Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 151757
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1157 AM CST Wed Nov 15 2017

...Updated for 18z Aviation Discussion and Near Term Weather
Trends...

.UPDATE...
Issued at 1156 AM CST Wed Nov 15 2017

Stratus has moved over northern Iowa mainly north of Highway 20 at
this time and continues to move slowly to the southeast. GOES-16
imagery shows that there are breaks in the clouds, especially on
the leading edge and on the western edge. Expect the broken to
overcast sky cover to sink farther into the area primarily north
and east of a line roughly from Spencer to Fort Dodge to Ames to
Oskaloosa with some more scattered or few clouds a bit to the
southwest of this line. Temperatures/dewpoints were also adjusted
over the north for the non-diurnal trend that has been observed
at Estherville, Algona, and Mason City as the secondary cold front
swings into the state. Otherwise, routine update with the
remainder of the forecast on track.

&&

.SHORT TERM.../Today/
Issued at 308 AM CST Wed Nov 15 2017

Front has pushed into the far northwestern portion of the forecast
area and will continue to drop southeastward through the morning
hours. Currently have some scattered showers across the far
east/southeast with drizzle still in other areas ahead of the front.
Any showers/drizzle should push east/southeast of the forecast area
in the next few hours as the front continues to drop through the
state. CAA to move in behind the front, with low level RH progs from
the NAM handling current areas of low clouds well. Therefore low
cloud bank behind the front across far NW IA into MN is expected to
waiver around near the IA/MN border this morning and then spread
ESEward across the north/northeastern forecast area today. With the
lingering cloud cover and CAA, expect temperatures to end up a bit
cooler than previously anticipated especially across the
north/northeast. Stronger winds in the lower levels behind the front
today, with BUFKIT showing 25-30kts at the top of the mixed layer
through the day. Therefore expect winds to pick up into the breezy
to windy category today behind the front, with gusts to 30 mph
possible. May even see a very brief, isolated advisory criteria
report with winds sustained around 30 mph with higher gusts.

.LONG TERM.../Tonight through Tuesday/
Issued at 308 AM CST Wed Nov 15 2017

Area of low pressure will continue to move east across the Great
Lakes tonight. Another short wave will wrap around the back side
of this low this evening. Iowa will be on the subsidence side of
this system. The main impacts from this system will be breezy
winds and another punch of cold advection across northeast Iowa.
High pressure will be settling over Iowa after midnight and will
diminish the winds. A few patches of high level cirrus may arrive
late. Overnight lows by Thursday morning will be in the low to mid
20s. The area of high pressure will move east on Thursday,
however the southeast flow through the day will still be
originating from the surface high pressure and this will keep high
temperatures in the upper 30s northeast to mid to upper 40s
southwest despite ongoing warm advection aloft.

The primary forecast challenge remains the system to impact Iowa
Friday into Saturday. This system is currently a close low
pressure over the Pacific, just off the coast of the Pacific
Northwest. The system will begin to eject out as an open wave on
Thursday then race eastward Friday and Saturday. Lee Side
cyclogenesis will become organized by Thursday night into early
from into western Kansas while the area of high pressure settles
into the southeast CONUS. This will lead to good southerly flow
lifting north from the Gulf of Mexico. Expect another surge of
stratus and drizzle to lift rapidly north late Thursday night into
Friday. After reviewing proximity soundings and moisture cross
sections, have begun to lower high temperatures on Friday due to
expected widespread stratus. Similar to Wednesday, high
temperatures will be reliant and low level moisture advection and
dew point increases, with temperatures remaining within 2-3
degrees of these values. The GFS is trying to bring some clearing
to western IA by the afternoon but given November cloud
climatology and more reasonable ECMWF/NAM prolonged stratus
solutions, the lowered highs probably will need to be lowered a
few more degrees.

General consensus will shift the low pressure rapidly east Kansas
and northern Missouri Friday night and will be in the Lake
Superior vicinity by 12z Saturday in large part due to a 150 kt
westerly jet aloft. The surface cold front will move through
Friday night as this occurs and will result in gusty northwest
winds. Still the potential for a period of advisory criteria winds
after midnight Friday night. Areas of rain or drizzle also
possible Friday into Friday evening. Have remove thunder mention.
Again similar to Wednesday, a strong elevated mixed layer should
hold much of the period, limiting instability aloft. A brief
switch over to light snow is possible yet over the north though
drier air arrives shortly after profiles drop below 0C therefore
any snow should have little to no impact.

The remainder of the extended will feature fast moving systems and
generally cool northwest flow with the exception of a ridge
passing by on Monday bringing warmer temperatures before cooler
readings arrive again by Tuesday. Little to no precipitation is
expected through this period.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1156 AM CST Wed Nov 15 2017

Stratus have been moving southeastward this morning into north
central Iowa with MVFR ceilings at KFOD and KMCW and will soon be
over KALO. Gusty winds will also prevail this afternoon at all
the terminals, but by tonight winds will ease and any lingering
clouds will depart as low pressure over the western Great Lakes
moves away and high pressure nudges into the state. Some high
level VFR clouds will begin to arrive tomorrow morning as winds
begin to switch around and come from the southeast.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Ansorge
SHORT TERM...Beerends
LONG TERM...Donavon
AVIATION...Ansorge



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