Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Des Moines Iowa
1139 PM CST Friday Feb 12 2016

Short term /tonight/...
issued at 322 PM CST Friday Feb 12 2016

As Arctic high pressure settles into the state overnight the wind
will gradually diminish through the evening. The combination of
clear or mostly clear skies and diminishing wind with the fresh snow
cover will allow temperatures to plummet into the single digits and teens
below zero. It will not take much wind to create advisory criteria
wind chill values. The current advisory was well placed with the
exception of having to add SAC County.

As the axis of the surface high pressure shifts more towards the
center of the state...winds will begin to come around to a more
southeasterly across the west by 12z.

Long term /Saturday through Friday/...
issued at 322 PM CST Friday Feb 12 2016

Surface high pressure will be over Iowa to begin the period but hints
of the next system will be around with middle level clouds
undercutting the high and moving in from the west. Theta-E
advection will occur through the day and will gradually saturate
the column however the saturation process will take some time with
residual dry air from the high pressure in place. The strongest
forcing arrives Saturday night as an upper level short wave
arrives bringing good kinematic forcing across the state. Snow to
liquid ratios are going to vary throughout the event. A few brief
periods with good dendritic growth while other periods the primary
forcing is occurring at less than optimal temperatures in addition
to periods of dry air trying to wedge into the area. Trends
continue to suggest a 2 to 5 inch snowfall from central to
northern Iowa with little to no accumulations over southwest Iowa
through Sunday morning. Some blowing snow with this events is
likely though southerly winds which will be more associated with
weak warm advection and some weak vertical lift that will dampen
the momentum Transfer of peak mixed layer winds of around 30 kts.
This combined with a lack of a strong pressure gradient that
remains 30 ubars/km or less also will limit stronger wind
potential. Therefore have remained headline free for Saturday
night through Sunday though expect a Winter Weather Advisory will
be warranted with upcoming forecasts.

Warm advection will follow this event on Monday and Tuesday with
highs in the 30s to lower 40s. A cold front will arrive on
Wednesday and will bring a brief cool down with highs back into
the lower 20s across the north. Much warmer to end the weak with
strong warm advection arriving by Thursday. Highs in the 50s
possible over southern Iowa Thursday and Friday and can not
discount a few sites reaching 60 over the far southwest. There is
another chance for snow Monday night and Tuesday morning otherwise
little to no precipitation for the extended.


issued at 1136 PM CST Friday Feb 12 2016

VFR conditions will remain widespread for much of the forecast
despite ceilings increasing late tonight into Saturday. Ceilings
will gradually lower Saturday afternoon into evening as warm
advection intensifies with snow developing in portions of western
and southern Iowa toward the end of the period. Snow development
will lead to MVFR conditions in those areas...mainly near kdsm and
kfod by the end of the period. Surface winds will become light and
variable overnight as surface ridge moves overhead with increasing
southeast winds later Saturday.


Dmx watches/warnings/advisories...
Wind Chill Advisory until 8 am CST Saturday for Black Hawk-Boone-
Bremer-Butler-Calhoun-Cerro Gordo-Emmet-Franklin-Greene-Grundy-
Hamilton-Hancock-Hardin-Humboldt-Kossuth-Marshall-Palo Alto-



Short term...fab
long term...donavon

National Weather Service Glossary of Abbreviations