Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 181118
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
618 AM CDT Tue Apr 18 2017

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 314 AM CDT Tue Apr 18 2017

Back door cold front has snuck into portions of northeast and east
central IA at 07z. Lake enhanced cool northeast winds post frontal
are allowing temperatures to drop down into the upper 30s to mid 40s
east of Dubuque to the Quad Cities. The front turns stationary then
transitions to a warm front as it connects to surface low pressure
over SD just west of Aberdeen, with pressure falls expanding
throughout the Midwest. Water vapor shows a shortwave trough
shifting east across the Northern Plains early this AM, with bands
of convection on the east/southeast flank within diffluent flow
aloft, zone of positive vorticity advection, and strong low level
moisture transport aided by 50+ kt LLJ. 850 mb and 00z RAOB analysis
showed a reservoir of drier air over the region with easterly fetch
from Great Lakes anticyclone aiding in keeping the region quiet early
this AM.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 314 AM CDT Tue Apr 18 2017

Northern Plains shortwave trough will track eastward reaching the
northern Great Lakes tonight. This will send a surface cold front down
into the CWA tonight north of I-80. Initial reservoir of drier air
will hold any precipitation at bay to start today and also aid in
weakening the bands of convection as they approach by late AM north/west
CWA. However, will see moisture increase markedly this afternoon
and especially tonight, between pool of Plains moisture attendant
to shortwave migrating eastward and strengthening southerly low to
mid level flow advecting moisture northward from the Lower Mississippi
Valley. This will eventually lead to small rain chances later today
north/west, with POPs increasing modestly and expanding across portions
of the CWA tonight for scattered elevated convection as isentropic ascent
atop the frontal zone increases amid strengthening branch of LLJ (40-
50 kts). The primary zone for rain and higher POPs tonight will
consequently be north of the front generally suggested along/n of I-80
at this time. MUCAPE of 200-500 J/kg and steep mid level lapse rate
around 7c/km support some thunder with perhaps even some small hail
possible with any stronger cores. Rainfall looks to be more scattered
and amounts light to moderate, and mostly around 0.25 inch or less.

Highs today should be widespread low to mid 70s boosted by breezy
southerly winds and partly to mostly sunny skies, with even a few
upper 70s/near 80 possible far south in favored sites with more solar
insolation. Lows tonight coolest north of Highway 30 post frontal with
mid 40s to lower 50s, while upper 50s to lower 60s likely south ahead
of the front.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 314 AM CDT Tue Apr 18 2017

An active weather pattern will be seen the second half of the week
with periods of dry weather. Temperatures will be cooler than normal.

The models continue to have a lack of run to run continuity with the
main system Wednesday and Wednesday night. Adding to this lack of
continuity is the fact that none of the 00z models had any Canadian
surface data to ingest. This lack of data may have created a
northward bias in the position of the front and other features.

Internally, the models suggest a decaying thunderstorm complex will
move across the area Wednesday morning. The strength and track of
this complex will dictate how far south the frontal boundary is
pushed before it stalls. Climatologically this time of year, the
front moves south of Lake Michigan and stalls either around I-80 or
closer to the IA/MO border. Regardless, there will be a large
temperature gradient across the area on Wednesday and some areas may
not see their high temperature until late in the afternoon.

Late Wednesday afternoon and night the main surface low will move
through the area. New convection will develop and should grow
upscale into a nocturnal thunderstorm complex Wednesday night. The
models have been suggesting the northern half of the area has the
best chance of seeing rain but this signal has been inconsistent.
The potential does exist for heavy rainfall Wednesday night. How the
thunderstorm complex evolves and tracks Wednesday night will dictate
the heavy rain threat.

Given what is being suggested by the models, there is a risk of
severe storms Wednesday afternoon and night. How warm it gets south
of the warm front will dictate the overall severe threat. The
primary threats look to be large hail and damaging winds. Any
tornado threat looks to be confined to a narrow corridor on either
side of the warm front.

Thursday, lingering showers will be seen across the southeast half
of the area during the morning. Thursday afternoon and night will be
dry as cool Canadian high pressure builds into the Midwest. Thursday
night looks to be quite chilly with 30s across the north half of the
area.

Friday on...

The next storm system arrives in the Friday through Saturday night
time frame. Model trends suggest a slight slowing in the arrival of
this storm system so the possibility does exist for a dry Friday.
Right now the model consensus has slight chance pops on Friday south
of an Ottumwa to Peoria line.

A trend that has been fairly consistent with the models is that the
south third of the area had the best chances for rain.

Friday night the model consensus has slight chance to chance pops
south of I-80. Saturday and Saturday night...slight chance to likely
pops from the highway 30 corridor on south.

Sunday through Monday the model consensus has dry conditions as the
next high pressure builds into the Great Lakes.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
ISSUED AT 605 AM CDT Tue Apr 18 2017

Winds will turn gusty from the south at 15 to 25 kts today. Some
decaying showers may reach DBQ and CID terminals this afternoon,
but confidence is too low for any mention. A cold front is shown
to push across DBQ and CID terminals after 06z with winds
shifting to northwest and north. Some shower and storm activity
will likely accompany the frontal passage, but coverage remains
uncertain and therefore opted to keep vcsh wording at CID and DBQ
for now. Anticipate MVFR cigs developing at CID and DBQ overnight
in the wake of the frontal passage. The cold front appears likely
to remain north of MLI and BRL tonight, therefore have kept these
sites vfr throughout the entire period.

&&

.HYDROLOGY...
Issued at 314 AM CDT Tue Apr 18 2017

Recent heavy rainfall has resulted in minor to moderate flooding on
some area rivers between highways 30 and 34. Refer to the latest
river flood statements (FLS) and river flood watches (FLA) for
details.

The models continue to suggest the potential for a heavy rain event
Wednesday night. If this heavy rain occurs, it would increase the
risk of flooding on area rivers.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...08
AVIATION...McClure
HYDROLOGY...08



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