Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 221932
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
232 PM CDT Sun Jul 22 2018

.SHORT TERM.../Tonight through Monday/
Issued at 224 PM CDT Sun Jul 22 2018

Expecting fog development overnight tonight across much of the CWA,
which will begin to lift around 12Z. A weak boundary will move
across Iowa tomorrow, with shower and thunderstorm chances
increasing by mid morning and continuing through much of the day.
Although there is sufficient instability with 1000-1800 J/kg MUCAPE,
shear is relatively weak, around or under 25 kts, so severe
potential is low. Most of the precip chances will be confined to the
northwestern half of the state with the boundary weakening as it
moves across the state. Precip chances decrease around 00Z, though a
few showers may linger Monday evening before dissipating.

.LONG TERM.../Monday night through Sunday/
Issued at 224 PM CDT Sun Jul 22 2018

The large scale evolution and features remain consistent with
prior thinking with the subtropical high centered over the
southwest US and a deepening large-scale upper trough over the
Upper Midwest and Great Lakes. The upper trough will be
unseasonably strong for late July resembling an upper air pattern
more typical of September. The 12 UTC ECMWF/GFS operational runs
are in fairly good agreement with the large scale features over
the Upper Midwest.

Early in the period, we should have near normal temperatures
ahead of a cold front which is associated with a shortwave trough
which is next is a series of shortwaves curving out the upper
trough over the region by early next week. The cold front should
cross the CWA late Wednesday or Wednesday night. The GFS is a
little faster with this boundary than the ECMWF. There might be
scattered convection associated with the upper forcing and front,
but given fast movement and relative lack of moisture, will keep
pops north on Wed afternoon and in the southwest early on
Thursday. This could change as the event nears.

Temperatures should be well below normal late in the week. Both
the GFS/ECMWF support this with 850 mb temperatures of only 8-11C
over north central Iowa Thursday afternoon. This supports highs
only in the mid 70s.

With the deeper trough over the region next weekend, we will be
exposed to shortwaves moving west to east through the flow over
the Central Plains and Missouri Valley. There is support for
small pops next weekend and continued cool temperatures.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1219 PM CDT Sun Jul 22 2018

VFR conditions through much of today as low morning clouds
continue to lift. Higher clouds expected to persist today. The
main concern this period is overnight/early morning fog
development across all sites. Greatest impacts will be at
FOD/ALO/MCW, with minimal impacts at DSM/OTM. This will be fine
tuned some with later issuances as confidence increases.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Hagenhoff
LONG TERM...Johnson
AVIATION...Hagenhoff


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