Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
531 am CST Wednesday Nov 26 2014
Short term...(today and tonight)
issued at 318 am CST Wednesday Nov 26 2014
The main concern today is whether a dry layer blw 5k across southeast/ec
Minnesota and into wc WI will erode faster due to anticipated dendritic
zone enhancement expected in the next several hours. However...
models hold onto the drier layer longer into the morning...or
until the northern shortwave and associated frontogenetic forcing
moves into the region by late morning/noon.
Mesoscale models have trended for the heavier bands of snow to
hold from the SW metropolitan area...south/SSW toward mkt and form. A
secondary band develops after 18z along the line from northwest WI...SW
to the Twin Cities which again is associated with the secondary
Due to some uncertainties of where this dry slot holds will
continue with the same advisory area where locally 3 to 5 inches
will fall by early-middle afternoon. Highest confidence of locally 3
to 5 inches will fall from mkt...southward to the Iowa border as
both the stronger lift and deeper moisture resides. After
21z...there will be a sharp cutoff from northwest to southeast as the main
shortwave moves through the upper Midwest. Most areas will taper off
to flurries or light snow in southeast/SC Minnesota and wc WI by early evening.
Surface winds will become gusty in wc/SW Minnesota as the surface low moves into
southern Iowa. There will be localized lower surface visibility due to
blowing snow. But not expecting blizzard conds. The strongest
winds will occur SW of mpx County Warning Area. Wind chill values will likely fall
well blw zero overnight as temperatures fall into the single digits blw
zero...to around 5 above zero.
Long term...(thursday through tuesday)
issued at 318 am CST Wednesday Nov 26 2014
A fairly progressive pattern is expected to remain in place
starting on Thanksgiving and continuing into early next week...
both in terms of a roller coaster of temperatures and in
occasional quick-hitting minor winter weather events.
A strong surge of cold air will accompany high pressure sliding
across the region during the day on Thanksgiving...but this area
of high pressure will quickly move off to the southeast Thursday
night in advance of an organizing area of low pressure over the
Pacific northwest. This low will gradually drive southeast then east over the northern
plains and upper miss River Valley Friday through Saturday. In
advance of this low...strong warm advection combined with surging
southerly moisture into the region will be able to produce at least a
couple inches of accumulating snow for mainly northern and eastern portions
of the weather forecast office mpx County warning forecast area for Thursday night through Friday. How much and when
snow falls will be dependent on the amount of moisture and warm
air being brought into the region...but at this time there is no reason to
believe there will be anything more than minor accumulations. That
said...there is also the possibility of some mixed wintry
precipitation for southern and southeastern portions of the coverage area on
the backside of this system for Friday into Friday night. Again...not
looking for much in the way of icing but with some warmer air
aloft...it is not unreasonable to potentially have some glazing
before the precipitation ends. This system finally ejects off to
the east Sat night into sun...with any remaining snowfall from
this system Friday night through Sat remaining just north of the mpx
County warning forecast area. The warm air remains in place through Sat...then the associated
cold front pushes through early sun... bringing a return of much colder
air to the region for the start of next week. Another low pressure
system looks to impact the area for Tuesday into Wednesday...but confidence
is low on there actually being measurable precipitation so have capped
probability of precipitation at 20 percent for Tuesday and Tuesday night. A brief warmup for Tuesday
is expected with this system...but not enough to produce a p-type
to anything other than -sn. Another cold surge will follow this
system for the latter half of the week.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 514 am CST Wednesday Nov 26 2014
Since 3 am...an enhanced area of snow had developed across SC Minnesota
which has moved northward into portions of ec Minnesota. Other areas of
SW Minnesota have deteriorated as both the next disturbance moving southeast
across wc Minnesota and the departing surface low converge. Based on the
latest model guidance and surface observation/reflectivity pattern...the
enhanced area in SC Minnesota will likely produce 1/2 to locally 3/4 inch
per hour snowfall rates with visibilities less than 1/2sm at times. Only
krwf/kmsp will be affected by these higher rates...but should only
last 2 to 3 hours as the main upper support moves southeast of our region.
Confidence is high for krwf to continue with IFR/LIFR through
15-18z...with MVFR during the afternoon. Kaxn/kstc/krnh will likely be
on the edge of IFR visibility in snow...but ceilings should remain at or above 1.5k.
Confidence in these areas remain moderate. Keau will likely remain
VFR until this afternoon. Surface winds initially will be from the
N/NE...then back to the north/northwest during the afternoon. Spds will hold in
the 10-15 knots range...with occasional gusts above 20 kts in wc/SW Minnesota.
Confidence has increased to support IFR ceilings/visibilities during the next
6 hours. Confidence remains low on snowfall rates of 3/4 to 1 inch
per hour. The best scenario is 1/2 inch per hour between 13-17z as
both the deeper moisture and lift are present. There remains a
possibility of a secondary band of -sn to continue across the
Airport grounds between 18-21z...but confidence remains low with a
faster scenario of MVFR/VFR conds developing. Winds will remain
from the NE this morning...with winds backing to the north-northwest/north during
the afternoon and increasing to 10 kts.
/Outlook for kmsp/
Friday...chance MVFR and -sn. Winds southeast 5 kts.
Sat...chance MVFR. Winds north 10 kts.
Sun...VFR. Winds northwest 10 kts.
Minnesota...Winter Weather Advisory until 6 PM CST this evening for mnz059-
Winter Weather Advisory until noon CST today for mnz054-056>058-