Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191127

Area Forecast Discussion
National Weather Service Des Moines IA
527 AM CST Sun Feb 19 2017

.SHORT TERM.../Today through Tonight/
Issued at 300 AM CST Sun Feb 19 2017

A dense fog bank over north central and northeastern Iowa should
slowly erode this morning, dissipating by a couple of hours after
sunrise. No changes to the advisory are being made at this time, but
it is expected that over the next several hours we may begin
canceling a few counties at a time from southwest to northeast as
the fog bank erodes in that direction.

After the fog is gone, it will be another unseasonably warm, dry and
quiet day. Forecast highs are once again in the lower 70s across
southern Iowa with record or near record readings expected areawide.
Despite modest southeast breezes, the dry conditions and warm
temperatures will support an elevated fire danger once again, and
will highlight this in the appropriate products.

Late tonight an approaching trough/low pressure system will spread
showers and a few thunderstorms into our forecast are from the
west/southwest. Latest prognostic guidance shows that precipitation
will not begin in our area until after midnight, and possibly not
until around 3 or 4 am, so have trended POP timing in that direction.

.LONG TERM.../Monday through Saturday/
Issued at 300 AM CST Sun Feb 19 2017

Monday through Wednesday...Confidence High.  First in a series of
higher amplitude short waves this week will impact the region
through Monday.  Main H850 moisture plume will arrive into area by
12z over the west. Water vapor imagery tonight again shows strong
flow coming across the Pacific and southwest with the storm pulling
moisture from both the Pacific and eventually Gulf as it crosses the
mid Mississippi River Valley. Precipitable water rises to 1.25 to
1.35 inches...record levels for this time of the year and up to 400%
of normal. Though moisture will be ample...instability will be
marginal through the event with only isolated to scattered thunderstorms
expected during Monday. With a rather fast moving wave expected...brief
heavy rain with iso to sct thunder is expected. Rainfall totals may
approach a third to half inch over the east as morning and afternoon
periods of rain move through. Though Monday will remain warm...clouds
and showers will likely cap highs in the mid to upper 60s south
and lower 60s north. Record highs will again be in jeopardy due to
a generous start to the day with overnight mins in the 50s. With
the quick passing wave exiting the region Monday evening...both
the GFS and Euro suggest weak thermal ridging and another push of
warm air will move into Iowa Tuesday. H850 temperatures once
again warm to 11 to 13C over the area by afternoon with highs well
into the 60s to lower/mid 70s south. Both models also show the
warmest air arrives over the region during the overnight hours
Tuesday night with another warm day ahead on Wednesday. Records
are again possible into the mid week with highs again in the 60s
to lower 70s Wednesday. By mid to late day Wednesday a weak trough
passes southeast of the region. This is the beginning of the
change toward colder weather as another strong system arrives by
Thursday into Friday over the region.

Wednesday Night through Saturday...Confidence Medium.  Beginning
Wednesday night more clouds are expected to signal the arrival of
the first wave of moisture.  A warm front will be forming just south
of the state across Northern Missouri along with another upper level
boundary over northern Iowa. With isentropic lift increasing across
both boundaries...some light showers will increase in coverage on
Thursday over the region. Guidance temperatures are currently in the
lower 40s north and upper 50s far south. Depending on the onset of
light rain...the south may need some downward adjustment due to both
clouds...light precipitation and expected increasing northeast surface
winds. By this time an area of low pressure crossing the Rockies will
consolidate over Kansas and deepen as it moves northeast into Iowa.
The GFS/Euro differ slightly with regard to storm track with the GFS
slightly farther south and not as deep as the Euro. There is also
a more pronounced dry slot over southern Iowa with the Euro run versus
the GFS. In either case some isolated to scattered thunder will be
possible over the southeast or east while rain/snow changing to snow
will become more likely over the northwest...then gradually changing
over everywhere on Friday as the storm departs. In all features...the
Euro is significantly deeper than the GFS with this system and also
farther northwest. Both models are generating strong wind fields
on the north/northwest side of the wherever snow does and visibility will be impacted quite a bit. Both
models suggest ample moisture output...with 1 to 1.25 qpf projected
at this point in the northwest deformation axis precipitation band.
Temperatures will be somewhat problematic with this system as a
wide range of highs may occur Friday...with readings in the upper
20s/lower 30s northwest to the upper 40s southeast...falling throughout
the day. With a trending signal toward a stronger winter storm
potential...will continue to slowly ramp wording in the hazardous
wx outlook...but any attempt at details at this point bears discretion
since there is plenty of uncertainty regarding storm track...timing
of any mix to changeover to snow and extent of wind magnitude and
coverage. Overall temperatures trends remain intact by weeks end...
with both the Euro and GFS advertising a shift toward northerly
flow aloft and colder heights/H850 temperatures building into the
Northern and Central Plains. Highs will fall back toward seasonal
norms with highs in the 30s to 40s.


.AVIATION.../For the 12Z TAFS through 12Z Monday morning/
Issued at 527 AM CST Sun Feb 19 2017

VLIFR fog will affect MCW and ALO for the next two or three hours
before dissipating. Otherwise, VFR conditions are anticipated for
the rest of today and most of tonight. After midnight tonight low
clouds and showers will move into the area from the west and
southwest. However, these will not reach FOD/DSM until right
around or just before the end of the current TAF period, so they
have not yet been included. It is anticipated that these will be
added to the 18Z TAF package.


Dense Fog Advisory until 9 AM CST this morning for IAZ004>007-



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