Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1232 PM CDT Thursday Mar 26 2015

Synopsis...
issued at 320 am CDT Thursday Mar 26 2015

At 07z...the main synoptic front was well to our south and southeast...lit
up with rain and thunderstorms from northeast Texas...reaching northeast
along into the Ohio River valley. An Arctic cold front was well to
our north...extending from low pressure over southeast Quebec west across Lake
Superior and along the Minnesota/Ontario border. A large cyclonic flow and
extensive area of low clouds around the Canadian low covered the
upper Great Lakes as well as much of WI into NE Minnesota. In between...
the local area was in an area of weak ridging that reached east from
the center of high pressure over SW Nebraska across Iowa into northern Illinois.
Drier air and cold air advection in the cyclonic northwest flow aloft was
eroding the low clouds over the local area...with the clearing line
roughly along the MS river. Temperatures were mainly in the 30s over
the local area.

&&

Short term...(today and tonight)
issued at 320 am CDT Thursday Mar 26 2015

The main challenge centers on temperatures as cold air advection in
a deepening northwest flow will lead to below to well below normal
temperatures.

Skies should start out mostly clear this morning...then become at
least partly cloudy late morning through through afternoon as
stratocu may form based on upstream satellite imagery trends from
yesterday...dry upstream soundings and the model cumulus rule tool. These
indicate more extensive cloud coverage likely over the far north and
northeast...which may briefly be impacted by the edge of the low
cloud deck currently over WI. Northwest winds will continue to advect a
winter-like dry airmass resulting in dewpoints only in the 20s
through the day. Forecast soundings depict mixing up through at
least 850 mb...where models have temperatures cooling to a range
from -4 to -8 celsius by afternoon. This supports highs from the
upper 30s north to middle and upper 40s central and south...which is
close to MOS guidance and the previous forecast.

Tonight...Canadian high pressure begins to nose south into the
northern plains and upper MS valley...allowing the modified Arctic
airmass to advance into region. Skies should be mostly
clear...outside possible low clouds that may accompany a weak
backdoor front out of the Great Lakes that models suggest may be
pushing into the northeast toward morning. The position of the ridge
center to the west should provide enough mixing on light north winds
to hold mins close to a guidance blend from the upper teens north to
middle 20s south. If winds were to decouple and skies remain completely
clear...this airmass would support mins as low as 10 to 15 f...and
possibly colder in the far north and northeast...closest to any
remaining snow cover.

Long term...(friday through wednesday)
issued at 320 am CDT Thursday Mar 26 2015

With the surface ridge sliding across...Friday will mark the coolest
day of the 7 day forecast period. However...ample sun and light
winds should take the edge off of the chill. Heading into the
weekend...Saturday will be a few degrees warmer but otherwise much
the same as the ridge continues to dominate the Ohio River valley.
Saturday night...strong low level warm air advection sets up. Forecast highs
Sunday are currently 10+ degrees warmer than Saturday and this may
still be several degrees too cool.

The system for Sunday continues to take shape. Model runs continue
to gradually slow the system...and consequently have removed all
probability of precipitation from Saturday night and extended into Sunday evening for
eastern parts of the County warning forecast area. Otherwise no change to the expected
impact with a progressive system and generally light precipitation amounts.

Next cold front passage in continued progressive pattern on tap for middle week. Low
probability of precipitation in the forecast for the cold front passage.

&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1228 PM CDT Thursday Mar 26 2015

A dry cold front will slowly move south through eastern Iowa and
Illinois through 12z/27. Cloud ceilings along/behind the front are
generally VFR but some MVFR ceilings are present. Thus VFR conditions
should be seen through 18z/27 with any ceilings above 3 kft above ground level.

&&

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

$$

Synopsis...sheets
short term...sheets
long term...dmd
aviation...08

National Weather Service Glossary of Abbreviations