Area Forecast Discussion
Issued by NWS Des Moines, IA
FXUS63 KDMX 181735
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1135 AM CST Wed Jan 18 2017
.SHORT TERM.../Today through Tonight/
Issued at 343 AM CST Wed Jan 18 2017
Cloud cover and temperatures were the main forecast problem today
into tonight. Lingering low stratus deck finally showing signs of
progressing east-northeast out of the forecast area with a few
holes across the south to southwest. This has allowed some thicker
fog to develop across the south and have mentioned patchy dense
fog through 13z. Kept with mention of patchy fog elsewhere.
Southwest flow at the surface and aloft should provide a nice warm
up across the forecast area today. The caveat is if this low stratus
deck clears the area, which appears to be doing so from current IR
satellite trajectory. Plus, the stratus should dissipate once the
sun rises and the southwest flow increases this morning. Thus, have
clearing skies b/t 14-16z from west to east where there is currently
cloud cover. Confident to at least raise maximum temperatures 3-4
degrees today across the area, with central to southwest likely to
see the warmest temperatures. Especially with the stratus deck
holding temperatures up slightly warmer than previously anticipated.
The WAA continues tonight into Thursday morning with some mid-level
moisture returning past 06z tonight. Likely to see temperatures
remain fairly steady overnight tonight and nudged up minimums a
degree or two to coincide with the increasing cloudiness.
.LONG TERM.../Thursday through Tuesday/
Issued at 343 AM CST Wed Jan 18 2017
Active pattern across the United States with strong Pacific jet
bringing several systems into the country over the next week.
Initial upper low to affect Iowa has been lingering over the
southwest United States for a few days but is ejecting northeast
as strong onshore flow commences into California. This low and a
subsequent upper system to advance across the Midwest on Saturday
will both bring similar threat of precipitation to Iowa. In
general, low level moisture will be filling back in across the
state late Wednesday night into Thursday and should remain into
the weekend. Therefore, stratus is expected to be widespread
during this time with only limited sunshine, mainly in the south.
As the upper lows progress through the state, moisture never
deepens much past the boundary layer despite the forcing
associated with the systems. Therefore, precipitation will be
light and mainly drizzle or very light rain with QPF values of a
few hundredths through Saturday.
A more significant system that was set to affect the state late in
the weekend on yesterdays model runs is now trending southward in
more recent output. Therefore, have backed of the precipitation
threat on later Sunday into early Monday and mainly confined to
the east. Extended guidance does continue to suggest a system
passing through the state toward the end of the forecast period
with rain and snow across the state. Temperatures will mostly
remain above normal through day 7, especially at night with
overnight readings near daytime highs for this time of year,
especially through the end of this week.
.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1133 AM CST Wed Jan 18 2017
The forecast area is split by an extreme gradient in conditions at
18z with VFR/clear skies west and a quick drop to LIFR fog and
stratus east. The fog and stratus should gradually improve to MVFR
into early this evening, but with persistent weak southerly flow
over the cold, wet ground in IA expect a return to IFR/LIFR to
blossom across much of central IA into the night with only slow
recovery in the morning.