264
FXUS63 KDVN 291935
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
235 PM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Pleasant weather into Monday.

- Showers and storms return Monday night through Tuesday with
  the threat for heavy rain, and some severe weather potential
  Tuesday PM/evening conditional upon sufficient instability.

- Independence Day forecast looks wet.

- Moderate to Major flooding is expected on several area rivers.
  Crests could be delayed or altered with any heavier rainfall,
  depending on where it occurs Tuesday through Friday.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 230 PM CDT Sat Jun 29 2024

Give the AC a break!

Surface analysis at 18z places an initial cold front along a
line roughly from Chicago, Illinois southwest to an area of low
pressure near Wichita, Kansas. A secondary cold front extends
from low pressure over eastern Lake Superior through central
Wisconsin and northeast Iowa. It`s this latter front that
brings a refreshing airmass, denoted by cooler temperatures in
the 60s/70s and a marked lowering of dew points into the 40s/50s
on gusty NW winds. This front will sweep across the area through
late afternoon ushering in the pleasant airmass that will stick
around into early next week, as high pressure builds across the
western Great Lakes through 12z Monday. Lows tonight are
expected to be mainly in the 50s, with a few upper 40s not
out of the question in the northern counties pending the extent
of decoupling in the boundary layer. Widespread highs in the
70s is expected for Sunday, around 10 to 15 degrees below normal.
Monday AM lows will be cool once again, and could even be close
to records in a few spots. The combination of 850 hPa temperatures
of 10-12C (50-54F), light easterly winds and mainly clear skies
suggest lows near to 3-5 degrees below the progged 850 hPa
temperatures, or in the upper 40s to mid 50s generally. Please
refer to the Climate section below for record low information
for Monday at the main climate sites.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 230 PM CDT Sat Jun 29 2024

On Monday the high pressure system over the Great Lakes will
gradually pull away. Strengthening southerly flow surface to
850 hPa will usher in a return of warmer and moist air into the
region. This along with ejecting lead shortwaves ahead of
Northern Rockies/Great Basin trough will lead to ramping shower
and storm chances Monday night and Tuesday, with the higher
PoPs (60-80%) favored mainly north and west of the Quad Cities.
More widespread coverage of showers and storms is expected for
Tuesday night into early Wednesday, as stronger synoptic forcing
aided by a shortwave aloft and the right entrance region of a
100-120 kt 250 hPa jet steak overspread the Upper Midwest while
at the surface a cold front moves through. The primary concern
by Tuesday/Tuesday night looks to be heavy rain. 00z NAEFS and
ENS PWATs climb to 1.75 to around 2 inches by 00z Wednesday,
which is 2 to 3 standard deviations above climatology and
is approaches the 99.5 percentile or is near max of their respective
climatologies. NBM 4.2 probabilities support widespread 0.5
inch to 1 inch from 12z Tuesday to 12z Wednesday, especially across
the northwest 2/3rds of the service area. However, given the
convective nature and magnitude of the synoptic ascent doubling the
PWAT would give a general idea of the higher limit, which in
this case with PWATs around 2 inches would yield potentially
higher amounts of 4 inches. With rivers rising will be watching
this heavy rain potential closely, as this could delay or
change crest forecasts depending on where it occurs. In addition,
the significant moisture advection (IVT) and a southwesterly
LLJ of 40 kt could contribute to backbuilding and an elongated
MCS and a risk of flash flooding. Severe weather potential may
exist by Tuesday PM/evening, as deep layer shear 0-6km increases
to 40-50+ kts aided by the approaching shortwave trough. Models
try to build in the instability during this time, especially
west of the Mississippi River with MLCAPE increasing to 1000-
2000+ j/kg. However, if rain/clouds persist for much of
Tuesday that could limit instability or keep the primary
instability axis further west, similar to what we saw occur
yesterday. So at this time it`s looking like a more conditional
severe weather threat for Tuesday PM/eve, possible upon sufficient
destabilization. Stay tuned!

Behind the cold front high pressure looks to bring a brief dry and quiet
period midweek, with the emphasis on brief as already the next
system is slated to drop down into the Northern Rockies and Northern
Plains by 12z Thursday. This shortwave looks to evolve into a
closed low that traverses the Upper Midwest and western Great Lakes
Thursday night through Friday night. This will support a return
of shower and storm chances during this time, as the surface boundary
is drawn northward. For those keeping a close eye on the weather
for 4th of July festivities unfortunately it`s looking potentially
wet, and while PoPs are likely (55-70%) it won`t rain all of the time.
Nonetheless, many of us may have to rely on Mother Nature to provide
the fireworks.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1143 AM CDT Sat Jun 29 2024

VFR conditions are expected through the TAF period. There is a
low chance (20-30%) for a brief MVFR ceiling at KMLI, KBRL at
the beginning of the TAF period with abundant low level moisture
lingering ahead of a cold front. Another low chance for a brief
MVFR ceiling will re-focus back north at both KCID and KDBQ
toward late afternoon into early evening associated with cold
air advection, ahead of an upper trough and secondary cold
front. Winds may back to the SW for a brief time early in the
TAF period ahead of a secondary cold front, but overall look to
be predominantly from the W/NW around 10-15 kts and become gusty
to 20-25 kts before dropping off later this evening/overnight.
Northerly winds are expected Sunday at around 10-15 kts.

&&

.HYDROLOGY...
Issued at 1143 AM CDT Sat Jun 29 2024

No significant changes for the tributary rivers from this
morning`s new forecasts. The crest on the Cedar River has gone
through Cedar Rapids and should reach Conesville by Monday
morning. The Iowa River forecast has come in a little lower, but
minor flooding is still forecast at Wapello and Oakville. The
Rock River continues to fall and have just cancelled the flood
warning at Joslin.

On the mainstem Mississippi, the new forecasts have resulted in
flood category changes for Dubuque, Camanche, and Le Claire LD14
to Major flood and Keokuk LD19 and Gregory Landing to Moderate
flood. Overall, rises are still expected through the next 7 days
and beyond for most sites. Broad crests are beginning to show
up in the last day of the forecast for Dubuque LD11 downstream
to Bellevue LD12. However, with additional rain expected Monday
night through Tuesday, these crests may be delayed or change
depending on where the rain falls.

&&

.Climate...
Issued at 145 PM CDT Sat Jun 29 2024

Record low temperatures for July 1

Burlington......51 in 1918
Cedar Rapids....43 in 1924
Dubuque.........47 in 1995
Moline..........48 in 1988

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...McClure
HYDROLOGY...Gross
CLIMATE...McClure