Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service quadrant cities Iowa Illinois
725 am CST Friday Feb 27 2015

Update...
issued at 721 am CST Friday Feb 27 2015

Record low cold temperatures occurred tonight with the clear skies
and fresh snowfall. Wind chills in a few locations were below -30.
The only change to the forecast were the temperature trends. Expect a
warm up once the sun starts heating as it is starting to become the
season of higher sun angles. Wind Chill Advisory should still be
okay through 9am...a few sites may linger with sub -20 wind chills
through 10am.

&&

Synopsis...
issued at 307 am CST Friday Feb 27 2015

High pressure was moving into the Central Plains early this
morning. With fresh snowfall and clear skies temperatures have
plummeted this morning to quite possibly one of the coldest nights
of the year. Winds have stayed up...which has lead to widespread
wind chills between 20 and 30 below zero with a few pockets of 30
below or lower wind chills. Winds are starting to wane and
temperatures should drop more.

&&

Short term...(today and tonight)
issued at 307 am CST Friday Feb 27 2015

Main forecast concern for the short term are temperatures today
and tonight across the area. With high pressure in place and fresh
snow cover...guidance is of little help for temperature forecasts.

As far as the synoptic pattern is concerned...500 mb ridging is
building into the central United States as a surface high is forecast
to move directly over our County Warning Area today. Winds should wane...however
cold air and fresh snowfall will lead to cold temperatures today
and tonight. Models are of little help...this morning for lows I
loaded the observation and then made tweaks from there as the RUC was the
only model cold enough with temperatures. For today and tonight...went
with the allblend and then tweaked temperatures from there. Wind
chills tonight suggest the need for another Wind Chill Advisory
for areas north of i80. Will defer to the day to shift to decide
to issue this as there is already one out.

Long term...(saturday through thursday)
issued at 307 am CST Friday Feb 27 2015

Two storm systems will impact the extended forecast...and both
contain potential winter impacts. At this time...both systems are
relatively poor in confidence of exact details concerning these
impacts.

To begin the extended...high pressure will be moving off to the east
Saturday...and with a very cold start to the day...the weak warm air advection will
likely only result in highs in the middle teens north to middle 20s
south...despite a healthy amount of late February sunshine in the
morning. Warm advection by afternoon...will bring middle level moisture
northward...with some models continuing to brush our southwest with
deeper saturation by late afternoon. The model blend shows far more
significant moisture advection by Saturday night...and I will
continue to highlight that period through Sunday with high probability of precipitation.
This event is going to be all snow...and should have ratios in the
12 to 15 to 1 range...thus amounts from Saturday evening through
Sunday afternoon should range from around 1 inch northwest...to 2 to
3 inches from Iowa City through the quadrant cities to Sterling...to 3
to 5 inches over far southeast Iowa northeast Missouri to near
Princeton Illinois. While those amounts are supported by the most
likely blend of guidance that is indicated at this time...I am not
confident in them yet. The event is likely going to fall into the
advisory range...especially due to the longer than normal duration
for these range of amounts. Looking at uncertainty...the Canadian
model is farther south than the European model (ecmwf) and GFS...and keeps the
northern 3/4s of the County Warning Area dry...thus another reason for holding off
on any early headline at this time. The 06z NAM...through 12z
Sunday...also keeps the bulk of moisture and forcing south.

Monday will be a break between low confidence system...as the deep
western trough becomes even more amplified. The models have shown very
little consistency over the past few days and through tonight with
respect to the low track...upper energy track...and baroclinicity of
this potential system. One feature that has been shown
consistently...has been moisture...with a synoptic signal of an open
Gulf of Mexico...and even open Caribbean. The high amounts of
available moisture are reasons supporting likely probability of precipitation Monday night
and Tuesday. While not confident in thermal transition timing...it
is a best model blend...and conceptual model fit for precipitation to begin
as a wintry mix of snow/sleet/freezing rain Monday
night...transitioning to rain Tuesday...then back to snow again
Tuesday night. This wet mess could be high impact...or could be
largely benign. It is very difficult to tell...and will keep a
healthy dose of uncertainty in our products.

Following this system...colder dry weather settles back in the a few
days before moderation looks to occur in zonal flow.

Ervin

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 544 am CST Friday Feb 27 2015

VFR conditions through the period with light winds as high
pressure settles over the area. Winds should favor west to northwest today
and then favor S to southeast overnight. Overall winds will be very
light. Only concern would be frigid temperatures today and
tonight.



&&

Climate...
issued at 307 am CST Friday Feb 27 2015

Could see record lows this morning at a few sites and possibly
again tonight at other sites. Here are the records for tonight.

Record lows for February 28...

Moline.........-9 in 1962
Cedar Rapids...-17 in 1962
Dubuque........-10 in 1962
Burlington.....-7 in 1962

&&

Dvn watches/warnings/advisories...
Iowa...Wind Chill Advisory until 9 am CST this morning for Benton-
Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry Iowa-
Iowa-Jackson-Jefferson-Johnson-Jones-Keokuk-Lee-Linn-Louisa-
Muscatine-Scott-Van Buren-Washington.

Illinois...Wind Chill Advisory until 9 am CST this morning for Bureau-
Carroll-Hancock-Henderson-Henry Illinois-Jo Daviess-McDonough-
Mercer-Putnam-Rock Island-Stephenson-Warren-Whiteside.

MO...Wind Chill Advisory until 9 am CST this morning for Clark-
Scotland.

&&

$$

Update...Gibbs
synopsis...Gibbs
short term...Gibbs
long term...Ervin
aviation...Gibbs
climate...Gibbs

National Weather Service Glossary of Abbreviations