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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
410 am CST Thursday Nov 27 2014

Short term...(today through friday)
issued at 322 am CST Thursday Nov 27 2014

Clear skies...fresh snow...and building high pressure resulted in
another very cold morning across the region. Overnight lows are
expected to be below zero across most of Minnesota...with
lingering clouds keeping Wisconsin slightly warmer. Today the cold
will continue as highs struggle to reach double digits. Later
tonight light snow will develop out west and spread eastward along
and north of i94 Friday morning which will slicken up the roads
for the black Friday shoppers.

The aforementioned surface high pressure will gradually shift
southeast today. The 27.00z radiosonde observation at kmpx measured -10c at
h850...which is quite mild compared to the -22c recorded just
upstream at kinl. As the cold air to the north advects across the
region it will limit the afternoon heating resulting in another
day where the high temperature will be colder than the normal low
temperature.

Later tonight a weak shortwave resulting more from the speed shear
along the poleward side of the jet than from actual curvature
will cause a warm front to lift through the region. Isentropic
ascent along this frontal boundary will lead to a band of light to
moderate snow that will be heaviest along and north of the I-94
corridor. Forecast soundings show a favorable veering wind
profile...but the Omega is fairly weak throughout. This is because
there isnt a deep frontogenetic circulation which would focus the
ascent along a narrow corridor. There is still an fgen
signal...especially in the h850-700mb layer...but it is a
transient feature that doesnt become anchored and allow for
persistent banded precipitation and high snowfall totals. Feel the hires
arw and nmm models have a good handle on the northwest/southeast
oriented area of precipitation that develops across western Minnesota late
Thursday evening...and slides eastward over western WI Friday
morning.

Sref plumes show snowfall totals will be only around 1-3
inches...with a 4 inch total at the high end of the spread in the
northern counties of the forecast area. This seems reasonable and
by itself wouldnt normally have much impact. However...it will
be most intense early Friday morning when shoppers are driving to
the stores...so issued a Winter Weather Advisory northeast of I-94
where the heaviest snow is expected. The airforce snow ratio
method of the GFS had 20:1 ratios...which seem high considering
the weak lift and narrow dendritic growth zone...but the veering
wind profile and relatively weak surface winds should support
ratios that are higher than climatology in the advisory area.
Finally...forecast soundings show the potential for freezing
drizzle/wintry mix on the back side of this area of snow once the
ice crystals disappear. This could lead to a light glazing if it
does indeed occur.

Long term...(friday night through wednesday)
issued at 322 am CST Thursday Nov 27 2014

Once the low pressure system over the north-central Continental U.S. That is to bring
additional wintry precipitation to the weather forecast office mpx County warning forecast area exits the area Friday
night...there is very little to speak of for additional
precipitation through the rest of the extended portion of the
forecast. That said...mid-winter type cold air will be highly
prevalent through the end of this week into the first half of next
week.

The low pressure center over the Dakotas at the start of the period
will shift east-northeast into southeast Canada while its trailing cold front slogs
through the northern plains and upper miss River Valley. Some residual
warm air aloft atop the influx of colder surface air with just enough
pre-frontal lift and moisture will squeeze out some lingering
areas of -fzdz and/or -shsn over far northern and eastern portions of the
County warning forecast area Friday night. Drier/colder air rushing in on the backside will
efficiently keep this icy precipitation to a minimum...but still may
produce some glazing over any snow received earlier on Friday. The
other concern will be fog developing in southern portions of the County warning forecast area
Friday night into Sat morning with the warmer air over the colder
recently-received snow...so have indicated as such with fzfg in
gridded and text products. Clouds will linger Sat into sun as the
frontal system in its entirety will be slow to exit the
region...but am not expecting any further precipitation as moisture will
be lacking and best lift will be east of the County warning forecast area. High pressure then
takes hold Sun night through Monday night...resulting in clearing
skies but much colder conds. The roller coaster trend in temperatures
will continue going into the middle portion of the week as
indications are that another weak low pressure system driving eastward across
the northern tier states brings warmer southerly air but also possibly
additional wintry precipitation. However...this system is rather weak and
there is considerable model disagreement so have kept slight chance
probability of precipitation confined to only far southern portions of the County warning forecast area.

Regarding the temperature trends...will look for the warmest day of the
next 7 days to occur on Saturday as highs hit the middle 30s to near
40. But...as mentioned above...the cold frontal passage looks occur by Sat
night so this brings a return of teens and lower 20s for highs on
sun into Monday. Temperatures do looks to increases on Tuesday and Wednesday but still
remain below the freezing mark.

&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1046 PM CST Wednesday Nov 26 2014

Renegade flurries will pass across west central WI and southeast Minnesota in
the 06z-08z time frame as weak middle level forcing moves through.
Ceilings/visibilities are forecast to remain VFR. Elsewhere...
skies will be mainly clear. Northwest winds near 12 knots will be
common overnight diminishing to less than 10 knots Thursday
morning and them becoming light and variable in the afternoon. A
warm front across the western Dakotas Thursday evening will move
into Minnesota by Friday morning. Snow will develop ahead of the front
and reach krwf and kaxn near the end of the taf period (04z-06z).
Ceilings/visibilities are forecast to quickly lower to MVFR/IFR
respectively.

Kmsp...VFR through Thursday evening. A warm front will approach
during the early morning hours on Friday with a period of light
snow/MVFR ceilings and IFR visibilities. Currently have the snow
beginning by 28/07z. The snow should be east of the airfield by
middle morning on Friday but MVFR and perhaps IFR ceilings will
persist.

/Outlook for kmsp/
Sat...VFR. Winds S 5-10 kts.
Sun...VFR. Winds northwest 10-15 kts.
Monday...VFR. Winds northwest 5-10 kts...becoming S.

&&

Mpx watches/warnings/advisories...
Minnesota...Winter Weather Advisory from 10 PM this evening to 4 PM CST
Friday for mnz042>045-050-052-053.

WI...Winter Weather Advisory from 10 PM this evening to 4 PM CST
Friday for wiz014-015.

&&

$$

Short term...jrb
long term...jpc
aviation...rah

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