Flash Flood Watch 9, NWS Topeka, KS

Anderson County, KS, Clay County, KS, Cloud County, KS, Coffey County, KS, Dickinson County, KS, Douglas County, KS, Franklin County, KS, Geary County, KS, Jackson County, KS, Jefferson County, KS, Lyon County, KS, Marshall County, KS, Morris County, KS, Osage County, KS, Ottawa County, KS, Pottawatomie County, KS, Republic County, KS, Riley County, KS, Shawnee County, KS, Wabaunsee County, KS, Washington County, KS

Area Forecast Discussion
National Weather Service Topeka KS
303 AM CDT Wed Aug 7 2019

.SHORT TERM...(Today and tonight)
Issued at 253 AM CDT Wed Aug 7 2019

Main forecast concern is heavy flooding rains tonight.

Sfc map shows a messy convectively contaminated pattern with broad
low pressure across western KS extending north into MN.  Water vapor
showed a discernible wave across SD and another across the OH
Valley. VAD wind profilers show 30-40kt LLJ feeding into MBE across
NE at this point with downstream environment likely going to sustain
this convection that will bring a threat for wind this morning to at
least some parts of the CWA.

This morning complex will push an outflow boundary southwest across
some parts of the state by afternoon.  Wherever this boundary ends
up it could become another focus for afternoon t-storm re-
development which given environment could pose a wind or hail risk
but again this will be determined by strength of cold pool this
morning and placement of boundary this afternoon.

By tonight...the 850-925MB boundary will set up across the CWA while
the sfc/effective boundary may still be just southwest of the CWA. A
developing 40KT LLJ will transport moisture and produce convergence
focusing t-storm development across some part of the CWA after 00Z.
The combination of 850mb LLJ normal to the low level boundaries and
PWAT values in excess of 2" suggest high intensity and potentially
long duration heavy rain event across some part of the CWA. Training
will be a risk as well given expected northwest to southeast
orientation of storms so very concerned about another excessive
rainfall/flooding event tonight across some part of the area.  Exact
location is uncertain but moisture/forcing and duration along with
training potential suggest rainfall amounts up to or in excess of 6
inches could occur in heaviest areas. As a result will issue a flash
flood watch focused on overnight hours when heaviest rains are
possible.

.LONG TERM...(Thursday through Tuesday)
Issued at 253 AM CDT Wed Aug 7 2019

Thursday, a cluster of intense thunderstorms with heavy rainfall
will be ongoing across portions of east central KS after through
18Z THU. Most numerical models show a more amplified mid level
perturbation digging southeast across northeast KS into western MO
during the early to mid morning hours. If these storms are
elevated the primary hazard during the morning hours would be
heavy rainfall across east central KS from I-70 southward across
the southeast counties of the CWA. Most guidance forecast the
heaviest rainfall from 12Z to 18Z Thursday to fall across southern
Osage, Franklin, Coffey and Anderson counties. If the cluster of
storms or MCS is surfaced based then there could be a chance of
damaging wind gusts across the southeast counties of the CWA
during the early morning hours.

As the more amplified mid level perturbation translate southeast
across central MO the thunderstorm cluster will move southeast into
west central and southwest MO. Low-level CAA across the upper
midwest will build a surface ridge southwest into northeast and
north central KS through the afternoon hours. The ECMWF model is a
bit slower moving the H5 trough southeast of the CWA and back builds
the elevated thunderstorms across the CWA through the day Thursday
with the front remaining across the northern counties of the CWA. If
the ECMWF were to verify much of the eastern half of the CWA would
see the potential for heavy rainfall through the day Thursday. At
this time I'm leaning more towards the NAM and GFS.

Thursday night the surface front wil push southward along the OK/KS
border. The zone of stronger isentropic lift may shift south of the
CWA across south central and southeast KS. Thus, strong to severe
thunderstorms with heavy rainfall may move east just south of the
CWA as forecasted by both the NAM and GFS. The ECMWF does show
the heavier rain developing south and southeast of the CWA
Thursday night as well. East to northeast surface winds will keep
high temperatures in the lower to mid 80s.

Friday through Friday night, is looking drier than previous
forecasts, as a broad surface ridge builds southwest across eastern
and central KS according to both the NAM and GFS models. Even the
ECMWF looks drier with only a few hundredths of an inch of QPF
across the CWA Friday morning. Highs will remain cooler in the mid
80s.

Saturday, the H5 ridge across the southern high Plains will shift
east across the southern and central Plains. An intense upper
trough will move onshore across the Pacific northwest. Saturday
looks dry but hotter with highs in mid 80s to lower 90s. The ECMWF
and GFS show a perturbations rounding the upper ridge axis across
eastern CO into western KS. The combination of upslope flow and
ascent ahead of the mid level perturbation will cause a complex of
thunderstorms to develop across east central and northeast CO
into northwest KS and southwest NE.

Saturday night both the GFS and ECMWF show this complex of storms
moving east along the NE and KS border. The best chances for
heavier rainfall will probably occur across the northern counties
of the CWA but an outflow boundary may cause storms to build
southward towards I-70 through the night.

Sunday, the upper trough across the Pacific Northwest will shift
east-northeast across the northern high Plains, the H5 ridge axis
will dampen and thunderstorms may develop along and south of the
outflow boundary left by morning storms. This will be more of a
mesoscale forecast but there is the potential for a line or
cluster of thunderstorms to develop during the afternoon hours and
move east across the CWA overnight.

Monday through Wednesday, the upper flow will increase and become
more zonal across the Plains as the H5 trough moves east across
the northern and central Plains into the upper Midwest. There may
be stronger ascent ahead of the H5 trough for more widespread
thunderstorms across the CWA Monday night into Tuesday. We may see
a break on Wednesday as a cold front shifts south of the CWA but
it may become stationary across southern KS, so I cannot rule out
elevated showers and thunderstorms even though the forecast is
dry. Highs will only reach the lower to mid 80s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1201 AM CDT Wed Aug 7 2019

Confidence is increasing for at least a period of TSRA around 15Z
as the complex to the north-northwest comes toward the terminals
and have trended the forecast in this manner. Another round of
elevated TSRA is possible late in the forecast but uncertainty in
outflow and the location of the effective front keeps any mention
out at this point.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from this evening through Thursday morning for
KSZ021>024-026-034>040-054>056-058-059.

&&

SHORT TERM...Gargan
LONG TERM...Gargan
AVIATION...65

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