Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 231757

Area Forecast Discussion
National Weather Service Duluth MN
1257 PM CDT Thu Mar 23 2017

Issued at 1128 AM CDT Thu Mar 23 2017

The forecast was overhauled through tonight, focusing on the
threat of freezing rain. A mixture of 00Z, 06Z, and 12Z model
guidance was used. There is no question rain will spread into the
Northland later this afternoon and this evening, but it now
appears to be a little slower at moving into the Northland
compared to the previous forecast. The key to the freezing rain
threat will be the timing at which surface temperatures drop to
near or below freezing. Think the extensive cloud cover,
relatively warm air aloft, and falling rain will help slow down
the rate at which temperatures will fall, so forecast now has
slower cooling this evening compared to the previous forecast,
especially in northwest Wisconsin. Leaned a little bit on the 06Z
regional Canadian, which was among the warmest guidance, for
tonight`s temperatures. The new temperatures, and timing of the
precipitation, lessened the degree of freezing rain over parts of
northwest Wisconsin, but it is still enough of a threat to
maintain the winter weather advisory. The greater concern was for
northeast Minnesota, especially the Arrowhead, Duluth area, and
Iron Range, where we had ice accumulation in the forecast but had
not yet felt confident enough to issue an advisory. The confidence
in icing for those areas has increased, and threat looks greater
than in Wisconsin. Up to a tenth of an inch of icing is possible
for parts of far northeast Minnesota. Decided to issue an advisory
for those parts of northeast Minnesota for tonight, and might need
to expand to some areas to the west. We debated whether to issue
a winter weather or freezing rain advisory, since the main threat
is the freezing rain, but decided on winter weather advisory since
there could be periods of sleet and snow, as well to keep things
simple considering the winter weather advisory in Wisconsin. The
beginning time of the advisory in Wisconsin was pushed back from 8
pm to 10 pm to reflect the slower cooling in the evening.

It still looks like parts of the Northland could get rumbles of
thunder late this afternoon and this evening. Much of the guidance
indicates the potential for elevated thunderstorms, with most
models having up to a few to several hundred J/kg of most unstable
cape. The shortwaves and nocturnal low-level jet will be the main
trigger for the development of any thunderstorms. The storms
should be relatively weak, but will look into this threat more
with the afternoon forecast.


.SHORT TERM...(Today through Friday)
Issued at 438 AM CDT Thu Mar 23 2017

A very complicated forecast for the next 24 hours, with some
sensitive fluctuations that will have a very large impact on the
forecast area, but that`s for tonight. As of early this morning,
yesterday`s ridge of high pressure has slid to the eastern Great
Lakes region, with a developing surface low over eastern Colorado
this morning, and an inverted trough extending north up into
Manitoba and Saskatchewan where a weak low was centered. A lobe of
mid level moisture over eastern Nebraska and Kansas this morning
is going to surge north today on a wave of isentropic lift, moving
into the forecast area this afternoon, and remaining over
northern Minnesota and Wisconsin through tonight before narrowing
and shifting back south again on Friday. Rain and even a little
embedded thunder is expected to spread into the forecast area from
the south this afternoon. The initial wave of snow/sleet from a
leading wave is moving across the area early this morning and
should move out of the area to the east fairly early this morning,
and expect a period of drier conditions for at least a few hours
before the next wave moving in from the south gets here. A fairly
major complicating factor are the temperature profiles associated
with this system. The warm air advection should bring our mid
level temperatures above freezing, and while we should warm above
freezing during the day today, tonight they are going to dip to
near or just below freezing for a large portion of the area. This
is going to produce a mixture of freezing rain, sleet and rain to
a fairly large portion of the area overnight tonight, and could
make for some significant travel problems for the Friday morning
commute. However, these temperature profiles are very dependent on
getting the temperatures at the surface and aloft right, and with
tonight`s Min temperature guidance ranging from the low to mid
30s  the Canadian- on the warm end, to the 20s  bias
corrected NAM12 - on the cold end, this puzzle is not making
itself easy this morning. For now, I have decided to go with a
winter weather advisory for portions of northwest Wisconsin,
knowing that it may need to be expanded to include portions of the
north shore as well, or dropped entirely depending on temperature
trends in the next 18 hours. It seemed to better to get the
notification of the potential out now rather than wait.

.LONG TERM...(Friday night through Wednesday)
Issued at 438 AM CDT Thu Mar 23 2017

While a vertically stacked upper/surface low meanders through the
Southern Plains Friday night, high pressure will be drifting through
northwest Ontario. An upper short wave trof with weakening area of
vorticity moves over western Lake Superior. This will be just enough
lift to continue to mention some mixed precipitation over much of
Pine county and northwest Wisconsin. Dry elsewhere due to the
surface ridge axis from the aforementioned high extending through
the area. On Saturday, upper level and surface ridging covers the
region. However, only the GFS is trying to back build some
precipitation into northwest Wisconsin as it has an embedded impulse
lifting into this area. Cannot rule it out completely and have small
pops for mixed ptypes in the early morning, then rain by mid morning
into the afternoon. The GFS continues to be the only model with
precipitation over the forecast area Saturday night, but is then
joined by the GEM. The NAM/ECMWF are dry. Used a blend for
ptypes/pops. The vertically stacked system departs Sunday, which
allows for the next pair of upper waves to affect the region through
Monday. Embedded impulses will cross the area between and with these
features, and will use a blended approach to pops/ptypes to resolve
differences in models and their thermal profiles. A Hudson Bay high
sets up for Monday night through Wednesday which will keep the
region dry. The only model bringing in any precipitation is once
again the GFS on Wednesday afternoon. Will have a small pop to
account for this option. Temps will be above normal.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1257 PM CDT Thu Mar 23 2017

VFR to start at the beginning of the forecast, with a gradual
spread of MVFR ceilings as precipitation moves in. Expect
precipitation to begin around 20-23Z. As precipitation moistens
up the column, ceilings will gradually lower to IFR/LIFR at all
terminals. In addition, visibilities will gradually lower to
MVFR/IFR as heavier rain moves in. There is a chance of
thunderstorms impacting KHYR, KDLH and KBRD around 00Z, but
confidence is low and have left out for now.

Based on the NAM/RAP and HRRR soundings expect a freezing rain
threat at KDLH/KHIB and KHYR. Confidence is low as temperatures
are right on the border of a freezing rain or rain threat at these
locations. Right now the best timing is for between 00Z and 11Z.
After precipitation moves out, expect ceilings to gradually lift
to MVFR as high pressure builds in from the north. KHYR will
remain in IFR ceilings as precipitation still lingers around at


DLH  35  32  43  26 /  50  80  20  10
INL  43  29  40  23 /  50  60   0   0
BRD  39  33  47  28 /  60  70  20  10
HYR  38  34  45  29 /  40  80  60  20
ASX  40  33  43  28 /  50  80  30  20


WI...Winter Weather Advisory from 10 PM this evening to 9 AM CDT
     Friday for WIZ002>004-008-009.

MN...Winter Weather Advisory from 7 PM this evening to 7 AM CDT
     Friday for MNZ011-012-019>021-037.



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