Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 222119
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
319 PM CST Wed Nov 22 2017

.SHORT TERM.../Tonight through Thursday/
Issued at 250 PM CST Wed Nov 22 2017

For the rest of this afternoon through mid evening, a weak
shortwave will pass across northeast into eastern Iowa. There is
warm advection aloft and the moisture associated with this
advection is producing a pretty solid shield of mid/high level
cloud cover. Along with this is some weak forcing that make
promote a few sprinkles/flurries as the upper wave passes. However
the lower levels are so dry that precip is having a hard time
making it to the ground. A few observations however from time to
time do report a sprinkle or flurry. Since the going forecast has
this in it already and there are stronger radar returns yet to
pass through and some obs from time to time are carrying precip,
will leave the non-measurable mention in.

Later tonight, after the wave passes, we will clear out and winds
will shift to the west then northwest. Temps will likely be slow
to fall or steady given the clouds and the southwest to west
surface wind.

On Thanksgiving Day the surface high that slides through late
tonight into Thursday morning will be far enough east that surface
flow goes back to the west or southwest. With clear skies this
should give a little boost to afternoon temps and highs should be
pleasant in the mid 40s to mid 50s.

.LONG TERM.../Thursday night through Wednesday/
Issued at 250 PM CST Wed Nov 22 2017

Thursday night a surface low approaches the Northern Plains and
with an upper ridge moving in, we will be in even stronger warm
advection so temps will likely bottom in the evening then begin to
rise overnight. Temps by daybreak Friday will already be at or
above normal highs for this time of year.

On Friday, a surface low and front will be pushing across the
Northern Plains and Upper Midwest as a shortwave drops across the
Northern Plains. This will put most of the southern portion of the
Upper Midwest in strong warm advection and we should see mid 50s
to mid 60s across the area for highs. By mid to late afternoon
Friday the front will push through the state with the coldest air
lagging but arriving Friday night into Saturday dropping temps
back into the 40s and 50s with lows in the 20s and 30s. As for
precip, it now looks as though the better forcing now remains well
north of the state so precip was removed from northern Iowa,
though the Euro model still hangs on to some qpf Friday with a
little deeper wave passing. Trends with the past couple of systems
have been for the shortwaves to dampen some so I discounted the
Euro for now.

Behind this wave, a huge ridge builds across the west, putting
Iowa in northwest flow for Sunday but as the ridge axis shifts
into the Plains for Monday warmer air returns and we see temps
climb back into the 50s and 60s. This see-saw in temperatures will
continue into next week.

Beyond Monday models diverge enough to make a significant
difference in solutions. The GFS and Canadian models bring a less
amplified trough through us Tuesday into Wednesday though the
Canadian is much more bullish on precip while the Euro digs this
trough into a closed low out west then lifts the low across Iowa
just beyond the forecast period. This would tend to keep temps
warmer Tuesday into Wednesday but give us much more precip
Wednesday into beyond this forecast period. For now I buy the less
amplified solution with slightly cooler temps a little more qpf
like the Canadian suggest. Will be interesting to see this system
evolve.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1132 AM CST Wed Nov 22 2017

VFR conditions expected through the TAF period.  A weak disturbance
will pass from the Northern Plains through northeast Iowa spreading
VFR cigs and some sprinkles or flurries.  Behind the disturbance,
winds switch briefly to the northwest.

&&

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

$$

SHORT TERM...FAB
LONG TERM...FAB
AVIATION...FAB


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