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fxus63 kdmx 191740 

Area forecast discussion
National Weather Service Des Moines Iowa
1140 am CST Tue Nov 19 2019

Short term.../today through Wednesday/
issued at 320 am CST Tue Nov 19 2019

This morning, shallow moisture in the wake of the passing shortwave
is producing fog across much of the area...especially northern Iowa.
Most visibilities being reported are in the 1 to 4sm category but
local visibility of a half to a quarter mile is occurring across the
far north. The low level moisture stays across this area through
mid morning so fog is expected across this area through 10am. For
the rest of today...the passing shortwave that brought light rain to
the forecast area last night will be exiting to the east by 18z.
Upper level ridging to the west will keep US in northwest flow aloft
today but will drift across the upper Midwest tonight bringing a
more westerly flow across the state. A surface high will build
across the forecast area and slowly push east tonight. Low level
moisture will remain across the area however while winds start out
light, they do increase starting around 12z and thorugh the morning.
This may result in fog development once again tonight though it is
more conditional on winds. I did include fog again tonight into
Wednesday morning. Temp-wise, still looking at mild conditions today
and tonight with highs from the low 40s northeast to the mid 50s
southwest and lows tonight around 32 north and mid to upper 30s most
other locations. Warmest lows will be southwest.

On Wednesday the upper ridge shifts east through the day as a deep
trough starts to take shape to the west. A shortwave ejects out of
the base of this western trough and up the back side of the ridge.
Initially there is little moisture over the state but we start to
saturate in the afternoon. Most locations will still be dry
Wednesday but after 18z forcing does start to increase across the
far southwest as the shortwave nears and between 21z and 00z the
shortwave does make it into southwest Iowa and this along with
deepening moisture and even stronger forcing coming into the west
and southwest, we will see precip start to break out across these
areas. By 00z Thursday, a surface low is expected to move into west
central Iowa with a warm front extending from the low and into south
central Iowa. Temps across this area will be warm and the thermal
profile shows precip to be all rain. There will be some instability
that works into the state but at this point it does appear to be
after 00z so thunder was kept out of the forecast through 00z

Long term.../Wednesday night through Monday/
issued at 320 am CST Tue Nov 19 2019

/Wednesday night through Friday/...

Confidence: high

Quiet pattern coming to an end with southwest flow returning to the
area from Wednesday night into Thursday morning. Closed h500 low
off the Pacific Mexico coast will phase with digging West Coast
trough by 12z Tuesday and begin to amplify over the southwest by
Wednesday. About the same time, a short wave will be ejected
northeast into the Central Plains, inducing a sfc wave and a quick
return of southerly flow aloft. With the Gulf opening up by mid
week, ample moisture return should take place from late wendesday
afternoon into Thursday. This will result in an expansive area of
rain and scattered thunderstorms as the system intensifies across
Iowa into Thursday morning with both mechanical forcing and strong
warm air advection feeding the rain and thunderstorm development.
Colder air being ingested into the system as it departs should
allow for a changeover to some snow on the backside as the low
lifts into Wisconsin Thursday afternoon. Little accumulation is
anticipated. With the strong warm air advection and strong surface
winds ahead of the system coming into Thursday, highs will be
quite mild over the southeast half as the low pulls into the
state. Temperatures in the southeast will reach the mid to upper
50s with upper 30s to lower 40s in the northwest. Winds Wednesday
night into Thursday will reach 15 to 25 mph with gusts over 30 mph
at times. As the low departs, northwest winds will increase to 15
to 25 mph through Thursday evening. With some component of
Pacific moisture and Gulf moisture also streaming north,
precipitation amounts are likely to reach 1/2 to 1 inch near the
track of the h850 low with widespread 1/2 inch amounts across the
area. The system will quickly exit the region Thursday evening
with dry high pressure moving east into the area. This will allow
temperatures to fall back into the upper teens to upper 20s from
northwest to southeast. Friday will also be below normal with high
in the mid 30s northwest to the lower 40s in the southeast.

/Friday night through Monday/...

Confidence: medium

A modified west to northwest flow will develop into the weekend.
This will initially bring some adiabatic warming to the region as
compressional heating east of The Rockies results in a milder
airmass streaming southeast into Iowa. After lows in the 20s Friday
night, highs Saturday and Sunday are likely to reach or exceed 50
degrees by Sunday and be well into the 40s on Saturday. Currently
some of the ensemble members continue to carry a slight chance for
some light precipitation over the south late Friday night into
Saturday. The operational models suggest otherwise, but for now will
make no changes to the early portion of the weekend with regard to
rain/snow chances. By Sunday, some differences in the medium range
models begin to emerge. The European model is showing a slow
migration to more northwesterly flow and energy beginning to carve
out a larger mean h500 trough over the central US in the next 7 days
while the GFS remains largely tilted toward a warmer solution as it
seems to maintain its usual northerly solution bias. A series of
shortwaves in both models yield a colder solution in the Euro and
fail to bring the cold air south in the GFS. Initially, this has
little bearing on the forecast into Monday, but has great
implications for the midweek system by Tuesday/Wednesday. Both
models continue to diverge with regard to the midweek solution;
though there remains a strong signal for active weather toward peak
travel just prior to Thanksgiving and will be the focus of
subsequent forecasts into next week.


Aviation.../for the 18z tafs through 18z Wednesday afternoon/
issued at 1140 am CST Tue Nov 19 2019

Stratus continues to hang tough across eastern Iowa affecting Kalo
and kmcw this afternoon. However, much of the areas will see
unrestricted ceilings and visibilities this afternoon and tonight
with west to northwest surface flow. Mid and high clouds will
drift over the state tonight with light surface winds. This may
lead to some light fog development, especially in eastern areas
tonight with MVFR to locally IFR conditions. Surface winds are
forecast to increase from the southeast on Wednesday morning as
mid level ceilings begin to increase.


Dmx watches/warnings/advisories...none.



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