Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
632 PM CDT Wednesday Jul 23 2014

Short term...(this evening through thursday)
issued at 313 PM CDT Wednesday Jul 23 2014

Tonight...Canadian high pressure will look to continue to dump down
across WI and the southwestern Great Lakes through Thursday morning...with
northeasterly low level fetch continuing dry/cooling infusion across the
region. Winds to go light and variable overnight...but drying
influence will have settled in with upstream low 50 surface dewpoints
advected in portions of the area. After diurnal cellular cumulus decays
for mainly clear skies...light winds...drier surface dewpoints and cooling
column all support an unseasonable cool night across the County Warning Area. The
entire forecast area to cool down into the 50s...with some low to middle 50s
possible across the northeastern half of the dvn County Warning Area in lower dpt pool
closer to ridge axis. The 850 mb mb ridge cool rule even supports some
upper 40s in some spots such as cool air drainage locations. Will be
advertising close to record lows at mli...but other climate sites
the lows should fall 3-5+ degrees short. Will keep the patchy fog
wording going across the northeastern third or bit more of the local
forecast area for late tonight after 09z...but wonder if today/S drying
and lowering dewpoints may alleviate that. Fog may be more confined to
the river valleys.

Thursday...the anticyclone will continue to migrate eastward across the
region and toward the Great Lakes...while steering middle level northwest
flow organizes across the upper MS River Valley to Lee of Western Plains
upper ridge axis. Despite inherent weaker mixing regime under passing
ridge axis...will still side with the warmer of temperature guidance highs
with dry air in place and mostly sunny to sunny skies...depending on
the amount of cellular cumulus that forms again. Plus there is the chance
that the northwest flow may dump some debris cirrus off northern
plains ridge-riding convection down across the County Warning Area later in the
afternoon filtering the insolation some. ..12..

Long term...(thursday night through next wednesday)
issued at 313 PM CDT Wednesday Jul 23 2014

The main forecast issues in the long term period are convective
timing/coverage/intensity through Friday night.

Medium range model guidance is in reasonable agreement in pointing
to a potential mesoscale convective system affecting the forecast area Thursday night into
Friday morning. Mesoscale convective system diagnostic tools indicate a 50 knots low level jet
pointing into the region with favorable upper level diffluence and
pwat's around 2 inches. Storms will likely be elevated and pose a
limited severe weather threat. General 1/4 to 3/4 inch rains seem
reasonable...with a few locations likely in the 1 to 2 inch range.
With dry conditions most areas of late...flash flooding is not
expected to be an issue. The focus of the decaying mesoscale convective system is expected
to shift along and east of the river Friday morning.

Looking ahead to storm potential Friday afternoon and night...
confidence is not as high for a couple of reasons. First...the
impact of overnight convection on the location of boundaries
across the forecast area. Second...the strength of the warm air
aloft and potential for strong capping over most if not all of the
forecast area. For now...have favored the far north and east
portions of the County Warning Area with the higher chance probability of with
the fringe of slightly cooler 700mb temperatures.

For Saturday...expect afternoon dewpoints in the low to middle
70s...with afternoon heat indices of 95 to 100 degrees along/south
of Highway 34. Isolated to scattered storms can't be ruled out
Saturday night into Sunday due to a compact upper trough pushing
through the upper Mississippi Valley.

For the rest of the long term period...look for a transition back to
northwest flow...with cooler and mainly dry conditions.


Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 627 PM CDT Wednesday Jul 23 2014

Clear to mostly clear skies and VFR conditions to prevail through at
least 25/00z. Patchy light aviation fog may develop in River Valley/S
toward morning but risk too low due to current temperature and dewpoints spreads
as of 23z are to wide to consider in terminal forecasts. Winds light
NE tonight...shifting to the southeast Thursday am. Some fair weather
cumulus clouds once again expected middle day Thursday.


issued at 313 PM CDT Wednesday Jul 23 2014

Record lows for July 24...

Moline.........54 in 1957
Cedar Rapids...50 in 1927
Dubuque........51 in 2003
Burlington.....51 in 2003


Dvn watches/warnings/advisories...



Short term...12
long term...rp Kinney

National Weather Service Glossary of Abbreviations