Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdvn 250004 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
704 PM CDT Wed may 24 2017

..00z aviation update...

Synopsis...
issued at 308 PM CDT Wed may 24 2017

Upper level low pressure/cold pocket has shifted into central MO
with spokes of vorticity rotating cyclonically around the center
of the low. In the dvn cwa, the more concentrated area of
instability showers and even a couple of brief lightning strikes
have been in our southern cwa. This is where temperatures managed
to push into the mid 60s (thanks to some sun) allowing for sbcapes
of 250 j/kg. However, shear is very weak and so are mid level
lapse rates. There are also a few weakening showers noted on
Doppler radar in NW Illinois and extreme eastern Iowa. These showers are
moving southwest to south at about 15 to 20 mph. In our northern
counties, where clouds have been more persistent, temperatures
were only in the mid to upper 50s early this afternoon. Very cool
for late may concerning normal highs are in the 70s.

&&

Short term...(this evening through thursday)
issued at 308 PM CDT Wed may 24 2017

Forecast focus on fog potential tonight then plenty of sun and
warmer temperatures on Thursday.

Tonight: with loss of heating any lingering showers should have
ended by around 7 PM or so, but basically we have a dry forecast
for tonight. This trend is indicated on esrl hrrr/hrrr/namnest
models. However, the challenge will be any fog development later
tonight and how dense or widespread it may become. High pressure
ridge will be moving into our western counties after midnight,
with clearing skies expected. Winds will also become rather light
and models suggest plenty of low level moisture, beneath a
somewhat strengthening low level inversion. Will mention "areas of
fog" in our west where skies should clear and "patchy fog" in our
east where clouds should linger the longest. With low confidence
at this time I will pass concerns to the upcoming shifts to
monitor trends if a headline is needed. Minimum temperatures will
range from the mid 40s to lower 50s.

Thursday: other than early to mid morning fog until the inversion
breaks, skies should be or become mostly sunny and a delightful
day is expected. High pressure ridge will be over the cwa with
light winds along with warmer temperatures. Afternoon highs should
push into the lower 70s at most locations.

Long term...(thursday night through wednesday)
issued at 308 PM CDT Wed may 24 2017

The long term will feature mostly unsettled weather for the region
through Memorial Day weekend, along with temperatures mainly below
normal.

Thursday night...while much of the night will remain dry, chances
for rain showers will gradually increase from southwest to northeast
early Friday morning. Forecast instability remains low, so not
expecting much, if any, thunderstorm chances.

Friday...models continue to remain uncertain on precipitation
placement, but overall confidence is high that showers and
thunderstorms will occur across the region during the day as a mid-
level shortwave moves across the mid Mississippi Valley. Have
decided to follow the blend at this time, which appears to be
following the lead of the NAM and candian in keeping higher amounts
to the south and east of the Quad Cities. There is a low potential
of severe weather across the southern County Warning Area where modest instability
and shear will be present, but these values have been consistent in
the latest guidance.

For Friday night, look for a brief break in precipitation coverage
as a weak ridge of high pressure builds across the region.

Saturday...a trough will move into the Great Plains/Midwest Saturday
morning, and will increase our potential for showers and
thunderstorms beginning Saturday afternoon. The latest global models
continue to keep the warm front just south of our cwa, and are in
agreement of placing the higher quantitative precipitation forecast towards the I-70 corridor. The
potential for severe weather remains low at this time, and would
mainly be over the southern County Warning Area where higher instability and shear
will be present.

Sunday through Tuesday...a pattern similar to what we have
experienced over the past few days looks to be on tap from the end
of Memorial Day weekend into mid next week. All models are generally
in agreement of an upper level low in place just north of the Great
Lakes, which will keep northwesterly flow over the region. Expect a
chance of precipitation each day as pockets of moisture and weak
shortwaves round the low, with high temperatures near or slightly
below normal.

Wednesday...overall, good agreement is in place on surface high
pressure building across the Mississippi River valley, with dry
conditions and temperatures climbing to near normal.

&&

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 652 PM CDT Wed may 24 2017

Challenging forecast with respect to cloud cover. Upstream Western
Plains upper ridge will build eastward and have a subsidence
scouring effect on the more cellular cumulus to the west and locally as
well. But this process will battle southwestern Great Lakes upper low
which will still try and whirl a more extensive MVFR stratocu
deck currently acrs WI down acrs the local area overnight and
into early Thu morning. The dbq and mli sites will be especially
prone to this deck coming in after midnight after a possible
temporary mid evening clearing. Besides the clouds, any clear
spots or clear sky trends combined with light winds of 5 kts or
less, may Foster areas of fog, some possibly dense, late tonight
into early Thu morning. Rather light and variable winds on Thu
under passing ridge axis, along with ambient sctrd-broken cumulus of
2000-3000 feet above ground level lifting to 4000 feet by afternoon. ..12..

&&

Hydrology...
issued at 1220 PM CDT Wed may 24 2017

Confidence has increased this morning along the Mississippi from
Camanche to Keithsburg reaching flood stage, and thus have
upgraded to flood warnings from the watches already in effect. It
should be noted that forecast crests will likely change at these
locations, so these will need to be monitored with later forecasts
and statements. For specific height forecasts, please see that
latest Flood Warning statements. Flood warnings continue for both
Dubuque locations, Gladstone and Burlington.

Have decided to go with flood watches for Bellevue, Fulton and
Gregory Landing this time as confidence of these locations reaching
flood stage remains low. That being said, these 3 locations will be
monitored, with a final decision of Flood Warning issuance
with Bellevue and Fulton occurring within the next few days.

&&

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

$$

Synopsis...haase

National Weather Service Glossary of Abbreviations