Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
617 am CDT Friday may 29 2015
Short term...(today and tonight)
issued at 410 am CDT Friday may 29 2015
A complex frontal passage in terms of precipitation timing...placement...
and coverage is the main concern in the short term. At 3 am...that
front was stretched from NE Wyoming across sodak to the Minnesota/Dakotas
border then up toward Lake of The Woods from there. There is a hint
of a surface low over eastern sodak in the surface observation...and the hrrr shows
this feature tracking east across southern Minnesota through the day today. To
this point...the cold front is tracking well with what the forecast
from yesterday had...so there were not drastic changes made to the
forecast other than to slow down the precips departure some later in
Right out The Gate...there really is not any model that has
initiated all that well. The hrrr and 3z hopwrf members got closest
to what is happening around SW Minnesota now...but have been a couple of
hours late in getting this activity going. Still...favored the pop
forecast today heavily toward the hrrr/hopwrf...just knowing we had
to spread activity in a bitter faster than what they would show.
What we are expecting for today is lead warm air advection showers over eastern Minnesota/western
WI will largely be out of the mpx County Warning Area by about 15z...though at that
time the combination of an upper wave currently over NE Nebraska moving
into SW Minnesota with the surface low and cold front arriving as well will
lead to a blossoming of thunderstorms in SW Minnesota that will work out to
the east of the front through the morning. This expansion of precipitation
will be supported by more winter-like forcing features as Minnesota/western WI
find themselves within the right entrance region of a strengthening
jet streak over Lake Superior with strong fgen noted in the 850 mb-700 mb
layer. This synoptic forcing will get an added boost from the
presence of 1000-1500 j/kg of MUCAPE out ahead of the front.
Rap/hrrr have been consistent with showing a heavy rain signal with
this activity...with the 3z hopwrf lending support to the idea of a
band of 1-3 inches of rain developing from SW Minnesota toward the western Twin
Cities metropolitan. Not expecting any severe weather with this frontal passage as
deep layer shear looks to largely be under 30 kts...with extensive
cloud cover and precipitation this morning limiting the amount of
instability that can develop as well.
Other tough part of the forecast will be temperatures. 850 mb temperatures
this morning are still up around 14c...so there is potential for
highs in the low 80s again out toward eau...though current thought
is cloud cover will hold things back in the 70s. On the other end of
the County Warning Area...the combination of rain and cloud cover in the morning
followed by strong cold air advection in the afternoon will hold temperatures out
around axn in the lower 60s. This will set the stage for a chilly
night tonight in western Minnesota...where clearing skies combined with dewps
dropping through the 30s will allow temperatures Friday morning to
start out in the upper 30s in west central Minnesota.
Long term...(saturday through thursday)
issued at 410 am CDT Friday may 29 2015
A very pleasant Saturday will begin the long term with plenty of
sunshine. High temperatures will be a tad cool with mix-down
from the GFS at 850mb providing the foundation for highs in the
upper 50s to lower 60s. It will be a cool night Saturday night as
a high pressure system covers the forecast area. Frost is likely along
Highway 8 in our west central WI counties. Wind and dew point
forecasts from the mavmos suggest lows could reach the freezing
mark Sunday morning for an hour or two.
A little bit of a change in the Sunday forecast from a day ago.
There will be more cloudiness working in from the west during the
day. However...00z model solutions are trying to develop/spread some
showers into west central Minnesota Sunday afternoon. This is from a
combination of elements beginning to come together...including middle
level waves working across the northern plains along with moisture
transport on the increase on the backside of the high. At this
point...allowed for small probability of precipitation into west central Minnesota during the
afternoon. This is a compromise of the GFS which would have
showers all the way to the Twin Cities and the European model (ecmwf) which would
stop the showers at our western border. Certainly Don/T see the
showers per the GFS as profile data shows quite the dry wedge from
700 mb on down with any forcing well to our west.
Small shower/thunderstorm chances will then work slowly east
across the forecast area next week as the flow aloft becomes more southwest
ahead of a large western trough along with increasing southerly
low level moisture transport. High temperatures will be on the
rebound with highs climbing into the 70s on Tuesday with upper 70s
to lower 80s for Wednesday and Thursday.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 615 am CDT Friday may 29 2015
A low confidence set of tafs this period with a cold front working
across the area. No model has really picked up well on activity
moving across southern Minnesota this morning...which makes it hard to believe
the widespread activity the hrrr has this afternoon...though it is
certainly plausible given the forcing. With these tafs...tried to
maintain consistency as much as possible with the previous
forecast. Main change with the thunder is the hrrr has been slow
in generating activity all night...so did speed up arrival some at
msp/rnh/eau. Behind the front...MVFR with pockets of IFR ceilings
have developed across nodak into northwest Minnesota. This band will work down
through the terminals this afternoon and followed the sref MVFR
ceiling probabilities for both timing these ceilings in and out of tafs.
Other area of low confidence at the start of the tafs is with the
winds. Baggy pressure gradient out ahead of the front has resulted
in winds being a bit variable until becoming northwest quickly behind
Kmsp...am confident it will rain much of the day...but lower
confidence on timing of showers along with any potential thunder
late this morning into the afternoon. May see ceilings dip under 017
as the front is working through...with timing back to VFR tonight on
the later as opposed to the earlier side of the timing envelop.
Also have tricky timing for changing of winds that will require a
runway swap this morning. Winds will likely go light and vrb from 14
to 17z before northwest winds become established after 18z.
/Outlook for kmsp/
Sat...VFR. Winds NE 10 kts.
Sun/Mon...VFR. Winds southeast 10 knots.