Area Forecast Discussion
Issued by NWS Des Moines, IA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KDMX 160023

Area Forecast Discussion
National Weather Service Des Moines IA
723 PM CDT Thu Mar 15 2018

...Updated for 00z Aviation Discussion...

.SHORT TERM.../Tonight through Friday/
Issued at 354 PM CDT Thu Mar 15 2018

Precipitation timing and type were the main forecast concerns
overnight tonight into Friday afternoon. First, pulled back timing
of pops to just the southwest portion of the forecast area prior to
12z Friday with dry air to overcome as well as slower progression
via the hires models.  Utilized a blend of the ARW/NMM/HRRR/NAM12
for timing of precip through 00z Saturday. Overall, no significant
changes to the ongoing forecast with only minor tweaks to the snow
amounts over the northwest tomorrow afternoon.

From CRL to FOD to EST area will be the area of concern for
snow/ice. The ice looks to be mainly in the form of sleet as
soundings (from the aforementioned locations) suggest a large mid-
level warm layer to melt any snow falling through the column and a
deep enough cold layer near the surface to allow for refreezing.
Still a shallow layer of dry air to overcome near the surface b/t 12-
15z Friday over western portion of the forecast area. However, with
the decent frontogenetical forcing with the precipitation onset, this
should be strong enough for the wintry precipitation to overcome and
reach the surface. Surface temperatures look to rise above freezing
by the afternoon Friday and with road temperatures well into the 40s
this afternoon and the likelihood of them not to cooling off too
drastically tonight as well as the factor of latent heat release,
have low confidence with much freezing rain attm over the west to
northwest. Certainly the strong omega within the dendritic layer is
a concern Friday afternoon as the frontogenetical bands shifts north-
northeast. There likely will be a quick period of moderate to heavy
precipitation in the form of the heavy sloppy sleet/snow mix b/t 18z
to 00z Saturday over the northwest to north central. Winds increase
to around 30 to 35 mph through the day and with the falling
precipitation, this could be problematic for travel. However, with
the short duration nature of the event, held off on an advisory
attm. Nudged up the snow amounts slightly during this time to roughly
a half to near 2 inches around Emmet County.

.LONG TERM.../Friday night through Thursday/
Issued at 354 PM CDT Thu Mar 15 2018

The area of low pressure will move east across central Missouri and
into southern Illinois Friday night. As this occurs, high pressure
will begin to settle southward. Precipitation will be ongoing at the
start of the period. A wintry mix is possible across the north with
rain or drizzle to the south. A brief period of moderate to heavy
snow is possible over the north as saturation and forcing are
maximized. Even then, the forcing does not align with good dendritic
growth. Dry mid level air will arrive overnight and should
transition any precipitation to drizzle except possibly the far
north. The biggest potential issue is the chances for freezing
drizzle and some icing. Temperatures likely will hover in the the 30-
32 range for much of the area under the stratus clouds Friday night.
Any icing and associated latent heat release should further keep
temperatures near freezing. In addition, road surface temperatures
should still be at or above freezing in many cases that would limit
any icing potential excluding some elevated surfaces. Therefore, at
this time, not expecting a big impact.

Precipitation will be ending Saturday across the southeast as the
area of high pressure settles further south. Some potential that the
low stratus lingers much of the day across portions of the area and
in this case, could hold high temperatures in that region in the
upper 30s. Areas with sun should reach 40 or above. Warm advection
arrives Saturday night into Sunday especially across the south and
west while a pocket of cooler air remains over northeast Iowa. Highs
Sunday will range from the low to mid 40s northeast to the low to
mid 50s central and southwest. Low chances for precipitation arrive
Sunday night and Monday over western and far southern Iowa followed
by better chances over the entire Monday night and Tuesday as a
strong short wave passes through the area and colder air arrives.
Any precipitation during this period would likely fall as light
snow. Northwest flow and cool temperatures will persist on
Wednesday. Ridging over the west will move east toward the end of
next week and will begin to bring warmer temperatures to the state
by Thursday through the warmest readings would arrive just beyond
this forecast period into next Friday and Saturday.


.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 719 PM CDT Thu Mar 15 2018

Winds to be on the increase overnight tonight through the day
tomorrow. Strongest winds will be in central to western Iowa...
where winds may approach 25kts sustained with gusts to 35 kts.
KFOD TAF site most likely to be impacted by mixed precip tomorrow.
KDSM and KOTM should mainly experience rain. At this time,
visibilities kept above IFR conditions... there may be periods
during heavier rain where vsbsys drop to 2 SM or so at KDSM... but
confidence not high enough to insert into a new FM group at this
time. CIGS should stay above IFR through this TAF period.

There may be widespread IFR fog overnight tomorrow night
across Iowa.




SHORT TERM...Podrazik
LONG TERM...Donavon
AVIATION...Kotenberg is the U.S. government's official web portal to all federal, state and local government web resources and services.