902
FXUS63 KDMX 051957
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
257 PM CDT Fri Jul 5 2024

.KEY MESSAGES...

- Scattered showers and isolated non-severe thunderstorms into
  this evening.

- Quiet tonight into Saturday morning. Storm chances return late
  Saturday afternoon into Saturday night. Few stronger storms
  possible far west.

- Additional chances for showers and isolated storms persist
  into early next week with temperatures in the upper 70s to
  80s.

&&

.DISCUSSION...
Issued at 252 PM CDT Fri Jul 5 2024

An active pattern remains into at least early next week with an
elongated upper trough in place across much of the central U.S. This
will keep rain showers and/or storms in the forecast off and on over
the next several days but on a positive note, will also keep
temperatures from getting excessively warm with the heat dome stuck
over the southwest into western U.S.

Up first is the scattered showers which have been ongoing at times
this morning into early afternoon over mainly the north to east
driven by an upper low moving through southeast MN/southern
WI/northeast IA today before moving off to the Great Lakes Region
into tonight. This low is also responsible for the partly cloudy
skies over much of the area. Although coverage will remain mostly
scattered at best, the diurnally driven showers with a few isolated
storms possible will continue through the rest of the afternoon into
early evening, dissipating with time into the later evening hours.
Although instability values may approach 1000 J/kg late this
afternoon, bulk shear values remain weak, generally under 15-20
knots through much of the forecast area with the slightly stronger
shear of 20-30 knots across the far south offset from the higher
instability values (relatively speaking) further north. Severe
storms are not anticipated given this parameter space, though can`t
completely rule out some small hail or gusty winds if a stronger
storm can develop with ambient winds out of the northwest already
breezy to gusty this afternoon with gusts up to around 25-30 mph.

Environmental winds will diminish this evening with conditions
drying out and clouds gradually clearing leading to a cool night
temperature-wise as lows fall into the 50s to low 60s. Can`t
completely rule out some patchy fog developing, especially east to
northeast.

Saturday will start out dry but the next shortwave drops through the
northern Plains through the day helping to kick off storms over
South Dakota into Nebraska which look to near the Iowa/Nebraska
border late afternoon and ultimately reaching the area tomorrow
evening. Guidance varies significantly in overall coverage of storms
as they reach into central Iowa but most models agree on a general
weakening trend at this point. Increasing warm air advection through
the afternoon may lead to a few isolated storms prior to the main
line as well. Overall the severe threat remains low at this time
with low level shear very weak and a limiting factor despite
otherwise stronger and more favorable bulk shear values. In
addition, a warm layer in the mid-levels limits any steepening lapse
rates to the low levels and keeps the skinny CAPE profiles all
elevated. Won`t rule out some stronger storms with hail or gusty
winds in the far west depending on overall storm intensity as it
nears the area, which is captured well by the SPC Day 2 Marginal
(Level 1 out of 5) which clips several of our far western counties
on Saturday night. Storms do have the potential to bring some
locally heavy rain as pwats near 1.5", but overall QPF amounts
remain under 1" except for highly localized areas of 1-2+
inches, mainly in the south to southwest which certainly has a
bit more capacity for some rain than areas further north. See
the hydro discussion below for a bit more information.

Any lingering rain ends in the east late Saturday night/early Sunday
morning but additional chances for showers or storms exist at times
later Sunday into early next week, as noted above, as additional
shortwaves move through the otherwise prevailing northwest flow.
Temperatures stay in the upper 70s or 80s through much of the week,
though warmer temperatures may be on the horizon just beyond
the work week with the Climate Prediction Center noting a 60-70%
chance for above normal temperatures in the 8-14 day outlook
which covers the period of July 13-19.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1251 PM CDT Fri Jul 5 2024

Mixture of MVFR and VFR ceilings for the start of this TAF
cycle as cumulus clouds filter in from the northwest. May see a
few scattered showers near the KMCW and KALO vicinities this
afternoon, reducing ceilings to MVFR at times. Winds may be
gusty at times across the northern terminals this afternoon, but
expect winds at all sites to gradually decrease this evening
becoming light and from the northwest. Ceilings will gradually
lift with widespread VFR conditions through the rest of the
period. May see some fog potential across the far north or
northeast with the clearing skies and light winds, but
confidence is low currently for any direct impacts to TAF sites.

&&

.HYDROLOGY...
Issued at 252 PM CDT Fri Jul 5 2024

River forecast updates from this morning continue to show gradual
decreases in stage heights across area rivers. Spotty chances of
scattered showers and thunderstorms today may cause local rises in
area rivers and streams. This may result in river levels
receding slower. Our active upper air pattern will result in
continued off and on shower and thunderstorm chances into the
weekend and next week. Deterministic model output shows PWATs
across southern Iowa Saturday night approaching 1.5 inches,
which may result in locally heavy rainfall here if storms
develop. PWATs Sunday night into Monday are also in the 1.50 to
1.75 inch range across southern, central, and eastern portions
of the CWA. However, ensemble guidance is not too impressive
with this activity as significant rises across area rivers
aren`t anticipated.

&&

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

&&

$$

DISCUSSION...KCM
AVIATION...Castillo/KCM
HYDROLOGY...Castillo/Zogg