-- Discussion containing changed information from previous version are highlighted. --
836
FXUS63 KMPX 160200
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
900 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Widespread rainfall continues through the evening, with a few
  strong to severe thunderstorms possible tonight mainly in
  southern Minnesota.

- Hot weather tomorrow with heat indices briefly exceeding 100
  tomorrow afternoon in the metro and across southern Minnesota,
  with a Heat Advisory in place. WBGT creeps into the mid 80s
  with air temperatures in the low 90s.

&&

.UPDATE...
-- Changed Discussion --
Issued at 851 PM CDT Sat Jun 15 2024

The last of the initial batch of widespread rain is moving
through western Wisconsin at this hour. Locations to the west
across south central Minnesota have observed a brief lull in the
sustained rainfall, with just on and off shower activity the
last few hours. As expected, showers and thunderstorms have
redeveloped across southern Minnesota thanks to a strengthening
low-level jet and favorable moisture transport into the Upper
Midwest. The main threats with this evening`s thunderstorm
activity will be frequent lightning and the potential for
localized flooding. A Marginal Risk remains in place roughly
along and south of I-94, where an isolated instance of large
hail or damaging wind cannot be ruled out. A lack of instability
and stable lapse rates aloft will work against a greater threat
for severe weather. Latest hi-res models keep most of the
convective activity east of a line from Redwood Falls to Saint
Cloud. Showers and storms will gradually end from west to east
overnight, with rain set to end in western Wisconsin shortly
after daybreak. The focus will then shift to a hot and humid
Sunday, with highs in the upper 80s/low 90s and heat index
values set to climb into the upper 90s/near 100 degrees during
the afternoon. More details on the Heat Advisory can be found in
the discussion below.
-- End Changed Discussion --

&&

.DISCUSSION...
Issued at 321 PM CDT Sat Jun 15 2024

MPX Radar imagery shows a large swath of echoes from western WI all
the way through the I-90 corridor, with light to moderate showers to
continue this afternoon and evening. Satellite shows what has to
this point been a lack of any significant convective activity with
relatively warm cloud tops within infrared imagery as we await
sunset and better forcing to produce better chances for
thunderstorms. We still maintain a slight risk in far southern MN
for storms later this evening although the overall risk is greater
where instability is higher for portions of Nebraska & western Iowa.
As of around 3pm we have little surface instability to work with and
remain capped with only a few lightning strikes observed over the
course of the several hours of rainfall thus far. We will rely on
growing low level moisture from a strengthening low level jet to
strengthen our lower level moisture profile to be able to produce
some actual thunderstorms, which does not look to occur until near
sunset this evening. Rumbles of thunder will be evident overnight
from lingering showers and storms before exiting by sunrise
tomorrow, setting up what will be a hot and humid Sunday.

Sunday brings up the next trouble point of the forecast period,
which will be our first attempt at 90 degree high temperatures this
year coupled with lingering humidity from the overnight showers and
storms, resulting in rising heat index & wet bulb globe temperatures
tomorrow. With relatively cool nights and only one day of truly hot
weather, we hopefully can avoid the risks to vulnerable populations
that are typically associated with days of 100+ heat index values
and mid 80 wet bulb globe temperatures. The Heat Advisory is in
place for the metro as said heat indices rise towards 100, however
brief the window is with only a 3-4 hour period of truly hot weather
tomorrow afternoon before improvement is seen tomorrow evening. It
would still be a good idea to avoid prolonged periods of strenuous
outdoor activity without a break tomorrow, with plenty of shade and
breaks for water being essential to keeping cool. The highest
temperatures will focus on the Twin Cities metro, western Wisconsin
and southern Minnesota, with lower temperatures as you head
northwards down into the low to mid 80s by the time you reach
Alexandria or Brainerd. Low temperatures then drop back into the 60s
overnight as further showers and storms arrive after midnight and
continue through much of next week.

