Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 192146
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
346 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
situation.

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 18Z TAFS through 18Z Friday afternoon/
Issued at 1148 AM CST Thu Jan 19 2017

Main concern will continue to be cigs and fog. Some improvement
continues over the east/north as -ra is developing with the weak
short wave moving into the area. Tonight periods of -dz/--ra will
be possible east while fog becomes more widespread over all of the
area. Likely to see 1/4sm or less along with LIFR/VLIFR cigs aft
02-05z. Will monitor trends over the south as fog from MO is
beginning to spread north once again with some advection fog
possibly arriving sooner. /rev


&&

Dense Fog Advisory from 8 PM this evening to 10 AM CST Friday
for IAZ004>007-015>017-023>028-033>039-044>050-057>062.

Dense Fog Advisory until 10 AM CST Friday for IAZ070>075-081>086-
092>097.

&&

$$

SHORT TERM...REV
LONG TERM...Donavon
AVIATION...REV


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