visibilities -- possibly to LIFR 
tonight -- should be confined to TOP/FOE. Visibilities should 
gradually improve late Wednesday morning. With temperatures below 
freezing tonight, any areas of dense fog could result in minor ice
accumulations especially on elevated surfaces. IFR to occasional 
MVFR ceilings are expected to persist through the period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 1 PM CST this afternoon for KSZ008-009-
020-021-034>037-054.

&&

$$

SHORT TERM...Prieto
LONG TERM...Prieto
AVIATION...Cohen