Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 182027

Area Forecast Discussion
National Weather Service Des Moines IA
327 PM CDT Tue Jun 18 2019

.SHORT TERM.../Tonight through Wednesday Night/
Issued at 319 PM CDT Tue Jun 18 2019

Confidence: Medium

Main challenge continues to be the MCV over northeast Kansas and the
track tonight into Wednesday. Models have been tracking the system
mainly to the east with the heavier precipitation expected to remain
south of the forecast area. Weak trough over the south will likely
be the focus of additional showers/thunderstorms this afternoon and
evening as some mechanical forcing from the MCV combines with the
boundary. The high res models are somewhat divergent on the track of
the MCV overnight with the NMM farther north than the ARW with the
HRRR not tracking the system very well at this time. Current trends
suggest that the track may be a bit farther north. With that in
mind, have boosted PoP and rainfall amounts over the south during
the late overnight and into Wednesday morning.  Across the weak
boundary, precipitable water values remain in the 1 to 1.5 overnight
into Wednesday morning. Warm cloud depths continue to reach about
9500 to 11000 feet over the south third of the forecast area this
afternoon and tonight.  This may again result in some locally heavy
downpours with brief heavy rainfall in some of the heavier storms.
Though overall rainfall amounts should range from 0.25 to 1.25 in
the southern third, local amounts may again approach 2 to 2.5
inches in some of the heavier storms. Though widespread water
issues are not expected, there may again be some localized urban
runoff that may impact streets due to the slower movement of some
of the showers and thunderstorms this afternoon. Will maintain
higher pops and qpf over the south tonight into early Wednesday as
the MCV tracks across Missouri. Lows tonight should hold in the
lower 60s south and in the lower to mid 50s over the north.
Similar to previous nights, some patchy fog may also occur over
the region. For tomorrow, highs will be held down over the south
with generally thick cloud cover and showers and storms in the
area. Have cut back highs into the lower 70s south and left the
north in the mid 70s for the afternoon hours. The system will pull
east of the region Wednesday night and with some clearing, fog is
going to be more likely over the region; especially in the south
where more rain is expected tonight through Wednesday. Lows
Wednesday night will fall into the mid 50s to around 60 south.

.LONG TERM.../Thursday through Tuesday/
Issued at 319 PM CDT Tue Jun 18 2019

Confidence:  Low to Medium

Though the early portion of the extended forecast looks similar to
previous forecasts, as the weekend rolls around some changes are
beginning to show up in the medium range models and this is lowering
day to day confidence on details of the forecast at this time.

Overall, the transition to southwest flow is still intact with
instability increasing by Friday and wind fields strengthening as
well.  First off for Thursday, a northern stream shortwave will
swing northeast with a warm front moving back north through Iowa
with warm air advection and chances for showers and thunderstorms
Thursday.  Highs Thursday will be similar to the past milder days
with upper 70s south and mid 70s over the north where rain chances
will be higher. By Thursday night into Friday morning, both the
GFS/Euro are now initiating an MCS along a new resurgence of thetae
advection into Iowa, though at this time the spread of solutions
lowers confidence on whether southern/central Iowa would be more
favored for the track of the mesoscale system into Friday afternoon.
With precipitable water values in the 1.50 to 1.75 inch range,
rainfall amounts with any system tracking across the region could
drop another 1 to 2 inches of rainfall. In fact, through much of the
weekend now, values remain in the 1 to nearly 2 inch category from
time to time across the region. With the southwest flow aloft in
place from Friday through Sunday, several pieces of shortwave energy
continue to track northeast over the area during the period. Each of
the waves has the potential to bring repeated rounds of storms into
Sunday night. With this change to a extended period of more active
weather, the threat for hydro issues could increase along with
chances for stronger to severe storms. There is some consensus that
by Tuesday, quieter weather will return for a brief time. Highs
during the period from Friday into Sunday will daily remain highly
dependent on convective trends, but should range from the upper 70s
to mid 80s on average; with lows in the 60s to lower 70s with more
summerlike humidity expected through the period.


.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1240 PM CDT Tue Jun 18 2019

SHRA on the decrease at 1730z...but expect that uptick in
convection will occur southwest of KDSM between 19-23z. Weak sfc
boundary over region now will also focus more showers aft 00z
south sections. Sites most vulnerable to shra/-tsra risk will be
KDSM and KOTM with some shower up to KALO/KFOD through 12z Wed.
Confidence on overall coverage of showers/storms increases aft 06z
into 15z timeframe south and southeast. Current cig forecast
suggests MVFR conditions return return to KDSM/KOTM aft 12z and
may extend through remainder of period. Also, may need to lower
VSBY aft 12z south due to rain as well. Wind remains light during
period. /rev




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