Area Forecast Discussion
Issued by NWS Duluth, MN

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KDLH 272106
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
306 PM CST Mon Feb 27 2017

.SHORT TERM...(This evening through Tuesday night)
Issued at 306 PM CST Mon Feb 27 2017

Rain mixing with snow late tonight into Tuesday leading to light
snowfall accumulations over parts of northeast Minnesota, but mainly
rain/wintry mix over northwest Wisconsin. Some uncertainty remains
for a variety of factors, but generally think about 2 to 4 inches of
snow across northeast Minnesota, with the highest totals confined to
the Minnesota Arrowhead where locally higher amounts are possible.

On the synoptic scale the upper Midwest is within west-southwest
flow at mid to upper levels ahead of a trough deepening across the
west coast. As this trough ejects into the Great Plains a weak
surface low develops. However, unlike most "Colorado Low" scenarios,
this system fails to produce strong large-scale lift, and thus
without strong frontogenetical forcing mechanism the surface low
itself barely deepens to 1000mb by the time it reaches southern Lake
Michigan Tuesday night. As an inverted surface trough associated
with the low reaches into the upper Midwest this evening, light
precipitation (mainly snow) will eventually develop given the vort
max advecting into the region. However, a lack of deep moisture
ahead of the low along with its fairly elongated nature will result
in poorer-than-usual moisture advection through the column ahead of
the low, which result in a slower start to precip than some guidance
is indicating. Low level temperatures will also be fairly warm ahead
of the low with temperatures remaining near or above freezing
overnight in most of northwest Wisconsin - possibly as far north as
the Twin POrts. This would mean precipitation starting as rain
instead of snow, or more of a wintry mix scenario to start out.
Farther north precipitation will be all snow, but by the time
precipitation processes really get going a strong high pressure
building in from the north will result in precipitation coming to an
end during the day Tuesday from west to east.

Some uncertainties still remain as guidance has had a tough time
with the progression of this system, though the 12z guidance
consensus seems to be leaning towards a lighter precipitation
solution which makes sense given the expected synoptic evolution.
Snowfall amounts have been adjusted down slightly from the previous
forecast, but locally higher amounts are possible across the
Minnesota Arrowhead. A narrow band of higher amounts is possible,
but overall agree with WPC`s assessment that the GFS (and to some
extent the NAM) are a bit too aggressive on the QPF, though the 12z
ECMWF is probably a little too light. The probability for any sleet
or freezing rain seems low, but it`s tough to really rule out an
hour or two of freezing rain, especially in the Twin Ports where wet
bulb temps should remain below freezing but a small nose of warm air
aloft will exist for a short time before the inverted surface trough
crosses and colder air begins to advect in from the north. If
freezing rain were to happen it would be most likely in the hours
just before and through dawn, which could result in a hazard to the
morning commute. Again, the probability for this seems fairly low
right now but will need to be monitored closely.

Given the trend in guidance and well below normal confidence in the
forecast, held off on any advisories at this point. While snowfall
amounts may certainly approach winter weather advisory criteria (3-
5" in 12 hours), locations that reach over 3 inches will be limited
to higher elevations of the Minnesota Arrowhead and could be limited
in areal extent because of the overall "weak" nature of this system.

Rain/snow ends as snow as colder air advects in from the north
Tuesday night. Winds may be breezy at times late Tuesday into
Tuesday evening given the strong high pressure building in across
northwest Ontario, but otherwise temperatures will be falling
through the night. Lake effect snow showers will impact the south
shore for a time Tuesday evening, with up to an inch or so of
additional snowfall expected. Lows falling to near zero along the
international border, teens in the Twin Ports to Brainerd Lakes, and
low 20s across northwest Wisconsin.

.LONG TERM...(Wednesday through Monday)
Issued at 306 PM CST Mon Feb 27 2017

While no major storms appear to be on the docket for the extended
periods, it appears as though the weather will be fairly active for
the Wednesday to Monday time frame, with several fast-moving
disturbances and at least a couple fairly significant airmass
changes.

A weak, but rather cold arctic surface ridge should be in place at
the beginning of the period Wednesday morning, which will then
quickly give way to southerly return flow during the day.  Most of
the operational models depict a fast-moving, low-amplitude NW flow
wave diving southeastward from the Dakotas into southern MN/northern
IA Wednesday night/Thursday morning.  The GFS/NAM are by far the
most aggressive with forcing for ascent with this wave (with the NAM
by far the farthest north), and would suggest at least some chance
of light snow across the southern DLH CWA.  However, the new ECM
damps the wave out almost completely, and takes it farther south,
and we are inclined to believe that this is more of a correct
solution. Thus, we have held with the dry forecast for this time
period. Although, there could be some flurries during the day
Thursday as arctic air deepens/strengthens during the day.

Arctic high pressure will then be briefly in charge from late Wed
into Friday.  Thursday morning will likely be the coldest morning
we`ve seen in some time, especially across interior northern MN
where temps in some of the favored locations could drop into the
minus teens.  Arctic air flowing across Lake Superior will also
result in chances for lake-effect snow showers along the south shore
during this time frame.

Strong S/SW return flow will commence Friday night/Saturday, which
will begin the transition to a much warmer airmass for the weekend.
However, the strong warm advection regime will also likely drive a
short period of wintry mixed precip Friday night into Saturday. Mild
temps are then expected Sunday-Monday.  There is some hint in the
medium range extended models that a more significant system could
spin up in the Upper Midwest right at the end of the 7-day forecast
window, but this is somewhat low-confidence at the moment.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1216 PM CST Mon Feb 27 2017

A rather weak surface warm front extends roughly from KBRD to the
southwest tip of Lake Superior at midday, and this frontal zone
along with a couple of disturbances that will ride along it will
be the primary area of focus for this TAF period. Early morning
light snow has largely ended, with most aviation conditions
improving to VFR conditions (the only exception being KHIB where
MVFR ceilings continue to hang on) within the past couple of
hours.

We expect mostly VFR conditions to prevail until sometime this
evening when ceilings will begin to lower with time. Overall, we
have stayed similar to the previous TAF issuance with snow/rain or
a rain-snow mix developing overnight, and persisting through the
end of the TAF period. However, the major change was to delay the
onset of steady precip by a few hours at all TAF sites, in line
with the newest model guidance for the 06-18z time period.
Conditions should lower to IFR or near-IFR for a 6-8 hour period
at all TAF sites during the main period of precip late tonight and
Tues morning.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  26  35  13  26 /  80  90  30  10
INL  14  27   3  24 /  80  20   0  10
BRD  29  35  17  31 /  70  70  10  20
HYR  33  41  21  30 /  90  90  30  10
ASX  29  37  21  28 /  80 100  50  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

SHORT TERM...JJM
LONG TERM...Miller
AVIATION...Miller


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.