ia discuss
Office: DMX
FXUS63 KDMX 020751
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
251 AM CDT Thu May 2 2024
.KEY MESSAGES...
- Moderate to Heavy Rain & Small Risk for Severe Today
- Pleasant Friday || Showers & Storms Saturday || Dry Sunday
- Storms Return Monday Evening With Some Severe Risk
&&
.DISCUSSION...
Issued at 245 AM CDT Thu May 2 2024
.Short Term /Today through Friday/...
Confidence Short Term: Medium
Active weather pattern for the foreseeable future. Despite some brief
breaks from time to time, the overall periodicity of rainfall/storms
remains about every two to three days. This is certainly good news
in the short term, given our remaining areas of drought across the
state. Given the rainfall in the past 3 to 6 days; however, some
decent improvement should occur over areas west of I35. The latest
monitor will be released later today. Back to the forecast: Subjective
surface analysis early today shows high pressure parked over the
northern Great Lakes with a well developed low pressure over western
Kansas. Aloft, H850 remains impressive with a 138dm low over southeast
Colorado. A stronger ridge of high pressure extends from the eastern
GOM northwest into Iowa, but is beginning to break down over our
area. Extending east from the CO low is a strong warm front being
fed by a large river of H850 moisture of +10C to +15C dew points
from southern KS south to the Gulf of Mexico. As anticipated,
we are seeing a large MCS now over Nebraska with a fairly well
defined warm air advection wing extending east from eastern
Nebraska across central to north central Iowa at 0545z. This
entire system will continue to build east northeast overnight.
The main impact right now will be moderate to heavy rainfall and
the outside chance of limited severe weather early today over
the west where some small hail or gusty winds could occur. Otherwise
rainfall rates have remained at 0.25 to 0.50 so far, but should
increase a bit to around an inch per hour after 10z northwest
to our area during the morning commute arriving around 3 to 4 am
near US71 and then east to I35 by 530 to 700 am. This will likely
cause some early morning traffic challenges with ponding of water
and lowering visibility during this time around the I80 to
metro corridor and from Des Moines north to Ames/MCW as well as
areas northeast where the warm air advection wing has arrived.
As the KS surface low moves northeast over Iowa today and
continues to weaken, the later morning and early afternoon
showers and storms will be more focused east of I35. There will
be a small ribbon of higher instability developing along the
trailing cold front near I35 around 17-18z with the bulk of the
deeper moisture channel now south into Missouri, southeast Iowa
and western Illinois. There is modest cape above 1000 J/kg with
limited shear of 30 to 35kts roughly over the southeast 1/2 of
the state. Though our window of opportunity is about 4 to 6
hours in the southeast/far east today, this is still looking
like a minimal event with perhaps a report or two of hail, some
wet downburst wind and maybe a funnel or rather brief tornado.
Soundings are rather moist, so moderate to heavy rain still is
expected later this morning and early afternoon over the southeast.
PWATs for today are about 1.5 inches and warm cloud depths are
running 10 to 11 kft; both supportive of warm cloud processes
and rainfall totals of 2 to +4 inches. It is also worth noting
that MBE velocity is running rather low this morning, from
under 5kts to 10kts at times this morning and again late this
morning and early afternoon. This will likely promote some backbuilding
cells along the boundary in the southeast and areas late this
morning into the early afternoon. With this in mind, there may
be a small risk for some county areal or minor flash flooding in
the southeast 4 to 5 county area around Ottumwa today. Confidence
on that happening is still lower than 50% and the current probability
of a mean of 2.5 or more inches of rain in that area in a 6 hour
period is running around 40%. SPC HREFs 6 hour probability matched
mean suggests the potential for 2 to +4 inches which supports
some of the other guidance. Will be passing this onto the day
shift for monitoring. With the persistent showers and storms
over most of the east today and the west half only seeing some
sun after 5 pm, highs will be held back a bit today. The west
should warm into the 60s to near 70 due to sunshine, while the
east will be held to the 60s to lower 70s ahead of the boundary
due to warm air advection. Tonight will clear with rather cool
overnight mins; ranging from the lower 40s north to the lower
50s in the south. Highs Friday will be pleasant with some fair
wx cumulus; in the lower 70s just about everywhere.
