Scientific Forecaster Discussion
fxus63 kmpx 191859
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
159 PM CDT Fri Jul 19 2019
issued at 559 am CDT Fri Jul 19 2019
Updated for the 12z aviation discussion below.
Short term...(today through saturday)
issued at 428 am CDT Fri Jul 19 2019
Two primary concerns in the short term period:
1) excessive heat. Guidance has trended warmer and higher dew
points are forecast as well. Today will be the hottest day of week,
possibly the season.
2) severe thunderstorms (mainly central mn). The frontal boundary
will lift across central Minnesota today and bring the extremely unstable
airmass with it northward through central & southern Minnesota, and western
As of 4am local time, the front was analyzed along the Minnesota/Iowa border
and will begin lifting north through the morning. By mid afternoon,
the front will be north of the Twin Cities, stretching form a subtle
surface low west to east from west central Minnesota through western WI.
Dew points in the upper 70s and temperatures in the low 90s are
expected across most of the area by the afternoon. An eml will
spread over the region by the afternoon leading to lapse rates of
around 8 deg c per km. This will lead to MLCAPE values of 4,000-
6,000 j/kg this afternoon across the area. Strong westerly flow will
be present aloft, despite the main jet being displaced to the north.
Southerly surface winds along and south of the front will veer with
height with 500h winds expected to reach 50 knots from the west.
Effective shear will reach 45-55 knots- ample for supercell
thunderstorms to develop. In terms of cape and shear, today will be
one of the more favorable setups we've seen in a while.
The question then revolves around forcing to spark thunderstorms.
There is no strong upper shortwave to aid in development of storms,
but low level convergence along the surface low and frontal boundary
should provide the lift needed to generate thunderstorms. This is
most likely to occur across west central Minnesota early this afternoon,
with areas south of there potentially remaining capped.
With storms that develop in the vicinity of the low or front,
tornadoes, strong downburst winds, and very large hail will all be
possible. Given the thermodynamic environment, storms that initiate
will quickly become strong and potentially interact with the frontal
boundary, leading to the risk of tornado development. Storms will
continue to grow upscale this afternoon toward evening, merging
into a strong to severe line as storms become cold pool dominant. At
that point, downburst winds would become the main threat but large
hail and isolated tornadoes would still be possible. This evolution
looks most likely to occur across eastern Minnesota into west central WI.
The heat and humidity concerns have increased today. With the
subtle low pressure area lifting northeast out of South Dakota, the
thermal ridge will nose it's way across southern Minnesota by the midday
near peak heating. The airmass has fairly widespread dew points of
75-80 degrees which we expect to lift north across southern Minnesota and
parts of western WI. Heat indices will rise over 100 degrees by
this afternoon for most of the area, with a few places possibly
approaching 110 degrees. Hence, the heat advisory has been converted
to an excessive heat warning and expanded northward. A heat advisory
has also been issued along the frontal boundary in central Minnesota.
Lastly, an organized cluster of thunderstorms has developed early
this morning across the western Dakotas. The expectation with those
storms is for them to dissipate after daybreak as the low level jet
subsides. However, if these storms become self-sustainable, they
would really throw a wrench into the forecast for today's heat and
thunderstorm outlook if they make it to our area by later this
Long term...(saturday night through thursday)
issued at 428 am CDT Fri Jul 19 2019
On Saturday night we finally get to say goodbye to the front
that's plagued the area this week, and greet a more mild and dry
This will all take place as we transition to a large scale pattern
featuring a western Continental U.S. Ridge and an eastern Continental U.S. Trough. Highs
in the 70s look to be likely for Sunday and Monday, and then we
creep into the mid 80s for the last half of the week. While minor
blips in the northwest flow and fleeting light precip can't be
ruled out, an overall dry pattern looks to be more likely as we
remain displaced from any major forcing mechanisms.
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 158 PM CDT Fri Jul 19 2019
Main concern today continues to be the potential for severe
thunderstorms this evening, primarily across central Minnesota
and northwest Wisconsin. Thunderstorms from this morning/early
afternoon are dissipating over central Minnesota, when and where
we see additional development later this afternoon remains in
question. The most likely area for redevelopment looks to be from
stc east to the WI border, with thunderstorms forming into a line
as they move east into northern Wisconsin. This scenario would
result in thunderstorms only impacting stc, with other terminals
remaining dry. However, given the extreme instability and
boundaries across the region, can not totally rule out
thunderstorm development farther south towards rwf/msp and into
west-central Wisconsin. Confidence in this scenario too low to
mention in the taf, but this trends will be monitored and amended
More widespread showers and thunderstorms are expected to spread
across the area tomorrow morning, with conditions primarily
expected to remain MVFR.
Kmsp... strong capping exists over msp and is anticipated to
result in any storms that develop this evening to remain north and
east of the terminal. As mentioned above, there is a highly
conditional threat for storms to develop further to the south, but
the probability of these storms forming and impacting the
terminal appears too low to warrant a mention in the taf. If this
scenario unfolds, the most likely time frame would be between 5-8
PM. More widespread rainfall is expected to spread into central
and southern Minnesota tomorrow morning, but some uncertainty
exists with how far north the main band of precipitation will set
/Outlook for kmsp/
sun...VFR. Chc thunderstorms and rain. Wind north 5 kts.
Mon...VFR. Wind north 5 kts.
Tue...VFR. Wind west 5 kts.
WI...excessive heat warning until 10 PM CDT this evening for wiz024-
Heat advisory until 8 PM CDT this evening for wiz014>016-023-025-
Minnesota...excessive heat warning until 10 PM CDT this evening for
Heat advisory until 8 PM CDT this evening for mnz049>057.