470
FXUS63 KDMX 011104
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
604 AM CDT Wed May 1 2024

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

.KEY MESSAGES...

- Brief Break then Showers/Storms Return This Afternoon.
- Periods of storms overnight/Thursday/Early Friday with 1 to 3
  inches of rainfall possible.
- Another System on Saturday with Scat Showers/Isolated Thunder
  and again by late Sunday into Monday.

&&

.DISCUSSION...
Issued at 308 AM CDT Wed May 1 2024

.Short Term /Today through Thursday/...

Confidence Short Term:  High

Active pattern continues for the next several days. Elongated trough
and sharp wave now lifting northeast of region early this morning.
Sfc map shows a weak lagging trough/front over our area which will
be the focus for renewed showers and lift by late morning into the
afternoon. In the wake of todays system, we have some patchy fog
developing over northeast Iowa and this will last into the early
morning. The next main wave will arrive tonight. Aloft at H850,
height fields show the exiting H850 wave and the sharp trough that
brought the large hail and wind damage to our area on Tuesday.
Upstream another wave in the TX Panhandle is recharging the Southern
Stream already at 00z with an open stream of moisture from the Gulf.
Though we are temporarily in northwest flow, we will be back in
south southeast flow already by late afternoon. Some scattered
showers will form along the lingering boundary over the west/north
this afternoon. By evening, stronger warm air advection/moisture
will begin to ascend the main H850 frontal boundary to our south.
This will create a widespread area of showers and thunderstorms
tonight. With instability remaining limited, the better chance of
any organized convection will be over the southwest/west with areas
of showers and isolated storms over the remainder of the region
through 12z Thursday. At this time, there is only a limited risk of
some severe storms over the south/southwest after midnight. After
highs today in the mid to upper 60s north and in the lower 70s
south, tonight will be mild south with lows in the mid 50s and in
the 40s north. Tomorrow the main wave will track through western
Iowa, bringing most of the region into the warm sector. The best
dynamics/lift will be from northern Iowa to MN/WI as the warm front
pulls north and along the trailing cool front over central/western
Iowa. By afternoon MUCAPE should exceed 1000 j/kg, but shear remains
just around 35 to 40kts nearer the boundaries and lesser southeast.
The best H500/H300 wind support lags the front, which is a better
forcing mechanism for moderate rainfall than severe weather. PWATs
are forecast to increase to 1.5 inches by 12z Thursday and remain in
that area for most of the day in the warm sector. Scattered rainfall
amounts of 1 to 3 inches will be possible from late tonight to early
early Friday as the system moves east. We continue to be outlooked
for a slight risk of excessive rainfall over the region. If any
hydro issues arise, they should be mainly from urban runoff and some
minor flooding of low lying areas. In the next 5 days, the HEFS
guidance shows a potential for some of our northern main stem rivers
to go into action stage or perhaps reaching minor flooding. A lot
will depend on the extent and location of the rainfall from tonight
through Saturday. By late Thursday afternoon, most of the
showers/storms will be over in the far northwest and still ongoing
in the east. The passage of the front around noon will limit any
stronger convection in the afternoon hours and we continue only with
a marginal risk tomorrow. Highs tomorrow will range from some cooler
upper 50s northwest to the lower 70s in the southeast.

.Long Term /Thursday Night through Tuesday/...

Confidence: Medium

The gradual shift east of the system Thursday night will bring most
of the rain to an end between 06 and 10z. Friday will be a pleasant
day with a weak ridge of high pressure edging east over the region.
Highs will reach the lower 70s with modest northwest winds. Some
fair weather cumulus are likely, given the recent rainfall. By early
Saturday morning, a weak cool front/trough will enter northwest
Iowa. This extends from a low over Manitoba/Quebec south into the
Central Plains. Moisture will be limited and only by late day will
some instability possibly result in some isolated thunder southeast.
Friday night will see mins in the mid 40s northwest to the lower 50s
south with highs Saturday in the lower to mid 60s over the area.
Saturday will not be a washout, but scattered showers will make it
feel cooler and add somewhere between a tenth to a third of an inch
of rainfall scattered across the south/west. By Saturday night, we
again dry out with high pressure building into the area Sunday
morning.  Most of Sunday will be pleasant, but already another
active wave is developing in the Rockies. This will be spreading
clouds back into the region by late day, along with some showers
southwest. Highs will climb back to the  60s to lower 70s. Medium
range guidance is showing that a ridge over the eastern CONUS will
limit the progression of the Rockies system into the Central Plains.
We will get in the eastern edge of the moisture field with some
showers Sunday night and early Monday; and again late Monday and
Monday night as a warm front swings northeast. With the system
occluding Monday night, Tuesday should be dry as we get into the dry
slot of the western system. With H850 temperatures averaging 10 to
12C Sunday through Tuesday, afternoon highs should remain in the 70s
with lower to upper 70s expected later in the period. Mins will be
in the upper 40s and 50s.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 603 AM CDT Wed May 1 2024

Return warm air advection mid level clouds and --shra across
sites through 20z; then higher chance -shra VCTS aft 00z most
areas with coverage nearing 100%. Cigs remain VFR for most of
period; some pockets MVFR aft 06z. Winds become ESE and increase
aft 03z to 12 go 17kts with higher gusts. /rev

&&

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

&&

$$

DISCUSSION...REV
AVIATION...REV