Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Des Moines Iowa
1144 PM CST Friday Dec 26 2014

issued at 924 PM CST Friday Dec 26 2014

A band of snow developed late this evening stretching from
northern Wright County up across Cerro Gordo and Worth
counties...producing a quick half inch to an inch of snowfall.
While this band is currently exiting the area...the additional
snowfall expected later tonight brings storm total amounts up into
the 2 to 4 inch range across Hancock/Cerro Gordo/Worth...thus
those three counties have been added to the ongoing advisory.


Short term /tonight/...
issued at 342 PM CST Friday Dec 26 2014

Upper level wave currently lifting out of The Four Corners region
and into the southwestern High Plains. System will quickly lift
northeastward through the state tonight...with the associated
surface low tracking across southeastern Iowa and into southern WI by 12z
Saturday. Inverted trough axis/cold frontal boundary currently
stretching across the far eastern/southeastern County Warning Area and should push
through entire County Warning Area by early evening. Isentropic lift to increase
across the west central to northwest half of the County Warning Area over the next
few hours...with low level saturation deepening. Initially little
ice introduction across much of the area with the middle levels fairly have potential for drizzle or freezing drizzle. Areas north
of Highway 30 and west of I-35 have the best potential for seeing the
light fzdz prior to a changeover to snow. Soundings quickly saturate
the middle levels by middle evening in the area northern/west central County Warning Area
where fzdz was more likely allowing for precipitation to change over to
snow at this time. As the wave ejects northeastward...the snow is
expected to intensify with some weak instability noted aloft by late
evening into the overnight some banding is expected with
the snowfall. High snowfall ratios are not expected as the lift
never really lines up well with the have kept ratios in the
10 to 12 to 1 range with a bit higher ratios possible as the snow is
tapering off and drier air moves into the state. Cross-sections
continue to show the chance for some elevated instability across the
southern County Warning Area toward middle/late evening with the potential for light
rain in that area. Hi-res runs hinting at some showery type precipitation
in that area as have increased probability of precipitation across the south for
this evening with light rain too.

Regarding snow amounts...have kept totals similar with with the
majority of the northwest half expected to see around 2 to 4 inches
of snow. Will expand the advisory a few counties on the southwest
side of the advisory for slightly higher snow amounts around 2-3
inches and potential for the fzdz early on. Otherwise highest snow
amounts still expected across the far northwest and along the Minnesota

Long term /Saturday through Friday/...
issued at 342 PM CST Friday Dec 26 2014

Precipitation will continue into the early portion of Saturday.
Light snow will be ongoing across the north however a lack of ice
introduction south of Highway 30 angling up to just south of
Waterloo. Therefore...the precipitation type south of this region
may switch to fzdz/dz pending surface temperatures. The
precipitation will shift quickly northeast between 9 am and noon
with the afternoon dry. Warm advection will set back into to Iowa
Saturday night through early Sunday which will keep temperatures
seasonal through Sunday. A cold front will already be entering
northwest Iowa by late Sunday. Currently have Sunday dry however
moisture will be deepening over northern Iowa by middle to late
afternoon Sunday as a short wave approaches from the west. Light
snow is possible Sunday night and Monday over central and northern
Iowa. Any accumulations will be an inch or less. Colder air will
settle south through Iowa through the day on Monday with falling
temperatures by the afternoon. Monday night will be cold with lows
below zero forecast over northern Iowa. High temperatures Tuesday
will be the coldest through the period with highs in the single
digits north to teens south.

The remainder of the extended will feature a large upper level low
over Hudson Bay while a cut off upper low develops over the
southwest Continental U.S.. this pattern will keep the area mostly dry
through the extended. The influence of the Hudson Bay low will
expand toward the end of the period and will help push another
system south along the West Coast. This will dislodge the cut off
low and begin to send it east toward Friday. This system could be
the next weather maker for the Midwest just beyond the extended


issued at 1144 PM CST Friday Dec 26 2014

As expected IFR or lower conditions have been prevalent at
fod/mcw/dsm tonight...however the eastern edge of the low ceilings has
held steady just to the west of alo/otm where heights have been
MVFR. Still expect the IFR ceilings to move eastward later tonight as
the flow switches to more northwest...but have had to delay this
transition a couple of times already. Meanwhile -dz/fzdz and snow
have spread across much of the area as anticipated...and will
persist until clearing out around/after sunrise. On Saturday ceilings
will lift then probably break up late in the day...but given
recent persistence have held off on a late group to go from broken to
scattered-few and will leave this to the 12z taf issuance.


Dmx watches/warnings/advisories...
Winter Weather Advisory until 9 am CST Saturday for Cerro Gordo-
Crawford-Emmet-Hancock-Kossuth-Palo Alto-Pocahontas-SAC-



short term...beerends
long term...donavon

National Weather Service Glossary of Abbreviations