Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 290429
AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1129 PM CDT THU JUL 28 2016
...Update to aviation forecast discussion...
.SHORT TERM...(This Evening through Friday)
Issued at 324 PM CDT THU JUL 28 2016
Profiler and water vapor data suggests a shortwave moving towards
the area within the northwest flow aloft, and is likely responsible
for the MCS moving into northwestern KS. At the surface, a weak
boundary has been set up near NEB/KS state line and is gradually
becoming more diffuse.
With the shortwave evident in satellite imagery, think there isn`t
much to keep the MCS from continuing to move southeast along the
instability axis and the HRRR seems to be catching on with some
consistent outputs the last couple hours. The RAP tends to want to
mix out the the boundary layer moisture quite a bit across northeast
KS resulting in the better instability mainly across the
southwestern counties. The latest OBs tend to support this idea as
dewpoints have fallen into the lower 60s over Brown and Marshall
counties. So the expectation is for storms to move more towards
south central KS. With better mid level flow, models are showing 0-
6KM shear around 40KT so some organization is probable with the MCS
and the main reason for a damaging wind risk. Freezing levels remain
fairly high for large hail, but there could be some marginally
severe hail with some of the stronger updrafts.
Have continued with some chance POPs into the morning Friday with
indication from the models that there could still be some vorticity
overhead. Although the expectation is for the chance to diminish
through the day with the vorticity moving southeast of the area and
surface ridging building in. Have not changed the temp forecast much
from the previous shift. Lows could be a little tricky if rain
cooled air knocks reading down into the lower 60s. Otherwise would
anticipate lows in the mid 60s for most area. Models show good
mixing of the boundary layer to near 800MB. However there is also
progged to be cooler air advecting in. So highs in the lower and
middle 80s seems to be in the ballpark.
.LONG TERM...(Friday Night through Thursday)
Issued at 324 PM CDT THU JUL 28 2016
Friday Night through Sunday...
Upper flow transitions from northwest to west during the weekend
periods. Low level winds respond with a slow increase from the
southwest with a stronger low level jet develop Saturday night. Best
convergence Friday night into Saturday looks to be to the southwest
of the area, with Saturday night into early Sunday bringing much
better convergence, moisture, and instability. Severe weather
threats look low given elevated nature, warm temps aloft, and meager
lapse rates. Temperatures become somewhat of a challenge, with
little wind and potentially rather clear skies Friday night, then
ongoing precip into Sunday for uncertainty in daytime heating. Have
trended a bit cooler Friday night, and tightened the gradient Sunday
with temps pushing the mid 90s west.
Sunday Night through Thursday...
The biggest take away from the extended period is: THE HEAT IS BACK!
A few showers and thunderstorms are possible Sunday night as a weak
shortwave within the northwest flow moves across the Central Plains.
The better chances look to be north and east of the outlook area.
The stubborn upper-level ridge across the Western US, will migrate
eastward early next week, setting up its axis across the Plains.
Guidance suggests high temperatures will remain above average for
the period with highs in the middle to upper 90s. With predominately
southerly low-level flow, plentiful BL moisture will remain in place
with surface dew points in the upper 60s and lower 70s (West to
East). The combination of heat and humidity will result in the heat
indices in the 100 to 105 degree range Monday through Wednesday.
These heat indices may continue into Thursday, however confidence is
lower due to the possibility of showers and thunderstorms associated
with a weak cold front.
.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
Issued at 1127 PM CDT THU JUL 28 2016
As showers clear east of KTOP/KFOE, conditions return to VFR for
the remainder of the forecast. Higher confidence for TSRA centers
south of terminals so will not mention for overnight period. Sfc
high in place results in light northerly winds and partly cloudy