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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
626 am CDT Thursday Oct 30 2014

issued at 308 am CDT Thursday Oct 30 2014

Analysis at 2 am depicts a fast moving...moisture starved upper wave
entering far northwest Iowa with pressure fall pattern supporting best forcing
to pass across south 1/3 of area next 12 hours. Lots of elevated returns
with local tools supporting patchy sprinkles and area of light rain
in the south with passage. Vigorous short wave in central Canada
to arrive with strong cold front late evening with moisture profile
supportive again of sprinkles and possibly isolated .01 inch amounts
along cold front passage. Thermal fields all suggest this cold front
to bring coldest air of the season with a hard freeze.


Short term...(today and tonight)
issued at 308 am CDT Thursday Oct 30 2014

Short term forecast confidence assessment...below average or poor due
to question of coverage and amounts of light rain versus sprinkles.
Warm advection Wing tool suggests risks of likely probability of precipitation may be needed
late morning into early afternoon along and especially south of Highway
34 corridor with amounts to around a tenth of inch possible to monitor
the next 6 hours with trends with a narrow deformation zone formation
band of 5 to 20 miles wide suggested. Clouds and precipitation amounts
will impact highs with some areas possibly 2 to 5 degrees too mild due
to evaporative cooling with precipitation.

Today...mostly cloudy to cloudy with areas of sprinkles to develop
by daybreak and lasting until late afternoon with passage of wind
shift or weak occlusion. Have gone with highs 53 to 59 degrees but
locations SW 2/3 may need lowering...again due to evaporative cooling
of precipitation and thick clouds by up to 3+ degrees.

Tonight...strong cold front to arrive around 10 PM and pass rapidly
south by 4 am. A band of sprinkles suggested along and just behind
front of 5 to 15 miles width. Strong subsidence and mixing combined
with evaporative cooling supports north winds 20 to 30+ miles per hour with some
gusts T around 35 miles per hour with isallobaric maximum. Temperatures to crash 10
degrees or more within 2 to 3 hours and wind chills falling into the
teens northwest sections by daybreak. Area lows with strong cold air advection
should occur after 7 am...most areas 8 or possibly 9 am. Some location
mins may need trimming by 2 to 3 degrees if skies clear faster behind
cold front.

Long term...(friday through next wednesday)
issued at 308 am CDT Thursday Oct 30 2014

Friday through Sunday...00z run model solutions still on track with
strong Canadian high and Stout cold air advection/cold slam down across the upper MS
River Valley Friday. Tight cyclonic flow and low level pressure gradient to
drive northerly surface winds of at least 15 to 25 miles per hour sustained...and
gusts to 35 miles per hour or higher for a good part of the day before
decreasing some by late afternoon especially west of the MS river. With
morning temperatures in the upper 20s to lower 30s across much of the
area...wind chills will be in the teens to low 20s through middle
morning. Mostly sunny however...although some bouts of cold air cumulus
may push partly cloud coverage at times Friday especially east of the
MS river. With ridge sliding overhead for surface wind decouple and sky
clear out...widespread hard freeze still on track. A freeze warning
will eventually be needed to be hoisted for the southern third of
the dvn County Warning Area. Interesting that some of the MOS guidance has come in
even colder with lows in the upper teens to around 20 for some
locations in the northern County Warning Area by Sat morning. For now will keep the
widespread low to middle 20s going. Surface high and upper Omega blocking
ridge to get pressed eastward across the region for the rest of the
weekend for generally fair weather with some temperature modification by Sunday.
Prefer the 00z GFS delaying any elevated warm air advection type showers trying to
develop across the County Warning Area to Lee of organizing upstream l/west trough across the
western rockies not until late Sunday night. Will ignore the 00z
European model (ecmwf) aggressive showers by Sunday morning for now with strength of
ridge and low to middle level dry air in place. High temperatures to return to
the 50s for the southwestern half of the County Warning Area on Sunday.

Monday through next Wednesday...longer range indication suggest that
the upstream trough will have to shear out across the middle Continental U.S.
Sometime early next week...with increasing warm moist conveyor from
the south interacting with associated low level frontal system. Where
that lays out for a decent precipitation chance is all up to phasing of the
trough and any upper jet rounding trough base lays out. The latest 00z
runs now suggest everything coming together for the frontogenetical
forced precipitation swath/band to move across much of the County Warning Area from late
Monday into Tuesday morning and high chance probability of precipitation will ride in the grids. But
still am Leary of the potential of everything to get adjusted in a
way that the bulk of the precipitation eventually misses the dvn forecast area
to the south and east. Upper ridging looking to re-establish off to
the west and no real cold fetch evident suggests seasonably mild
conditions to follow what ever trough complex develops/ occurs in the
Monday to Tuesday time-frame for middle next week.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 623 am CDT Thursday Oct 30 2014

VFR conditions next 24+ hours. Clouds to increase with bases at or above 7k above ground level
ahead of a weak upper level disturbance. Isolated sprinkles all terminals
and light rain possible at brl terminal through today with light southeast
winds. After 31/03z...a strong cold front will bring north winds of
5 to 25+ kts with its passage all terminals by 31/06z. Ceilings will
lower to near marginal MVFR or more likely low end VFR for 2 to 4 hours
after front passes with clearing all terminals after 31/07-12z.


Dvn watches/warnings/advisories...



short term...Nichols
long term...12

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