Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
402 am CDT Sat Mar 28 2015
Short term...(today and tonight)
issued at 402 am CDT Sat Mar 28 2015
Dry...cool and breezy conditions are expected today light
precipitation arrives late tonight or early Sunday morning.
There is a lingering surface high over the eastern Great Lakes this
morning and at the same time mslp pressure falls are ongoing across
the northern High Plains as a West Coast system continues its
advance to the east-southeast. The resulting pressure pattern today
will bring about a breezy southerly flow. Even though we are
expecting highs in the 40s today /the first time we've been that
warm in a week/...the wind will make it feel much cooler in reality.
The precipitation event expected to affect Minnesota/WI late tonight is already
well inland per the morning water vapor imagery. There have even
been a few lightning strikes in Washington/or out ahead of the vorticity maximum
overnight. We only made minor changes to the forecast. The best
chance for 0.10"-0.25" of liquid looks north of the I-94 corridor.
The precipitation type is tricky given the relatively cool atmosphere at
the onset of the precipitation...this could lead to a little snow/sleet -
especially across central Minnesota. The dominate precipitation type should
eventually be light rain by the time middle Sunday morning rolls
around. We are't expecting much in the way of snow or ice
Long term...(sunday through friday)
issued at 402 am CDT Sat Mar 28 2015
Large scale pattern evolution...
the western ridge looks to break down through the first part of
the week... with the upper level flow becoming more zonal across
the Continental U.S.. rising heights will bring much warmer temperatures into
the upper Midwest by midweek... while a decent shortwave and
associated surface low are prognosticated to move through the region on
Wednesday. By the end of the week things look to cool back down a
bit as the Hudson Bay upper low re-asserts itself southward into
Forecast item/S/ of concern...
chances for precipitation on Sunday... along with strong winds in the wake
of a cold front. Gusty winds and the potential for deep mixing
behind the front could lead to some fire weather concerns over
southwest Minnesota. Midweek system looks like it could bring
first chance for thunder to much of the area.
guidance is in good agreement during the warmup period through
midweek... but diverge a fair amount after Wednesday with respect
to how much it will cool back down... with the GFS and gefs
keeping the flow more zonal than the cooler European model (ecmwf). At this
point... stuck close to the previous forecast... which is
essentially a blend of GFS/European model (ecmwf) solutions.
Sensible weather expectations...
precipitation will continue to shift east across the area on Sunday... with
things quickly drying out behind the cold front. In fact... with
the expected decrease in cloud cover and good mixing we/ll likely
warm during the afternoon behind the front... which could lead to
some relative humidity values near 30 percent over southwest Minnesota. That in
combination with gusty winds could lead to some fire weather
concerns... but much will depend on how well we mix and whether we
see relative humidity values plummet. Surface ridge will bring benign weather
Sunday night through Monday... except for a slight chance for some
light rain over the northern portion of the area late Monday and
across the east Monday night... with perhaps a few wet snowflakes
mixed in by that point. This activity will be associated with a
weak shortwave and surface feature moving through on northwest
upper flow. The next chance for precipitation after that looks to be on
Wednesday as a fairly strong shortwave moves along the northern
tier of the Continental U.S. And through Minnesota Wednesday evening. A
surface low around 990mb will move east-northeast near the
US/Canadian border... dragging a cold front across our area
Wednesday afternoon/evening. We should see strong warm advection
ahead of this... along with some decent moisture return. MUCAPE
values from the GFS get at or above 1000 j/kg for part of the day...
particularly over southwest and south central Minnesota... so
we/ve got a shot for some thunder as the front moves through the
region. At this point... there doesn/T appear to be a sufficient
combination of cape/shear for much of a severe threat... but will
be something to at least keep an eye on over the coming days
should we see higher dewpoints than currently expected or better
timing of the deep layer shear with respect to the instability
confidence in warming temperatures through midweek is high... as
is potential for at least some precipitation on Sunday. Confidence is
moderate that we/ll see some rain showers on Wednesday along with isolated
thunder. Confidence is low to moderate with respect to the
evolution of the large scale pattern by the end of the week.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1115 PM CDT Friday Mar 27 2015
VFR conditions expected. Middle level cloudiness will decrease
overnight but will return Saturday afternoon/evening. Winds will
remain light...but will increase and gust from the south Saturday
Kmsp...no additional concerns.
/Outlook for kmsp/
sun...VFR. Am -ra ending with clearing skies. Winds northwest 25g35kts.
Monday...MVFR possible. Winds west 5-10kts.
Tuesday...VFR. Winds light/variable becoming S 5-10kts.
Minnesota...Fire Weather Watch from Sunday afternoon through Sunday evening