Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 011114
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
614 AM CDT SAT OCT 1 2016

.SHORT TERM...(Today and tonight)
Issued at 330 AM CDT Sat Oct 1 2016

Main question for the short term is what will happen with cloud
cover. Closed low over the mid Ohio River Valley will drift north
across Indiana today. Cloud cover associated with this has spread
out across southern MN. Over central MN, we have again seen low
stratus drop down from the Lake Superior region.  The going thought
to this point has been that cloud cover from the upper low to our
east would keep a rather steady supply of stratus going for us, but
the HRRR has been showing much of the area going mostly clear by the
afternoon. This may be a little too optimistic, though the GFS and
NAM show clearing skies/drier air working southwest out of northern
WI, so seeing a bit more sun then originally thought, especially for
eastern MN/western WI is looking more likely. Beside that, water
vapor imagery is showing drier air over the MPX area as we sit in an
upper convergence zone and subsidence between the closed low over IN
and a sheared out trough over the Dakotas.

One thing we did remove were the precip chances in the east for
today. Rain overnight has been confined to east of I-39 in central
WI and with the subsidence overhead, it`s hard to envision that
precip making too much farther west today. CAMs and deterministic
models alike keep the MPX area dry today, so didn`t take much
convincing to remove what little pops we had. The main issue for
today is the lack of forcing, with vorticity associated with the IN
low remaining well off to our east.

For temperatures, the key will be the cloud cover. We have a similar
airmass to yesterday in terms of 925-850 temps and as we saw, mix in
a little sun and temperatures have no problem warming into the 70s.
With the thought that we may see more sun than originally thought,
did nudge up highs a couple of degrees. The cloud impacts will
continue into tonight, with a surface ridge axis still expected to
be extending down from Lake Superior. If skies are clear like the
HRRR thinks they will be, it will be a chilly evening, with lows
down in the 40s north of I-94. Beside the cooler temps, if skies are
clear tonight, dense fog will likely become an issue.

.LONG TERM...(Sunday through Friday)
Issued at 330 AM CDT Sat Oct 1 2016

The focus in the long term is a weather system moving through in
the Tuesday through Thursday timeframe. Prior to that, some fine
early fall weather will occur Sunday and Monday as low level
ridging slowly weakens across the Upper Mississippi Valley. We may
have to contend with some fog once again Sunday morning, but this
will depend on how much wrap around cloud cover still exists from
the upper low to our east.

The mid week weather system is a powerful upper level low pressure
system driving through the western half of the country by
Wednesday. The onset of the showers into western MN for late
Monday night and early Tuesday is in good agreement between the
GFS/EC and Canadian. However, the GFS and Canadian drive much of
the system through our FA from Tuesday through Wednesday while
the EC is more Wednesday into early Thursday. This delay in the EC
is tied to a secondary upper trough pushing across the central
plains which the other two solutions don`t have.

All three solutions are pretty adamant on rainfall totals being
around an inch. This seems plausible given we are in the right
entrance region of the upper jet, strong moisture transport occurs
with 925-850mb layer winds around 45 knots, surface dew points
reaching near 60 with 850mb dew points near 50 degrees. In
addition, the PWAT forecast from the GFS is near 1.5 inches, which
is a daily max from our sounding climatology for early October.
The GEFS plumes for KMSP are highly concentrated in the 1 to 1.5
inch range with one member over 2 inches.

The area of concern for the heaviest rain right now is south
central MN into west central WI, certainly an area that has been
quite wet lately. This is where the low level frontogenesis is the
strongest as well as the location of the best differential layer
divergence. We`ll be working on the timing over the next few days.
For now, likely pops are indicated for far western MN on Tuesday,
across much of MN Tuesday night and over western WI on Wednesday.
This progression from west to east would be a little fast if the
EC ends up being more correct. The long term then ends with
surface ridging building in.

Temperatures from Sunday through Tuesday will be some 5 to nearly
10 degrees above seasonal normals with readings a few degrees either
side of 70. After the frontal passage with the low pressure system
around midweek, temperatures will be headed down with highs mainly
in the 50s for Thursday and Friday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 614 AM CDT Sat Oct 1 2016

Like 24 hours ago, we are dealing with low stratus and fog coming
out of central MN and expect it to act in a similar way today,
though it will not get as far south as it did yesterday. The HRRR
continues to show skies clearing out today, though forecast
sounding show lots of moisture hanging out in the 8k-10k foot
range. Eventually, the NAM/GFS show even this layer drying out
tonight with clear skies and calm winds taking hold. As a result,
was very aggressive with fog mention for all but MSP Sat night/Sun
morning.

KMSP...Like yesterday, MSP may see a sub 500 foot cig this
morning, though the expansion of the fog out of central MN into
the north metro began later than it did yesterday, so will go with
these clouds staying north this morning. Tonight could be a very
foggy night across the region if we see skies clear out. It would
be a radiational fog, which MSP does not typically deal with,
though that could result in some low cigs for Sunday morning as
well.

/OUTLOOK FOR KMSP/
Sun...VFR. Wind NE at 5 kts.
Mon...VFR. Wind SE at 10G20 kts
Tue...Chc MVFR -TSRA late. SE at 10-15G25 kts.

&&

.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&

$$

SHORT TERM...MPG
LONG TERM...RAH
AVIATION...MPG



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