Area Forecast Discussion Issued by NWS Des Moines, IA
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000
FXUS63 KDMX 292340
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
640 PM CDT Fri Mar 29 2024
...Updated for the 00z Aviation Discussion...
.KEY MESSAGES...
- Scattered storms tonight with a few marginally severe
- Seasonal Weekend with rain returning Sunday
- Rainfall & storms continue into Tuesday; bulk of severe
potential south of Iowa
&&
.DISCUSSION...
Issued at 242 PM CDT Fri Mar 29 2024
.Short Term /Tonight through Saturday Night/...
Confidence Short Term: Medium to High
Generally on track for some convection over the area by evening
across central to eastern Iowa. Already on satellite, some
destabilization is taking place aloft with the development of mid
level cumulus. The surface boundary remains in place over west
central to southeast Iowa. H850 analysis this morning at 12z showed
a narrow plume of moisture being rapidly advected north within a 40
to 55kt low level jet. Though the moisture is still rather limited
with Td of 0C to 5C, that will increase toward the evening hours as
slightly deeper moisture from northern Texas begins to get closer to
the area. Also, surface moisture at this time remains low with
dewpoints in the 30s to lower 40s in southwest Iowa. Late afternoon
and early evening will see more moisture pooling at low levels near
the front in southern to eastern Iowa. This will help focus
available moisture/lift from central to eastern Iowa this evening
with the help of a H700 wave, another push of warm air advection and
approaching weak surface low. Once storms develop, H700 flow will
push them east later into the evening. Current HRRR operational runs
are forecasting CAPE to peak at 700 to 1200 j/kg early in the
evening from around 22z to 02z, then the area of better instability
advects east with the system. It may take until 23-00z for
initiation, and thereafter a short window of storm potential in our
southeast to east as the storms move out. Overall, some turning in
the winds will give rise to slightly better chances for larger hail
and the HRRR reflects some weak helicity tracks with the elevated
convection. SPC continues with a marginal risk over those areas
this evening. The upper level wave will be east of our area by 12z
with decreasing clouds and some sun on the way for Saturday. Lows
tonight will drop to the lower 30s northwest while the southeast
will hold in the upper 40s. Though tomorrow will feature some weak
northwest flow, little if any cold air advection will follow the
system tonight. Thus, expect another pleasant day to round out the
last few days of March. Highs tomorrow ahead of the more robust
large scale trough will warm to the upper 40s far northwest to the
lower 60s in the south. A sun/cloud mix is on the way for Saturday.
As we approach Saturday night, low pressure will begin to gather
strength over Kansas as the frontal boundary just pushed south of
the state will become more focused again over northern Missouri.
Models are beginning to diverge somewhat on the timing and placement
of the first round of showers and scattered storms Sunday. There is
now a little better consensus on a more southern track of the next
storm system with the GFS deterministic more closely mirroring the
Euro of the past couple of days. As anticipated, the southern stream
is still dominating the preferred path of synoptic energy. With the
lessening chances for precipitation for most of Saturday night, have
cut back on PoPs through the period to 15 to 30%; and mainly south.
Saturday night mins will remain mild with upper 20s north to the
lower 40s in the south.
.Long Term /Sunday through Friday/...
Confidence: Medium
With the models now coming into better consensus of a more southern
track, the risks of any additional severe weather over our area is
lessening. The main challenge now is the evolution of the system and
how rapidly the low strengthens. This will make the difference
between 1 to 1.5 inches of rainfall versus 2 to 3 inches of
rainfall. The GFS continues to quickly amplify the H850 system prior
to it tracking near Iowa, rather than the Euro which deepens the low
as the low is exiting east of the Mississippi River. The 12z
deterministic Euro continues to amplify the low later with the bulk
of the expected qpf east of Iowa. The 12z GEFs supports some heavier
totals in the southeast/eastern areas of Iowa including a portion of
our southeast. That being said, the trends continue to suggest a
slightly slower amplification which would keep rainfall totals
roughly between 1/2 inch to 2 inches across the south while the
north receives a couple of tenths to up to a half inch in some
areas. The Euro deepens the system much more as it gets into
northern Ohio with a decent cyclone and stronger area of low
pressure. Temperatures will be cooler with the low tracking farther
south. Highs Sunday are anticipated to mainly in the 50s and with
higher chances for showers and some thunder Sunday night into Monday
night, highs are again likely to remain in the 50s for Monday.
Breezy conditions will also develop within northwest flow Monday as
the deepening low departs. By Tuesday there is a hint of a northern
stream trough possibly swinging around the parent upper low. Due to
the differences in model spread progression east of the region, this
feature may not impact Iowa at all. If it does, an area of light
rain or snow would accompany the weak wave. Our blended approach
keeps a chance of light precipitation east, otherwise the remainder
of the forecast sees a drying trend until late week. With that
temperatures will initially be rather cool in the lower to mid 50s
for Tuesday and Wednesday, then transition to a moderating trend by
late week. We may need to trim back expectations a bit and delay the
rapid warming depicted by the NBM with todays model runs slowing the
large system across the eastern CONUS.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
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Issued at 633 PM CDT Fri Mar 29 2024
VFR ceilings were widespread across central IA due to expansive
mid and high cloudiness at 00z. This should persist through the
evening with scattered showers and a few storms developing
southeast, mainly near KOTM, during the evening. Thunder is
possible there, but has been omitted for the time being until
confidence in location and occurrence increases. A brief period
of MVFR stratus may brush KALO Saturday morning, but otherwise
confidence is fairly high for VFR conditions later in the day.-- End Changed Discussion --
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.DMX WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
DISCUSSION...REV
AVIATION...Small