Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 240430

Area Forecast Discussion
National Weather Service Des Moines IA
1130 PM CDT Fri Jun 23 2017

...Updated Aviation Discussion...

.SHORT TERM.../Tonight through Saturday/
Issued at 203 PM CDT Fri Jun 23 2017

Cooler air spilling southward into the region today marked the
beginning of a stretch of below normal temperatures. This is a
result of a large trough that has established itself over the
eastern two-thirds of the conus. A potent shortwave embedded
within the cyclonic flow aloft will dive southeast across MN into
WI on Saturday. ARW/3km NAM advertise scattered showers and
storms once the convective temperatures are reached early in the
afternoon over southern MN and northern IA. POPs were bumped up in
this area to reflect the increasing forecast confidence. Dry low
levels within this cool Canadian airmass will limit instability
during peak heating and should keep the severe threat to a
minimum. Expect the activity to quickly wane with the loss of
daytime heating.

.LONG TERM.../Saturday night through Friday/
Issued at 203 PM CDT Fri Jun 23 2017

Below normal temperatures will continue into early next week as
the long wave pattern is slow to evolve. Diurnal heating will
spark off the development of CU Sunday but little upper level
support is available to support deeper convective growth. A weak
shortwave passing through on Monday may help trigger a few showers
and storms during peak heating, mainly across the southern half
of the forecast area.

Pattern begins to shift on Tuesday as the large upper level low
finally pushes east. A ridge will build up the Plains while the
next trough digs into the northern Rockies. Height falls to the
lee of the mountains will foster a deepening area of low pressure
over the northern high Plains. It will feel more like summer
again as southerly flow advects a warm, humid air mass back into
the area. Showers and thunderstorms are likely mid-week as a lead
shortwave ejects northeast and flattens the ridge. The potential
will exist for severe weather given the rich theta-e air and
stronger flow aloft. However, latest model runs continue to show
the potential for morning convection Wed-Thurs, which makes the
extent of the severe weather threat a bit unclear at this time.

Chances for showers and storms persist through the end of the
forecast period as the upper level low slowly moves into the
northern Plains. This pattern has the potential to deliver
widespread soaking rainfall to much of the area, but confidence
remains low at this time as models diverge on timing and
placement of key synoptic features by the end of the week.


.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1126 PM CDT Fri Jun 23 2017

VFR conditions are expected throughout the TAF period with winds
again mixing by Saturday afternoon.





LONG TERM...Martin
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