Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 220542
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1142 PM CST Fri Nov 21 2014
...Update to aviation forecast discussion...
.SHORT TERM...(This Evening through Saturday)
Issued at 445 PM CST FRI NOV 21 2014
Current water vapor shows a weak shortwave moving over the forecast
area. This shortwave and weak isentropic lift is responsible for
drizzle and light rain moving through eastern KS at the moment. As
the shortwave continues to lift to the northeast there will be a
break in the more widespread precip. Warm advection over the cold
surface air in place this morning has caused an increase in
temperatures and dewpoints all morning. The models are forecasting
weak isentropic lift lasting most of the overnight hours, which may
generate either showers and or drizzle depending on the strength.
Cooler surface temperatures have caused quick saturation in southern
portions of the forecast leading to the development of fog behind
the advancing precip. Observations across south central KS and north
central OK have been showing dense fog in those areas all morning.
The upper 40 dew points in those regions are forecast to move into
northeast KS during the evening. With surface temperatures not
forecast to rise much overnight dense fog is possible across most of
the area with this moisture advection. Some of the fog may be dense
as evident in southern KS, although it is uncertain where this will
occur and how widespread it will be. Also, not sure how much diurnal
cooling will take place with stratus overhead. At this point fog is
most likely after sunset in southern counties, and northern counties
after midnight. Will have to let the evening shift evaluate the
latest surface and model trends to see if a advisory is needed. This
low level saturation appears to last until late morning hours.
Across the far southeast counties the visibilities are not forecast
to drop as much and there is a slight chance for shower activity.
The 850 mb winds will gradually veer tonight allowing for some
clearing of lower clouds in north central KS during the morning
hours. As the shortwave over NM lifts into the plains another push
of moisture works back into the area. There is also hints of
instability in the far southeast counties so can not rule out
isolated thunder within the general showers.
.LONG TERM...(Saturday Night through Friday)
Issued at 445 PM CST FRI NOV 21 2014
Water vapor satellite imagery was showing an impressive amount of
jet energy moving into the Pacific Northwest this afternoon. How
this energy is dealt with as it moves into the central CONUS is
the medium range forecast problem today. For the past several
days, we have watched the models deal with this energy and a
downstream short wave moving into the Southern Plains. The current
12Z models all suggest the northern stream energy moves into the
central CONUS and deepens. Given the impressive look to the
offshore wave on water vapor, prefer the stronger looking GFS
concerning the deepening of the northern stream upper trough
moving into the central CONUS and it`s associated surface features.
Through Sunday morning, northeast Kansas should remain in
southerly low-level flow keeping low clouds, fog and occasional
light drizzle around. All the models produce some precipitation
over eastern Kansas, albeit relatively light, Saturday night into
Sunday as the southern stream wave lifts northeast to our east and
as the northern stream energy digs into the central CONUS.
A strong Pacific cold front will cross northeast Kansas on Sunday
and it should clear the low-level moisture out and end
precipitation chances. Cold advection and breezy conditions
prevail early next week. Monday still looks breezy with a deep
mixed layer with 25-35 knots of wind within the layer. Given the
source region of this airmass, temperatures will be cool, but not
as cold as the recent, unseasonably cold airmasses.
Another shortwave is expected to dive into the mean trough towards
the middle of next week. The airmass associated with the
post frontal high looks polar in nature and it should drop
temperatures well below normal again. The fast moving nature of
the wave, the location of the forcing and an overall lack of
moisture should result in mainly dry weather. Will have a dry
forecast after Sunday evening.
.AVIATION...(For the 06Z TAFs through 06Z Saturday Night)
Issued at 1137 PM CST FRI NOV 21 2014
For the 06z TAFs, areas of drizzle or light rain will continue to
develop across portions of northeast and east central Kansas through
the overnight hours before diminishing some in coverage by Saturday
morning. Areas of stratus and fog will continue to spread northward
over the TAF sites overnight with prolonged periods of LIFR and IFR
conditions and even some VLIFR conditions (especially near KMHK) due
to 1/4sm visibilities with areas of dense fog. These conditions are
expected to gradually improve by mid to late morning, however MVFR
cigs/vis will likely persist at the TAF sites through the afternoon
and evening hours on Saturday. There is the potential for cigs/vis
to lower once again Saturday evening with areas of fog possibly
developing as well, however did not include a mention of this in the
TAFs at this time due to uncertainty this far out in the forecast.
DENSE FOG ADVISORY until 8 AM CST Saturday FOR KSZ022-023-