Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 212311

Area Forecast Discussion
National Weather Service Quad Cities IA IL
611 PM CDT Sun May 21 2017


Issued at 330 PM CDT Sun May 21 2017

Large closed off and blocked upper low currently seen on water vapor
imagery spiraling slowly north acrs northern MN and Ontario, will
gyrate back southward and be a weather maker through mid week, as
well as continue below normal temp trends with it`s cool air draw
acrs the upper Midwest. A dry Thursday with ridging behind the upper
low as it migrates eastward, then return flow precip chances return
for the start of the weekend.


.SHORT TERM...(This Evening through Monday)
ISSUED AT 330 PM CDT Sun May 21 2017

Afternoon temps struggling to even make the mid 50s under stratocu
field and ongoing llvl cold conveyor wrapping in acrs the region
from the west and northwest. Most sprinkles have exited the area,
leaving a dry forecast into the evening. Winding down of diurnal
processes as the sun sets under instability cold pool induced
steep lapse rates, as well as upper low continuing to pull north-
northeast should allow for the extensive stratocu field to
diminish and rotate northeastward out of the area as the evening
progresses, but it may be close to midnight in the northeast half.
Then clear skies after midnight with some temporary sfc wind
decouple will make for a seasonably cool night with lows in the
low to mid 40s acrs most of the fcst area. If winds were to stay
calm through sunrise Monday morning, there may even be a chance
for some upper 30s in cool air drainage locations of the northern
CWA. But do expect some southwest llvl return flow beginning
before dawn and may even make for non-diurnal temp trends late

Monday...Portion of the northwest GRT LKS closed upper low will look
to gyrate southeastward and dig toward the upper MS RVR Valley
through Monday evening.  Associated vort max/upper trof embedded in
approaching cyclonic flow aloft will make for increasing lift as the
day progresses and especially during the afternoon. The main llvl
cold front is progged by most models to remain to the west acrs
southwest through north central IA thru 00z Tue, but pre-frontal
warm air advection convergent signatures increase acrs the local
area as the day progresses. Thus it appears increasing development
and coverage of thunderstorm clusters in and close to the area as
the day progresses, with most coverage during the afternoon into
early evening heating window.

With at least partial sunshine and some boundary layer southwesterly
flow warming moderation, expect highs to recover into the upper 60s
to mid 70s acrs most of the DVN CWA. But sfc dpts/llvl moisture
return look meager with values of low to mid 50s acrs the CWA not
til later afternoon. Thus instability/CAPES marginal at 500 to maybe
1000 J/KG by late afternoon. But forecast soundings show moderate
unidirectional shear values, and inverted-V soundings suggesting any
more robust thunderstorm may be capable of producing gusty winds
possibly near severe levels. Freezing and WBZ levels also conducive
for hail production. Thus the Marginal Risk appears to be on track
for tomorrow afternoon and evening. As for rainfall amounts,
projected PWATs and shear values suggest localized swaths of a half
inch up to at least three quarters of an inch by late afternoon, and
areas that get hit by a few storm clusters will go over an inch.

.LONG TERM...(Monday Night through next Sunday)
ISSUED AT 330 PM CDT Sun May 21 2017

Monday Night, There will be a chance of showers and thunderstorms
ahead of a cold front slowly approaching the forecast area from the
west. Overnight low temperatures will be in the mid 50s.

Tuesday, 12Z Sunday runs of GFS/ECMWF are in fairly good agreement
through mid week. The models show a surface cold front, associated
with a shortwave rotating around an upper low over the Great Lakes,
will slowly move across the area. The fronts slow movement will
provide continued chances of showers and thunderstorms throughout
the day. Temperatures will be cool with highs only in the mid 60s
and ovenight lows in the mid 40s.

Wednesday, A cold core upper level closed low will be centered over
the mid Mississippi Valley. Cold temperatures aloft with this low
will create steep mid-level lapse rates which could trigger
scattered instability showers. Cool surface temperatues, at least 10
degrees below normal, will continue. Highs will be in the mid 60s
with ovenight lows in the mid 40s.

Thursday, This will be the best day of the week as an upper level
ridge builds over the midwest in response to a digging trof over the
eastern United States and another trof moving into the northern
Rockies. Skies should be partly to mostly sunny under this ridge
with temperatues warming to near normal. Daytime highs will be in
the mid 70s with overnight lows in the mid 50s.

Friday through next Sunday, Chances of showers and thunderstorms
return for next weekend as a series of shortwave trofs move through
the upper level ridge and pass over the forecast area. High
temperatues will be in the 70s.


.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 608 PM CDT Sun May 21 2017

The large area of stratus will continue to lift northeast
tonight, and as of 23Z this evening, we are finally VFR throughout
all TAF sites in eastern Iowa. A VFR overnight with clearing is
expected to continue into Monday, with increasing mid clouds
through the late morning and afternoon. Some showers and a few
storms are possible, but timing and locations are not yet
confident, and this is not included in specific TAFs yet.


Issued at 1111 AM CDT Sun May 21 2017

Recent heavy rainfall from Friday and Saturday are resulting in
rises on many local rivers. In particular, the Iowa River at Marengo
continues to rise with a potential to reach flood stage by early
Tuesday morning. However, confidence still remains fairly low on
this potential, and therefore have elected to keep this location
under a watch.

Along the Mississippi, a flood watch has been issued this morning
for Dubuque as confidence has increased that routed flow and
tributary input will lead to minor flooding beginning later this
week. This has already occurred south over Burlington and
Gladstone, which are currently above minor flood stage this




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