Area Forecast Discussion
Issued by NWS Des Moines, IA

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906
FXUS63 KDMX 160830
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
330 AM CDT Tue Jul 16 2019

.DISCUSSION.../Today through Monday/
Issued at 330 AM CDT Tue Jul 16 2019

Iowa continues to rest on the southern edge of the westerlies as
the remnants of Barry pass just southeast of the state. The
proximity of the westerlies will continue to present challenges
through late Wednesday prior to a northward migration of the flow
by late in the work week. Currently, convection has moved south
into the state overnight as the outflow has surged southward.
Convection has maintained the best across the northwest where the
instability axis resides and low level inflow is strongest.
Meanwhile, convection in Nebraska continues to move east toward
the state and should push into the west by daybreak. CAMs output
has the bulk of this activity dissipating as it moves into the
western CWA this morning. However, outflow and surface boundary
will reside mostly likely in northern Iowa this afternoon and
should provide a focus for thunderstorm redevelopment as
instability increases. Storms will likely be strong with a severe
storm or two given the stronger instability along with locally
heavy rainfall with plenty of moisture around. These storms are
forecast to move ESE into the evening with some break in activity
by late evening. Additional convection in the Plains is then
forecast to move ESE overnight on nose of decent low level jet
towards the forecast area late tonight. This will likely produce
another round of storms across the north and west late tonight
into Wednesday morning.

At this point, heights begin to increase across the state with the
main synoptic boundary lifting northward. This should limit any
additional convection later Wednesday and Wednesday night in
northern Iowa as cap builds into the state. Thermal ridging into
the Plains will begin to move into Iowa on Wednesday becoming
firmly entrenched on Thursday, Friday and likely much of Saturday.
This will be the warmest period with highs well into the 90s and
dewpoints in the 70s. Heat index values from 100-110 will be
common during this time with overnight lows holding in the mid to
upper 70s, therefore the heat watch is still looking good. Have
extended the watch into Saturday as the thermal ridge appears to
remain in place during this time. However, northern Iowa may begin
to see some relief as the westerlies begin to drop farther south
allowing a surface boundary to approach Iowa by later Saturday.
Beyond this time, much more uncertainty exists in the forecast
but cooler air appears likely into early next week as the
westerlies continue to drop farther south providing some relief
from the heat.

&&

.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1119 PM CDT Mon Jul 15 2019

Thunderstorms are pushing into northern Iowa and have TSRA at the
start of the period at MCW. Less certainty if these would maintain
toward FOD or ALO so have not mentioned at this time. Farther
southeast, high end MVFR ceilings are encroaching on OTM and are
expected to arrive toward sunrise. There is even a chance of fog,
but continue to favor clouds vs fog. Otherwise, there should be a
period of MVFR or VFR ceilings over the central Iowa terminals
before those ceilings lift and scatter. There will be another
round of storm chances over northern Iowa mid to late afternoon
Tuesday, but will defer to future TAFs to include with ongoing
convection and low ceilings in the nearer term.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Wednesday afternoon through Saturday
evening for IAZ004>007-015>017-023>028-033>039-044>050-057>062-
070>075-081>086-092>097.

&&

$$

DISCUSSION...Cogil
AVIATION...Ansorge



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