Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 281739
AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1239 PM CDT SAT MAY 28 2016
...Update to aviation forecast discussion...
.SHORT TERM...(Today and Tonight)
Issued at 333 AM CDT SAT MAY 28 2016
08Z water vapor imagery shows an upper low pressure system over the
middle MO river valley slowly lifting north. Further west a broad
cyclonic flow was seen with a weak wave moving towards southern CA
and an upper trough from the northern Rockies into British Columbia.
At the surface, objective analysis showed a weak area of low
pressure from central KS onto eastern NEB while the axis of higher
surface dewpoints has shifted more towards the MS river valley.
For today the trend for lowering POPs should continue as the upper
low pressure system continues to lift north. Have held onto some 20
to 30 percent POPs for this afternoon as models show some moisture
wrapping around the upper low with modest instability possible from
day time heating. The NAM and GFS may be overdone with their
instability progs as they have shown a high bias with afternoon
dewpoints. Nevertheless there could be 1500 to 2000 J/kg of CAPE
develop this afternoon. The better chances for precip will be along
the NEB state line in closer proximity to the upper low. Models show
deep layer shear weakening through the afternoon so severe storms
appear to be unlikely with the better forcing to the north. And
with the moisture axis having shifted east, the risk for flash
flooding looks to have diminished also. Therefore will cancel the
flash flood watch before the expiration time. Models mix the
boundary layer to around 850MB. This should help afternoon highs
warm to around 80. Although more clouds associated with the upper
low across the northern counties may limit insolation and mixing so
have highs in the upper 70s.
Tonight should remain dry for a change as models show no synoptic
scale forcing and the low level jet is progged to remain southwest
of the forecast area. With this in mind, have decreasing cloud cover
through the night with lows falling into the upper 50s. This is a
little cooler than MOS guidance thinking light winds will aid in
radiational cooling. Forecast soundings show the boundary layer
moisture to be pretty shallow overnight. This should limit fog
potential, but later shifts can reevaluate this.
.LONG TERM...(Sunday through Friday)
Issued at 333 AM CDT SAT MAY 28 2016
The next mid level open wave arrives onshore on Sunday, backing
winds towards the southwest across the central plains. A minor
disturbance within the mid levels may trigger scattered showers and
storms during the afternoon across central Kansas, otherwise expect a
mostly sunny day for much of northeast Kansas with light winds.
Increased highs a few degrees than previous forecast given the lesser
Pattern once again becomes unsettled Sunday evening through
Wednesday as the Pacific Northwest shortwave trough gradually tracks
southeast while the southern stream trough becomes positively tilted
as its picked up by the mean winds and lifted through the region.
Highest chances for showers and thunderstorms focuses on Monday
evening through Tuesday evening as all guidance points to a cold
front passing southwest through the region. While lapse rates are
fairly steep, bringing MUCAPE up to near 4000 J/KG on the GFS, shear
profiles are very weak at 20 kts or less so severe weather is not
expected. Heavy rain though may easily lead to localized flooding
and river flooding.
Confidence is increasing that the area will finally be entering into
a dry period as cooler and drier air fills in behind the departing
trough. Have adjusted pops to dry in the extended to highlight model
trends. Light northerly winds and mostly clear skies are the rule
from Wednesday through Friday with highs in the 70s and lows in the
50s. Humidity levels become more pleasant as well with dewpoints
falling back into the 50s.
.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1237 PM CDT SAT MAY 28 2016
Expect SCT to at times BKN ceilings at 3,000 to 4,000 feet this
afternoon. The clouds will dissipate after sunset. Mostly clear
skies Tonight along with light winds and a moist ground may cause
patchy fog to develop at the terminals from 9Z through 13Z SUN.