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fxus63 kdvn 201121 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
621 am CDT Thu Jun 20 2019

..aviation update...

issued at 318 am CDT Thu Jun 20 2019

As of 230 am, the last of the rain showers are ending in north
central Illinois. The wave produced widespread rain has moved off,
but patches of low clouds and mid clouds remain. Despite this, the
over all trend has been slight dry advection at low levels,
resulting in a reduction in cloud cover in our north half, while
this may also lead to fog formation. In this wet pattern, nothing
is without some sort of moisture related problem it seems.


Short term...(today and tonight)
issued at 318 am CDT Thu Jun 20 2019

Today, the break up of clouds, and new increase in mid clouds from
the next band of warm advection will be the main challenge to an
otherwise dry and pleasant day's forecast. There should be enough
hours of at least partly cloudy sky cover that a recovery to the mid
to upper 70s is expected. With dewpoints in the 50s and 60s, this
should be a very pleasant day for those outside.

Tonight, a diffuse signal for elevated showers and thunderstorms
is indicated by models. Without much of a distinct trigger, I feel
coverage will be limited, and will forecast slight to low chance
pops over a broad area after midnight. Spotty quantitative precipitation forecast should be on the
light side tonight. This should give creeks a chance to lower
today, before the more significant rains return by Friday night.


Long term...(friday through wednesday)
issued at 318 am CDT Thu Jun 20 2019

The main forecast concern are chances of precipitation through
Monday. Models are in good overall agreement on the overall
evolution of the synoptic pattern but differences exist in the
smaller details. Given the active pattern I will first broad brush
the forecast and then focus on the Friday into Saturday period.

The long term period opens Friday morning as Rex block is in place
over western North America with a closed 500 hpa low over
western Montana and southeastern Alberta with a closed 500 hpa high
pressure over northern Saskatchewan and Manitoba. This Rex block
will begin to breakdown on Friday as the upper level low wobbles and
digs southward and ridge strengthens across the area resulting in
southwesterly flow aloft Friday through Monday and Tuesday. Key
differences between the models show up quickly at this point. The
NAM, ECMWF, and Gem continue to break off a piece of energy from the
main low and dig a deeper trough while the GFS does not. The GFS
solution results in the trough over the western US lifting into the
Great Lakes faster than the other solutions. Closed upper level
lows move out slower than forecast and the overall forecast reflects
that. This will allow multiple pieces of shortwave energy to
eject out of the trough towards the area bringing the risk of
multiple rounds of showers and storms into early next week. After
this trough exits, models are in good agreement strong
ridging building across the plains by the middle of next week which
would result in a dry end of the 7 day forecast.

On Friday, a shortwave moving across the region quickly on the heels
of the riding will encounter an elevated mixed layer across the
region which will work to inhibit surface based convection during the
day. By 00z Saturday, models depict a low level jet of 30 to 40
knots veering into eastern Iowa. Models forecast soundings show
substantial elevated cape above the mixed layer of 2000 to 4500 j/kg
from north to south across our County Warning Area with 40 to 50
knots of 0 to 6 km shear. A mesoscale convective system will generate Friday night and move
across the area. For this reason, Storm Prediction Center has the southwestern part of
our area in a convective slight risk for Friday night into Saturday
morning. In addition to the severe threat, heavy rainfall is also
possible with this round of storms with precipitable water of 1.50
to 1.75 inches.

Another shortwave is forecast to arrive during peak hitting on
Saturday afternoon into the evening but the overnight mesoscale convective system may
dictating the overall severe potential for Saturday. Currently, Storm Prediction Center
has all of eastern Iowa, northwest Illinois, and northeast Missouri
in a marginal risk of severe thunderstorms. Precipitable water will
recover during the day on Saturday with 1.50 to 1.75 inches by
Saturday afternoon and evening.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 619 am CDT Thu Jun 20 2019

Low clouds are now sinking south of the airports in eastern Iowa
and northwest Illinois, with a VFR day ahead as dry air
temporarilymoves into the region. Tonight, mid clouds will
increase overnight as warm air spreads back over the region, this
could bring isolated thunderstorms, and possibly a more widespread
rain chance after 12z Friday.


issued at 846 PM CDT Wed Jun 19 2019

Recent heavy rainfall has led to some minor rises on the
Mississippi downstream of Burlington. The rise is just enough to
nudge Gregory Landing back above moderate flood stage over the
next 12 hours, thus a warning has been issued for the change in
category. Otherwise, heavier rain earlier is resulting in just
some within bank rises on several tribs in far southeast Iowa,
northeast Missouri and west central Illinois.

Previous discussion issued at 1210 PM CDT Wed Jun 19 2019

The Mississippi River continues a general fall trend at most sites,
and should continue into the start of the weekend. The exception is
at ld19 at Keokuk and Gregory Landing where locally heavy rain
and run-off is producing a small bump up in river levels there.
It will start falling again by tonight after the rain lets up.
Other sites from Rock Island ld15 on down to Keithsburg have
either finally dropped below flood stage, or dropped out of
moderate into minor flood category over the past 18-24 hours. Will
have to watch for rising trends on portions of the la moine, Fox,
Des Moines, and lower skunk rivers this afternoon in response to
ongoing bands of heavy rain moving north across southeast IA,
northeast MO and west central Illinois today.

Looking ahead, the pattern still appears will become more Summer-
like and active with periodic rounds of heavy rain producing
thunderstorms by the weekend. While it is still too early to
determine exact rainfall amounts and where the heavy swaths may lay
out, the coming synoptic pattern suggests the potential for
occasional rounds heavy rainfall which may cause rises again on some
of the rivers, or at least slowing or stalling the current falling
river trends. This includes portions of the mainstem Mississippi
River, where sites such as ld15 in the Quad Cities and ld16 Illinois City
which have recently just slipped under the flood stage, may
experience new rises and possibly near their respective flood stages
again by early next week. Stay tuned for later river forecasts and
trends through the weekend.


Dvn watches/warnings/advisories...



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