653
FXUS63 KDVN 061039
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
539 AM CDT Mon May 6 2024

.KEY MESSAGES...

- Today`s potent severe weather event in the Plains will impact
  our area in a weakening phase after Midnight.

- Scattered storms remain possible on Wednesday before
  temperatures cool off late in the week.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 113 AM CDT Mon May 6 2024

First off, though it`s late tonight, we need to be clear that
the high end potential event today will not translate downstream
in the same supercell tornado mode into our area, but rather
evolve into a QLCS/squall line as it moves through Iowa and
Missouri late this evening. Confidence is high that wind fields
aloft and available instability will be waning as it approaches
our CWA after Midnight tonight.

HREF soundings support deep layer shear around 35 kts ahead of
the line late tonight, with 0-1km shear of 25kts. This is
supportive of some continuation of damaging winds in bowing
segments that are normal flow. However, this same data set
shows quite a bit of CINH ~ -170, thus the boundary layer may
not support winds reaching the ground without a significant loss
of magnitude. Thus, I feel that this line in a past-
mature/weakening phase should mainly arrive with 30-50 mph wind
gusts and little if any hail threat. A QLCS tornado would be
isolated in nature in this stage and stable boundary layer.
These threats discussed, are largely for our southwestern CWA,
with less supportive values for severe winds farther northeast.

SPC has western Scotland County, MO in a Slight Risk (level 2
of 5) for severe storms with a Marginal Risk to the east and
northeast (level 1 of 5). The primary threats are damaging winds
with a low risk for an isolated tornado (2% within 25 miles of
a point). The day 2 risk, is an eastward continuation of the day
1`s marginal risk into Illinois.

Rainfall tonight, with PWAT values of 1.25-1.5 forecast and
strong forcing, should be heavy w/r/t rates, but with the quick
movement of the line, w`re looking at most locations receiving
0.5 to 1 inch of rain. Pops between midnight and 7 AM are very
high, and are expected to be a 100% coverage event.

By 7 AM, the storms will be entering our northeast CWA, and rain
quickly ending over the central CWA. There could be some
additional elevated showers/storms that quickly move over the
CWA within the LLJ during the morning hours, but that activity
should be brief and quite fast moving to the northeast, possibly
over 50 mph.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 113 AM CDT Mon May 6 2024

The rest of the week will be dealing with the upper trof that
develops in the wake of today`s system.

Wednesday continues to show potential for more widespread shower
and thunderstorm activity, with global models still showing a
second surface low moving near the area, as the upper low begins
to shift southward. The upper low nearby will keep shower and
some thunderstorm potential going through the end of the week,
which still appears to be somewhat diurnally driven as we warm
up to the 60s under a cold upper low`s cyclonic flow.

Temperatures through Wednesday will continue to be mild in the
70s, then under the influence of the cool trof aloft, Thursday
through Friday appear to be mainly in the 60s, though some
guidance suggests that mid to upper 50s are possible if
showers/clouds are more widespread.

The upper low/trof is forecast by the bulk of availible
guidance to shift into the northeast CONUS by Saturday and
Sunday, resulting in a warming trend over our CWA and the
Plains. A clipper may drop into the trof in that period,
continuing the shower chances.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 537 AM CDT Mon May 6 2024

Another very quiet VFR period of aviation is expected through
this evening, with the high clouds or clear skies and light
southeast winds expected. An increase in speeds is anticipated
Monday evening, with some 14 to 25 kts southeast winds
developing over eastern Iowa as a line of showers and storms
begins to approach the area. These storms are expected to move
through all terminal sites in the 07z to 12Z period Tuesday.
Early indications suggest they will be decreasing in intensity
as they move through. I have added a 2-3 hour period of thunder
towards the end of the period given the strong probability (over
90%) of thunder occurring in that period.

&&

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

&&

$$

SHORT TERM...Ervin
LONG TERM...Ervin
AVIATION...Ervin