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Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
524 am CST Thu Nov 21 2019

..12z aviation update...

issued at 306 am CST Thu Nov 21 2019

Widespread rain was falling over the area early this morning ahead
of a strong low pressure system centered over northwest Iowa. A
surface warm front extending southeast from this low, roughly from
Fort Dodge through Ottumwa to Quincy Illinois. This marked the leading
edge of a warm and very moist airmass. Temperatures and dewpoints
were in the 50s to near 60 in this warm sector over southern Iowa
and Missouri, while mainly 40s were found over the forecast area
with strong south to southeast winds, gusting as high as 40 mph
at times. Further west, a cold front, accompanied by a line of
showers and thunderstorms, reached southward from the low along
the Missouri River into eastern KS, with brisk northwest winds and
temperatures in the 30s in its wake. Sharp changes will occur in
the near term as this warm sector sweeps through the area this
morning, followed by falling temperatures this afternoon through
tonight in the wake of the deepening low pressure system rapidly
advancing into the western Great Lakes.


Short term...(today and tonight)
issued at 306 am CST Thu Nov 21 2019

Forecast concerns center on trends with the ongoing showers, gusty
winds and potential for thunderstorms this morning, then changing
temperatures throughout.

Anomalously high moisture levels, as evident by observed 850 mb
dewpoints from 5 to 10 c and precipitable water values from 1 to 1.4
inches (nearly 300 percent of normal) upstream across Kansas and OK,
were resulting in heavy rainfall rates. However, with a very strong
southwest flow aloft, the showers have been racing to the northeast
around 45 mph tonight, limiting rainfall amounts and impacts. At
least isolated bursts of strong wind gusts into the 35 to 45 mph
range will be possible early this morning with showers and due to
the 50 to 60 mph winds observed by Doppler radar around 2000 to
3000 ft above ground level. Latest radar trends and short term hi-
res models track the main axis of rain, along and northeast of
the advancing warm front, out of the forecast area by 4 or 5 am.
Showers should then become more isolated as seen in the warm
sector to our west and southwest, until the cold front pushes
through with perhaps a broken line of more organized showers
around mid morning. There will be at least a low threat for
thunderstorms especially along the cold front as an area of mid
level lapse rates over 6 deg c/km and MUCAPES of 300 to 500 j/kg
pushes through before 9 am.

Temperatures will surge into the mid 50s, possibly near 60 early
this morning as the warm sector pushes through. These will be the
highs for the day, and likely the warmest temperatures many areas
have seen in over two weeks. Temperatures will then fall with the
passage of the cold front and continue falling through the afternoon
through the 40s, then 30s by evening. Current timing of this front
has it reaching the MS river around 9 am, then exiting our Illinois
counties around 11 am. This will also be the end of our rain
chances, but cloud cover will remain in place through the afternoon.

Tonight should see clearing skies with the help of a confluent upper
level flow and in-building surface high. The clear skies and
continued cold air advection will lead to low temperatures toward
morning ranging from the lower 20s north to mid 20s south.

Long term...(friday through wednesday)
issued at 306 am CST Thu Nov 21 2019

Key messages:

1) primarily dry and quiet through Monday

2) chance of snow showers Friday night/Saturday morning

2) continued low confidence of weather evolution for mid next week

Friday through Monday...

Isentropic downglide and increasing subsidence aloft behind the
departing cold front will lead to a quiet and cool day Friday. Skies
will mostly sunny with more clouds expected primarily south of
Interstate 80 late in the day. The air following behind the front
will not be a traditional cold punch we normally see as 850 mb temps
barely fall below 0 c. Expected afternoon highs will be in the upper
30s to low 40s.

The increased cloudiness south of Interstate 80 is due to a 500 mb
closed low developing over central Kansas and western Missouri,
which is progged to move into the mid-Mississippi River valley
Saturday morning. Cva will wrap around this low as it moves
eastward, leading to some pockets of enhanced lift. While much of
the area will remain dry, there remains a chance of a snow shower
around the Highway 34 corridor south due to that cva. The best
timing for this would be from Friday evening through early Saturday
morning. If any snow showers were to fall, accumulations would only
be a few tenths.

For the remainder of the weekend, flow around 500 mb will generally
be out of the northwest, with a few weak disturbances expected with
it. Moisture remains fairly limited at the surface, so the worst to
be expected with them is increasing clouds from time to time. Around
850 mb, ridging and warmer temperatures will begin to build back
across the region, helping temperatures rise once again. However,
they will not be anywhere what we are currently experiencing.
Widespread afternoon highs in the 40s are expected Sunday and
Monday, with some low 50s even possible south of Highway 34 Monday.

Tuesday on...

Little to no agreement in the deterministic solutions continues for
this period. Much of the reason for the flip flopping is due to
sharp disagreements in respective ensemble members. Until these
start to come to a consensus, confidence on how this period will pan
out remains low. However, with such a upper level deep trough
progged to dig into the eastern rockies, there is decent confidence
on active weather somewhere across the Midwest during this period.
Please continue to monitor the latest information, especially if
you're planning to travel for the Thanksgiving Holiday.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 524 am CST Thu Nov 21 2019

Scattered showers ahead of a cold front moving through the region
will affect all sites until around 15z. Conditions will be
predominantly MVFR, but a mid to late morning period of IFR
conditions due to low ceilings is likely at Cid and dbq. The
strong circulation around low pressure moving into the western
Great Lakes will provide strong gusty winds ahead of the front
this morning, which will veer to the west, then northwest with
gusts as high as 30 kts through the afternoon. Conditions are
expected to become VFR this evening with diminishing northwest


issued at 306 am CST Thu Nov 21 2019

The latest 6-10 day outlook from the climate prediction center
paints potentially active weather across the Midwest for the
Thanksgiving Holiday. Currently, there is a high probability of
above normal precipitation (50-60%), but no clear trend to above or
below normal temperature (labeled as equal chance). Average highs
for the period are in the upper 30s to low 40s, while average lows
are in the low to mid 20s.


Dvn watches/warnings/advisories...


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