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000
FXUS63 KDVN 210210
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
910 PM CDT Sat Apr 20 2024

.KEY MESSAGES...

- Freeze Warning entire area tonight. Take precaution to protect
  any sensitive/tender vegetation!

- Active pattern into next week will bring additional rounds of
  rain and thunderstorms Monday night into Tuesday and into next
  weekend.

&&

.UPDATE...
Issued at 908 PM CDT Sat Apr 20 2024

Clearing is generally occurring as forecast, through it`s left
some patches of cloudy skies remaining in eastern Iowa and
Illinois. Still, this forecast retains enough confidence for
freezing conditions that no change in messaging is needed.

ERVIN


&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 216 PM CDT Sat Apr 20 2024

Brrrr! The region is entrenched in cyclonic flow which is shuttling
in an anomalously cold airmass. 12z DVN RAOB sampled a 925 hPa
temperature of -3C, one of the coldest for DVN in April per SPC
sounding climatology. The cold air and destabilization has promoted
considerable stratus/stratocumulus. Some pockets of sun have
occurred, most notably far south, but given the impressive cold air
aloft surface temperatures haven`t responded very much. 2 PM
temperatures range from the upper 30s to the mid 40s, which is well
below normal by around 20-25+ degrees in many areas, and near
a record low max for Dubuque (39 in 1918). Moline`s record low max
for today was 36 in 1918. Gusty northwest winds to 25-30 mph
are also making it feel even chillier with feels like temperatures
mostly in the 30s.

Early this morning had seen a few reports of some flurries or
sprinkles upstream into far N Iowa and southern MN, and can`t
totally rule out some into early evening with a weak mid level
wave passing although confidence is low given lack of reports and
radar returns upstream aided by more widespread stratus and
relative lack of open cellular cumulus.

The wave and attendant subsidence building in the wake will
aid in clearing skies tonight. With the anomalously cold airmass
in place, sub-freezing lows are a good bet with HREF and
NBM 4.1 probabilities for temperatures less than 32F at 60% to
near 100% across most of the CWA. With diminishing winds will
have forecast lows dropping mainly in the upper 20s to around
30F, but mid 20s are possible in sheltered and drainage areas.
With this we have issued another Freeze Warning and included the
entire area from 05z-13z Sunday. Northern portions will likely
be closer to the freezing mark by the start time of 05z, while
the southern areas may still be a few hours after (07z-09z) from
reaching it.

Sunday, will bring a return of sunny skies with some fair weather
cumulus. Deep mixing will bring winds up from the northwest at
10-20 mph, and with the aid of solar insolation boost highs into
the upper 50s and lower 60s making for a nice recovery after the
chilly start.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 216 PM CDT Sat Apr 20 2024

Our next chance (60-80%) of precipitation in the form of showers and
possibly a few storms will occur by Monday night into Tuesday, as a
progressive shortwave /Saskatchewan screamer/ shifts across the
Upper Midwest and Great Lakes. Warm air advection may bring a few
showers by late in the day Monday, but the better rain chances will
evolve Monday night into Tuesday from north to south in time with
the passage of a cold front. Precipitation amounts look to be mainly
light with NBM 4.1 probabilities of 0.25 inch or more at just 20-
30%. Despite strong deep layer shear Tuesday (0-6km 50-60 kt)
instability is limited (0-1km MLCAPE around 100 j/kg or less, and 0-
3km MUCAPE (100-300+ j/kg) and thus the severe threat appears very
low. However, proxy soundings support deep mixing into stronger
winds of 30-40+ kts 800-700 hPa which coupled with a tightening
pressure gradient will support strong gusty surface winds Monday. A
similar deep mixing post frontal day on Tuesday with decent inverted-
V profiles could bring the potential for showers to mix down some
stronger winds gusts 40+ kt.

Beyond, the medium range model guidance continues to support a
more active pattern developing by late next week through next
weekend. Starting to see more agreement in the deterministic
guidance of a lead shortwave ejecting from a digging western
CONUS trough at the end of the week. Moisture will be ramping
ahead of a strengthening Colorado Low, which coupled with
forcing could lead to moderate rain amounts. NBM 4.1
probabilities for 24 hour rainfall of 0.5 inch of rain ending
12z Saturday are around 60%, and 25-40% for 1 inch. Deep layer
shear 0-6km is generally at least 30-40 kt in the deterministic
guidance on Friday, but uncertainty lies in the magnitude of
instability which varies considerably amongst the guidance.
Nonetheless this will bear watching in the coming days, and SPC
has already placed a 15% risk area covering nearly the entire
area on their Day 7 (Friday, April 26th) convective outlook.

The pattern stays active next weekend and continuing right into the
start of May, as the digging western CONUS trough eventually lifts
out. This will foster above normal temperatures (CPC 60-70%
probability April 27-May 3) with also the potential for rounds of
active storm clusters and heavy rain.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 623 PM CDT Sat Apr 20 2024

VFR conditions will prevail through the TAF period, with breezy
northwesterly winds decreasing through the night. Tomorrow,
winds will pick up once again. Currently, we have a broken deck
of clouds around 4500 ft, which will scatter out through the
night, becoming clear by sunrise. No sig wx is expected at this
time.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Freeze Warning until 8 AM CDT Sunday for IAZ040>042-051>054-
     063>068-076>078-087>089-098-099.
IL...Freeze Warning until 8 AM CDT Sunday for ILZ001-002-007-009-
     015>018-024>026-034-035.
MO...Freeze Warning until 8 AM CDT Sunday for MOZ009-010.

&&

$$

UPDATE...Ervin
SHORT TERM...McClure
LONG TERM...McClure
AVIATION...Gunkel