.Long Term /Friday Night through Wednesday/...
Confidence: Medium
We continue quiet Friday night, but already the next upstream wave
will spread clouds and showers and storms into the west by sunrise.
The trough/front will move through the area during the day,
providing for a quick line of rainfall/iso thunder and amounts of a
few hundredths to up to a half inch in the south/southeast. Brief
heavy downpours are expected. Friday night mins will be in the 40s
to lower 50s with afternoon highs Saturday in the mid 60s northwest
to the lower 70s south. Another area of high pressure builds
southeast for Sunday with sunshine over much of the area, with some
clouds in the far south. The southern stream wave will stay south of
the region as another stronger area of low pressure begins to wrap
up and occlude over the Northern Rockies to Western Plains on
Monday. We will continue quiet for early Monday with clouds over
most of the region. Southeast flow will help push highs back into
the lower to mid 70s. As the low deepens and occludes Monday night,
a warm front/wing of instability will drive north through the
region. We should see a period of showers and stronger thunderstorms
develop along the occluded front in the evening hours. Though wind
fields dont line up favorably for significant severe weather, there
will be some support for a few stronger storms during the evening
along and west of I35 with 0-6km BWD approaching 40kt. Overnight
mins into Tuesday morning should remain mild as there is no real
cold air behind the boundary; staying in the lower 50s west to the
lower 60s southeast. Though the boundary will be heading off into
eastern Iowa, both medium range models EC/GFS shows secondary
southern stream wave tracking north into central/eastern Iowa
Tuesday afternoon. Uncertainties remain, but there appears to be
another window of opportunity for stronger storms east of I35 and
across portions of Missouri, Illinois and southern Wisconsin. The
remainder of the forecast into Wednesday lacks any real confidence
for dry vs wet with some divergence in features late in the forecast
cycle. The one constant is warm temperatures and we should remain
in the 70s over the area for highs with lows in the 50s.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1142 PM CDT Wed May 1 2024
Scattered showers and thunderstorms have spread across central
Iowa this evening with more widespread activity anticipated
overnight and Thursday morning. Ceilings will drop to IFR as
precipitation becomes more widespread, along with occasional
visibility reductions within heavier rain. Thursday morning
will see occasional gusts of 20-25 kts across all sites. As
precipitation moves east of the area later Thursday ceilings
return to VFR and winds shift to out of the northwest and
diminish.
&&
.HYDROLOGY...
Issued at 253 PM CDT Wed May 1 2024
Recent heavy rainfall may lead to some flash flooding concerns over
the next day or two along with longer term river flooding concerns.
In terms of short-term response (flash flooding potential and urban
flooding potential), the main concern would be later tonight through
Thursday night. Antecedent conditions show the soil moisture is
highest across the southern 2/3rds of the CWA with the highest
values across the southwest quarter. Runoff would be increased where
soil moisture is highest, however higher rates may lead to local
issues regardless.
As far as longer-term concern (rivers), hydrologic ensemble and QPF
ensemble guidance is showing significant within-bank rises are
likely on many rivers with several locations in the Des Moines,
Raccoon, Skunk, Cedar and Iowa river basins reaching action stage. A
few locations may reach flood stage especially if the rainfall comes
in on the high side mainly in the Des Moines River basin above Des
Moines. The peaks would occur later this week into this weekend.
Conditions will have to continue to be monitored.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...REV
AVIATION...Hagenhoff
HYDROLOGY...Zogg
Office: DVN
FXUS63 KDVN 020755
AFDDVN
Area Forecast Discussion
National Weather Service Quad Cities IA IL
255 AM CDT Thu May 2 2024
.KEY MESSAGES...
