Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KTOP 212332

Area Forecast Discussion
National Weather Service Topeka KS
532 PM CST Thu Nov 21 2019

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday)
Issued at 309 PM CST Thu Nov 21 2019

At 20Z, the upper trough that lifted across northeast KS this 
morning has shifted to the Great Lakes region with another upper 
level trough over western AZ as seen on satellite imagery. This 
upper low will continue to move east across the southwestern US 
today and will bring the next chance of precipitation to the CWA on 
Friday. At the surface, high pressure is building into the area from 
the north behind the cold front that moved through the region early 
this morning. Northerly winds and cloud cover will keep highs this 
afternoon in the low to mid 40s. 

Tonight, the aforementioned upper low across the southwestern US 
will shift east into the central and southern high plains by 12z 
Friday bringing with it the chance for a light rain/snow mix. Upper 
forcing and mid-level frontogenesis develop across southern and 
eastern KS by Friday morning providing modest large-scale ascent 
across the area. However, cold and drier air will be advected into 
north central KS, so the low-levels may be slow to saturate. As 
temperatures warm during the day Friday, light snow may mix with 
rain before changing over to light rain across the eastern portion 
of the CWA in the afternoon. Warming will be slower in the western 
portion of the CWA; thus, the transition to rain will be delayed and 
a light rain/snow mix could dominate through the afternoon. 
Temperatures will fall back into the 20s Friday evening which may 
allow the light rain to transition back to a light rain/snow mix or 
light snow before precipitation ends early in the morning on 
Saturday. A dusting to a half inch of snow is possible Friday mainly 
across the western counties of the CWA where snow will be slower to 
change over to rain. With little to no impacts to travel expected 
and minor snowfall accumulations, have decided against a Winter 
Weather Advisory for this period.

.LONG TERM...(Friday night through Thursday)
Issued at 309 PM CST Thu Nov 21 2019

By Saturday, the upper low will move out of our area and lift 
northeast into the Great Lakes region, which will result in 
northwest flow for the day before transitioning into nearly zonal 
flow on Sunday. This will keep a dry forecast for the weekend with 
WAA in the low levels bringing a gradual warming trend in 
temperatures. Saturday will see highs in the upper 40s to near 50 
while Sunday will reach the mid to upper 50s. Lows will be in the 
20s for the weekend, then increasing to the low to mid 30s by Monday 

A shortwave trough will develop out of the Pacific Northwest Monday 
morning and amplify as it travels through the western US, with lee 
surface troughing in eastern CO by Monday evening. A cold front 
ahead of that trough looks to arrive during the afternoon with 
temperatures reaching the mid to upper 50s before its arrival, 
although cloud cover and CAA could keep us cooler depending on the 
timing of the front. Frontal passage at this time looks dry, with 
the best precip chances coming early Tuesday morning and continuing 
throughout the day. It is at this time that we'll see the primary 
upper level support with CVA providing lift as the trough axis 
passes through the state. There is some variability between the 
GFS/ECMWF as to how deep the trough becomes and as a result, how far 
south we have QPF and how quickly precip moves out Tuesday night. 
However, even more variability exists with the track of the low 
between model runs, as the GFS has brought the deformation zone 
progressively further south with each run since 12Z yesterday. This 
has resulted in the bulk of QPF aligning more with the ECMWF, but 
now across most of KS compared to NE as was the case yesterday. 
Forecast soundings show support for light snow to start off the 
morning before transitioning to rain in the mid-morning as 
temperatures warm, but decreasing moisture in the profile through 
the day could lower amounts as well. Any lingering precip that may 
be left Tuesday evening could transition back to snow before 
completely exiting the area.

The upper trough will move northeast Wednesday morning as surface 
low pressure deepens into the Great Lakes region, which could cause 
significant impacts for those traveling for the Thanksgiving 
holiday, but here in KS we look dry on Wednesday with weak mid-level 
ridging overhead. A deep trough off the coast of CA and northern 
Mexico will eject a few smaller embedded waves through our area on 
Thursday, which could bring some light rain during the day, possibly 
mixing with a few snowflakes in the morning. However, finer details 
related to this feature will likely remain up in the air until after 
the Tuesday system. Temperatures look to stay similar Tuesday 
through Thursday with highs in the upper 40s to mid 50s and lows in 
the 20s and 30s.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 532 PM CST Thu Nov 21 2019

MVFR cigs are expected to continue through 07Z-09Z then become
vfr. Light precipitation may affect the MHK terminal after 14Z
with snow, later mixing with rain after 20Z. Chances look best
around 20Z so added vcsh at that time. Further east at TOP and FOE
expect best chances near the end of the period and added vcsh
after 22Z. Also winds will continue from the north near 10 kts
through much of the period.




National Weather Service Glossary of Abbreviations