National Weather Service Raw Text Product

658 
FXUS63 KDMX 081747
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1147 AM CST Thu Mar 8 2018

.SHORT TERM.../Today through Tonight/
Issued at 323 AM CST Thu Mar 8 2018

Upper low pressure which moved across the western 
Great Lakes region on Wednesday will be moving east towards 
Pennsylvania today. Despite the transition to the east, upper 
northwest flow will persist today. At the surface, a ridge of high 
pressure will move into Iowa today. Thermal profiles will remain 
near to slightly warmer than Wednesday and temperatures will remain 
seasonably cold with highs in the mid to upper 20s north to the mid 
to upper 30s south. Generally mostly sunny skies to start the day 
except for the far southwest where a few clouds are passing through. 
Cirrus overtopping the surface ridge may arrive by this afternoon. 

The forecast area will remain dry through this evening. The 
combination of a short wave passing across Minnesota and Wisconsin 
and warm advection developing in the wake of the departing ridge may 
result in light snow developing across South Dakota and approaching 
northwest Iowa by late tonight. Have kept the the forecast dry 
with any precipitation chances remaining to the northwest. 

.LONG TERM.../Friday through Wednesday/
Issued at 323 AM CST Thu Mar 8 2018

Bottom Line up Front... 
Sensible weather impacts confined to this weekend via a 
potentially low-impact wintry weather system. General trend 
towards above normal temperatures next week.

Saturday through Sunday...
An upper low currently located off the Pacific Coast looks to 
come onshore today, riding along the U.S./Canada border and 
dropping down through the Plains Region Saturday into Sunday. 
Models initialize well with this low, but are somewhat struggling 
with run-to-run consistency of its track on the leeward side of 
the Rockies... dropping confidence to medium/low-medium. 

Continued from the previous AFD, the GFS has been the most bullish 
with this system as it develops a closed sfc low which it propagates 
through Nebraska and into western Missouri Saturday into Sunday 
morning. The 00z Thu ECMWF/00z NAM tend to have a more flatter 
wave/inverted trough versus the closed sfc low of the GFS. At this 
point, find it difficult to back either of the general solution 
camps, so have gone with a blend. Obviously, if the GFS solution 
pans out, snowfall amounts and subsequent impacts will have to be 
increased.

Forecast sounding analysis keeps low-level cloud thicknesses around 
3kft and under through around 00z Sun. Therefore have gone with 
drizzle for ptype as temps into the 40s across most of the CWA. 
Lower levels gradually begin to Saturday evening into Saturday 
night. Temperatures also fall to near to below freezing Saturday 
night. GFS and NAM sounding profiles drop to below-freezing aloft, 
with no warm nose aloft. With CAA continuing, warm nose aloft to not 
develop Sunday, so keeping with either rain or snow mix and have 
nixed sleet/freezing rain mention. Even with the more ambitious 
general forcing with the GFS, profile does not saturate very much 
per the GFS soundings. So finding it plausible to begin a downward 
trend to QPF.... and subsequently any snow accumulation. 

Impact-wise, impacts from this system appear to be minimal at this 
time. By Sunday late morning/early afternoon, temperatures should be 
near to above freezing across most of the CWA. This means any snow 
that may have accumulated should melt off of most roadways and 
surfaces. Impacts will likely arise from slippery surfaces and 
reduced visibility confined to the time period of Saturday night 
through Sunday morning.

Monday and Beyond...
Behind this weekend's system, long-range models have been 
extremely consistent in blasting a 1035mb sfc high pressure 
through the upper Midwest. Slight forecast changes have been to 
slow the propagation of this high. Yesterday's 00z runs had the 
high near western Iowa by 06z Tue. Today's 00z runs have the high 
near western Iowa by 06z Wed. So, have lowered Wednesday and 
Thursday highs in anticipation of WAA being delayed until Thu-Fri.
By late-week, as this high propagates east of the CWA, 850mb 
temps of +10C may make it to Iowa... which would likely translate 
to highs in the 50s and probably 60s across Iowa.

&&

.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1147 AM CST Thu Mar 8 2018

Mainly VFR conditions expected throughout the TAF period. Have a
SCT MVFR CU deck currently at KOTM and KDSM and could see this 
become a CIG this afternoon, but it also may lift to low VFR as it
does. Otherwise some mid/high clouds moving in late tonight into
early Friday. Northwesterly winds becoming easterly through the
period. 

&&

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

&&

$$

SHORT TERM...Donavon
LONG TERM...Kotenberg
AVIATION...Beerends