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000 
FXUS63 KDLH 121102
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
502 AM CST Thu Dec 12 2019

.SHORT TERM...(Today through Tonight) 
Issued at 502 AM CST Thu Dec 12 2019

High pressure stretched from the Mid-Atlantic States to southern 
Manitoba this morning with a warm front extending from an area of 
low pressure in southern South Dakota into the Mid-Mississippi 
Valley. Snow was seen north of the warm from from the eastern 
Dakotas into much of Minnesota, Wisconsin and upper Michigan.

A compact shortwave trough will move from eastern South Dakota this 
morning to northern Lake Michigan by this evening. A surface low in 
association with the trough will move from northeastern Nebraska 
this morning to near Albert Lea by midday to near Green Bay this 
evening. Snowfall this morning is seen at the nose of an area of low-
level warm advection and weak fgen. As was the case in the days 
leading up to the event, the best isentropic lift and strong Thaler-
QG forcing remain just to the south of our area. HREF runs from 
earlier this morning were keying in on some higher snowfall rates 
and forcing across northwest Wisconsin and have slightly bumped up 
QPF in the Price County area as a result where a time of 1 inch plus 
per hour snowfall rates will be possible for a time this morning. 
Timing of the system has been slowed a bit as well with a later 
arrival observed and a corresponding later departure. Additional 
snowfall amounts of around 2 to 5 inches are expected today from the 
I-35 corridor into northwest Wisconsin with lesser amounts 
elsewhere. Tweaked the ending time of the Advisory for Price/Iron 
and Ashland Counties and extended it to 21z to account for the 
delayed departure. We may yet see some isolated higher amounts in 
excess of 6 inches in that area, but expect this to be pretty 
localized and overall low confidence, so continuing to run with the 
Advisory. 

As the synoptic snowfall ends through the day today, expecting lake 
effect snow showers to set up along the North Shore of Lake Superior 
and across the Bayfield Peninsula as winds turn easterly as the low 
passes to the south. With Lake Superior still mainly open, a long 
fetch with easterly winds and 850mb temps in the -10 to -12C range, 
chances for lake effect snow are fairly high, but not expecting a 
lot of accumulation with it through the overnight hours. Totals of 
around an inch will be possible across the Bayfield Peninsula with 
generally an inch or less along the North Shore. However, some of 
the CAMs are hinting at slightly higher amounts neat the Castle 
Danger area with perhaps isolated spots to around 2 inches in the 
higher terrain. Aside from the lake effect snow, quiet conditions 
are expected tonight across the remainder of the Northland. Highs 
today will be in the lower teens to lower 20s above zero with lows 
tonight in the single digits above zero.

.LONG TERM...(Friday through Wednesday) 
Issued at 502 AM CST Thu Dec 12 2019

Our next weather maker moves across the area on Friday and Saturday. 
A fairly potent shortwave in combination with a decent mid level 
baroclinic zone and surface based inverted trough produces a band of 
snow that slides across the area from west to east beginning early 
Friday morning, continuing through Friday afternoon and night before 
ending during the day on Saturday.  This is a fairly long period of 
snowfall, but the dynamics are not very strong and am only expecting 
between 2 and 4 inches for most of the area. Most of this snow will 
fall in the Friday and Friday evening time range, with easterly flow 
off Lake Superior.  Am a little concerned that the lake effects will 
produce higher snowfall amounts over the higher terrain of the North 
Shore, and we may eventually need an Advisory there. However, for 
now most of this event appears to be kind of marginal, and we have 
one out for the ongoing event which I do not want to create 
confusion with, so have held off doing anything more than mentioning 
it in this AFD and the HWO.  

A ridge of high pressure builds into the area for Saturday night and 
Sunday, which should leave us with a period of quieter weather with 
cold temperatures.  

The first half of the work week will be affected by a strong low 
pressure system that develops over Oklahoma as an upper low moves 
across the Rockies.  This system moves northeast across the mid 
Mississippi river valley and up into the Ohio river valley region, 
then across the eastern Great Lakes.  This system will stay too far 
south and east of the forecast area, but will put us into a bit of a 
lull as far as active weather that directly affects us.  Thus, I 
have an effectively dry forecast for Sunday night through Wednesday, 
with only some lake effect snow showers along the South Shore on 
Tuesday and Wednesday as we get into northwest flow behind this 
system.  It also allows a fresh pool of cold air to move into the 
area aloft, and high temperatures for Monday through Wednesday stay 
in the single digits to around 10 above.   Thursday, we get a shot 
of warm air advection as the pool of cold air slides off to the east 
which may produce a chance for snow, but for now the timing and 
position of it is too uncertain and have left no more than slight 
chance pops for now, and these mainly focused in the lake effect 
areas along the South Shore.  This will also allow temperatures to 
moderate for Thursday, with highs creeping in to the teens.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1133 PM CST Wed Dec 11 2019

Plenty of IFR overnight as a system crosses bringing snow. Current
VFR conditions will quickly deteriorate except near KINL. This 
system will move out of the area Thursday with a return to MVFR.


&&

.MARINE...
Issued at 502 AM CST Thu Dec 12 2019

Snow will affect western Lake Superior today with winds becoming 
northeast and increasing during the afternoon and tonight.  These 
winds will cause building waves, which will produce marginal 
conditions for Small Craft, especially along the North Shore and 
into the southwestern tip of the lake late this afternoon and 
tonight.  The winds switch around to southeast early on Friday, 
shifting the marginal conditions out of the tip of the lake, but 
maintaining them up the North Shore.  For now it does not appear 
that we need a Small Craft Advisory, but it will be fairly close and 
we will have to watch conditions carefully.  Any reports that ships 
can send us would be appreciated.  Winds diminish on Friday and 
Friday night as another wave of snow moves across the area. Behind 
the snow winds should become northwesterly and increase for 
Saturday, which may also produce hazardous conditions for Small 
Craft.  

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  18  10  21  13 /  80  30  90  80 
INL  10   1  19   8 /  10  10  90  80 
BRD  14   4  18   7 /  90  10  80  50 
HYR  19   6  24  15 / 100   0  70  70 
ASX  21  10  25  18 /  90  20  60  80 

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until noon CST today for WIZ001-002-
     006>008.

     Winter Weather Advisory until 3 PM CST this afternoon for WIZ003-
     004-009.

MN...Winter Weather Advisory until noon CST today for MNZ037-038.

     Winter Weather Advisory until 10 AM CST this morning for 
     MNZ033>036.

LS...None.
&&

$$

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