Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 131125

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
625 AM CDT Sun Aug 13 2017

.SHORT TERM...(Today and tonight)
Issued at 349 AM CDT Sun Aug 13 2017

Strong shortwave can be seen on both radar and satellite spinning
to the north of Aberdeen, SD. Farther upstream, there`s a
shortwave ridge along the MN/WI border, which is helping to keep
high pressure in place across Wisconsin. Rain and embedded storms
out in western MN have moved very little overnight, as the
shortwave forcing it and its associated LLJ and fgen in the h85-h7
layer have moved little as well. There`s good model consensus
from both deterministic and hi- res models that through the
morning, as the Dakotas upper low slowly shifts east, we`ll see
the precip do the same, with the area of rain out in west central
MN slowly tracking northeast across central MN through the
morning. There`s good model agreement as well that the heaviest
rain, likely in the form of a band of 2-3" will fall out in west
central MN, but for the rest of the area, amounts of 0.5-1" are
more likely.

Though there`s good agreement on this first batch of rain lifting
into central MN, there`s less agreement on how precip will evolve
the rest of the day. Given the incoming upper low and it`s
associated cooler temps aloft, we should see scattered showers
bubble up pretty quick as we build some instability. There`s even
an outside threat for some strong to severe storms today over
southwest MN. Both the GFS/NAM show 1000-1500 j/kg of mucape
developing with 30-40 kts of 0-6km shear. The SPC has a marginal
risk coming up to I- 90 on the first rendition of the Day 1
outlook, but seeing a stronger cell or two up to the MN River
looks possible.

For tonight, the upper low/wave will continue a weakening trend
that will begin this afternoon. We`ll have a remnant tongue of
moisture working east through the night, with scattered showers
continuing to slowly move east with it. We`ll see it dry out in
western MN, though expect what we are seeing west and south of
Bismark this morning to happen over western/central MN tonight,
which will be the development of low stratus.

.LONG TERM...(Monday through Saturday)
Issued at 349 AM CDT Sun Aug 13 2017

Monday through Wednesday...The period will commence with the
departure of a shortwave trough originating from a large upper low
over Hudson Bay swinging over the western Great Lakes. This will
also coincide with a weak surface low pressure center shifting
east over southern Minnesota into WI/IL. Showers will gradually
end from west to east as this system exits to the east. After a
brief respite in the form of a sharp ridge axis moving in from the
Dakotas, a more organized deep system will impact the area Tuesday
through Wednesday. Setting the stage, a longwave trough developing
over the western CONUS coast will adjust the upper level pattern
to one of a more southwesterly flow, tapping into a poignant and
moist subtropical jet. This will shunt deeper moisture into the
Upper Mississippi River valley in advance of both this longwave
trough along with a developing low pressure system moving across
the Rockies Monday night into Tuesday. Models continue to show
PWATs rising to the 1.50"-2.00" range in advance of the trough
which also continues to take on a pivoting action to a negative
tilt by the time it moves into the Central Plains by Tuesday
evening. As such, the deep lift and tilted nature of this
approaching system may lead to efficient precipitation generation
across much of the WFO MPX coverage area, to the tune of rainfall
over 1". In addition, there are growing signals for the potential
of isolated severe weather for Tuesday into Tuesday night should
enough insolation be available to further destabilize the
atmosphere. However, lapse rates are unimpressive and shear is
fairly weak so am not too enthralled with severe weather potential
at this point. The timing of greatest coverage and heaviest rain
looks to be Tuesday night through the first half of Wednesday with
precipitation then diminishing Wednesday night, thus have kept
pops in the likely to low-end categorical range at this point but
would not be surprised to see pops continue to rise.

Thursday through Saturday...A more zonal pattern aloft combined
with surface high pressure looks to be the story for the end of
the week. While a stacked low pressure system looks to develop for
south-central Canada, there is little influence to be made of it
moving across the international border into the north-central
CONUS, thus have advertised a mainly dry end of the week.
Temperatures will continue to run near normal with nearly
identical day-to-day values.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 614 AM CDT Sun Aug 13 2017

Though heaviest rain is over AXN and will continue ENE across
central MN this morning, light precip has quickly expanded south
toward the Twin Cities and Mankato this morning. Therefore, have
sped up mention of rain quite a bit, not anticipating an all day
rain, but rain will be off and on pretty much all day into
tonight. Thunder looks pretty minimal today, with greatest
destabilization expected this afternoon in southwest MN, so only
have a TS mention at RWF for this afternoon/evening. Like we have
seen out toward Bismark overnight, expect low stratus to expand
across western/central MN tonight as the rain and deeper moisture
shift east. The LAMP is probably a bit too aggressive with how
low cigs go tonight, but followed its general idea for bringing
restricted cigs in tonight at AXN/STC/RWF.

KMSP...Expect on and off rain with VFR cigs pretty much all day.
Thunder threat looks pretty low, but greatest potential looks like
it will come between 00z and 4z, but confidence/expected coverage
of TS is too low to include in the TAF right now. GFS/NAM sounding
both show cigs should be going downhill rapidly around 12z Monday
and confidence is fairly high in MVFR cigs to end the TAF, with
sub 1800 foot cigs certainly not out of the question.

Mon...Bcmg VFR in afternoon. Wind lgt and vrb.
Tue...VFR. MVFR/IFR possible late with SHRA/TSRA. Wind SE at 5-10
Wed...Chc MVFR/TSRA. Wind S-SW at 5-10 kts.




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