Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1134 PM CST Wednesday Jan 28 2015

issued at 1127 PM CST Wednesday Jan 28 2015

Updated to include 06z aviation discussion below.


Short term...(this evening through thursday)
issued at 342 PM CST Wednesday Jan 28 2015

An active short term ahead as a low pressure system over the
eastern Dakotas slides southeast into northern Illinois by Thursday
morning. Little ice is indicated aloft over northern and eastern
areas of the forecast area tonight with deepening low level saturation. In
addition...southerly low level winds increase rather dramatically
early tonight across eastern Iowa on northward into west central
WI...with a veering profile through 800mb. This should add the
turbulence factor to allow freezing drizzle to become widespread
across much of west central WI from around middle evening into early
Thursday morning. This is collaborated by runs today of the
hopwrf...hrrr and rap showing some a few hundredths of quantitative precipitation forecast in the
aforementioned areas. Therefore...issued a Freezing Rain Advisory
from 9 PM through 3 am from Rice Lake and Ladysmith on south
through Menomonie and Augusta. The evening shift will need to keep
a close eye from the Twin Cities on northward where confidence on
the freezing drizzle is lower.

In the wake of the low pressure system...the surface pressure
gradient increases significantly across eastern South Dakota and SW Minnesota
after midnight (12 millibars). In fact...6 hour pressure changes
are near 14 millibars to our west. BUFKIT profile data showed two
things. First...the NAM profile had the strongest top of The
Channel winds nearing 50 knots across the Minnesota River Valley around
09z while the GFS profile had 32 knot winds at 200 feet at kfrm.
The combination of cold air advection and a unidirectional flow to the top of The
Channel resulted in a Wind Advisory being issued along and south
of a line from Appleton to Albert Lea from midnight through 9 am.

Temperatures tonight and Thursday are interesting. Because of the
low pressure system coming into the area tonight...temperatures
will warm a little this evening and then drop back to a little
below where we are now. Thursday's highs will be early in the
morning with readings falling into the teens and lower 20s by
this time Thursday afternoon.

Long term...(thursday night through wednesday)
issued at 342 PM CST Wednesday Jan 28 2015

By tomorrow evening...the pressure gradient will be weakening and
those strong northwesterly winds will start to slowly decrease. A
surface high will drift southeast through our area overnight
through Friday morning...which will be one of the cooler
mornings we've had in two+ weeks with lows ranging from near zero
near about 10-15 above toward Redwood Falls. The
core of the cold will essentially miss US to the east as it is
dragged south behind the system impacting out region tonight.

On Friday...modest warm air advection will ensue and allow
temperatures to warm to very near seasonal normals. With the colder
air in place to the east of the area...highs will struggle to reach
20 in west central WI...but warmer air the further west you go will
yield highs in the middle 20s for eastern Minnesota and low 30s across far
southwestern Minnesota.

The main change from the previous forecast was to the Saturday
night system. Both the GFS and ec runs came in with a strong
surface high pushing south from Saskatchewan into the upper
Midwest as the northern stream jet buckles southward allowing dry
Arctic air to advance further south than previous runs indicated.
This is a great hindrance to the potential for snow from a system
developing in the southwestern Continental U.S.. but...there is potential for
light snow from a northern stream shortwave Saturday night. This
lines up well with an enhanced area of pv advecting southeast and
in conjunction with the left exit region of a 120kt jet streak.
Any snow that does fall through will be very light with the pre-
existing low level dry air.

It looks like we'll begin February with temperatures slightly below
normal after an impressive warm stretch for the last 3 weeks of
January. Bouts of Arctic air will drop south through the
northern/northeastern Great US more of a glancing
blow. Another possible clipper system could bring another shot of
very light snow Monday night/Tuesday.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1127 PM CST Wednesday Jan 28 2015

Large area of -fzdz slowly eroding away to the east as cold front makes
progress through the County warning forecast area. This is allowing western Minnesota to have ceilings
rise from IFR range to MVFR range while visibility increases to VFR. This
trend will continue eastward slowly through the early morning hours. In
conjunction with the clearing will be a strong surge in wind
speeds in the wake of the cold front. Northwest winds will increase to 15-25
knots with higher gusts during the early morning hours...lasting through Thursday
afternoon before speeds dissipate Thursday evening. The increases in wind speeds
will help scour out near-surface moisture...allowing visibilities to quickly
increases but the low stratus will linger for much of the day. By late
afternoon...any lingering low stratus will scatter out...resulting in
VFR conds by late Thursday afternoon into Thursday evening.

Kmsp...have initialized with IFR conds but as the cold front continues
to shift east across the area...visibility will quickly improve between 06z-
08z to VFR conds. Ceilings will be slow to follow by am expecting ceilings
to rise into MVFR range by 08z. Still some question as to how
quickly ceilings rise about the 1700 feet threshold...and if anything...
the timing may be later than the 14z timeframe currently
advertised. Otherwise...conds are on track to reach VFR levels by
late Thursday afternoon with continued improvement through Thursday night.

/Outlook for kmsp/
Friday...VFR. Wind S 5 knots.
Sat...mainly VFR...chance MVFR cigs/-sn. Wind north 5-10 knots.
Sun...mainly VFR...chance MVFR ceilings. Wind north 10 knots.


Mpx watches/warnings/advisories...
Minnesota...Freezing Rain Advisory until 6 am CST Thursday for mnz041>045-

Wind Advisory until 9 am CST Thursday for mnz054-056-064-065-

WI...Freezing Rain Advisory until 6 am CST Thursday for wiz014>016-



short term...rah
long term...speed

National Weather Service Glossary of Abbreviations