Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 301134
AREA FORECAST DISCUSSION
National Weather Service Topeka KS
634 AM CDT TUE AUG 30 2016
...Update to aviation forecast discussion...
.SHORT TERM...(Today and Tonight)
Issued at 316 AM CDT TUE AUG 30 2016
Convection redeveloped in north central and central Kansas early
this morning in an area of upper level divergence and within the
tropical moisture plume. Within the plume satellite and profilers
show weak embedded waves. Satellite also showed an mid level trough
over Colorado. Models continue to show some differences with
precipitation placement and QPF. General trend is for convection
across north central Kansas early this morning the spreading
eastward across northeast Kansas this afternoon and evening. Models
suggest upper level difluence will overspread north central and
northeast Kansas into southern Nebraska this afternoon. Potential
remains high for locally heavy rainfall given weak flow and
precipitable water values remaining in the 1.8 to 2.0 inch range.
Diurnally driven convection along with the embedded waves enhancing
lift should maintain scattered thunderstorms through the afternoon.
Will continue with the flash flood watch for much of the northern
half of the forecast area for today where heavy rainfall has fallen
over the last couple of days. Highs today will range from the upper
70s in parts of north central Kansas to the mid 80s in east central
Kansas. Lows tonight mainly in the mid to upper 60s.
Tonight, convection may focus along a slowly moving frontal boundary
across Nebraska and far northern Kansas. There is some convergence
in the 925-850mb layer, but wind fields remain weak and expect
storms to be slow moving once again. Precipitable water values will
remain around 2 inches across the area, so there is still the
potential for locally heavy rainfall. Main question remains where it
focus for much of the night. After coordination will keep expiration
for the flash flood watch at 7 PM. Later shifts will need to
monitor for any extension in area or time.
.LONG TERM...(Wednesday through Monday)
Issued at 316 AM CDT TUE AUG 30 2016
By Wednesday morning, a ridge will be building across the Rocky
Mountains, with an embedded shortwave skimming southeastward across
the area. In addition to this passing shortwave, models show a back-
door cold front sinking southward across the forecast area through
the day as surface high pressure builds southward into the Central
Plains. The presence of this front and mid-level shortwave will help
to provide enough forcing to support the development of scattered
thunderstorms across much of the forecast area. Instability looks to
be pretty weak over most of the CWA, with maybe upwards of 1000-1500
J/kg possible across far southern portions of the CWA. These
instability values combined with 0-6km bulk shear values of only 20-
25kts should result in storms remaining sub-severe. The primary
concern will be for heavy rain potential as this passing front may
be slow-moving, which may keep storms over some areas for a more
prolonged period. Plus, with PWAT values of around 2 inches, high
rainfall rates will be possible with these storms.
This front will sink south of the CWA by Wednesday night, with a
stretch of dry conditions expected through Friday night as the ridge
shifts into the central U.S. and surface high pressure prevails over
the area. These drier conditions will also be accompanied by cooler
conditions as high temperatures Wed-Fri will be below normal in the
upper 70s to low 80s, with overnight lows plunging into the 50s.
By the weekend, models show a mid-level trough moving into the
northwestern U.S. with southwesterly flow aloft shifting into the
central U.S. This advancing trough will help to push an area of
surface low pressure into the High Plains region. As a result,
southwesterly flow at the surface will help to moderate temperatures
into the mid/upper 80s late weekend into early next week. Models
show the potential for a few embedded shortwaves to develop within
the southwesterly flow aloft, which could potentially bring some
isolated to scattered thunderstorms into the area. However, there
are still plenty of model discrepancies with regards to the timing
and location of these waves and any associated precipitation. As a
result, have only slight to low-end chance PoPs Saturday-Monday.
.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
Issued at 634 AM CDT TUE AUG 30 2016
Isolated to scattered tsra to continue through much of the period.
VFR conditions are expected outside of convective activity. Have
added VCTS to the forecast as timing when convection will make it
to the terminals. Highest confidence in MHK this morning after 15Z
so inserted a tempo group until 17Z. Models suggesting an mvfr cig
may develop toward the end of the forecast.
Flash Flood Watch through this evening for KSZ008>012-020>024-