Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 212052
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
352 PM CDT WED SEP 21 2016

.SYNOPSIS...
Issued at 330 PM CDT Wed Sep 21 2016

Latest sfc obs and Vis satellite loop were indicating ringing
outflow boundary lined with enhanced CU from northeast of Macomb
Il, up north of Burlington IA and to northwest of Waterloo. This
feature matching up with Main warm front in northwestern IA and
far southwestern MN. Large ambient temp spread from north to
southwest acrs the CWA...low to mid 70s to around 90. Water Vapor
loop indicating another upper short wave trof/vort max acrs
central Neb, rolling northeastward riding the upper ridge axis
acrs the central MS RVR Valley.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 330 PM CDT Wed Sep 21 2016

Tonight...Will have to keep isolated to widely scattered POPs along
the outflow boundary during late afternoon and into the early
evening, then expect a decrease with loss of heating. Most of the
storm clusters currently northwest of ALO should drift to the
northwest and north of the DVN CWA through evening as well, but will
keep low POPs for potential additional development making it into the
far northwestern CWA through at least 01z this evening. Then most of
the latest run model MCS generation tools as well as conceptual H85
MB flow point to another evening of storm cluster/MCS formation acrs
the southern third of MN and western IA/Mo RVR Valley. Will have to
watch for storms from both of these generation regions eventually
bleeding down into portions of the local area mainly after midnight
into early Thu morning. Will target CHC POPs in the northwestern
third or so of the CWA late tonight into Thu morning, but upstream
evolution will have to be monitored to see if POPs need to be raises
and expanded further to the east/southeast.

Most models suggest a weakening mode as they/convective storm
clusters enter the local area getting away from more optimum
support/shear profiles to the north, but there may be some lingering
overnight CAPE and low to mid lapse rates to allow for a few storms
riding a cool pool to produce gusty winds. Locally heavy rain also
possible of at least a half inch to an inch of rainfall possible
into the northwestern CWA before storms weaken further. But current
thinking suggests still not enough to warrant matching up with the
ongoing upstream Flash Flood Watches in the northwest for now. See
what happens tonight and reassess tomorrow. Lows in the mid to upper
60s.

Thursday...For now will keep POPs confined mainly to the
northwestern and northern third of the fcst area for lingering
activity out of tonight and new development possibly festering on
it`s remnants or more outflow boundaries. Again, POPs may have to be
expanded east and southeast of these areas of concern if incoming
storm clusters want to feed further south on higher thermodynamics.
POPs for the afternoon for isolated to sctrd new development on
remnant boundaries much like today, but best storm support shifts
back to the northwest/north of the region by late afternoon and Thu
evening.  Will use a model blend for high temps with convective
debris and outflow boundaries a concern again making for high temp
variability acrs the forecast area. If not much in the way of
clouds/storms make it down acrs the area or linger well into the day
Thu, these advertised highs may be too cool.    ..12..


.LONG TERM...(Thursday Night through NEXT Wednesday)
ISSUED AT 330 PM CDT Wed Sep 21 2016

Overview: Very warm Friday and Saturday by late September standards.
Another wet period possible Sunday into early next week - heavy rain
is possible but it is too early to determine amounts and duration at
this time.

Thursday Night...Models in good agreement on warm front location
remaining quasi-stationary along the MN/IA border into southern WI.
If the forecast does not change, the focused area of showers and
thunderstorms would be mostly north of the CWA. Outflow boundaries
sinking southward could easily fire off isolated to scattered
storms, so have 20-50% PoPs across the northern two-three tiers of
counties (highest north of highway 20 and west of the Mississippi
River). Lows are forecast in the mid 60s.

Friday and Saturday...Very warm and humid for the end of September.
Forecast highs are near 80 F across the north but in the mid to
upper 80s further south - about 3-5 degrees below daily record
highs. 850-500mb ridging amplifies over the Central U.S.
northward into Central Canada ahead of a deep upper-low over the
Central and Northern Rockies. Anomalously warm ~850mb temps in the
upper teens Celsius will cap the atmosphere, limiting chances for
precipitation. Also, synoptic forcing and areas of low-level
convergence are forecast to stay well north/northwest of E Iowa and
NW Illinois.

Sunday...Cooler temperatures are likely as a cold front and large
upper-low move in from the WNW. ECMWF/GFS in reasonable agreement
with timing of initial wave of showers and storms on Sunday. PoPs
increase to 40-60%, highest western third and may go higher in
future updates if inter-model consistency continues.

Monday into Tuesday...Model solutions quickly diverge with respect
to the evolution of a large upper-level low in the Central U.S. The
ECMWF offers the most ominous solution, digging the upper trough
furthest to the south, all the way down to the Gulf of Mexico. If
this occurs, eastward progression is halted, and a deep tropospheric
layer of WV transport develops on the eastern flank of the low.
There is an impressive Atmospheric River signal from the Gulf
northward into the Midwest. This scenario could result in impactful
rainfall amounts from a flooding standpoint; however, it is not
backed by other models, so have to message low confidence on the
rainfall forecast for now. Certainly something to monitor over the
coming days. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1241 PM CDT Wed Sep 21 2016

After current shower/thunderstorm activity gets out of the MLI
VCNTY, will keep the terminals dry through early evening. But
isolated to wdly sctrd storms may still POP up during the
afternoon. Will have to watch the BRL site through 3 PM CDT for
the outflow boundary to kick up and isolated storm and
temporarily switch the winds to the northeast, gusting up to
25-30 KTs or so for 10-20 minutes. Expect any lingering MVFR CU to
lift to VFR levels as well as the afternoon progresses. Then will
keep the TAFs dry tonight with most new thunderstorm activity
taking place to the northwest and north of the local area. But
saying that, still plenty of chance for some storms to bleed down
toward the area again late tonight with the CID/DBQ terminals most
at risk of getting some activity into the VCNTY late tonight into
Thu morning.    ..12..

&&

.HYDROLOGY...
Issued at 330 PM CDT Wed Sep 21 2016

MROI4 and DEWI4 is steady at crest. CNEI4 is rising again toward a
second crest above flood stage.

The overall weather scenario points to well above normal rainfall
through Thursday night across the upper Midwest. This rainfall will
be associated with several organized thunderstorm complexes that may
result in excessive rainfall of at least 6 inches, occurring mainly
north of the DVN cwa. The headwaters of the Iowa and Cedar Rivers in
northern IA and southern MN may potentially get hit hard with very
heavy rain, which will then be routed into eastern IA. Very heavy
rainfall will also be occurring in southwest WI. This will also
route water down the Mississippi River.

This prolonged rain event will result in the Wapsipinicon,Cedar,Iowa
and Mississippi Rivers to start rising again and going into flood
from late this week through next week. The location and amount of
rainfall will dictate how high rivers will rise but at least minor
to moderate flooding is possible. There is the potential for major
flooding at some forecast points if rainfall is more than expected.

Flood watches for specific forecast points may need to be issued
over the next day or two.

&&

.DVN Watches/Warnings/Advisories...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Uttech
AVIATION...12
HYDROLOGY...Haase



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