Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
328 PM CST sun Jan 25 2015
Short term...(this evening through monday)
issued at 328 PM CST sun Jan 25 2015
The afternoon turned out pretty nice weather-wise across portions
of west central WI...the Twin Cities as well as from Hutchinson on
north through Little Falls. A dry northeast low level flow into
these areas has lowered dew points into the teens. This will allow
for temperatures to drop rather quickly this evening before
turning around and rising during the late night hours. The turn
around in temperatures overnight is associated with a clipper
passing to our north along with a warm front moving in. Model
trends today have been consistent on showing snow developing
across far northern Minnesota late this evening and then spreading southeast
into far eastern areas of Minnesota and all of western WI during the
overnight hours. The snow will continue for a time in western WI
Monday morning. Confidence is high on an inch or two of snow
accumulation in our far eastern WI counties by middle morning on
Monday (rice lake to Eau Claire on east). Forecast snow amounts
dwindle to a half inch or less in eastern Minnesota.
Complicating matters tonight is a warm layer aloft spreading into
western Minnesota this evening along with the loss of ice aloft towards
daybreak across eastern Minnesota and then eventually across adjoining
areas of western WI Monday morning. Various wrfs today have
become more convective looking with the simulated radar
reflectivity in western Minnesota with a brief period of freezing rain
indicated with the ptype. Therefore...expanded low chance probability of precipitation
farther west to the South Dakota border and south to Iowa to handle the
potential for some light freezing rain. Coverage is spotty and the
duration at this point is a couple of hours. NAM BUFKIT profile
data show more of a low level saturation (sfc-800mb) and strongly
veering wind profile across eastern Minnesota and far western WI early Monday
morning. With this in mind...switched ptype to a chance for freezing
drizzle. No Winter Weather Advisory planned at this time with only
low chances for wintry precipitation.
Its now looking like Monday will be the warmest day of the
week...although Tuesday and Wednesday will not be far behind.
Used pretty much British Columbia raw blend for guidance which resulted in
highs from the middle 40s in SW Minnesota...the upper 30s from kstc
through kmsp with middle 30s at Keau.
Long term...(monday night through sunday)
issued at 328 PM CST sun Jan 25 2015
Picking up the forecast Monday night...we'll be dealing with pushing
lingering light precipitation off to the east of the western WI. The
remainder of the forecast area will already be dry by this time. Model
soundings indicate we could lose middle level saturation...a recipe for
drizzle or freezing drizzle. So that remains in the forecast for
now on the back edge of the expected snowfall in the short term
Heading into Tuesday...the upper level jet overhead will drift
northeast of our area as the western U.S. Ridge pushes eastward.
Model guidance remained pretty consistent in terms of how much
warming will occur with the ridge through midweek. Tuesday will be a
quiet weather day as a surface high moves through the upper Midwest.
The ridge axis will still be upstream during the day...so we won't
see much warm air advection...but still expect highs around 10
degrees above normal with the lack of snow cover...sunshine...and
modest low level temperatures.
Low level warm air advection increases late Tuesday night through
Wednesday. As the previous discussion indicated...the magnitude of
the advection was dialed back in the model runs last night...and
this held consistent today. So...little change was needed for the
high temperatures on Wednesday. It still looks like cloud cover were
quickly increase through the day on Wednesday...which will hinder
additional warming due to solar radiation.
On Wednesday night...another shortwave is expected to drop southeast
through the upper Midwest. The vast majority of the precipitation looks to
remain north of our area at this time...with limited moisture toward
central/southern Minnesota and west central WI. So...stuck with chance
probability of precipitation for this period. Once this feature slides by...cold air
advection will ensure...but won't be overly strong as the true
Arctic air remains to the north through the end of the work week.
Indications remain that temperatures will cool further for next
weekend as the polar jet buckles and Arctic air advances south. The
forecast issue though is where does the core of the cold line up.
The GFS has shifted the core of the cold just east of our
area...which would be more of a glancing blow. The ec however
indicates a colder solution for our area. Temperatures will be fine
tuned over the coming days. Regardless...we can expect an overall
cooling trend toward the end of the weekend.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1200 PM CST sun Jan 25 2015
Low level dry air from the northeast has temporarily parted the
MVFR ceilings across much of west central WI and the Twin Cities.
This should last into the evening hours before the flow veers to
a more southerly direction and brings MVFR ceilings back from the
west and south. A concern however is that the MVFR ceilings
around kdlh to kcbg apprear to be moving slowly south and may
arrive before this evening at krnh and kmsp. Hence a low
confidence VFR forecast into this evening for these two sites.
The western taf sites will be mainly MVFR with a few breaks
possible. A clipper moving by tonight and early Monday to our
north will push a warm front across the local area. Light snow is
expected to develop across far northern areas of Minnesota tonight and
push southeast across kstc...kmsp....krnh and Keau during the
late night hours. Keau has the best chance for seeing around an
inch of snow by middle morning on Monday with amounts dropping back
to a few tenths at kmsp. One problem for early Monday morning is
the loss of ice aloft from kaxn through kstc to the Twin Cities.
NAM BUFKIT profile data indicates a potential freezing drizzle
scenario. Hence...for this cycle...included snow along with a
chance of freezing drizzle at all of the tafs except krwf.
Kmsp...low confidence forecast of VFR ceilings continuing through
this evening with MVFR located as close as kcmg. Main concern late
tonight and Monday morning is a few hour period of freezing
drizzle. Confidence highest in the 11z-14z time frame.
/Outlook for kmsp/
Tuesday...VFR. Wind light/variable.
Wednesday...VFR. Chance MVFR. Wind southeast 10 knots.
Thursday...chance MVFR/-sn. Wind northwest 10-20 knots.