284
FXUS63 KDMX 070709
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
209 AM CDT Tue May 7 2024

.KEY MESSAGES...

- Thunderstorms and a severe weather threat lingering early this
  morning, but clearing out by sunrise.

- Scattered showers and storms forecast at times over the next
  couple of days, but not as widespread or strong. There is a
  Marginal Risk of severe thunderstorms on Wednesday afternoon
  and evening.

- Daily high temperatures in the 60s and 70s for the
  foreseeable future.

&&

.DISCUSSION...
Issued at 209 AM CDT Tue May 7 2024

A line of thunderstorms is currently crossing Iowa, having
produced sporadic severe weather reports and warnings overnight
and tracking to exit our forecast area early this morning, with
stratiform rain lingering for a couple hours behind the line but
still likely to clear out before 12Z. For the remainder of
today and tonight, a large gyre will keep spinning around the
western Dakotas/eastern Montana region, sending additional
shortwave impulses careening over Iowa and possibly generating
additional isolated showers or thunderstorms at times. Have
maintained some low POPs across the north, but with instability
being very low and the overall forcing weaker than with the much
stronger initial wave, believe any convection will be very
spotty and brief, with no hazardous weather expected.

Tonight into Wednesday morning the aforementioned gyre will
shift south/southeastward and reassemble itself, with the
resulting cold core low drifting somewhere over South Dakota
during the day Wednesday, though there is uncertainty in how far
west or east it will be centered. Regardless, as it
reconsolidates nearer to Iowa it will renew warm air advection
and push an effective warm front from Missouri up into southern
or central Iowa. With large-scale diffluence setting up east of
the gyre, this will support an increase in coverage of showers
and thunderstorms on Wednesday, especially by the afternoon and
evening. Close to the core of the approaching low, lift,
low-level convergence, and shear will be maximized. Even with
only modest instability in place, this scenario could support a
low end severe weather threat primarily in the form of weak
funnels/tornadoes. However, much will depend on the degree of
clearing/low-level destabilization that can occur by Wednesday
afternoon, as well as the location/proximity of the parent low.
For example, the NAM is considerably further west with the low
and associated threat, while the GFS is further east. Given the
large degree of uncertainty in this set-up, the Marginal Risk
outlined by SPC across Iowa is appropriate.

From Wednesday night through Thursday the large, stacked and
gradually filling low pressure center will slide southeastward
over Iowa and promote continuing cloud cover and showers at
times, but with no hazardous weather anticipated and rainfall
amounts generally light. It will make for a cool and damp day on
Thursday, and have bumped forecast high temperatures down a bit
into only the lower 60s. If the clouds and rain are more
persistent then temperatures might not even get out of the 50s
in some areas on Thursday afternoon.

A brief bout of ridging will help temperatures rebound somewhat
on Friday, but then a deepening 500 mb low will dive
southeastward from Minnesota into the Great Lakes and Ohio
Valley regions at the end of the week. This results in lingering
low end POPs through the extended forecast, however, it is
likely that any rain will be intermittent/scattered and of
little consequence overall.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1221 AM CDT Tue May 7 2024

Thunderstorms will move through the area overnight, producing
IFR ceilings/visibilities at times. Amendments are likely based
on short term radar and observational trends. Once the storms
and lingering rain clear the area, by later Tuesday morning,
prevailing VFR conditions are then expected for the remainder
of the TAF period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Lee
AVIATION...Lee