590
FXUS63 KDVN 170905
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
405 AM CDT Fri May 17 2024

.KEY MESSAGES...

- Areas of fog, with some dense fog, will continue this morning
  generally along and east of the Mississippi River

- Largely dry conditions expected for the reminder of the day
  through tonight

- An active pattern returns next week, particularly for the Sunday
  night through Tuesday night time frame

- There is now a Slight Risk of severe weather for Tuesday across
  the entire forecast area

- Very warm this weekend, with more seasonal temperatures coming
  for the middle of next week

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 404 AM CDT Fri May 17 2024

Areas of fog have developed early this morning, mainly for areas
along and east of the Mississippi River. Latest observations reveal
that dewpoint temperatures here have hovered in the upper 50s to
lower 60s, compared to Tds in the lower 50s to the west. This is due
to a surface front becoming stationary and bisecting our forecast
area from southwest to northeast. We are now starting to see dense
fog reported, with visibilities of 1/2 mile or less from Burlington,
IA northeast towards Sterling/Rock Falls, IL. With that being said,
we have issued a Dense Fog Advisory through 9 AM this morning to
encompass the aforementioned areas. Use extra caution if travel this
morning!

Eventually, the fog will dissipate by mid-morning, leading to an
overall dry period for the remainder of the day and tonight.
Guidance indicates we will remain under a shallow mid-level
shortwave trough, but given very dry air in the HREF ensemble
soundings, most of the area will see sunny skies. The only exception
we will need to watch will be over our extreme southeast in Hancock
and McDonough counties in west-central Illinois, where some high-res
models suggest surface temperatures warming to the convective
temperature, which could spark off a few isolated showers, but
chances of this happening are very low (less than 20%). Today`s
highs should warm to the lower 80s.

Tonight will be dry and quiet, as the aforementioned trough scoots
off to the east. Lows should fall to the middle to upper 50s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 404 AM CDT Fri May 17 2024

The upcoming weekend will overall be dry and quiet, thanks to a dry
air mass in place. Synoptically, we will be between a northern jet
stream across the northwestern CONUS, and a sub-tropical jet to our
south. A brief period of mid-level ridging will keep our conditions
quiet Saturday before a weak surface cold front sweeps through
Saturday evening. Confidence in showers and storms developing along
the front is pretty low, given the amount of dry air in place, but
there are some hints for at least slight chances (20 to 30 percent)
for precipitation. Mixed-layer CAPE values progged around 1000 to
1500 J/kg could fuel some thunderstorms, but deep-layer shear
appears to be quite meager, with values around 20 knots, so any
organized convection should be hard to come by.

A more active pattern then takes shape for Sunday night through
Tuesday as the northern jet stream begins to amplify over the
Intermountain West, while the southern stream jet lifts northward
and strengthens as it meets the northern jet. A series of mid-level
shortwave impulses will sweep through our region Sunday night
through Tuesday night. With temperatures warming to the lower to
middle 80s Monday and Tuesday, and dew point temperatures in the
lower to middle 60s, instability values will be elevated. However,
there are some differences on just how much, with the GEFS
probabilities of CAPE 1000 J/kg or greater around 80 to 100 percent
Tuesday, but the ECMWF were more around 40 to 70 percent for a
similar threshold. The kinematics appear to be rather strong, with
both the GEFS and ECMWF ensemble mean 500 mb jet magnitude of 50+
kts on Tuesday, nosing into central Iowa. Not only will the deep-
layer shear be enhanced, but so will the low-level shear, given
clockwise-curved hodographs from the various coarser-resolution
ensembles (GEFS, ENS, GEPS). The most recent CSU machine-learning
severe weather probs are painting some decently high values for
Monday and Tuesday (especially Tuesday, which is when the better
kinematics are expected). Additionally, the ECMWF EFI for the
CAPE/Shear combination are showing values around 0.6 to 0.8 along
and south of I-80 - additional evidence for a possible severe
weather event Tuesday. Just before we sent this discussion, SPC
introduced a Slight Risk (level 2 of 5) for severe weather across
our area for Tuesday. Confidence on the exact timing of severe
weather remains uncertain, but with this new outlook, the situation
will need to be watched as we approach Tuesday as all hazards of
severe weather appear possible. In addition, some heavy rainfall
will be possible with this event, given Pwat values around 1.3 to
1.7 inches, which would be above the 90th percentile for DVN from
the SPC sounding climatology.

For Wednesday and Thursday, confidence in the forecast decreases as
models aren`t in as much agreement. The NBM PoPs reflect this
disagreement in the GEFS/ENS ensembles, with PoP values around 20 to
30 percent, despite a strong signal for rainfall Wednesday evening
from the GFS deterministic model. It does appear that temperatures
will return to more seasonal values by mid-week, however, with
values in the lower to middle 70s.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1244 AM CDT Fri May 17 2024

Mostly VFR conditions were observed early this morning as of TAF
issuance, with exceptions of MVFR to IFR fog for some areas
along and east of the Mississippi River. Fog potential should
only increase tonight in these areas, leading to likely IFR and
perhaps some LIFR, especially for the MLI and BRL TAF
terminals. Probabilities of vsbys 1SM or less is around 50 to
70% off the high-resolution ensembles for these areas, so a
pretty strong signal. Confidence is a bit lower on when the fog
will dissipate, but it is expected to occur around the 13z to
14z time frame. Once the fog dissipates, expect VFR conditions
for the remainder of the forecast period, with southerly winds
around 5 to 10 knots.

&&

.HYDROLOGY...
Issued at 1051 AM CDT Thu May 16 2024

Changes: None.
Discussion...

Most tributary rivers in eastern Iowa have crested and are
slowly dropping. The exception is the lower Iowa River where the
crest is currently working its way through Wapello and Oakville.

On the Mississippi, Gladstone and Burlington will begin a broad
crest just above flood stage that will continue through Friday.

After a relatively dry weekend, the active weather pattern will
return next week with the potential for several rounds of rain.
While rainfall amounts continue to be somewhat uncertain, any
heavy rainfall would prolong the high river levels on tributary
rivers in eastern Iowa, northern Illinois and on the Mississippi
River.

The longer range outlook through the end of the month has a
40-42 percent probability of above normal rainfall. This outlook
suggests the potential for additional improvement with the
severe drought conditions across eastern Iowa. Unfortunately,
this outlook would also suggest that river levels could remain
higher than normal.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ066>068-
     078-088-089-099.
IL...Dense Fog Advisory until 9 AM CDT this morning for ILZ007-009-
     015>018-024>026-034-035.
MO...Dense Fog Advisory until 9 AM CDT this morning for MOZ010.

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Schultz
HYDROLOGY...08