Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1241 PM CDT Friday may 29 2015
Updated for aviation discussion below...
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 18z tafs through 18z Saturday afternoon)
issued at 1230 PM CDT Friday may 29 2015
Surface front moving slowly southeast through the first half of
the forecast. Rain showers/thunderstorms and rain limited o mainly along/ahead of front into
the evening...mainly affecting kmsp for a couple hours...and
exiting to Keau through early evening. Low confidence on overall
timing of lower clod trends into the evening. Lagging upper
trough could continue light rain threat through about 01z over
central Minnesota...then reforming to the southeast this evening. Will
still break out to VFR from west to east in Minnesota through about
04z...then remaining VFR into WI through the night. May see VFR
develop through the 12z-14z period there. Confident on VFR
forecast over Minnesota through the rest of the period...and into western
WI by Saturday afternoon. Northerly surface winds developing and
gusting to 25 kts over the west into the late afternoon with wind
guts developing into the east through 00z Sat. Should diminish
this evening with gusts possible developing Saturday morning.
medium confidence on trend of thunder for the next couple of
hours...then should move off to the southeast into the evening.
Lower MVFR ceilings/-shra through the afternoon...with frontal passage winds
becoming north and gusty to 22kts into the evening. Expect VFR
conditions developing through 04z Sat...with layered clouds
exiting after 06z. Will see winds diminish again after 06z and
become gutsy after 14z Sat.
/Outlook for kmsp/
Sat...VFR. Winds NE 10 g20kts.
Sun/Mon...VFR. Winds southeast 10 knots.