Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
632 am CST Monday Nov 24 2014
Update..for 12z aviation discussion
Short term...(today and tonight)
issued at 421 am CST Monday Nov 24 2014
The broad upper trough pivoting across the central Continental U.S. Today and
tonight will facilitate prolonged lift locally...a bit stronger
over west central WI. Expect snowfall accumulations in the 2 to 4
inch range from Durand...to Eau Claire to Ladysmith. The hopwrf
supports this theory...with all four members indicating advisory
criteria snowfall being met by sunset there. Although the
landscape typically does not support widespread blowing snow and
there was significant fog/snowmelt yesterday..still could see
reduced visibilities in the falling/blowing snow over west central
WI. The western gradient of the accumulating
snow will likely back up to the eastern edge of the Twin
Cities....with up to an inch possible from the Twin Cities south
to Mankato and Fairmont.
Meanwhile...to the west over west central and south central
Minnesota...winds will be continue howling at 30 miles per hour with gusts
to 45 miles per hour under the influence of the tight surface pressure
gradient. The Wind Advisory therefore looks to be in good shape. A nearly
steady to falling temperature trend will ensue today in the wake of the
front...with lows tonighttempered somewhat by lingering clouds.
Lows will generally range from 8 to 16 degrees.
Long term...(tuesday through sunday)
issued at 421 am CST Monday Nov 24 2014
There will be two chance/S of precipitation in the extended period.
One will occur late Tuesday/early Wednesday...while another affects the
region late in the week.
Models have trended further SW with Tuesday/Wednesday system...with the surface
low now moving across far SW Minnesota...and into central Iowa by Wednesday
morning. The 500 mb vorticity maximum is also further SW creating a dilemma on
how far east/NE does the measurable precipitation occur before drier
air erodes the deeper moisture. This air mass remains limited on the
amount of moisture it can ring out based on precipitable water values
and mixing ratios. The only problem would be enhanced forcing which
may aid in a small area of higher quantitative precipitation forecast amts. Would like to stay close
to a blend of the ec/wpc quantitative precipitation forecast amts which create an area of 0.08 to
0.13 through most of the event. This translates to 1-3 inches of
snow...with locally higher amts NE of the surface low track. The cips
analog guidance for this event has a narrow band of 2-4 inches from
wc Minnesota southeast to near kael. Current high chance/low likely probability of precipitation seem
reasonable based on the current trend of the SW shift.
After this event...the coldest air for the next 7-10 days will
settle across the upper Midwest. A strong thermal boundary will
likely set up across the plains late in the week as winds shift to
the SW/S. This will set the stage for another light snowfall event
sometime late Thu/Friday. However...any deviation to the return flow
and thermal boundary will lead to problems with quantitative precipitation forecast. Chance probability of precipitation at
this time seems reasonable.
As said before...the coldest air in the next 7-10 days will occur
late this week as the upper ridge begins to break down in the
western Continental U.S.. this will lead to a modified Pacific/Canadian air
mass to filter across our region as the upper flow becomes more
zonal next week. Temperatures will likely rise to near or above freezing for
the first week of December based on this type of pattern change.
Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 631 am CST Monday Nov 24 2014
Snow will affect the taf sites today...particularly Keau and krnh.
A 2-3 hour window of freezing drizzle is possible at east central
Minnesota and west central WI sites as moisture in the dendritic growth
layer is lost. Ceilings will remain low-end MVFR through the
day...scattering out this evening. Strong northwest winds through the
day subside below 10 kts this evening as well.
patchy light freezing drizzle to start the period...should
transition to light snow and/or flurries by 15z. VFR ceilings return
around 05z Tuesday...with winds decreasing below 10kts.
/Outlook for kmsp/
Tuesday...VFR. Winds west 5-10 knots becoming southeast.
Wednesday...MVFR/IFR chance -sn early. Winds northwest 10-15kts.
Thursday...VFR. Winds light/variable.
Minnesota...Wind Advisory until 6 PM CST this evening for mnz054>056-064-065-
WI...Winter Weather Advisory until midnight CST tonight for wiz016-