Area Forecast Discussion
Issued by NWS Topeka, KS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
FXUS63 KTOP 081055

Area Forecast Discussion
National Weather Service Topeka KS
455 AM CST Fri Dec 8 2017


.SHORT TERM...(Today and tonight)
Issued at 258 AM CST Fri Dec 8 2017

08Z water vapor imagery shows an upper trough stretching from the TX
Big Bend northeast through the mid MS river valley and the Great
Lakes region. The axis of this upper trough had already pass over
the forecast area. To the west, an upper ridge extended north into
British Columbia. At the surface, high pressure had sunk to south TX
with a surface trough stretching from MN to northeast CO. A wind
shift was noted along the trough axis with area OBS showing warmer
temps and higher dewpoints behind the wind shift.

For today and tonight, northwest flow aloft will persist. There may
be some differential vorticity within the flow aloft but model
solutions and latest water vapor do not really indicate any obvious
shortwave immediately up stream of the forecast area. There are some
signs of mid level frontogenesis with the wind shift and models do
show RH increasing in the 850 to 700MB layer. This appears to be
associated with the weak radar returns over central NEB. Although
OBS show the base of the clouds generally in the 10 KFT level with
no reports of flurries so far. Forecast soundings show a brief
window when the column could saturate across north central KS
through the mid morning hours. But they still maintain a shallow dry
layer near the surface and isentropic surfaces struggle to show a
very deep saturated layer. Because of this am not inclined to
reintroduce flurries into the forecast for this morning. Certainly
if there are some flurries, they shouldn`t amount to much of an
impact. By this afternoon the dry air moves back in with the
frontogenesis falling apart and the isentropic surfaces showing
increasing downglide. So dry weather is expected for the afternoon
and overnight.

For highs today, models show the boundary layer mixing to around
875MB or perhaps a little higher and there really doesn`t appear to
be much cold air behind the wind shift today. However mid level
clouds are expected to inhibit insolation. This cloud cover is
expected to keep highs around 40 for this afternoon. Lows tonight
are forecast to be in the lower and middle 20s as northwest winds
keep some mixing of the boundary layer and prevent the bottom from
dropping out of temps overnight.

.LONG TERM...(Saturday through Thursday)
Issued at 258 AM CST Fri Dec 8 2017

On Saturday the arctic air mass begins to retreat eastward as the
main trough digs over the eastern US. Highs tomorrow are expected to
range from the mid 30s to the mid 40s. On Sunday the region will be
influenced by the upper level ridge over the western US. As a result
the 850 mb temperatures should increase, which will translate into
highs on Sunday in the upper 50s and lower 60s. On Monday a
noticeable cold front pushes through the area as a mid level
shortwave digs over the upper Midwest and Great Lakes region. It
appears the brunt of the arctic air mass will stay confined
northeast of the area. Although Tuesday will be about five degrees
cooler than Monday with highs in the mid 40s to mid 50s. More
shortwaves are forecasted to drop out of Canada mid to late week.
One of those waves tracks over the western ridge and either dives
southward and becomes cut off or digs into the eastern trough. The
first favors a warmer pattern while the later seems to steer
additional waves further south, which deepens the eastern trough and
re-enforces the cold air. Due to model uncertainties confidence in
the temperatures in the extended is somewhat low. In fact the
difference in the EC and GFS high temperatures on Friday is 25
degrees. Regardless the pattern continues to be dry with the
exception of very light precipitation from each passing wave. It
could be in the form of flurries or sprinkles. As of now none of
these precipitation chances are really obvious.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 455 AM CST Fri Dec 8 2017

I expect VFR conditions to prevail through the early afternoon.
There is some question whether some MVFR CIGS may move into
northeast KS late in the afternoon as the NAM suggests. There are
a few OBS showing MVFR CIGS along the NEB/SD state line, but it
doesn`t appear to be a widespread deck of low clouds. So for now
will remain VFR and let later shifts see if the low clouds make
it. The other concern is for potential LLWS overnight tonight.
Models develop a 30 to 40KT low level jet. If the boundary layer
is able to decouple, LLWS could pose a problem.




SHORT TERM...Wolters
LONG TERM...Sanders
AVIATION...Wolters is the U.S. government's official web portal to all federal, state and local government web resources and services.