Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201804

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
104 PM CDT Thu Jul 20 2017

.SHORT TERM...(Today and tonight)
Issued at 338 AM CDT Thu Jul 20 2017

The short term concern is timing next bout of convection later

The heavy rain producing convection has exited the cwa for the most
part. We did receive 2 to 5 inches of rain from the south metro to
along the Mississippi River to the southeast. Should be a mainly dry
day into this evening as the frontal boundary sags farther south
into Iowa and high pressure builds into the state. Some patchy fog
developed into central MN as the clouds cleared and this should burn
off quickly this morning. High temperatures are expected to warm
through the 80s.

Later tonight we see return flow/low level waa developing to the
southwest along with a possible short wave moving into southwest MN
from South Dakota. We will retain the chance PoPs for that
development later tonight. Clouds will thicken over the southwest as
well. Farther east, with light winds and the possibility of a mostly
clear sky much of the night, we could see some patchy fog develop
into west central WI later tonight as well.

.LONG TERM...(Friday through Wednesday)
Issued at 338 AM CDT Thu Jul 20 2017

In the big picture, we`ll see fairly zonal upper flow on Friday
transition to northwest flow by sunday with cooler and drier air
working into the region. However, an upper trough looks to dig
along the west coast during the first half of next week, leading
to the redevelopment of upper ridging over the center of the CONUS
by Tuesday/Wednesday. This looks to remain in place through the
remainder of the week. So, although we briefly see temperatures
dip below normal for Sunday/Monday things should quickly return to
at or above normal values for the remainder of the period.

In terms of the details, the main concern will be the possibility
for a few more rounds of showers and thunderstorms Friday into
Saturday, with locally heavy rainfall and some possibility of
severe weather again. The warm frontal boundary looks to get up
into the southern portion of the area on Friday as a weak surface
low slowly moves east from the central and northern Plains. Plenty
of instability and moisture will be present across the southern
half of the area, so the modest warm advection forecast should be
more than sufficient to get showers and thunderstorms going again
on Friday. The steering flow looks to be somewhat parallel to the
baroclinic zone and instability gradient, so some training of
storms seems possible, which would lead to a heavy rain threat,
particularly over the southern portion of the area. The surface
low will slowly push east Friday night and Saturday, working into
the lower Great Lakes by Saturday night. The guidance is
consistent in showing an inverted trough/occluded front north of
the surface low, and we may see additional showers and storms
develop near/ahead of that on Saturday, primarily impacting
locations near and east of I-35. The main cold front looks to drop
south across the area Saturday night into Sunday morning, with
high pressure building in for Sunday and Monday. We`ll get on the
backside of the surface high by Monday night and Tuesday, with
return flow setting up and a renewed chance of showers and
thunderstorms working in from west to east Tuesday and Tuesday
night. The guidance has some significant differences at that point
in time with respect to how far north the baroclinic zone and low
level moisture return, and don`t have particular confidence in any
specific solution at this point. The GFS would hang onto more in
the way of northwest flow into the second half of the week, while
the Canadian is more aggressive in building the ridge over the
area. A compromise may be best at this point, which the ECMWF
somewhat suggests. Regardless, it appears we`ll be near the
periphery of the ridge and instability gradient, so chances for
showers and thunderstorms look to be a good bet into at least


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1254 PM CDT Thu Jul 20 2017

VFR conditions are expected through tonight, but showers and
thunderstorms may spread in from the south early tomorrow morning
for parts of western and southern Minnesota. High clouds and light
winds will last through tonight, but the next disturbance riding
over the upper ridge will move in tomorrow. On top of that, a
deepening surface low will move into the NE/SD area by tomorrow
morning with strong theta-e advection and unstable air working in
from our south. Included a VCSH at a few sites (KAXN, KRWF, KMKT)
for the end of the period. MVFR ceilings will be possible with
this activity lifting in, but leaned more optimistic at this
point. Lastly, fog will once again be a concern, but mainly in
western WI where wind remains the weakest overnight.

KMSP...main concern is for precip tomorrow and while confidence is
below average, currently thinking the afternoon presents the
greatest opportunity for precip and possibly thunderstorms in the

Fri night...Mainly VFR. -SHRA/TSRA likely. Winds SE 5-10 kts.
Sat...Mainly VFR. Chc MVFR in -SHRA/TSRA. Winds lgt and vrbl.
Sun...VFR. Wind NW 10 kts.




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