Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 231113
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
613 AM CDT THU JUN 23 2016
.SHORT TERM...(Today and tonight)
Issued at 455 AM CDT Thu Jun 23 2016
Fairly quiet short term is expected as high pressure slides across
the upper MS Valley through tonight.
This morning, remnant h7 low will move from near Duluth down to
Madison. This will keep scattered light showers going through at
least the morning in western WI, though the hrrr and some of the
HopWRF members show showers lingering into the afternoon as what`s
left of an inverted trough gets hung up and hangs around western WI
this afternoon. Right now, we have it dry out there this afternoon,
but if this trend continues, could see updates later this morning
needing hold on to PoPs for western WI later than we currently have.
For temperatures, we overachieved a bit yesterday, but that was with
925-850 temps that were between 16c and 20c, today we are more 12c
to 16c. Even mixing up to 825mb (unlikely to be that high), you only
get highs in the 70s, so going about 5 degrees below normal with
highs today looks plausible, especially out in WI where cloud cover
will hang on the longest.
Tonight, high pressure will be overhead, so did cool off lows some
from previous forecast, though by Friday morning, return flow and
moisture return will be in full force out in western MN.
.LONG TERM...(Friday through Wednesday)
Issued at 455 AM CDT Thu Jun 23 2016
The main show in the long term remains on Saturday with the
likelihood of widespread thunderstorms across eastern MN and
western WI Saturday afternoon/evening - there is a severe weather
risk on Saturday with the potential for all severe hazards (hail,
Our Saturday weather-maker is currently off the coast of Washington
and British Columbia this morning spreading moisture into the
Pacific Northwest. By 12z Saturday, this upper low will be
approaching the MT/ND border with 500mb height falls across the
Dakotas and a shortwave in the Southern/Central Plains lifting
northeast. Stepping down to 850mb yields strong moisture transport
with the LLJ across the Plains Friday night and Saturday morning.
We are gaining confidence that there will be elevated
thunderstorms in Minnesota (possibly western Wisconsin) Saturday
morning that will be lifting northeast with the warm/moist
advection. We have chance of thunder in the forecast, but we will
probably trend toward likely POPs with time. Current thinking is
that a lot of this morning activity (rain/clouds) will clear the
forecast area by the afternoon when southern MN and western WI
finds itself firmly within the warm sector of the occluded system.
This sets the stage for deep moist convection in the afternoon and
evening out ahead of the cold front.
Here`s what we know at this point. From a synoptic weather pattern
standpoint, Saturday is matching some notable, local severe
weather outbreaks that have happened in the past 10 years. Most
notably, the past 5 runs of the GFS have matched (via the CIPS
analogs) June 17, 2010 (Minnesota`s record tornado outbreak.) The
analogs this morning show that 3 of the top 4 matches to the GFS
on Saturday are all associated with significant severe weather
events: June 17, 2010, July 14, 2010, and July 11, 2008. This
morning, the SPC has added a Slight Risk to the forecast area for
the Day 3 outlook. Coincidentally, three days prior to June 17,
2010, SPC also added our area to a Slight Risk, which ended up as
a Moderate Risk the night before the event. Now, with all that
being said, there are some differences between the notorious June
17th event and what numerical guidance is showing for Saturday.
The 850-700mb troughs on June 17th were a bit cooler and therefore
yielded slightly stronger low level wind fields than what is
expected Saturday. In both the June 17th event and what`s expected
Saturday, the mid level jet and shear are lagged behind the cold
front back to the west. The 850mb flow on Saturday looks like it
will good enough to generate 20-30kts of 0-1km shear - that is
more than respectable, but not as good June 17th. The lack of mid-
level winds could end up limiting the overall severe potential,
but we are still concerned given the winds below 15,000ft. Some
of our local convective allowing models are simulating really good
updraft helicity streaks in Minnesota (suggesting the potential
for rotating thunderstorms). This is especially true in northeast
ND and northwest MN closer to the upper low. The instability and
forcing shouldn`t be much of a limiting factor locally - even with
the threat for the aforementioned morning convection and clouds.
In fact, morning convection could lay out some boundaries and
lower the LCLs. We`ll be in the warm sector with dewpoints near 70
and an approaching trough - we`ll have good SBCAPE/MLCAPE.
Instability uncertainty is more a problem for northern MN. Now,
it`s only Thursday, and the subtleties of the incoming system will
ultimately determine the type/intensity of severe weather, but
this is a system that certainly needs to be taken seriously. There
is a tornado potential if a few things come together.
.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 612 AM CDT Thu Jun 23 2016
Main issue this TAF period is timing improvement for MSP on east.
This area of clouds is at the nose of an inverted trough, which
will be slow to budge today. As a result, clouds will be slow to
budge as well and followed a blend of the LAMP and HRRR for
improvements. The hrrr and some of the HopWRF members have been
showing showers accompanying these clouds through much of the day,
though we think this is more just these models highlighting
moisture in the cloud bearing layers as opposed to something
reaching the ground as evidenced by the lack of ra reports we are
currently seeing in western WI. For tonight, high pressure is in
control, so no weather issues are anticipated.
KMSP...16z is a first guess for when mvfr cigs will leave MSP,
though improvements to VFR could happen as soon as 14z or be
delayed to as late as 19z.
/OUTLOOK FOR KMSP/
FRI...VFR. Winds SSE 5-10 kts.
SAT...Chc MVFR TSRA in mrng. TSRA likely aftn/evening. Winds S-SW
SUN...VFR. Winds W 10-20kts.