Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 200542

National Weather Service Des Moines IA
1140 PM CST Thu Jan 19 2017

.SHORT TERM.../Tonight through Friday/
Issued at 343 PM CST Thu Jan 19 2017

Confidence High:  Short wave currently lifting northeast with best
lift/forcing expected to persist into the evening hours over the
east. Elsewhere patchy/areas -dz will likely redevelop as fog
becomes more widespread tonight.  With moisture in place and lack of
any changes in airmass...dense fog is likely to develop over much of
the area tonight. Foggy areas over the south now so will begin the
first portion of the dense fog advisory at 22z this afternoon with
the package.  Hires models pointing toward the west as weak boundary
continues to lift north tonight focusing moisture along and near the
front.  Low clouds...fog...and patchy drizzle likely to persist into
late Friday morning.  Only question is how long to extend an
advisory for fog Friday.  Would expect that widespread fog with
areas of dense fog will last at least until 16z-17z similar to
today. Difference tomorrow is warm air advection may help to
diminish the fog as warmer air finally lifts north with the approach
of the second weak system. For now will keep advisory going to 16z
and let the subsequent shifts trim as needed.

Lows tonight will remain in the mid to upper 30s over the area with
highs tomorrow...based mostly on surface advection...will warm to
the upper 30s north to the mid to upper 40s in the far south by late
day.  As the second wave approaches southwest Iowa late in the
afternoon some light showers may again redevelop in the
south/southwest prior to the main forcing arriving in the
evening/overnight hours.

.LONG TERM.../Friday night through Thursday/
Issued at 343 PM CST Thu Jan 19 2017

Another short wave will follow the southwest flow and lift into
the Iowa Friday night and will bring good kinematic and
thermodynamic forcing across the state. Expect an area of rain to
develop and lift through central Iowa. Sounding profiles mainly
all above freezing below 2000 ft and surface dew points at 35 or
above will keep the precipitation all rain. The bulk of the
precipitation is expected to be done by 12z Saturday. The primary
concern for Saturday is temperatures. Current forecast with highs
generally in the 40s to even a few low 50s southeast may be a bit
generous. Sounding profiles and SREF vsby analysis would suggest
that stratus and fog may linger much of the day over northern
Iowa and possibly farther south. Dew points will rise into 40s
over the eastern half and will provide a relative high floor for
temperatures so while forecast highs may be a bit aggressive,
highs in the 30s and 40s will occur regardless of the stratus

High temperatures Sunday and Monday will remain mild for mid to
late January with highs in the 30s and 40s. The next system to
impact Iowa arrives Tuesday and Wednesday. Descent continuity
among long range guidance with a strong short wave arriving with a
surface low pressure reflection just south of the upper level
system. While there is good continuity, there still is uncertainty
regarding precipitation type. While 850 mb temperatures are below
0C aloft, there remains the potential for a near surface warm
layer that may result in melting. This system will likely have
snow within the deformation axis but the northward extent of the
low level warm nose will have an impact. In addition, considering
this system is still 5 days out, spatial and temporal adjustments
are expected. Once this system does pass, much colder air will
arrive to end the week.


.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1140 PM CST Thu Jan 19 2017

All TAF locations will remain mired in LIFR/IFR stratus and fog with
only slight improvement during the early to mid afternoon period of
Friday. Towards 20/00Z the next shortwave will approach bringing
back lower cigs and increasing chances for precip.  The precip may
actually scour out some of the lower vsbys but cigs will keep
IFR conditions in place.


Dense Fog Advisory until 10 AM CST Friday for IAZ004>007-015>017-



LONG TERM...Donavon
AVIATION...FAB is the U.S. government's official web portal to all federal, state and local government web resources and services.