Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 190937

Area Forecast Discussion
National Weather Service Quad Cities IA IL
437 AM CDT Wed Apr 19 2017

Issued at 342 AM CDT Wed Apr 19 2017

07z MSAS analysis places a cold front from eastern WI near Green
Bay into IA roughly along a Dubuque to Cedar Rapids line, and
then extends southwestward through northern KS where it turns
stationary ahead of a deepening cyclone emerging from the Lee of
the Rockies. Strongest low level jet and moisture transport is
aimed into the western flank of the frontal zone aided by
approaching mid level shortwave. This has led to more robust
coverage of showers and storms over portions of NE/northeast
KS/northwest MO/southwest IA. Weaker branch of jet and elevated
moisture transport is veered into our portion of the boundary,
thus only isolated showers are being found along and ahead of the
front for now. This aforementioned shortwave will lift ENE today
and bring showers and some storms to the region. A stronger
shortwave just crossing the Rockies will follow in behind and
organize into a deeper shortwave trough while lifting into the
Upper Midwest tonight. Attendant surface low will follow along
and lift the front back northward through the cwa as a warm front
thrusting cwa in unstable warm sector with a risk of severe storms
this evening into the overnight ahead of an approaching cold front.


.SHORT TERM...(Today and Tonight)
ISSUED AT 342 AM CDT Wed Apr 19 2017

Cold front looks to stall near the IA/MO border into west central IL
this AM before beginning to return nwd as a warm front this afternoon.
However, high pressure shifting through the Great Lakes will turn the
low level flow from the ENE over Lake MI and send another back door
cold front out way later this afternoon into evening. This will serve
to impede northward advancement of warm front to most likely between
I-80 and Hwy 34 through early evening. Will see shower and storm chances
greatest this AM into early afternoon from sw to ne attendant to passing
weak lead upper impulse. This activity looks to remain elevated and not
pose much risk aside from lightning, locally heavy rain and perhaps small
hail with strongest cores with MUCAPE around 500 J/kg and mid level lapse
rates around 7C/km. Once this impulse passes early this afternoon, then
a lack of forcing and an advecting EML on swly flow aloft look to largely
suppress any development rest of this afternoon and CAMS in pretty good
agreement on this scenario.

Late this afternoon and evening, as surface low pressure lifts northeast
into the Upper Midwest attendant to upper level shortwave forcing will
increase over the region. This should serve to weaken the EML and
allow convection to develop. Initial development is mostly likely to
occur to our west near the low and triple point. Some of these storms
may quickly become supercells given magnitude of shear, and likely scenario
is for these storms to congeal into a line with potential for bowing
segments while heading eastward through the evening. For our area the
severe weather threat will most likely to be attendant to this line of
storms, with damaging winds primary threat likely arriving into eastern IA
and northeast MO mid to late evening. If storms can form on the warm
front out ahead of this approaching line, then will likely be supercells
with threat being large hail further north of warm front, while all modes
would be possible along the warm front including possibility of tornadoes
with backed low level flow increasing 0-1km SRH. The warm front is
generally being suggested from around Manchester to the Quad Cities to
Princeton between 00z-03z. Aside from the severe risk tonight, there will
also be an attendant threat for heavy rain with PWATs increasing to over
1.3 inches. Can`t rule out a threat for flash flooding with the most intense
cells especially over portions of northeast and east central IA which is
saturated from recent rains. However, sufficient storm motion may preclude
or limit threat and may aid in keeping coverage of higher amounts to more
localized, as CAMs generally show some weakening of the convection while
approaching the Mississippi River late this evening.

Bottom line, threat for severe storms exists late this afternoon, and
especially tonight (5p-4a). Main threats will be damaging winds and
large hail but tornadoes are possible, especially with any interaction with
warm front and also possibly embedded in any lines with favorable shear-
vector orientation. Greatest severe threat is likely west of the Mississippi
River. Locally heavy rain and isolated flash flooding also possible.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 342 AM CDT Wed Apr 19 2017

Below normal temperatures to end the work week and over the weekend.

Thursday morning, lingering showers and possibly a few thunderstorms
will be seen across the southeast half of the area as the cold front
moves east of the area.

Quiet and dry conditions will be seen Thursday afternoon through
Friday as cool Canadian high pressure moves through the Midwest.

Friday night the next storm system will begin affecting the Midwest.
The strength of the high over the Great Lakes will be the key as to
whether or not there will be any precipitation across the area. The
current model consensus has slight chance to chance pops Friday
night south of an Ottumwa to Galesburg line.

Saturday on...

On Saturday, several model solutions keep the entire area dry with a
stronger high over the Great Lakes. As a result, the model consensus
has slight chance pops south of an Ottumwa to Macomb line during the
morning and dry conditions in the afternoon. Temperatures will
average below normal.

Saturday night through Tuesday the model consensus has mainly dry
conditions as high pressure moves toward the east coast and
southerly return flow develops across the Midwest. Temperatures
should average a little above normal.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1202 AM CDT Wed Apr 19 2017

Elevated band of showers, with possible embedded thunderstorms,
will work from south to north through E Iowa/NW Illinois between
07Z-20Z/Wednesday. Confidence is low on thunder occurring, so
only mentioned at KBRL where instability is highest. As sfc winds
turn to the ENE by early Wednesday morning, periods of MVFR
ceilings are possible through midday. Late in the TAF period, a
cold front will bring another chance for showers and
thunderstorms. Confidence is low on areal coverage because storms
should be weakening as they move to the east. However, there is a
risk for strong winds with this second round, especially at


Issued at 342 AM CDT Wed Apr 19 2017

Most tributary rivers in eastern Iowa and northwest Illinois have
either crested or will be cresting later today. The Mississippi
river continues to slowly rise. Refer to the latest river flood
statements (FLS) and river flood watches (FFA) for details.

More rain is expected later today and especially tonight that has
the potential to be heavy. Depending upon where and how much rain
falls, the potential is there for area rivers to begin rising again
which would increase the threat of flooding.




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