Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
304 am CDT Friday Aug 28 2015

issued at 304 am CDT Friday Aug 28 2015

Tropical...monsoon moisture was located over the High Plains this
morning. An upper level feature was aiding in cyclogenesis over
Nebraska. A surface low was located in central Nebraska. Showers and
thunderstorms were ongoing across the middle Missouri River valley
associated with these features. The surface low and monsoon moisture
from the Desert Southwest are forecast to slowly move east through
the day and overnight today.


Short term...(today and tonight)
issued at 304 am CDT Friday Aug 28 2015

Main forecast concern for the short term forecast are where the
best chances of rain and thunderstorms are today through tonight.
Current radar and guidance suggests that we will see appreciable
rain in the County Warning Area today and tonight.

Monsoonal moisture advecting into the area has saturated the
atmosphere according to the 00z dvn sounding. Deeper surface moisture
will advect into the area through the day today as low pressure
moves through the area. Two days ago the American models had
pegged areas to our south and European model (ecmwf) was further north. Todays runs
are somewhat reversed. The European model (ecmwf) is even further north and the
American models seem to be better at resolving what is going to
happen. Guidance suggests that areas just north of the County Warning Area will
see the heaviest rain.

Decided to bring the better rain chances further south in line
with 4km NAM and trends from this year that suggest if lse is
pegged with quantitative precipitation forecast then it is usually further south. This southern
trend was brought up in the day shifts afd and I think that a
southern push is more realistic. The 500 mb wave is rather open and
doesnt suggest that the surface low moves that further north. 850 mb flow
pegs the northern row of counties for the best mass convergence.
This paired with precipitable waters near or exceeding 2 inches...will result in
the heaviest rain falling from Highway 30 north. 6z wpc quantitative precipitation forecast also
pulls the best quantitative precipitation forecast south across our northern half. Have gone with
a blend with 00z and 06z quantitative precipitation forecast...this results in up to 2 inches
across the north to near half an inch in the qca.. cape values are
low...mostly due to low temperatures. As a result....high
precipitation efficiency is not forecast. Decided to hold off on a
flash Flood Advisory. My gut tells ME that categorical probability of precipitation may needed to be pulled
even further south. Will monitor and advise the day shift on this.

Long term...(saturday through thursday)
issued at 304 am CDT Friday Aug 28 2015

Warming trend to above normal temperatures and dry.

Long term forecast confidence assessment...fair or average with
limited sensible weather issues. Two main is the need
to add possible isolated precipitation as flow pattern supports this
may occur middle to late next week. The second issue is temperatures
as local tools suggests highs Saturday and Sunday may be a few
degrees too high if clouds hang around. Lows into Monday am also
may be too mild if bl decoupling and fair skies occur.

Overview...initialization and verification at 06z indicate poor
model quantitative precipitation forecast (too far north) and bl moisture issues too dry for a
change. Trends suggest a 75/25 mix of hi-res European model (ecmwf) to the too
unstable run to run of the GFS.

Saturday and Sunday...slowly clearing skies Saturday by late
afternoon with lingering chance of showers into middle day. Highs a
challenge with most locations rising into the upper 70s with some
sunshine by middle PM. Saturday night...winds to become light with
mins possibly still a few degrees too mild with patchy light fog a
risk for later shifts. Sunday...mostly sunny and warmer with highs
in the lower 80s and light winds and seasonably humid. Sunday night
suggest with light winds good decoupling and for lows to be a few
degrees cooler than forecast with a decent risk of fog for later
shifts to reassess.

Monday through Thursday...ridging and south winds of 5 to 10 kts and
lots of sunshine suggests very warm to hot and humid. Highs should
per local tools be mostly in the upper 80s with some readings around
90 degrees. Heat index values may reach into the lower 90s for at
last a few hours. Mins mostly in the middle 60s with risk of fog
toward sunrise. Flow pattern may allow for moisture to kick of some
patchy precipitation of showers or a storm for later shifts to


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1130 PM CDT Thursday Aug 27 2015

06z tafs updated for slightly slower timing of rain onset...from
late morning northwest to late afternoon southeast. MVFR ceilings
and visibilities in rain will become common through the afternoon
and evening.


Dvn watches/warnings/advisories...


short term...Gibbs
long term...Nichols
aviation...rp Kinney

National Weather Service Glossary of Abbreviations