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Area forecast discussion 
National Weather Service Des Moines Iowa
638 am CDT Wed Jul 27 2016

Short term.../today/
issued at 305 am CDT Wed Jul 27 2016

Aloft there is a warm front at h850 that crosses western Nebraska
and snakes east to North Platte then due south to near Oklahoma
City. The area of thunderstorms has been tracking both near a
ribbon of moisture along that boundary with the lessening
expansion to the east. Over Minnesota the shortwave forecast to
drop south later today will eventually enhance additional
thunderstorm development along the leading edge of the upper level
forcing. Along with a weak trough at the surface...this area of
thunderstorms should reach northern Iowa in the early to mid
afternoon then slowly drift south into the evening hours reaching
the i80 corridor by about 00z.

Between these two areas of precipitation...sunshine will mix with
cloud cover today bringing a mix of partly cloudy skies and
filtered sunshine across the south and southeast.

A lower confidence forecast is in store today. Somewhat
challenging due to multiple factors. Though the diminishing mesoscale convective vortex
over eastern Nebraska should weaken further as it encounters a
more stable air and limited moisture over western and central Iowa
early this morning...the cloud deck may survive long enough to
create a few sprinkles or light showers to briefly require slight
pop over the west. For now will monitor and update if the area
holds together prior to 7 am. Though none of the convective
allowing models nor the synoptic models are handling the current
convection well early today...the newest esrl hrrr now suggests
the mesoscale convective vortex may strengthen by early afternoon over central Iowa in
response to increasing instability over central/southern Iowa. If
this is correct... afternoon highs from central to southern areas
would need a slight downward modification by late morning and pop
would need increasing. For now will go with climatology which
would suggest a weakening complex of storms this morning and let
the day crew reanalyze the trends that develop by late morning.
Will maintain highs in the lower 80s north and mid to upper 80s
across the south. Winds will be light due to the lack of
forcing/synoptic systems...which is also the reason the mesoscale
will be driving todays forecast.

Long term.../tonight through Tuesday/
issued at 305 am CDT Wed Jul 27 2016

Main forecast concerns include pops through much of the
period...especially with the system early in the period. In
addition...return to Summer-like heat next week.

At the beginning of the long term period...convection is expected
to be underway. Surface front will slide southeast across the County Warning Area.
0-6km shear parameters are not favorable for organized
convection...with the best chance for any stronger storms being in
the vicinity of the front where convergence will be greatest. Main
threats would include winds and moderate to heavy rain. Having
said that...models have backed off considerably on pops
tonight...and have followed this trend. Quantitative precipitation forecast values are lower as
well...reflecting the lower probability of widespread organized
convection.

Pops increase on Thursday from tonight...as secondary shortwave
drops southeast through the upper-level flow to help intensify the
surface closed low tracking northeast along the surface front from
northeast MO into northeast Illinois.

Despite the surface low and frontal system to continue tracking
away the County Warning Area on Friday...have kept pops going. Additional
shortwave will provide for unsettled weather conditions. Thursday
or Friday will see the lowest Max temperatures of the long term
period for the County Warning Area...with the west seeing it on Thursday and the
east on Friday...due to combination of cold air advection...cloud cover and
precip. Additional shortwave on Saturday will bring more lower-end
rain showers/thunderstorms and rain chances. Another relatively cool day is
expected...although a couple degrees higher than on Friday.

Upper-level heights begin rising on Sunday and continue into
Monday as the western U.S. Ridge migrates toward the County Warning Area. Have
continued lower-end pops both days due to presence of additional
weak shortwaves. Having said that...am concerned that pops on both
of these days especially may be a little on the high side.

From Tuesday afternoon into Wednesday...the surface warm front
will lift northeast across the County Warning Area. Aside from this evening and
tonight...Tuesday night will provide the best chances for
organized convection. Another shortwave will drop southeast along
the southern fringe of the northward-retreating westerlies.
Theta-E advection along with strengthening low level jet will provide
enough moisture for thunderstorms and rain potential. At this time the actual severe
weather potential is uncertain but will bear watching.

With the ridge closer to the County Warning Area on Tuesday and
Wednesday...Summer-like heat will return. Highs behind the warm
front are progged to be in the lower to middle 90s. Humidity
levels will return to levels typical of early August...with
dewpoints generally in the upper 60s to middle 70s. Those
conditions would yield heat index values as warm as the middle to
upper 90s...possibly lower 100s.

&&

Aviation.../for the 12z tafs through 12z Thursday morning/
issued at 638 am CDT Wed Jul 27 2016

Main concern early today is remaining br/fog which will burn off
quickly. Remnant mesoscale convective vortex over eastern Nebraska may develop iso/sct
convection over central sections by 16-18z though confidence in
that occurrence remains low. Weak boundary over Minnesota will spread iso
to sct convection across north and central through 28/05z. Then
between 06-12z cold air advection expected to result in lowering
stratus to MVFR possibly IFR by 12z across north/central sites.
/Rev

&&

Dmx watches/warnings/advisories...
none.
&&

$$

Short term...rev
long term...zogg
aviation...rev

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