- Upper level pattern remains active, with periodic chances for
showers and storms through next week.
- There is the risk for heavy rain and a Marginal Risk for
Severe Weather today and into this evening.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 247 AM CDT Thu May 2 2024
A mild and wet day is expected throughout the forecast area today,
as a slow moving upper low passes north of the area. At the surface,
warm advection showers and storms will start the day, as the warm
front associated with the surface low passes through the area. With
that, the surface low will track southwest to northeast, skimming
our far northwest. Cold front will also pass through late this
afternoon and evening, which will be another focus for further
showers/storms this afternoon and evening. PWATs between
1.25-1.50" will be seen in a narrow axis along and west of the
Mississippi River, which will serve as a corridor for heavier
rainfall. These areas may see anywhere between 0.75-1.50" of
rain, with locally higher amounts possible. While we have a
Slight Risk for Excessive Rainfall in these areas, our
confidence remains low on the flash flood threat, as these areas
are abnormally dry or in drought. Thus, the ground should be
able to easily soak up much of the rain. Main areas that may see
some impacts will be urban centers.
We will have a low-end severe risk as well, with the SPC
highlighting our whole area in a Marginal Risk (level 1/5).
Confidence in this is low at the moment, with our focus being on
areas along/east of the Mississippi River seeing the best chance for
any strong to severe. Instability will be lacking throughout the
area, as dense cloud cover and rainfall will be seen through much of
the morning. Areas east of the Mississippi will miss out on much of
the rain early on, which may allow them to build more instability.
If we can get that, the shear is more than sufficient to favor
strong to severe storms. If we end up seeing strong/severe storms,
main hazards will be wind and hail, with the tornado threat being
secondary.
Much of these showers and storms will continue into the evening,
decreasing in coverage from west to east overnight. Much of the area
should be free of rain by sunrise Friday. Temperatures overnight
will stay relatively mild, with most in the 50s, thanks to residual
cloud cover moderating the temperatures.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 247 AM CDT Thu May 2 2024
Pattern remains active through at least the first half of the long
term period. Upper wave from Thursday continues to trek northeast
through the northern Great Lakes, with another wave digging south
into the area on Saturday. Much of Friday appears to remain dry
after the bulk of the precipitation pushes east, with more showers
and isolated storms approaching the area Saturday. Severe weather is
not expected Saturday. Rather, it is looking to be a gloomy day,
with light rain.
The next system to bring heavier rain and storms will be early next
week, as a deepening wave over the Rockies pushes into the Plains,
becoming negatively tilted and quickly punching through the Upper
Midwest Monday night. Although, that trough of low pressure stalls
over the northern US, slowing filling in and weakening. While that
remains north of the area, bouts of energy passing through may bring
the chance for persistent showers and gloomy conditions. There is
much uncertainty with how this will play out, generally given the
lacking moisture. While this does not seem to be a washout by any
means, there will be nearly daily chances for precipitation next
week, with plenty of dry periods in the mix as well.
Temperatures next week will be similar to what we are seeing now,
with much of the area remaining in the 70s to low 80s. Thus, aside
from the rain chances, it should be a nice week!
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1222 AM CDT Thu May 2 2024
VFR conditions will prevail through the start of the TAF period,
trending towards MVFR after 15z. Scattered showers and storms
will slowly fill in throughout the area after 09z, becoming
widespread after 12z. These showers and storms will bring
periods of cigs between 1000-3000 ft, with vis dropping to 3 SM.
TEMPOs were included through the remainder of the night,
highlighting the chance for scattered storms at CID and DBQ.
Winds will also be on the rise through the TAF period, starting
light and out of the northeast. Winds will shift southeasterly
through the morning, and then southwesterly after 18z, with
gusts upwards to 25 KTs possible.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.
&&
$$
SHORT TERM...Gunkel
LONG TERM...Gunkel
AVIATION...Gunkel
