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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
640 PM CDT Friday Oct 31 2014

Synopsis...
issued at 300 PM CDT Friday Oct 31 2014

Strong northerly winds 15-30 miles per hour... gusting at times around 40 to
45 miles per hour portions of northwest Illinois ushering in unseasonably cold
airmass. The strong winds courtesy of a tight pressure gradient
between low pressure over the Great Lakes and strong Canadian
high pressure over the northern plains. Just how unseasonably
cold... the 850 mb temperature sampled on 12z dvn radiosonde observation at -9.3c ties with
2006 (23rd/00z) for second coldest 850 mb temperature ever recorded by
dvn radiosonde observation in the month of October... with the coldest being -9.8c in
2001 (27th/12z). These cold temperatures aloft aiding scattered-broken diurnal
cumulus especially along/east of Mississippi River and limiting highs
to mainly lower 40s which is roughly 10-17+ degrees below normal making
it the coldest Halloween since 2002.

&&

Short term...(this evening through saturday)
issued at 300 PM CDT Friday Oct 31 2014

Widespread killing freeze tonight will bring an end to the growing
season... as center of unseasonably strong/cold high settles into the
region by morning. Middle afternoon dewpoints... 850 mb temperature rule and
verification of lows this am beneath incoming ridge all supportive
of lows tonight in the general range from upper teens to the middle 20s.
These temperatures would be close to record lows in a couple of sites...see
climate section below. The coldest lows are expected to occur west
of the Mississippi River being in close proximity to surface ridge axis
and longer duration of lighter winds.

Saturday... full sunshine with only some thin wispy cirrus as surface
ridge axis gradually traverses the County Warning Area. Despite the abundant sunshine
highs will remain well below normal given cold start and limited mixing.
NAM/GFS bufr soundings support mixing to around 925 mb which yields
highs mainly around 40 to lower 40s... but with dry ground and much less
wind I tacked on a couple degrees for general range on highs from 41-46.

Long term...(saturday night through friday)
issued at 300 PM CDT Friday Oct 31 2014

The cold high pressure will be exiting the region Saturday
night...but will remain close enough for clear skies and very light
southeast winds Saturday evening into the early morning hours. After
2 am...southeast winds will increase to around 10 miles per hour...especially
west. This increase in winds will help stabilize or even bring
temperatures up a few degrees from late evening low temperatures in
in the upper 20s. I have gone with middle 20s in the Rock River valley
region...where light southeast winds are known to maximize cold air
drainage.

Sunday will see a tight surface pressure gradient and warm air advection pattern
resulting in warming temperatures...as well as plenty of wind. South
winds will blow sustained 15 to 20 miles per hour...gusting to around 30
miles per hour...and with highs only in the upper 40s to lower 50s...we will
see wind chills in the lower to middle 40s most the middle day and
afternoon hours. Thus...while it warmer than Saturday...it likely
will not feel warmer unless you are in a sheltered area.

High clouds will gradually increase Sunday late afternoon and
night...and with continuing south winds around 10 to 15
miles per hour...temperatures Sunday night should be milder...with lows of 36
northeast to lower 40s southwest. The upper trough should emerge from
The Rockies in a split fashion...with the first ejecting into
southern Canada on Monday. This wave will drive a cold front into
Iowa...where is will slow to a certain degree as another more
sheared out wave slowly moves out of the southern rockies. Models
have varied greatly on the amount of phasing this upper wave will
have with the front while it is in the Midwest. Moisture return is
another variable that is been varying each run...but has been
supported by the past 48 hours of model runs to bring precipitable water values up
over 1 inch Monday. This should support at least light to moderate
rain amounts with this system. If dynamics were stronger...I could
see heavier totals over 1 inch...but with generally weak forcing
expected along the front...amounts should be generally a half inch
or less. With the highest totals in the south where have to 1 inch
is still possible.

Models are generally speeding up the exit of the system
Tuesday...which makes sense of the system is unphased as the European model (ecmwf)
solution strongly indicates. I have lowered Tuesday probability of precipitation by about 10
percent...but retained a chance level for now for
showers...especially in the early morning hours. For Tuesday night
and beyond...a dry forecast is in place...though some shower chances
may be needed for several clipper type systems beyond Wednesday.
Timing and position of these systems has no confidence...thus a dry
forecast is preferred.

Temperatures will remain forecast slightly below normal...in the
lower to middle 50s for highs...and lower 30s to lower 40s for lows.

Ervin

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 638 PM CDT Friday Oct 31 2014

Expect a diminishing wind under 10 kts and a clear sky overnight
with VFR conditions through the taf period.

&&

Climate...
issued at 300 PM CDT Friday Oct 31 2014

Record lows for November 1...

Moline.........19 in 1993
Cedar Rapids...15 in 1966
Dubuque........16 in 1951
Burlington.....21 in 1913

&&

Dvn watches/warnings/advisories...
Iowa...freeze warning from 10 PM this evening to 9 am CDT Saturday for
Des Moines-Henry Iowa-Jefferson-Lee-Van Buren.

Illinois...freeze warning from 10 PM this evening to 9 am CDT Saturday for
Hancock-Henderson-McDonough-Warren.

MO...freeze warning from 10 PM this evening to 9 am CDT Saturday for
Clark-Scotland.

&&

$$

Synopsis...McClure
short term...McClure
long term...Ervin
aviation...rp Kinney
climate...McClure

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