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Area forecast discussion 
National Weather Service Des Moines Iowa
1148 am CST Thursday Nov 26 2015

Short term /today/...
issued at 335 am CST Thursday Nov 26 2015

Challenging forecast for today with a wintry mix of snow and
freezing rain in store for much of the northern and western County Warning Area
during the period. Surface cold frontal boundary currently along a
line from Creston to Waterloo will only gradually sink southeastward
today and exit the southeast County Warning Area by around 21z...though the 850 mb
boundary will still be offset by over 100 miles to the northwest.
Cold air advection ahead of a building high pressure system is already taking place
across northern/northwest Iowa with temperatures below freezing from
Estherville on west and north. Temperatures in the warm layer aloft
initially will be in the +4 to +5 c range...cooling off as the cold air advection

Between a synoptic blocking pattern taking shape across the
Continental U.S....the NAM bufr profiles closest to radiosonde observation soundings in the cold
air...and some hints that models in general are slightly
underestimating temperatures in the warm layer aloft...leaned towards a
blend of the slower/warmer NAM/rap for determining p-type locations
and timing. The threat for the highest freezing rain amounts of over
two tenths of an inch will be across the west central and southwest
County Warning Area this afternoon. As has been alluded to in previous
discussions...there remains some uncertainty about how quickly ice
will accumulate on the ground and roads. Looking upstream...pavement
temperatures have already cooled below freezing...yet output from the metropolitan
Road model shows that the warmer ground temperatures further south may
limit ice accrual. However...trees and power lines should begin
accumulating ice fairly quickly after onset and the threat of downed
branches and power lines remains with the winds increasing from the
north during the day.

As the profiles cool throughout the day...precipitation will transition to
snow from northwest to southeast...with the transition line
extending from Audubon to Hampton at the end of the period. Modest
lift in the dgz should be enough to kick out a quick one to two
inches of snow across the northwest. The southeast half of the County Warning Area
will see widespread rain throughout the day with amounts of over an
inch possible in these areas as northward moisture transport
increases and fog forcing intensifies. While the ground is not
frozen...the lack of vegetation means that localized flooding may be
a concern in some locations.

Long term /tonight through Wednesday/...
issued at 335 am CST Thursday Nov 26 2015

Main concerns are timing for the remainder of the storm tonight and
then the systems on the weekend/next week. Zone of freezing rain
will move southeast into the evening hours. Changeover will make it
to a southwest to northeast line between 00 and 03z just northwest
of Polk County. Complicated mix of precipitation into tonight with
light snow over the north and northeast following the ending of the
freezing rain but little in the southwest. Thus...most of the area
will end up with winter weather advisories while the watch area...
extending south toward the Interstate a Freezing Rain Advisory.
Models differ slightly on the advance of the cold air...but overall
good consistency with surrounding offices on on mix of ptypes. For
now have left the far southeast out of any headlines...due to the
lighter amounts of freezing precipitation expected there with little
or no snow following. One challenge that is still problematic will
be the ground temperatures/Road temperatures and saturated soils from all
the rain today. This will again tend to lower the ice accumulate amounts
at the surface though any elevated or exposed surfaces will likely see
on average a bit more. This yields a lot of uncertainty with regard
to an absolute ice accumulation forecast for this event. Over the
southwest...we may end up near warning criteria in a few spots if
the cold air settles into the area a bit faster today. Will have to
evaluate later today...but certainly in some regard a higher end
advisory event over the west/southwest than most advisories. Temperatures
tonight will fall to the teens northwest and into the 30s in the
southeast. Friday will see some recovery...but not much as clouds
linger through the afternoon. By late Saturday into Sunday another
piece of energy arrives from the west bringing another chance of
measurable snow/frozen mix into the night hours. Though
uncertainties are still ongoing into early next week...we have
another chance at rain/snow into Monday/Tuesday. Will need to
evaluate that in coming days...todays focus has been coordination
of the current event. Temperatures remain slightly below normal for most of
the upcoming week.


issued at 1143 am CST Thursday Nov 26 2015

Conditions will be primarily MVFR and IFR at sites through period
with wintry precipitation affecting sites. Band of rn will
continue to push south changing to snow...with a period of freezing rain/ice pellets
possible at sites...especially northern sites kfod/kmcw. With
falling precipitation visibilities and ceilings will be reduced
to IFR or LIFR at times. Winds will be from the north and will
increase through period...with gusts to 25kts possible. Ceilings
will improve near 12z to MVFR...or to VFR beyond sites
as system pulls south though strong northerly winds will remain.


issued at 335 am CST Thursday Nov 25 2015

Still some potential for minor river flooding southeast over the
weekend...following the rainfall today. Given the previous snow melt
north and the combination of additional rainfall today and tonight.


Dmx watches/warnings/advisories...
Winter Weather Advisory from 6 PM this evening to 6 am CST
Friday for Black Hawk-Dallas-Grundy-Marshall-Polk-story-Tama.

Freezing Rain Advisory until midnight CST tonight for Adair-

Winter Weather Advisory until 9 PM CST this evening for Calhoun-
Carroll-Crawford-Emmet-Hancock-Humboldt-Kossuth-Palo Alto-

Winter Weather Advisory until 6 am CST Friday for Boone-Bremer-
Butler-Cerro Gordo-Franklin-Greene-Hamilton-Hardin-Webster-

Freezing Rain Advisory from 6 PM this evening to 6 am CST Friday
for Adams-Clarke-Decatur-Madison-Ringgold-Taylor-Union.



Short term...skow
long term...rev

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