Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 250932
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
432 AM CDT WED MAY 25 2016
.SHORT TERM...(Today and tonight)
Issued at 432 AM CDT Wed May 25 2016
An active morning/afternoon is in store for the area as
negatively tilted trough currently extending from central SODAK
down toward KC swings through the upper MS Valley region. CAMs and
deterministic models are all similar in showing a NW to SE
oriented line of thunderstorms coming up with a surge in moisture
transport and theta- e. There was also good agreement in the
models with this feature coming through a bit slower than what the
previous forecast had, so did slow the onset of precip down quite
a bit...with storms looking to move into SW portions of the MPX
cwa around 12z, reach St. Cloud and the Twin Cities around lunch
time and not push into western WI until the afternoon. Behind this
wave, models are showing strong mid level subsidence and drying,
which should really limit the amount of activity we see in the
wake of this system. As a result, did decrease PoPs considerably
in the wake of the main precip band. Left behind broad bushed low
chance pops for the afternoon, as a moist environment will remain
in place, which would become quite unstable if some sunshine can
be received, but is beginning to look like just about all of our
precip today will be with the wave moving in this morning.
For QPF from this convection, it does not look overly excessive.
Cell movement looks to be reasonable and there is not much
indication of there being training, with rainfall amounts around a
half inch looking common, though a few heavier corridors around an
inch will be possible.
Tonight, another shortwave will be coming out of the Dakotas.
Models overnight show this wave heading for northern MN, farther
north than what guidance was showing yesterday, so reduced PoPs
overnight as well. The most bullish model for tonight is the NCAR
Ensemble WRF. All 10 of its members show a bowing MCS working
across southern MN out ahead of the Dakotas wave. You can not find
any other support for this solution in the CAMs or deterministic
models, but given moist/unstable environment we will have in
place, it`s not completely out of the realm of possibility.
For the severe threat, our main chance looks to be with the wave
coming at us this morning. Instability with this line looks to be
on the order of 1000-2000 j/kg of MUCAPE and there is good turning
of the winds, so a few stronger cells capable of producing
marginally severe hail and for the afternoon, wind gusts will be
possible. Severe threat behind this wave is very much conditional,
but if storms develop this afternoon, they would find themselves
in a favorable supercell environment. For tonight, the NCAR WRF
solution has a good wind event for us. Unfortunately, the only
period we have much confidence in convection occurring is with the
wave coming up now and more limited instability and weaker mid
level lapse with it seem to point to another day of mainly non-
severe storms with a few stronger trouble makers.
.LONG TERM...(Thursday through Tuesday)
Issued at 432 AM CDT Wed May 25 2016
A warm, humid, stormy pattern will continue throughout the long
term period - although there will likely be prolonged dry periods
mixed in at any given location.
Thursday: Forecast Confidence - Medium to High.
Behind the wave today and tonight, mid level ridging will build in
Thursday. Subsidence with the ridging will scour out the clouds
early with forecast soundings showing a rather dry column for
much of the day. The drier air, full sun, and subsidence should
send temperatures into the mid or upper 80s over much of the area.
Much of the guidance appears a bit low in this situation,
particularly with 925 mb temps of +22 to +25C. By late afternoon,
the next upper wave will already be approaching from the
southwest. A strengthening 850 mb jet and surface warm front along
the I-80 corridor with very unstable air along and to the south
of it will spark thunderstorms across Nebraska and Iowa around mid
afternoon. As the wave lifts northeast across the Plains toward
the Upper Mississippi Valley, these storms should build northward
toward the Minnesota/Iowa border by late afternoon. A few of these
may be severe, especially if the deeper moisture can work north
toward Minnesota by early evening. This is somewhat in doubt
though given early day convection across Iowa and Missouri
earlier, which could keep the front further south for much of the
day than is currently forecast. While likely weakening, the
activity across Iowa and Nebraska will lift north across Minnesota
and Wisconsin Thursday night.
Thursday night through Saturday night: Forecast Confidence -
Activity across Iowa and Nebraska will lift north across
Minnesota and Wisconsin Thursday night and Friday morning. Not
expecting too much severe potential with this with a stabilizing
boundary layer and weakening lapse rates. The upper low over the
western High Plains Thursday night will slowly advance
northeastward toward the northern Plains/Upper Mississippi Valley
Saturday night and Sunday. Its energy will elongate with time and
several smaller scale disturbances may drift across during this
time. Potential for activity throughout this period will heavily
depend on previous days` convective evolution and resultant
outflow boundaries/mesoscale convective vortexes. However, given
the likelihood of some destabilization each day and favorable
upper support, scattered to numerous showers and thunderstorms are
expected each period through the first half of the weekend.
Sunday through Tuesday: Forecast Confidence - Medium.
With the upper low pushing out Saturday night, support will be
lost for widespread thunderstorm development Sunday and Monday.
Ridging will finally build across the southern Plains and should
cap disturbances from originating there early next week. Instead,
a trough dipping into the northern Rockies will spread height
falls eastward to the Upper Midwest Tuesday when storm chances
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 112 AM CDT Wed May 25 2016
SW flow aloft means energy helping generate TSRA from SODAK down
through KS will be heading this way through the night. Confidence
is increasing in a NW to SE oriented band of SHRA/TSRA moving
across MN during the morning and into WI during the afternoon.
Used a combination of the HRRR/RAP/NAM to time this activity in
to TAFs, which resulted in delaying precip onset from what the 00z
TAFs had by an hour or two. Behind this initial wave, uncertainty
in the forecast is high. There will be a lot of mid level drying
and subsidence in the wake of this mornings wave. Current thinking
is this drying and subsidence will limit storm redevelopment in
the afternoon, with extensive cloud cover limiting destabilization
and potential for seeing more SHRA/TSRA from the afternoon into
Wednesday night. Main concern with what these TAFs is they may
not be capturing the potential for a few hours of MVFR cigs in
the wake of the rain when looking at RH in the 925-850mb layer off
the RAP/NAM. Would like to see better MVFR ceiling probs in the
SREF and more clouds in that level forecast on the HRRR though
before getting too carried away with that.
KMSP...Although still a good deal of variability in the CAMS with
how widespread TSRA will be with the band moving up this morning,
there is good agreement on the 16z to 19z period being most likely
for seeing TSRA, so hit this period with a prevailing TSRA
group. After that, really don`t see much potential for SHRA/TSRA
the rest of the period.
/OUTLOOK FOR KMSP/
Thu...Mainly VFR. Chc TSRA/MVFR. Wind S to SW 5 kts.
Fri...Mainly VFR. Chc TSRA/MVFR. Wind SE 5 kts.
Sat...MVFR. TSRA/MVFR Likely. Wind SSE 5 kts.