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Area forecast discussion 
National Weather Service Des Moines Iowa
644 am CDT Wednesday Oct 1 2014

..updated aviation discussion...

Short term /today/...
issued at 337 am CDT Wednesday Oct 1 2014

Ongoing precipitation band will continue to track east-northeast this
morning before transitioning east of the forecast area early this
afternoon. The latest hrrr/hopwrf/arw/nmm all have the main precipitation
shield pushing east of the forecast area b/T 18-21z this
afternoon...with the hopwrf the quickest to move it out. Plus the
nam12/GFS/ECMWF agree on the more progressive nature of the precipitation
departing the forecast area sooner. Hence...transitioned
categorical/likely probability of precipitation east faster about 3 hours than previously
expected. With the slightly faster movement today...took out
mention of heavy wording. However...likely could see some isolated
pockets of up to 1-2 inches with the precipitable water values in
that range. But lower confidence in the widespread heavy rain
today. Still may see some linger light showers behind front with
some weak forcing and Theta-E advection.

Temperatures again will be problematic with the rain cooled air mass
this morning...leaned toward the colder solution of the nam12. It
seemed to have a better handle on maximum temperatures on Tuesday.

Long term /tonight through Tuesday/...
issued at 337 am CDT Wednesday Oct 1 2014

Main challenges similar to last nights forecast. With subtropical
moisture plume focused on western Iowa now with tonights short
wave tracking upstream wave arriving later this
afternoon and tonight and finally the third SW wave in a series
tomorrow...the active weather pattern continues. As usual...some
modifications to forecast moving forward but overall the general
trends remain on track. By late today the current short wave
impulse over western Iowa will be exiting the eastern portion of
the forecast area with surface trough/cool front approaching northwest
Iowa. The front is expected to slow Thursday night and Friday as
the final wave over the southern rockies begins to amplify into
the Central Plains. Models have continued to differ on details
with track of low and tonight the 00z Gem is digging the surface low
farther southeast and then northeast through far eastern Iowa on
Thursday. The 00z NAM is farthest west with the track and the GFS
is leaning toward the Gem...between the two. The 12z Euro this
morning and tonights 00z run continue to be the more stable
solutions...similar to last nights with the wave riding up through
just east of Des Moines. The one consistency between all models is
the 6 to 10 hour break in organized rainfall over the entire area
tonight...with only the south once again seeing the better forcing
beginning again after 06z as an h850 warm front will take shape
over central or northern MO between 06z and 12z tomorrow. The 12z
Euro focuses the best lift over the same locations and in
fact...the entire run is consistent with its predecessor with
forcing over northeast Kansas...northern MO through 06z and then the
moisture transport begins veering over time with the moisture
transport focused more toward northeast MO by 12z. This strong
isentropic lift with a weak wave peeling off the main upper short
wave will provide for rainfall well east of the main upper level
system. As the main h500 wave over central Nebraska moves east...a
surface low will track near Topeka by 18z...and deepen slightly as it
and the upper low track northeast through northeast Iowa the
remainder of the afternoon. There is some uncertainty as to how
rapid the system will develop...the best track...and expected
precipitation shield but the consensus is for a fall cyclone with def
zone precipitation northwest of low and areas of thunder southeast of
system on Thursday. The southeast may briefly get into the warm
sector Thursday afternoon and we have been included in a slight
risk for severe weather in the far southeast but window of
opportunity looks fairly limited for any severe weather. For
now...will probably hang on to similar solution as last night with
generally high pop event across the forecast area tomorrow.
Precipitable water will increase to about 1 to 1.5 inches by
Thursday afternoon southeast...but progressive nature of the
system should keep rainfall totals managable with widespread heavy
rainfall totals not being much of an issue...though some quick
downpours may bring 1 to 2 inch rains during the afternoon
southeast. Once again...much colder on Friday but some
differences on how cold to go. Newest 00z Gem paints a November
scene on Friday with highs only in the 40s...and increasingly
blustery northwest winds. It also deepens the surface low considerably and
mainly east of the area as a secondary h500 low drops south into
the large scale trough Friday night. H850 temperatures Friday hit -2 to
-4c by 00z Sat. The Euro is generating h850 temperatures of 0 to -2c by
00z Saturday with the cold core low dropping quickly south as
well. Both solutions suggest highs in the 40s to lower 50s Friday
with partly sunny skies early giving quickly to cloudy skies and
showers developing into the afternoon hours. The cold pool aloft
will continue to promote shower chances late Friday afternoon and
evening over the region. Other models are not far behind this
Gem/Euro scenario. The other wrinkle that has developed is that
the shortwave accompanying the cold core low Friday evening has a
very strong jetmax associated with it. Lapse rates steepen quickly
toward 00z Sat and strong mixing is anticipated late afternoon
through the evening hours. Solutions differ somewhat...but with
strong mixing...headlines for wind now look much more likely
across much of the area. The GFS suggests warning criteria
winds...while the Euro suggests middle to upper range advisory
potential. Will need another run or two to settle on details but
will mention in severe weather potential statement and pass along to oncoming shift. Highs
through the weekend have been knocked down and mins Friday
night/Sat morning easily reaching the lower to upper 30s over the
area. Frost will most likely be avoided though...due to the
expected mixing through the night. Saturday expect some clouds and
windy conditions...and a crisp fall day...emphasis crisp. As the
system pulls east on Sunday some warming is anticipated as
thickness rises replace the steep fall of the two previous days.
Another weak clipper is proggred to race through the region Sunday
with a few showers and another shot of cold air Sunday night and
Monday. Highs to recover to near normal by the end of the period
as upper level flow begins to turn more zonal with time.


issued at 643 am CDT Wednesday Oct 1 2014

LIFR/IFR ceilings will continue through much of the morning at
fod/mcw/alo with intermittent MVFR visible from rain. Dsm/otm may see
some brief stints of LIFR ceilings at or above 1000 feet but had lower
confidence with mentioning at this time as looks to be break in the rain
and significant length of time at those two locations. Expecting
a short reprieve this afternoon before fog looks to settle in
across much of the taf area late tonight into Thursday morning.
Introduce MVFR visible/IFR ceilings but likely could see LIFR visible/ceilings at


Dmx watches/warnings/advisories...none.



Short term...podrazik
long term...rev

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