Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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000
FXUS63 KEAX 211740
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
1240 PM CDT Mon Aug 21 2017

.Update...
Issued at 900 AM CDT MON AUG 21 2017

Latest radar trends now showing renewed convective development
across eastern Kansas and western Missouri out ahead of an MCV
circulation lifting east-northeast in well-established monsoonal
southwest flow aloft. Latest GOES-16 Visible and Cirrus channels
show an extensive canopy of cirrus associated with this feature,
and all indications suggest this cloud shield will continue
lifting northeast over our area this morning. Furthermore, a
lingering outflow boundary stretching from southeast Nebraska
through the St. Joe region may also serve as a focus for
additional shwr/storm development this morning/afternoon as the
affects of the MCV continue to lift towards our area. Latest SPC
meso page graphics show deep moisture convergence is maximized
along this residual boundary, so additional development this
morning/early afternoon appears possible. Its possible some of
the inbound cirrus cloud cover over central Kansas thins with
time, but additional clouds from developing convection could
still limit optimal viewing of the eclipse...

&&

.Discussion...
Issued at 302 AM CDT MON AUG 21 2017

Complicating factors are abound for today`s eclipse in an active,
unstable pattern across the Plains. A convective complex which
formed in northwest IA this evening has begun to propagate south
southeastward as its cold pool strengthens, and will likely
continue to do so over the next several hours as the LLJ feeds
into the system. Evolution of this complex is once again handled
very poorly by high-res models, but Corfidi vectors and the
orientation of the instability gradient suggest the south to
south southeast development should continue. Have hand-edited
cloud cover upward as the anvil plume develops south and spreads
to the east across the northeastern quadrant of MO, and then
allowed higher cloud cover to dissipate and advect off to the east
as storms weaken by mid-morning.

An outflow boundary currently evident on radar pushing through the
Omaha area will continue to slide southward this morning, and
while the eastern extent of the of the outflow will continue to
push quickly to the south, the western edge may stall near the
NE/KS/MO border without strong evaporative cooling due north of
the boundary to reinforce its southward propagation. This pre-
existing boundary could serve as a focus for convective initiation
as early as 12PM in an already unstable atmosphere, complicating
the forecast for the eclipse even further. At the same time,
cirrus streaming northward from convection in the High Plains will
continue to approach the forecast area, and most models indicate
the thickest cirrus will push into the NE/KS/MO corner just after
noon. The cirrus is probably the least of the caveats to eclipse
viewing since it may remain thin and broken enough to view the
sun, but the potential for developing low-based thick cumulus is
much more concerning, particularly if the outflow boundary stalls
near the path of totality.

Any storms that develop this afternoon have the potential to
quickly become strong as MLCAPE increases to greater than 2000
J/kg, and while deep-layer shear remains questionable with a
weakness in the wind field around 600-500 hPa, decent 0-3 km
shear and enhanced helicity from remnant boundaries could add
organization to any robust storms that develop, and could even
result in a brief tornado in storms that root along a boundary.

This "questionable" shear profile will only serve to enhance the
potential for heavy rain this evening along and ahead of the cold
front as it pushes through the region. GOES-16 WV imagery finally
shows a break in the tropical connection between Hurricane Kenneth
and the desert southwest, but the damage has already been done as
very high PWATs continue to advect northeastward into the Plains.
The combination of multiple convection rounds, PWATs approaching
2.5 inches, very high warm cloud depths, a deeply saturated
profile, and an increasing low-level jet below weaker steering
winds will definitely set the stage for very heavy rain across
the majority of the CWA. Have kept the flash flood watch as-is,
but will also need to watch how much precipitation falls along the
MO/IA border early this morning, which could lower flash flood
guidance even further after yesterday`s storms and on top of
additional expected rainfall tonight.

Quieter conditions are finally expected once the front clears out
of the area early Tuesday morning, clearing out low-level moisture
and slashing high temperatures back into the upper 70s to low 80s
for Tuesday through the weekend.

&&

.Aviation...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1239 PM CDT MON AUG 21 2017

Challenging fcst in the near term as latest radar trends continue
to show light precipitation over the area. Most likely impacts in
the near term are expected at STJ and MCI where light shwr
activity will be possible through 21z. Otherwise, attention will
then shift towards the late evening when fcst models show the best
chance for organized shwr/storm activity as a cold front slides
south over the region. As this occurs, expect widespread
shwr/storm coverage with all sites having the opportunity to fall
below MVFR and IFR thresholds. Considering the uncertainty of
timing this afternoon, with allow later updates the opportunity to
address expected restrictions once trends become better
established.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Flash Flood Watch from 10 PM CDT this evening through Tuesday
     morning for KSZ025-057-060-102>105.

MO...Flash Flood Watch from 10 PM CDT this evening through Tuesday
     morning for MOZ012>016-020>024-028>032-037>039-043>045-053-
     054.

&&

$$

Update...32
Discussion...Laflin
Aviation...32



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