Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 171230 AAA
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
630 AM CST Fri Nov 17 2017

.UPDATE...
Issued at 630 AM CST Fri Nov 17 2017

Update for new 12Z Aviation Discussion below.

&&

.SHORT TERM...(Today through Saturday)
Issued at 347 AM CST Fri Nov 17 2017

Complicated weather scene out there this morning, with a double
barreled surface low, one over Manitoba, with another weaker one
over central South Dakota. We are in the warm sector of this
system, with the warm air advection wing having passed across the
area during the evening hours. We have isentropic upglide ongoing
over much of the area this morning, and with the RH and thermal
profile we have out there, several locations are getting a wintry
mixture of rain, freezing rain/drizzle or snow. This pattern is
going to continue this morning until the cold front moves through
the afternoon and early this evening. This isentropic lift pattern
will be enhanced by a frontogenetic band that develops and moves
across the area from mid morning through the afternoon. For much
of this time range temperatures in the areas with higher
precipitation rates will be above freezing, producing rain. If it
were just a bit cooler we would be having some real icing
problems. For now have gone with an SPS as roads may be slippery
with this precipitation coming down, but do not feel we need a
Winter Weather Advisory at this time, though we will be monitoring
if this needs to change today. After the front moves through
tonight we get a lull in the precipitation chances, though there
may be some upslope/onshore flow to create precipitation along the
south shore late tonight/early Saturday. LES bands are unlikely
with not quite enough cold air aloft. We may also get some steep
low level lapse rates to form snow showers over northern MN during
the afternoon.

.LONG TERM...(Saturday night through Thursday)
Issued at 347 AM CST Fri Nov 17 2017

No major concerns for the long term. There will be a few chances
of light snow and lake effect snow through the period and mild
temperatures on Monday.

A split upper-level flow regime will be in place Saturday evening
across the CONUS. The sub-tropical jet will be located far to the
south with the polar jet north of the International Border. The
split flow pattern will limit available moisture for any of the
shortwave troughs which move through the region and the strongest
jet streaks will remain either north or south of the Northland.

An upper-level jet streak is forecast to move across the Canadian
Prairies and into the Great Lakes Region Saturday night. A mid-
level shortwave will accompany the jet streak with sufficient
height falls to wring out a few snow showers across northern
Minnesota. Northwesterly winds and strong cold air advection will
follow the trough, setting up a potential for light lake effect
snow over northwest Wisconsin. Lake delta-Ts between -15 and -20
degree Celsius are forecast with limited low-level shear, so
think conditions are favorable for around an inch of accumulation.
While the ambient airmass will dry out considerably as subsidence
arrives, the heat and moisture flux from Lake Superior should be
able to saturate deeply enough to support light snow. The threat
of LES will be short-lived, however, as surface high pressure
advancing across Minnesota quickly backs low-level flow southerly
by mid- morning Sunday.

Southerly flow continues into Monday as the surface ridge drifts
to the east of the forecast area. Warm air advection will boost
850 mb temperatures to between 0 and +6 degrees Celsius. The warm
air aloft will help push high temperatures on Monday near normal
to 10 degrees above normal. The warmth won`t last long as a fast-
moving clipper moves across the Canadian Prairies and grazes the
Northland Monday night and Tuesday morning. The region will see
another shot of light snow and a period of light lake effect snow
showers in northwest Wisconsin.

Mid- and upper-level ridging builds into the Upper Midwest
Wednesday and Thursday with quieter conditions expected. A warm
front is forecast to lift northeastward across the Northland late
Wednesday night and Thursday which may yield enough lift to eek
out a few snow showers. Temperatures will trend milder and near
normal Thursday into Friday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 630 AM CST Fri Nov 17 2017

Challenging forecast this morning with a potential for light
freezing rain or freezing drizzle, rain, and snow in the picture.
Sleet is also not out of the question. Expect ceilings to quickly
erode into MVFR and evenutally IFR categories this morning as
forcing for ascent indicated on RAP isentropic plots saturates the
lower atmosphere. A mix of precipitation was noted at INL within
the past hour and I suspect a snow/sleet mix based on upstream
reports from Grand Forks. Southerly winds near the ground and
aloft will continue to bring relatively warm and dry air into the
region interfering with snow production. Temperatures will be warm
enough for all rain in some spots with a rain/snow mix in others,
and also a potential for pockets of freezing or freezing drizzle.
Precipitation will come to an end late this afternoon or early
this evening but ceilings will remain low into tonight. Confidence
in this forecast is below average due to the challenging
precipitation and ceiling forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  35  22  27  11 /  80  20   0   0
INL  35  17  22   7 /  40  10  30  20
BRD  38  23  28  12 /  60   0   0   0
HYR  36  27  31  13 /  90  40   0   0
ASX  37  29  32  17 /  90  60  10  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 4 PM CST this afternoon for
     LSZ140>142.

&&

$$

UPDATE...Huyck
SHORT TERM...LE
LONG TERM...Huyck
AVIATION...Huyck


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