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fxus63 kdvn 202007 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
207 PM CST Wed Nov 20 2019

..hydrology update...

Synopsis...
issued at 201 PM CST Wed Nov 20 2019

After a cool and somewhat foggy morning, while the warm front was in
the cwa, the afternoon has been quite pleasant now that the warm
front lifted north. The result of this warm sector has been
temperatures rising through the lower 50s, and by late day, some 60
degree reading may be seen in the far south. Looking to the west,
low pressure is developing in northwest KS, and is helping draw very
moist air northward into the Midwest.

&&

Short term...(this evening through thursday)
issued at 201 PM CST Wed Nov 20 2019

1. Tonight, as this moist air mass surges toward the region, rain
will become widespread.

2. Precipitable water values over 1 inch will support moderate rains with brief
periods of heavy rainfall.

The period tonight with breezy, albeit dry conditions, as the
atmosphere remains unsaturated. However, by 9 PM, saturation will
begin to result in scattered showers, and by midnight, strong
lift and moisture in place will result in widespread rainfall over
the entire area. This rain should result in a widespread 0.25 to
0.5" event over the entire area, with a tendency towards higher
amounts of 0.5 to 1.0 over the north half of the cwa, where a
longer period of both moisture convergence and lift will occur. I
do feel the models focusing the moisture in the far northern County Warning Area
are not grasping the moisture available for this strong short wave
to work with. There are already showers and thunderstorms taking
place in the Western Plains, where lift is not nearly as strong as
it will be over the Midwest tonight.

This moisture transport will also be represented by increasing
surface south winds tonight, and by temperatures rising after late
evening, along with the dewpoints. By 12z, we may actually be rising
well into the 50s again. The result of this advection will possibly
raise morning temperatures to near 60 Thursday, before the low
passes, and cold advection sweeps in. While not overly cold, it will
certainly drop our County Warning Area back into cool November conditions.
Widespread moderate rains will diminish by 9 am or so, but until the
cold front exits the area, we will maintain high chance to likely
pops for showers and rains along the front and with the low passage.

By afternoon Thursday, rains should be done over the area, with
cloudy, cool, and windy conditions persisting into the evening.
Ervin

Long term...(thursday night through wednesday)
issued at 201 PM CST Wed Nov 20 2019

Forecast challenges in the long term center on the precipitation
chances the middle of next week just before Thanksgiving.

Thursday night-Saturday...quiet and cooler conditions will be seen
for most areas, as a surface high slides east and a weak upper level
low traverses the Great Plains. Latest model guidance keeps the
brunt of the southern stream wave associated with the upper low
further south of the region Friday night-Saturday. Slight chance
pops for light snow/flurries are maintained in the far south for
now, but may be able to be removed in later forecasts due to
increasing dry low levels. Friday and Saturday will see slightly
below normal high temperatures, with readings only in the upper
30s/low 40s.

Sunday-Monday...increasing warm air advection aloft and at the surface with mostly
sunny skies, will result in warmer temperatures and dry conditions.
Some areas may even reach the lower 50s by Monday, which will be
above normal for late November.

Tuesday-Thursday...most of the latest 12z model solutions agree that
somewhere in the Great Plains and Midwest will see a decent storm
system. Confidence remains low on actual track and timing of the
storm and associated precip types. The 12z GFS brings a closed upper
low right over the County Warning Area with rain initially, changing to snow on the
back side of the system on Wednesday. This would keep most of the
County Warning Area missing out on most of the snow. In comparison, the 12z European model (ecmwf) is
colder and brings a broad trof across the middle part of the country
and just grazes our far south with snow before increasing strength
further east. Dprog/dt of the GFS shows that it has been consistent
in showing a strong storm somewhere in the plains, whereas the European model (ecmwf)
has been back and forth showing a storm and then no storm impacting
our area. The 12z gefs h500 mean shows more of a broad trof across
the Continental U.S. And there remains considerable spread in its ensemble
members. To make things even more interesting, the Canadian model
has high pressure over the area with dry conditions. Needless to
say, this will be the period to watch over the next several days for
better model continuity since it is just prior to the Thanksgiving
Holiday.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1117 am CST Wed Nov 20 2019

Improving conditions will exist the rest of today, as a warm front
has lifted north of the area, with mainly VFR conditions expected
until rain arrives this evening. Rains will saturate from top
down, resulting in light showers from high cloud bases through 04z
tonight, then saturating to a moderate rain with lower clouds
around 1000 to 2000 ft through the overnight hours. Rains should
push east of the area around 13-15z Thursday, with scattered lower
clouds and light showers behind it. Winds will increase tonight,
with low level wind shear at 2000 ft/45kts from the south. By morning as the rain
ends, winds will switch from south to southwest, then towards 18z,
a shift to west / northwest will occur as the low pressure passes
by the region.



&&

Hydrology...
issued at 203 PM CST Wed Nov 20 2019

Rainfall tonight will broadly range from 0.25 to 1 inch. The
exact placement of higher totals favors the north half of the
area, but this could move latitude as rain trends shift tonight.
Thus, while the wpc quantitative precipitation forecast if robust over the Rock River basin, in
the 0.75-1.0" range, this is not with great confidence. Rises
above action stage are forecast, on the rock and Pecatonica, but
there are 100% quantitative precipitation forecast driven, and should not be viewed as high
confidence at this time. Tomorrow afternoon, high confidence
forecasts will be in place.

&&

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

$$

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