Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
FXUS63 KDVN 271208
Area Forecast Discussion
National Weather Service Quad Cities IA IL
708 AM CDT Thu Oct 27 2016
...12Z AVIATION UPDATE...
Issued at 404 AM CDT Thu Oct 27 2016
Surface low pressure was located over northern Indiana early this
morning, with an inverted trough extending back across portions
of northern Illinois and southern Wisconsin. This was providing
enough lift for IFR ceilings and patchy drizzle across northern
portions of the cwa. Stratus blankets the entire region early this
morning within cyclonic flow. Satellite shows the back edge of the
stratus deck approaching central Iowa, with the erosion tied to
leading edge of developing 925 mb warm advection and also NVA aloft.
.SHORT TERM...(Today and Tonight)
ISSUED AT 404 AM CDT Thu Oct 27 2016
Cloud trends with impact on temps, and fog potential are the main
00z DVN raob shows a fairly deep low level moisture to above 900
mb beneath strong inversion, thus it would appear any erosion of
stratus will be a slow process. However, 925 mb warm advection and
NVA aloft, working in tandem for the erosion to our west, look to
overspread the cwa toward midday through afternoon and should
bring about decreasing clouds generally from southwest to northeast.
Prior to that will likely have some patchy drizzle mainly in the
northern counties until mid morning. Also, a weak disturbance
in northwest flow is generating some light returns /sprinkles/
across portions of southeast North Dakota into west-central
Minnesota early this morning. Last few runs of HRRR/RAP have been
bringing some of this activity down toward the cwa later today
but diminishing likely due to subsidence, and therefore left out
mention. Goes without saying high temperatures today will be
quite challenging and dependent on clearing trends/timing. Would
expect the warmest readings (around 60/lower 60s) in the southwest
cwa where decreasing clouds likely to occur sooner. Coolest
readings likely in the northern cwa where any clearing likely last
to arrive, and as result there is some potential to stay in the
upper 40s along the Highway 20 corridor.
Tonight, any low clouds should be exiting north/east cwa by early
in the evening with mainly clear skies outside of some thin cirrus.
Strengthening warm/moist advection over a cooler/wet boundary
layer brings about concerns for some advection fog and possibly
even stratus north of a developing warm front. Some of the hi-res
models including the NMM and HRRR are also picking up on this
potential. I have therefore added patchy fog mention for the
overnight hours. Can`t rule out some of the fog being dense.
Temperatures may bottom out in the evening or around midnight before
becoming steady, if not rising a couple degrees due to continued
strengthening 925 mb warm advection and increasing southerly winds.
Continue to see MAV and MET guidance running too cool of late and
have sided toward blend of 2M temps favoring closer to ECMWF, with
lows ranging mostly from the lower 40 northeast cwa to the lower 50s
.LONG TERM...(Friday through Wednesday)
ISSUED AT 404 AM CDT Thu Oct 27 2016
Friday and Friday Night: Low pressure tracking along the
U.S./Canadian border will drag a +16 C 850mb thermal ridge through
the Upper Mississippi Valley. Breezy SW sfc winds gusting 25-35 mph
(isolated near 40 mph) and daytime mixing to result in optimal
warming, allowing temps to reach near 70 F far N/NE CWA to upper 70s
SW. Highest gusts are forecast in counties NW of a Fairfield, IA to
Freeport, IL line. Winds lower overnight but remain out of the south
and sfc dewpoints are forecast to hover in the mid 50s to lower 60s.
This will lead to a very mild night. Forecast lows near 60 F (on
avg) are roughly 20 F degrees above normal.
Temperatures: A cold front is forecast to sink southward through the
CWA during afternoon and evening. 850mb temps will eventually fall
below 12 C, but models have delayed the significant cooling until
the late afternoon or evening. Thinking the north to south max temp
gradient is going to be at least 10-15 F degrees. Have mid 60s far
north to upper 70s far south at this time - a few degrees above
Precipitation: Models now in better agreement grazing the CWA with
light QPF during the evening/overnight along the cold front/zone of
sfc convergence. Have 20-40 POPs for most of the area.
Sunday: Mid-level ridging will ensue setting up another stretch of
above normal temperatures and mainly dry weather. Highs are forecast
slightly above seasonal normals.
Monday and Tuesday: The mid-level ridge amplifies on Monday in
response to a digging trough in the Western U.S. Models have 1000-
500mb thicknesses peaking near 570 dam. The synoptic pattern
supports well above avg highs in the 70s and breezy conditions. Weak
cold front ushers in slightly cooler air for Tuesday. This front is
important because it is forecast to stall out across E Iowa/NW
Illinois and may become the focus for rounds of rain and isolated
storms by mid to late week.
Wednesday and Thursday: Better agreement/higher confidence in
active pattern developing in the Central U.S., including the Upper
In the initial stages of the pattern change, a warm front will
likely be the focus for repeated rounds of showers and
isolated/embedded storms. Upper-level vort. maxes are forecast to
ride along this low-level baroclinic zone from the Southwest U.S.
Will have to watch PWAT forecasts over the next several days because
the GFS is advecting anomalously high values of +1.25" into the area
via an 850mb connection to the Western Gulf. Potential is there for
significant rain but it is too far away to get into the details.
Looking further ahead: The Climate Prediction Center is forecasting
strong signals for above average temperatures through the first two
weeks of November. This would be the average temperature of the
period. Below average individual days are certainly possible. Uttech
.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 643 AM CDT Thu Oct 27 2016
Stratus with IFR to MVFR ceilings is trapped beneath an inversion
and will be slow to break up and clear. Have maintained similar
timing from previous TAFs of improvement to VFR conditions by
mid afternoon through sunset. However, confidence on timing of
improving conditions is low due to the strength of inversion and
depth of moisture. If any changes most likely it would be further
delay of improving conditions to mostly this evening from southwest
to northeast. Next challenge and concern is fog potential overnight
with warm advection over cool/wet boundary layer north of a warm
front. Mixed signals with LAMP and various MOS guidance showing
little to no reduction in visibility tonight. However, other
guidance including HRRR, RAP and NMM visibility plots support fog
and possibly areas of dense. Looking at observations early this
morning there is quite a bit of fog over portions of eastern
Dakotas into the Missouri River Valley ahead of a developing warm
front. Visibilities were quite variable from MVFR to pockets of
VLIFR. For now, I have introduced mainly MVFR visibilities, but
confidence is low and if any fog occurs potential will exist for
areas of lower conditions from IFR to local VLIFR. Northerly winds
5-12 kts will become light and variable this afternoon with high
pressure building in. Winds tonight then turn from the south-
southeast 4-8 kts.