Newton, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

641
FXUS63 KDMX 171143
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
643 AM CDT Thu Apr 17 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- 20-30% chance of a few storms over southern and eastern Iowa
  this morning with activity diminishing by midday.

- Storm chances increase as high as 60 to 80% north of US 34,
  mainly by this evening. Severe storms possible with main
  severe hazard being large hail although an isolated tornado is
  possible in far southwest/west central Iowa.

- Seasonal temperatures into the weekend with rain becoming
  likely by Sunday afternoon into Sunday night over much of
  central Iowa.

&&

.DISCUSSION...
Issued at 416 AM CDT Thu Apr 17 2025

Warm advection is underway with temperatures a good 15 to 20 degrees
warmer than this time yesterday morning. The low level jet with
increasing moisture is pointing towards Iowa early this morning with
an area of expanding low and mid clouds across about the eastern
half of the forecast area.  Short term CAMs indicate some likely
development of scattered convection over the next few hours, mainly
east of the Interstate 35 corridor along the MUCAPE instability
gradient where theta-e advection is maximized.  This convection will
bring a few brief heavy downpours with the strongest cells capable
of small hail production.  This activity passes to the east this
morning with an extensive cap pushing across much of the state by
early afternoon. This should effectively end precipitation
chances for much of the forecast area outside of the far north
and northeast.

Otherwise, surface dewpoints continue to increase into this
afternoon with increasing instability.  Convection is expected to
develop in Minnesota initially this afternoon where the cap is
weakest with the convection extending southward toward northwest
Iowa by late afternoon/early evening.  Otherwise, additional
convection is expected to develop in east central Nebraska toward
00Z near a triple point where the cap is weakest.  Soundings near
Omaha indicate some of these storms may become surface based where
dewpoints are maximized the cap nearly disappears. This
convection will have a large sweeping hodograph and ample shear
for rotating updrafts. The limitation for tornadoes at this
point are relatively high LCLs along with a relatively large
distance between the LCLs and LFCs. However, this threat may
become greater should dewpoints overperform, thereby increasing
instability and lowering both the LCLs and LFCs. Therefore, the
tornado threat remains limited in east central Nebraska into far
southwest/west central Iowa early this evening. Otherwise,
large hail is by far the main concern given the strong rotating
updrafts along with decent MUCAPES. All convection is expected
to spread eastward into the forecast area evening and the HRRR
continues to indicate rather robust updraft helicity swaths into
central Iowa. However, this convection is likely become more
elevated with time as the evening progresses given increasing
boundary layer stability. The bulk of the activity passes to the
east around 06Z with lingering showers into Friday morning,
mainly across the northern half of Iowa. Some additional showers
may clip the southeast into Friday afternoon closer to the
surface boundary as new convection develops just south and east
of the forecast area.

Cooler temperatures are expected behind the boundary on Friday into
the weekend. There will be plenty of activity on Friday into
Saturday just south of the state in Missouri into central and
southern Illinois where the surface boundary stalls and a few
showers may clip the far southern portions of the forecast area
right near the Missouri border, however the vast majority of the
area remains dry from later Friday through Saturday.  An
increasingly negatively tilted upper system ejects from the southern
Plains towards Iowa later Sunday.  This spreads rain back into much
of the state by Sunday afternoon into early Monday.  The Euro
ensembles continue to be most consistent and generally wetter across
Iowa than the GEFS output and this would suggest many areas
receiving upwards of three-quarters of an inch of rainfall,
particularly the eastern half to two-thirds of the state.  It
appears temperatures remain warm enough for a purely rain event at
this time as well.  A brief break is expected Monday afternoon and
night before another fast moving system brings additional chances
for showers on Tuesday into Tuesday night across the area.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 643 AM CDT Thu Apr 17 2025

Morning showers and isolated thunderstorms may impact Waterloo
and Ottumwa terminals early with brief MVFR conditions.
Otherwise, generally VFR ceilings and visibilities are expected
today with breezy south winds. Showers and thunderstorms are to
move from west to east across central and northern Iowa this
evening with ceilings lowering to MVFR and IFR across much of
Iowa tonight. Winds become northerly overnight behind a front as
it passes southeast across the state.

&&

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

&&

$$

DISCUSSION...Cogil
AVIATION...Cogil