Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 011729
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1229 PM CDT SAT OCT 1 2016
.updated for 18z taf discussion below...
.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1210 PM CDT Sat Oct 1 2016
Stratus and fog is lifting quickly now. We did see a near repeat
in coverage area of fog this morning and will continue previous
forecast trend of developing it once again late tonight. Best
threat area will be along the ridge axis...and most confident in
area north and west of the KMSP at the moment. There may be enough
cloud around to the far east to bar LIFR conditions at KEAU. We
will play a bit more conservative there. Any fog will burn off
again after 14z-15z. Will likely see some mid or high level
cloudsinto Sunday afternoon. winds remain e-se over the area...and
should remain less than 10kts...but a mix out gust to 17kts cant
be ruled out most areas early this afternoon. winds should become
lgt/vrbl under the ridge and eventually southeast into Sunday.
KMSP...Fog/stratus remained about 10sm to the west and north of
the airfield this morning and clouds from the eastern cutoff low
drifted east of the area the first half of night. Any mid clouds
held off to the far east. We remained mostly clear early this
morning...with just enough stratocu around to preclude the
stratus/fog from developing locally. We may not be as so lucky
into Sunday morning. Introduced at least a mention of some stratus
and light fog for now though kept it VFR. Should clear off again
into Sunday afternoon.
/OUTLOOK FOR KMSP/
Mon...VFR. Wind SE at 10G20 kts
Tue...Chc MVFR -TSRA late. Wind SE at 10-15G25 kts.
Wed...Chc MVFR -TSRA. Wind Wind S to SW 7-11 kts.