Area Forecast Discussion
Issued by NWS Des Moines, IA

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639
FXUS63 KDMX 221811
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1211 PM CST Sun Jan 22 2017

.UPDATE...
Issued at 1210 PM CST Sun Jan 22 2017

Although plenty of stratus and light fog remains across the
forecast area, only one or two locations is still down to advisory
criteria. With continued slow improvement expected through the
day, the advisory will be allowed to expire at Noon.

&&

.SHORT TERM.../Today through Tonight/
Issued at 345 AM CST Sun Jan 22 2017

09z Water vapor imagery sandwiches Iowa between two shortwaves. The
northern shortwave that impacted us yesterday is traversing
northeastward across the U.P. of Michigan. The second shortwave is
propagating east to southeastward along the Red River Basin.

Fog potential...
Confidence today: Medium-High
Confidence tonight:  Low-medium

Yet another morning contending with fog across much of Iowa. With
temperatures dropping into the 20s in some locations, freezing fog
mention this morning certainly with highlighting.

Difference in this morning versus previous mornings is two different
dense fog areas and generation methods. The area of fog across
northern to northeastern Iowa is advection-driven...similar to the
past few mornings. The fog to the south is more radiationally-
driven. This translates to fg/hz likely across the north most of the
daytime, whereas central to southern IA should merely have bkn ST by
the afternoon as the fog lifts.

Further, have added dz/fzdz to forecast in northern-northwestern CWA.
Bufkit soundings show cloud depths of 4kft-5kft. Paired with lack of
moisture above this cloud layer, drizzle vs rain suggested.

Fog form once again tonight. However, confidence low-medium fcst
soundings showing much less low-level moisture and are struggling to
decouple winds. Granted winds near 5 kts, but as of now, it appears
more patchy fog would be suggested versus widespread dense fog. Any
fog that may form may be of the freezing fog variety as temperatures
look to hover near freezing once again.

.LONG TERM.../Monday through Saturday/
Issued at 345 AM CST Sun Jan 22 2017

Initially some fog concerns tonight and again late Monday night,
otherwise main focus is on the system for Tuesday into Wednesday.
Brief upper ridging to be in place Monday with another strong trough
pushing ashore into the Pacific Northwest. Sfc ridge axis to move
through the state Monday with dry conditions expected. Southerly
return flow to set up Monday night as a large area of low pressure
develops across the western high plains. Low level moisture moving
in ahead of the Tuesday system may allow some additional fog
development late Monday night across the south/west. Otherwise
moisture to deepen in advance of that low associated with the Pac NW
trough that is digging through the intermountain west Monday night.
The trough continues to push east digging into the central US into
late Tuesday. GFS/EC close off the upper low over Iowa by Tuesday
evening, with the sfc low lifting into SE Iowa. Precipitation
expected initially with WAA across the cwa and strong moisture
advection Tuesday. Trowal feature sets up across NW/NC IA late
Tuesday, with deformation zone precip expected to continue across
the state into Wednesday. GFS/EC have been consistent bringing the
energy out in one piece and closing off the system, with the latest
NAM trying to bring it through the region in pieces with more of a
progressive open wave. This solution keeps the bulk of the precip
chances across southern IA Tuesday then into northern IA Tuesday
night with the second wave dropping through the state. This appears
to be more of an outlier solution, so have trended the grids more
toward the EC/GFS with better continuity. Precip trends Tuesday with
the warmer air in place with mainly be a rain/snow mix north with
rain further south, and as the colder air moves in Tuesday night
into Wednesday a changeover to all snow is expected. Therefore
anticipate snowfall amounts of around a trace to an inch far south,
1-3 inches central and around 3+ inches far north.

This system moves quickly east with another weak wave of energy
digging southward into the region keeping cyclonic flow aloft.
Therefore could still see some very light snow chances across the
northern CWA into Thursday. Colder air also to be in place through
the end of the week with h85 temps to be around -10C into the end of
the period with northwest upper level flow pattern expected into the
weekend as well.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1210 PM CST Sun Jan 22 2017

Widespread fog and stratus continues to affect central Iowa with
varied conditions ranging from MVFR to LIFR. Visibility trends
will slowly improve into the afternoon, but persistent low stratus
will likely result in little overall category change. Thus expect
IFR or less conditions through much of the valid period.

&&

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

&&

$$

UPDATE...Small
SHORT TERM...Kotenberg
LONG TERM...Beerends
AVIATION...Small



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