National Weather Service Raw Text Product

945 
FXUS63 KDMX 170959
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
359 AM CST Wed Jan 17 2018

.SHORT TERM.../Today through Tonight/
Issued at 358 AM CST Wed Jan 17 2018

There is little weather of concern in this period beyond 
temperature trends. The long wave trough will continue to depart 
with warm advection in place throughout the day. Moisture will be 
very limited however so there will be little in the way of cloud 
cover. The warm advection will wane somewhat into tonight however 
with the H85/H7 thermal ridge crossing the Plains into IA. 
Attention will turn to the current compact short wave/PV anomaly 
as it skirts the MN/Canada border later tonight. This will have 
little effect this far south however keeping skies mostly clear in
our dry airmass.

Current 09z obs show temps ranging from just above zero to the 
single digits below, but with the surface ridge moving through 
winds are fairly light. A few spots are showing wind chills near 
advisory criteria but this should be brief and not too impactful 
considering the light wind so no additional wind chill advisories 
this morning. Examination of soundings suggests highs today could 
rebound more than recently with the warm advection pushing highs 
closer to normal, into the lower to middle 20s.

.LONG TERM.../Thursday through Tuesday/
Issued at 358 AM CST Wed Jan 17 2018

The initial but secondary concern in this period will be temp 
trends as we continue to warm, but the primary impact will be the 
large storm anticipated for the weekend. At onset, the aforementioned
system will be passing through the Great Lakes with little impact
here besides ushering in additional warm advection in its wake. 
Surface flow will change little through the work week with highs 
pushing back to or even just above normal by Thursday. The bigger 
question will be how warm can we get by Friday. The 00z NAM snow 
depth initialization was fairly good, but it changes little into 
Friday, which seems unlikely, especially south. Considering the 
persistent warm advection and favorable trajectories it would seem
we could erode more of the inversion than depicted in soundings 
by that time, especially in the lesser snow depths south and west.
Have not gone as aggressive of what MOS depicts, but have warmed 
temps further through the 40s. It is often difficult to get beyond
mid 40s for highs with at least several inches of snow depth 
keeping readings there north, but 45-50 would seem attainable 
eroding at least a third of the inversion south and west. Would 
not be surprised to see some 50s depending on the degree of snow 
melt Thursday.

Looking into the weekend there continues to be high confidence 
and good agreement in larger scale features and some of the 
sensible weather. The ECMWF/EPS and GFS/GEFS all have similar 
depictions of a deepening surface low advancing from the Plains 
into Great Lakes Sunday into late Monday. There are some timing 
and track differences at this time range of course which will 
diminish confidence in details, but some higher confidence broader
things to key on at this point include strong winds as the system
exits, likely stronger than currently depicted in the forecast 
until timing and location can be better defined, and the potential
for accumulating, wind blow snow over some part of northwest 
Iowa.

Dropping down to medium confidence will be a period of convection
south and east in the warm sector, which has yet to be introduced
until timing confidence increases, and likely drizzle or lighter 
precip in the shallow moisture along and south of the triple point
track Saturday Night. Confidence decreases even further with 
regard to localized precip types early next week with surface 
temps and the location and extent of the potent dry slot all still
in question. Both of these will have an appreciable impact on 
precip type and magnitude and will not be better defined until the
coming days, if then. The current forecast only has rain or snow 
depicted, but all kinds of mixed wintry precip such as drizzle, 
freezing drizzle, and sleet are on the table wherever the 
transition zone lays out depending on the dry slot and ice 
introduction as well as warm layer and surface temps. Confidence 
may remain low with this system even right up to game time because
of all these moving parts.

PoPs will decrease later Monday as the system exits and will be 
followed by relatively benign NW flow aloft. The source region 
will have sufficient westerly component to keep our temps close to
normal into early next week. There are some token low end PoPs to
end the period, but confidence is low in model agreement and 
anything that does occur does not look too significant at this 
time.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1122 PM CST Tue Jan 16 2018

VFR conditions are forecast through the TAF period. Southwest
breezes will pick up a bit during the day on Wednesday, then
diminish again with sunset. No precipitation or obscurations
anticipated.

&&

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

&&

$$

SHORT TERM...Small
LONG TERM...Small
AVIATION...Lee