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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
651 am CDT Tuesday Oct 13 2015

issued at 327 am CDT Tuesday Oct 13 2015

Shortwave trough was shifting eastward through the Great Lakes
early this am... with wrap-around low clouds in lingering
cyclonic flow over northeastern half of County Warning Area with back-edge
roughly along an Independence Galesburg Illinois line at 08z.
Winds remain brisk from the northwest at generally 15-25 miles per hour...
and between well mixed bl and clouds temperatures are fairly uniform
around 50 or lower 50s at 3 am. Flow pattern aloft remains
northwesterly in wake of departing shortwave ushering in the
cooler air and thus will keep temperatures near to a little below normal
next 24+ hours.


Short term...(today and tonight)
issued at 327 am CDT Tuesday Oct 13 2015

Incoming subsidence /nva/ in wake of Great Lakes shortwave
should continue to Foster eastward translation and decrease of
stratus this am. Water vapor imagery though shows a low amplitude
wave crossing the northern rockies early this am. This wave is
forecast to dive east/southeast and pass through the region later today...
and will be accompanied by a cirrus deck... which satellite shows
already advancing quickly through the Dakotas into western Minnesota and
northwest Iowa. This cirrus looks to be fairly opaque in spots and
so may result in filtered sun at times... and coupled with
decreasing low clouds should generally result in pt-mosunny skies.
We are at that time of year where opaque cirrus for any duration
will have impact on temperatures... so between this and departing low
clouds presents a bit of a challenge for highs. Banking on
most areas seeing at least a period of good solar insolation
and deeper mixing to just below 850 mb to push highs mainly in
the lower to middle 60s. Where low clouds linger or cirrus more
opaque could suppress highs 58-60 range. Bufr soundings show
around 15-20 kts through the mixed layer today so will continue
with brisk/breezy conditions of 15-25 miles per hour for most of day
before settling middle-late PM as mixing abates and pressure gradient
relaxes. Still may have some agricultural field fire danger
threat again today... but with winds not as strong and temperatures not
as warm the threat does not appear to be nearly as high as what
was observed on Monday.

Tonight... expect mostly clear skies with just some high thin
cirrus as channeled vorticity axis shifts across County Warning Area. Winds will
diminish to around 5 miles per hour as surface ridge axis builds toward the
County Warning Area. With low level dry air...light winds and mostly clear skies
stayed near lower side of guidance with upper 30s to lower 40s
mainly on lows... which are also supported by 850 mb temperature rule
assessing 850 mb temperatures (which in this case are shown to be around
5c at 12z wed) and strength of low level inversion.

Long term...(wednesday through monday)
issued at 327 am CDT Tuesday Oct 13 2015

Main forecast concern in the extended are the chances for precipitation
Thursday and then cold air into the area behind this clipper system.
It looks like there is still a chance of precipitation Thursday and it is
looking more and more likely that widespread frost and a freeze will
occur Friday night.

Wednesday through Thursday afternoon...500 mb northwest flow will continue to
usher in drier air into the area along with surface high pressure. This
flow will slowly rotate and become a little more zonal...this will
lead to slight moisture return across the area. Thursday a clipper
types system approaches the area.

Thursday afternoon through Friday morning...the clipper moves
through the area. There are differences between the models as far
as where the precipitation will occur and where the overall forcing is.
The European model (ecmwf) is more south...which puts the area in line for showers.
The other models have the main vorticity advection to our north and precipitation
across that area. Im going to go with the consensus with the precipitation
to the north as the European model (ecmwf) vorticity does not seem reasonable. As
such...have a schc across the north and east. I have limited quantitative precipitation forecast
because model low level relative humidity seems saturation would need to
occur with the fast moving system...where like last night...I have
low confidence in.

After this...much cooler air is forecast to advect into the area and
lead to the real first chance for frost or even a freeze across the
area. 850 mb temperatures of -6c Friday night into Saturday am are prognosticated.
Friday night looks to be a cool night across the area. Added
widespread frost in across the northern County Warning Area and areas of frost
elsewhere. Headlines for frost and freeze will likely be needed for
Friday night.

Into early next week it looks like there is another warmup next
week. Temperatures should rebound to normal if not above normal with near
20c 850 mb temperatures. It looks like we may see Indian Summer this coming


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 644 am CDT Tuesday Oct 13 2015

Generally VFR conditions expected through the taf cycle with gusty
northwest winds diminishing middle-late PM eventually dropping below
10 kts early this evening. Back edge of stratus with MVFR to VFR
ceilings near dbq-mli is expected to continue shifting east of these
sites early this am. Some additional stratocu development possible
in the wake near and east of the Mississippi River but mainly scattered
coverage with bases 2500-3500ft above ground level. In addition... some cirrus will
spread across the terminals today.


Dvn watches/warnings/advisories...


short term...McClure
long term...Gibbs

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