National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2018-04-17 11:49 UTC


396 
FXUS63 KDMX 171149
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
649 AM CDT Tue Apr 17 2018

.SHORT TERM.../Today through Wednesday Night/
Issued at 332 AM CDT Tue Apr 17 2018

Confidence: Medium

Today will be pleasant compared to later tonight into Wednesday. 
Clouds will be on the increase today ahead of the storm with
cloudy skies tonight. Highs today will recover to the mid to 
upper 30s north and the upper 40s to lower 50s over the south. 
Tonight with the low passing southeast of the region temperatures 
will fall into the upper 20s north and in the mid 30s across the 
south. The freezing line will be near the US 30 corridor. 

Storm still on track to reach Iowa later tonight and bring a quick 
hit of snow/freezing rain/and wind.  Models tonight are tracking 
farther south and colder than earlier runs.  The GFS/Euro/NAM all 
suggest abundant moisture available for snow production across the 
north. Deep lift in the H700-H600 layer with potential for
elevated instability over the east may lead to more widespread 
heavy snow farther south. H850 inflow into the storm of 40 to 45 
kts from 09z through 17z will aid in 1 inch snowfall rates per 
hour across the north during that time. Though saturation may take
until about 07z across the northwest...went ahead and began 
warnings/adv over the northwest. Once the precip begins it will 
quickly cause some impacts with some light icing/sleet and a quick
changeover to all snow by 09z as rates pick up over the northwest
for the remainder of the day. Over the northeast rain/freezing 
rain will being initially with a changeover taking place nearer 
09z to 12z. None the less...morning commutes will be impacted over
most of the north. Farther south a mixture of light icing and 
light snow will be possible. Though road temperatures may limit 
any road icing along the US Highway corridor north toward US 
20...decided to add a row of counties to for chance that some 
bridges/overpasses may become slick or briefly ice up in the 
morning hours. If impacts lessen during the day Wednesday...this 
portion of the advisory may end earlier. This storm has a lot 
going for it...possible convection along with strong forcing. Some
uncertainty still remains regarding the amount of qpf and how far
south the storm may still trend which will affect snowfall 
amounts. Generally looking for a 6 to 8 inch area of snow north in
the warning areas with 2 to 5 inches in the advisory areas along 
with a glazing of ice there. Day shift will need to carefully 
evaluate trends and again later tonight. Highs tomorrow will warm 
into the mid to upper 30s south of US 30 - at best with 
temperatures holding in the lower 30s over the north. With the 
snowfall rates quite high...this event will support snow below 35 
degrees and likely some compaction will take place but with high 
snow:water ratios up to 15 to 17 due to tremendous forcing... 
should be able to see more than 6 inches in the warning areas. 

.LONG TERM.../Thursday through Monday/
Issued at 332 AM CDT Tue Apr 17 2018

Finally some quiet and spring-like weather in store through the 
weekend and into the early part of next week. The main focus of
the extended was on a another upper level low to pass to the 
south of the state Friday night into Saturday. Models continue to 
shift this system south from run to run and confidence is 
increasing with the better chances of remaining dry across much of
the forecast area. Hence the good news, no major winter storm for
the weekend for central Iowa and much of the forecast area looks 
to be near or even slightly above normal Saturday and Sunday. 

Thursday through Saturday...Surface high pressure builds into the 
region and becomes centered over Iowa b/t 03-09z Friday. There is 
plenty of dry and cool air with this airmass and expecting a good 
radiational cooling set up by Friday morning. Record or near record 
lows are likely, especially over the northern half of the forecast 
area with the anticipated fresh snow pack in place.  Something to 
mention in forecast after Wednesday's system. The strong surface 
high shifts to the Great Lakes area and looks to keep the next 500mb 
low tracking across Arkansas and Missouri. Ahead of the low, a weak 
ribbon of vorticity provides enough forcing to keep the mention of 
rain and snow going Friday night into Saturday. Soundings suggest 
either rain or snow during the day Saturday with ice introduction 
present, but there remains a deep layer of dry air to contend 
with below 800mb to the surface. Thus, QPF and any snow amounts 
look to be light attm. 

Sunday into Tuesday...GFS and ECMWF have come into agreement with 
warmer temperatures by Sunday and tweaked highs up slightly and may 
need to continue to trend warmer if models persist with this signal. 
Only caveat is some mid-level clouds across the state. Certainly
Monday and Tuesday are forecast to be around normal with highs
rising into the upper 50s to 60s, but with the latest MOS guidance
from the ECMWF and GFS, highs looks to be even warmer. 

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 648 AM CDT Tue Apr 17 2018

Few concerns through 00z as another winter storm bears down on the
region. Quickly after 02z cigs will drop from VFR to MVFR by 04z
then continue to drop overnight to IFR conditions between 07 and
12z at KDSM/KFOD. Farther east MVFR conditions will return. Snow
and -FZRA will occur along and north of US30 aft 03z while south
rain will impact KDSM. Northern sites KFOD will see vsby drop to
1sm by 12z with low vsby extending east to KMCW/KALO aft 12z.
Elsewhere expect MVFR vsby aft 09z. Conditions will remain poor
most of Wednesday with MVFR/IFR expected along with increasing
winds. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 AM Wednesday to 1 AM CDT Thursday 
for IAZ036>039-047>050.

Winter Storm Warning from 1 AM to 10 PM CDT Wednesday for IAZ004-
005-015-024.

Winter Storm Warning from 4 AM Wednesday to 1 AM CDT Thursday 
for IAZ006-007-016-017-025>028.

Winter Weather Advisory from 1 AM to 10 PM CDT Wednesday for 
IAZ023-033>035-044>046.

&&

$$

SHORT TERM...REV
LONG TERM...Podrazik
AVIATION...REV