Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
507 PM CST Wednesday Feb 10 2016
Update...for 00z aviation discussion below
Short term...(this evening through thursday)
issued at 349 PM CST Wednesday Feb 10 2016
Main feature driving the weather during the short term is the 1045mb
high centered between the between the Alaska/Canadian border
along the Arctic Ocean and the North Pole. Though the center of
this high will not get here until Saturday morning...there is a
ridge axis that extends from that high center...southeast across
the Canadian prairies and into Minnesota. This explains in large part why
highs today have been a good 15 to 20 degrees below normal. This
ridge axis will remain over the area through the short
term...though a weak trough within the ridge will be approaching
central Minnesota by Thursday afternoon. Subtle warm air advection out ahead of this
feature explains why highs Thursday will be about 5 to 10 degrees
warmer than today.
Main question for tonight is what happens with cloud cover.
Extensive band of clouds extends from Huntsville Alabama all the way
up into the Canadian prairies. These clouds are on the western
gradient of the Arctic airmass centered over/north of the Great
Lakes and through this period...said gradient does not look to
change/move a whole lot. The main changes we will see is a slight
weakening of the gradient and a slight shift to the west. This is
why we are not anticipating much change through the night in the
current cloud pattern...which will setup quite the gradient in lows
overnight from west to east across the area with upper single digits
above zero in western Minnesota beneath the clouds...while mainly clear skies
in western WI will allow for some negative teens below zero.
Have also kept the short term dry...though there will be another
short wave diving across the Dakotas with northwest flow Thursday
afternoon. As mentioned in the previous paragraph...with the 850 mb
temperature gradient shifting west a little overnight...expect snow with
this clipper to be SW of what we have seen today...with any light
snow remain SW of the mpx County Warning Area through the day Thursday. Beside the
fgen slipping west...surface high coming in behind this wave is even
drier than what we are seeing today...with that dry air also helping
keep snow at Bay.
Long term...(thursday night through wednesday)
issued at 349 PM CST Wednesday Feb 10 2016
The main concerns in the long term period include the cold
temperatures and wind chills this weekend. This will be followed by
a clipper system Sunday which may produce light snow accumulations
across the area. Looking to next week...a change in the jet looks to
bring a significant warm up by the latter half of the week.
By Friday night...an impressive core of Arctic air will be center
over southeastern Hudson Bay...with 850mb temperatures near an impressive -
40c. This Arctic air will advance through the eastern Great Lakes
this weekend...grazing the upper Midwest with 850 temperatures falling to
around -20c. However...a 1044mb surface high is expected to push in
from the north Friday through Saturday...setting the stage for quite
a cold night Friday night. Did not make significant changes to the
overnight low forecast for Friday night...as guidance is indicating
the possibility of cirrus working in overnight which could limit our
radiational cooling potential a little bit. So...still expecting
widespread minus teens and a few minus twenties across north central
For Sunday...a shortwave trough will traverse the area from northwest to
southeast...basically an Alberta clipper type system with generally light
quantitative precipitation forecast...but enough where the potential for light snow accumulations
exist thanks to low level warm air advection/isentropic
lift...especially across western Minnesota. Held on to the near 50 probability of precipitation out
west...mainly due to differences in timing and quantitative precipitation forecast placement with
this feature. As the shortwave moves east...both the GFS and ec
indicate potential for it to dry out a bit...so the eastern portion
of the forecast area may not see as much snowfall as the west. Temperatures
will begin warming at the surface with southerly winds...with highs
bounding back into the 20s.
Additional warming is expected into early next week as an upper
level jet builds across the western Continental U.S. And pushes east. Both the
GFS/ec indicate the possibility of another ripple with warm air advection lift next
Wednesday...and additional light snow. Further heating is expected
beyond that as the ridge continues to build and the flow becomes
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 507 PM CST Wednesday Feb 10 2016
VFR conditions are expected through the night...with middle/high
clouds filtering overhead. Do see some gradual lowering/thickening
of the cloud cover on Thursday. Should have VFR ceilings through the
period...but may have MVFR level ceilings sneaking toward western
sites /kaxn and krwf/ toward Thursday evening. Winds will become
light and variable tonight...then back to the southwest on
Thursday and increase to around 5-7kts.
scattered-broken middle high clouds will stream across through the
period...thickening/lowering to ovc050 Thursday afternoon. North-northeast
winds will back to the north-northwest this evening and decrease below 5
kts...then back further to west-southwest on Thursday.
/Outlook for kmsp/
Friday...VFR. Wind northwest 12g20kts.
Sat...VFR. Wind vrb3kts.
Sun...MVFR/IFR with -sn likely. Wind S 15 knots.