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fxus63 kdvn 210432 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
1132 PM CDT sun Oct 20 2019

issued at 1126 PM CDT sun Oct 20 2019

I have now delayed the onset of pops until after midnight, and in
general, have slightly trended the 6 hourly quantitative precipitation forecast downward,
especially in the northeast County Warning Area. The later onset, combined with a
consistent model signal that central Iowa through Minnesota should be the
main axis of heavy rain, rather than Wisconsin/IL. In any case, it
remains a very high probability that all sites receive some sort
of measurable rainfall through Monday morning, thus I have not
lowered the magnitude of pops.


issued at 254 PM CDT sun Oct 20 2019

We've managed to recover quite nicely from our pea soupish morning
early this afternoon. As of 2 PM, skies featured increasing upper
level clouds from the west with surface temperatures ranging from 56
in Clinton, to 68 in Vinton. These clouds were ahead of an area of
low pressure centered over northwest Nebraska and southwest South
Dakota, which was ahead of a 500 hpa low pressure ejecting out of
the eastern rockies. These two features will serve as our main
challenges in the short term period.


Short term...(this evening through Monday night)
issued at 254 PM CDT sun Oct 20 2019

Key messages...

1) strong system to bring rain, wind and potential for storms to the
area tonight and Monday.
2) rainfall amounts not expected to lead to renewed flooding
3) winds increasing to near advisory criteria Monday night.

12z guidance is generally in good agreement of the handling of this
low pressure and upper level low evolution and progression, with
generally few differences.


Surface low will progress eastward from north central Nebraska to
northern Iowa/southern Minnesota early Monday morning. At the same
time, the associated 500 hpa low/trough will become more negatively
tilted, bringing a sizable increase of cva and strengthening of the
surface low with its eastward movement. Rain showers, and even some
embedded thunder (which is possible given some hints of instability
aloft and plentiful vertical shear), will accompany this surface low
and trailing cold front as it passes. At this time, the most optimal
window for precipitation across the entire County Warning Area is from 2 to 10 am.
The heaviest precipitation is expected primarily over northwest
Illinois and northeast Iowa, where better lift associated with the
cva is organized. With this forecast package, currently have
rainfall amounts ranging from below half an inch south of I-80, to
just under three quarters of an inch around Highway 20. There may be
some pockets of heavier rainfall in stronger showers. Thankfully,
since we've had a fairly dry period of weather with time for soils
to dry and rivers to fall, this should not do much to aggravate any
rivers currently in flood or lead to renewed rises.

Monday and Monday night...

The primary area of rain will be exiting the area from west to east
with the passage of the front and increase in isentropic downglide
late Monday morning, with some holes opening up in the clouds by the
afternoon. By this time, winds should start to increase out of the
southwest as the low continues to deepen and pressure gradient
tightens around the center. Several model suites are advertising the
surface low pressure core dropping below 990 hpa by the time it
reaches Lake Superior Monday night. This will lead to surface winds
around 20-30 mph, with gusts near 40 mph, which puts US right near
advisory criteria. The strongest winds are expected across our north
and west late Monday night and Tuesday morning where the main vort Max
closely passes.

In addition to the winds, there will be a chance of some wrap-around
precipitation with the extra lift in the passing vort maxes Monday
night. Precipitation looks to be all rain with temperatures above
freezing below 850 hpa.

Long term...(tuesday through sunday)
issued at 254 PM CDT sun Oct 20 2019

Primary forecast concerns through this portion of the forecast lie
with winds on Tuesday then moves to the system to potentially impact
the region from Wednesday into Friday.

In the wake of the stong vertically stacked low system which will be
lifting to the northeast through the day Tuesday, expecting to
continue the strong winds from the previous period. Strong cold air
advection and deep mixing will continue through the day where
forecast soundings show a mixed layer to around 850mb. Winds at the
top of the mixed layer are around 40kts at the beginning of the
period and do begin to drop off by the end of the day Tuesday. With
the pressure gradient will also easing by days end, looking for the
boundary layer to decouple with a steady decrease in wind speeds
around sunset.

Wednesday. A potent shortwave trough looks through the Dakotas and
into the Central Plains during the day with warm air advection ahead
of it. The question is, will there be rain across the area during
the day. By far the best moisture and lift will be available north
of the area, but not sure how far south that will be and if it will
be in the forecast area or just to the north. Current deterministic
models are split on the existence of measurable precipitation so the
forecast continues to have chances across the northern half, but
there is considerable uncertainty and could see the forecast are
remaining dry through 00z Thursday.

Wednesday night into Friday. The trend continues for this period
with the progression of the aforementioned system as it transitions
across the Continental U.S.. the 20.12z European model (ecmwf) splits the system creating a
closed upper low over New Mexico/Texas Thursday into Friday while
the GFS keeps a progressive system moving across the plains and
Midwest. These 2 opinions both bring colder air to the forecast area
during the day Thursday but vary significantly in where there will
be precipitation. With stronger energy staying intact with the
original system, the GFS puts a decent precipitation event across
the area centered on Thursday. The European model (ecmwf) however has much less
energy across the area and instead focuses the precipitation south
of the area along the cold front as it doesn't get going until later
in the day Thursday.

Then going into next weekend, a warming trend look to occur in the
wake of the late week system, however large disagreement in eventual
outcomes has led to extremely low confidence in the forecast with a
difference of wet versus dry.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1126 PM CDT sun Oct 20 2019

A potent storm will bring a band of rain and possibly a rumble of
thunder through the area late tonight and early Monday morning.
Winds aloft are strengthening, and may produce low level wind shear for a short
period later tonight, mainly 08z to 12z. After this, winds will
switch to south to southwest and become well mixed into Monday. A
breezy, mainly VFR day is expected, with some scattered fast
moving showers north. A dry slot in the storm system is likely to
result in most of the area being dry after 15z. By late afternoon,
more low clouds will wrap southeast over the area as cold air
moved in on the backside of the low pressure area.


issued at 254 PM CDT sun Oct 20 2019

River levels continue to recede today. Rain is forecast across
the region through Tuesday which the majority is being taken into
account of in this mornings forecasts. Rain amounts over the next
48 hours will be highest across northeast Iowa, southern
Wisconsin, and into northern Illinois with widespread amounts of
around an inch, with lesser totals expected going south. For most
locations, this rainfall will only cause a slight delay in the
recession of the rivers. The exception will be along the
Pecatonica River which sits in the area where the heaviest rains
are expected. While amounts in todays forecast would only produce
a slight re-rise, it will bring it back just above flood stage,
therefore the Flood Warning will continue for the Freeport area as
the river should hover around that 13.0 ft mark for the next week
unless rainfall ends up being less than is anticipated.


Dvn watches/warnings/advisories...



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