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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
621 am CDT Wednesday Jul 23 2014

issued at 313 am CDT Wednesday Jul 23 2014

The surface cold front reached from near South Bend through St Louis
into southeast Kansas at 2 am. Area radars indicated a line of thunderstorms
along this front from north central Illinois east across northern Indiana
and Ohio. The Post-frontal transition to cooler and drier air has
been rather slow to take place over eastern Iowa and northern
Illinois...where temperatures ranged from the middle 60s to middle 70s with
dewpoints not far behind in the 60s to lower 70s. High pressure
anchored over southeast Manitoba and its associated cooler and drier
airmass will build southeast into the region today and
tonight...providing a sharp change from Tuesday/S heat and
humidity. Aloft...00z analysis indicated a large ridge of high
pressure anchored over The Four Corners region with a ridge axis
reaching into the Canadian prairies. The upper level northwest flow and
thermal gradient on the northeast perimeter of this ridge will Keep
Ridge running thunderstorm complexes well west of the area in the
short term and allow the Canadian high to migrate toward the Great
Lakes by Thursday.


Short term...(today and tonight)
issued at 313 am CDT Wednesday Jul 23 2014

Temperatures are the main focus as Canadian high pressure builds
into the region. Today...north to northeast winds and the
approaching high will pull yesterday/S airmass over northeast Minnesota and
northern WI southward into the region today. This will support
dewpoints lowering to the middle 50s to lower 60s by afternoon. Based
on this trajectory...MOS guidance highs from the middle 70s northeast
to near 80 central and south looked reasonable and only minor
changes were made to the previous forecast. Skies should be mostly
sunny with scattered fair weather cumulus clouds from late morning
through afternoon.

Tonight...the center of the high is expected to reach southern WI by
morning. Resulting clear skies and light winds should lead to a
rather cool night for late July with lows from the lower 50s
northeast to upper 50s southwest. This setup will be favorable for
at least patchy fog and have added mention for the late night hours
over eastern Iowa and northwest Illinois...closest to the high center.

Long term...(thursday through tuesday)
issued at 313 am CDT Wednesday Jul 23 2014

Changeable weather more like a transition season rather than middle
Summer is setting up for our area in the long term.

Thursday...high pressure settling over the Midwest will bring
cooler than normal and dry conditions ahead of the next storm system.

Thursday night through Saturday...a couple of opportunities for
rainfall are forecast in this time frame. Warm air advection
setting up Thursday night and continuing into Friday is the first
chance. At this point have tapered probability of precipitation highest in the northwest
and lower in the southeast in line with low-level forcing. Have
kept probability of precipitation in the scattered category due to lack of
cape...especially Thursday night. The focus will be along the 850
mb boundary. Moisture will be plentiful with the NAM forecast of 1.5
inch plus precipitable waters looking reasonable.

The GFS...European model (ecmwf) and Gem move a surface wave along the warm front
into southeast Iowa late Friday afternoon and night. Low-level
support looks pretty good with the proximity of the 850 mb
thermal-moisture boundary and a developing low-level jet in
addition to the surface wave. Decent cape...moderate-high shear
and hefty precipitable waters are prognosticated during that time frame. Thus both severe
weather and heavy rain are a potential threat...though it is too
early to get overly excited about this potential event.

Sunday...GFS and 12z European model (ecmwf) differ on the timing of the upper level
trough passage with the GFS the faster of the two. Quick look at
the 00z European model (ecmwf) suggests it has come more in line with the GFS. Thus
precipitation may linger Sunday and have some low probability of precipitation in the forecast to
account for this.

Monday and Tuesday...surface high pressure once again settling
into the area will deliver more below normal temperatures and dry
weather. There is a hint of return flow and possible warm air advection-driven
storms late Tuesday...but it is day 7. Wolf


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 621 am CDT Wednesday Jul 23 2014

High pressure dropping south out of Canada will provide mostly
clear skies and light northeast winds today and tonight. There is
a potential for patchy ground fog early Thursday morning...which
is included with MVFR visibilities at Cid and mli...where the fog
is most likely to occur. Otherwise...conditions will be VFR


the CPC week 2 outlook indicates a high probability that cooler
than normal temperatures will persist the end of July into early
August. Odds favor near to below normal rainfall during that same
time frame. Wolf


Dvn watches/warnings/advisories...


short term...sheets
long term...Wolf

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