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fxus63 kdvn 292332 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
632 PM CDT Wed Mar 29 2017

..aviation update...

Synopsis...
issued at 330 PM CDT Wed Mar 29 2017

18z surface data has high pressure over the Great Lakes with a storm
system in eastern Kansas. Dew points were in the 30s and 40s from
the Great Lakes into the central and northern plains. Dew points in
the 50s and higher ran from the Ohio Valley to the Gulf Coast.

&&

Short term...(this evening through thursday)
issued at 330 PM CDT Wed Mar 29 2017

The second round of rain is well established across the area and
moving toward the northeast. As moisture and forcing increase
further late this afternoon additional rain will begin to develop
across Missouri into southern Iowa. Trends with the rap suggests a
layer of unstable air aloft making it into the far southern areas
prior to sunset. This unstable air may allow some embedded
thunderstorms to develop south of an Ottumwa to Galesburg line.

Tonight the areal coverage of the rain will grow and encompass the
entire area by midnight. An unstable layer of air aloft will move
north during the night which is expected to allow embedded
thunderstorms to develop as far north as the Highway 30 corridor by
sunrise. No severe storms are expected but small hail cannot be
ruled out from the stronger storms.

Thursday, rain will continue during the morning hours with embedded
thunderstorms possible from the Highway 30 corridor on south. During
the afternoon, areal coverage of the rain will slowly decrease from
west to east but embedded thunderstorms will still be possible south
of Highway 30.

If a dry layer can develop in the atmosphere Thursday afternoon,
then a few storms south of a Monmouth, Illinois to Memphis, MO line would
have the potential of producing hail.

Long term...(thursday night through next wednesday)
issued at 330 PM CDT Wed Mar 29 2017

Thursday night and Friday...instability and forcing progs of the 12z
models suggest enough wrap-around support for bands of showers and
some thunderstorms acrs generally the southeastern third of the dvn
County Warning Area earlier on Thu evening, while the rest of the area may just have
patchy sprinkles or drizzle. But then some signs of this activity
coalescing more into a type of def zone of rain with just isolated
embedded thunder along and east of the MS river overnight before
shifting east by the pre-dawn hours of Fri morning. Top-down drying
on the fcst soundings/BUFKIT data suggests the precip regime may
trend to more drizzle as the night progresses into Fri morning as
long as the lift continues. Before the taper off in precip
intensity, could see an additional 0.10 to 0.30 tenths of an inch of
rain acrs the eastern half or southeastern half of the fcst area.

Brisk northeast sfc winds of 10-20 miles per hour overnight to limit any fog
potential Worth mentioning in the fcst. After a few lingering
sprinkles in the east Fri morning, will advertise a mostly cloudy
and cool day with north to northeast winds of 10-20 miles per hour decreasing
late in the day with sfc ridge arrival from the west. But there may
be enough top-down drying subsidence induced breaks Fri afternoon
for some peaks of sunshine. Clearing and cool Fri night into Sat
morning with lows well down in the 30s. With light winds and recent
rainfall, this may be a fog window to watch out for if not enough
sfc layer drying occurs on Fri during the day. If not the fog, then
a robust frost possible.

Saturday and Sunday...will keep Sat dry and seasonable while the
next upstream cyclone lurks acrs the southwestern plains. But then
several 21z medium range models eject out a lead impulse along with
elevated moisture feed to fuel bands of overrunning rain starting
Sat night some time and increasing in coverage and intensity by
Sunday morning. This lead system battling lingering Dry Ridge to
the east makes for lower confidence on precip timing Sat night into
Sunday. Depending on cloud cover an precip, Sunday highs may be a
bit aggressive.

Monday through next Wednesday...differences increase on Monday
between the 12z run European model (ecmwf) and GFS in handling the main cyclone
center roll out path. The GFS is far enough to the north where
showers/rain spreads up acrs much of the area later Mon into Mon
night, while the new Euro rolls the low eastward in southern stream
fashion, with it's associated precip bands missing the County Warning Area just to
the south. With the uncertainty and run-to-run variances, for now
will keep rather high chance probability of precipitation in the south and east this
early week period. The active pattern/wave train does not want to
quit, with both the GFS and European model (ecmwf) taking more of an aim at the
local area with the next wave by next Wed. A further north
trajectory with this mid week system would mean more of a
thunderstorm threat along with shear patterns supportive of
stronger convection if we get the heating or advection. ..12..

&&

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 627 PM CDT Wed Mar 29 2017

Extended periods of rain, heavy at times will occur for the next 24
hours resulting MVFR/IFR conditions developing this evening and through
Thursday. Breezy east winds will shift to the northeast by midnight
and then the north Thursday as a storm system moves slowly into the
Ohio Valley.

&&

Hydrology...
issued at 330 PM CDT Wed Mar 29 2017

Have gone ahead and issued a river Flood Watch for the Iowa river at
Marengo, with early rainfall and routed water from upstream
projections supporting it hitting flood stage there by Sunday. But
with lower confidence in this, again have went the watch Route as
opposed to an early warning. If widespread 1 to near 2 inches of
rainfall do indeed occur acrs much of the local area, a few other
fcst points on area tributaries will have to be watched for rising
near or even above bankfull by this weekend. ..12..

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

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