Monday and Tuesday will look similar in terms of sensible weather
with scattered showers likely to continue on and off throughout,
with a period of increased risk for thunderstorms during each
afternoon`s peak heating time period. The main cause of the pattern
will be ridging over the eastern CONUS as a trough digs across the
northern Rockies, resulting in a prime upper level pattern for
shortwave impulses and continued moisture influx across the northern
plains. PWAT anomalies within NAEFS are 2-3 standard deviations
above normal for this time of year which coupled with an environment
favorable for showers and storms could lead to some impressive rain
totals through Tuesday. WPC has produced a collaborated day 3
moderate Excessive Rain Outlook due to these factors coupled with a
relatively wet summer thus far as well as fairly moist vegetation
that may not be able to absorb as much liquid compared to a normal
period.  What this means is increased potential for flooding, both
river flooding stretching into the end of the week and beyond in
addition to flash flooding potential after a few days of rainfall,
especially should we see multiple days where showers and storms
train over a particular geographic region. Right now, the greatest
risk is focused north and west of the Twin Cities stretching towards
Duluth, with increased emphasis on the upper St. Croix river valley
regions as well as the Mississippi headwaters. We highly recommend
keeping an eye on area rain totals and checking water.noaa.gov if
you live close to a river or stream that has a tendency to flood.
The unsettled pattern continues with little change in the upper
levels through the end of the week, with the main change as we
progress being slightly cooler days mid to late week which should
help keep stronger thunderstorm chances at bay due to less
instability to work with. Be sure to check out the hydro discussion
issued yesterday as well as any further updates as we keep a close
eye on flooding potential over the coming days.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 639 PM CDT Sat Jun 15 2024

Initial batch of widespread rain continues to lift northeast of
the Minnesota terminals. Radar trends support the theme of
redevelopment across southern Minnesota, as captured on the
latest hi-res model data. Additional showers and thunderstorms
are most likely at RWF, MKT, STC, MSP, and RNH. Appears AXN may
be too far NW for potential thunder and storms may weaken to
general -RA/SHRA by the time they reach EAU late tonight.
Ceilings lower to MVFR/IFR overnight and then improve to VFR as
the system departs early Sunday. Southeast winds turn more
southerly overnight, eventually southwesterly into Sunday
morning.

KMSP...Expect off and on showers to continue into this evening,
with the chance for a storm or two. Better chances for thunder
will be later on tonight, between roughly 05-09z. Ceilings
lower to MVFR overnight and then improve to VFR Sunday. Winds
turn southwesterly Sunday morning, with gusts up to 20 knots.
Likely 200-220 direction late morning into the afternoon sets
up for a crosswind on 12R/30L.

/OUTLOOK FOR KMSP/
MON...VFR, likely MVFR/IFR/TSRA PM. Wind SE 10-15kt.
TUE...VFR, likely MVFR/IFR/TSRA PM. Wind S 10-15G25-30kts.
WED...VFR/MVFR/-SHRA, chc -TSRA PM. Wind N 5-10kts.

&&

.HYDROLOGY...
Issued at 315 PM CDT Fri Jun 14 2024

The extended period of heavy rainfall brings with it a potential
return to river flooding in the 5-10 day period, extending to the
end of the month on the mainstems. HEFS graphics show the potential
threat nicely, and also show the degree of uncertainty with large
ranges even within the blue "most likely" band by day 10.
Factors that will determine flood severity (minor vs. moderate or
worse) include how fast the rain falls...a number of 6-12 hour
periods with less than an inch adding up to 3-5 inches is better
than a couple of 2-3 inch events in a short period. We will also
need to be wary of a boundary setting up with training storms moving
from southwest to northeast over the same area.
In summary, this scenario bears watching closely over the next week,
with lots of uncertainty along the way.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Heat Advisory from 1 PM to 7 PM CDT Sunday for Anoka-Carver-
     Dakota-Hennepin-Ramsey-Scott-Washington.
     Excessive Heat Watch Sunday evening for Anoka-Carver-Dakota-
     Hennepin-Ramsey-Scott-Washington.
WI...None.

&&

$$

UPDATE...Strus
DISCUSSION...TDH
AVIATION...Strus
HYDROLOGY...CCS