567
FXUS63 KMPX 152022
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
322 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.

&&

.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 /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1220 PM CDT Sat Jun 15 2024

Radar shows most of the story within the short-term period, with
-SHRA to SHRA persisting to begin the period and lingering
 through the first 12-18 hours with a period of -TSRA/TSRA
 likely within as well. CIGS/VIS will drop to MVFR as showers
 expand throughout the day with the most likely period for
 IFR/-TSRA after 00z through around 06-09z. As the last of the
 -SHRA/-TSRA exit the region before 12z, expect VFR conditions
  to return and remain for most of Sunday.

KMSP...Favored a TEMPO for the highest confidence period for
stronger TSRA, with the following prevailing -TSRA being lower
in severity with a typical overnight lightning show type of
event. Otherwise the main concerns related to CIGS/VIS will lead
to MVFR and possible IFR conditions later today.

/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.

&&

$$

DISCUSSION...TDH
AVIATION...TDH
HYDROLOGY...CCS