Area Forecast Discussion
Issued by NWS Duluth, MN
FXUS63 KDLH 191802 AAC
Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
102 PM CDT Wed Apr 19 2017
Issued at 102 PM CDT Wed Apr 19 2017
Please see the new 18Z Aviation Discussion below.
UPDATE Issued at 1023 AM CDT Wed Apr 19 2017
Plenty of cloud cover over northwest Wisconsin and along the I35
corridor. Increased the cloud forecast over northwest Wisconsin
and along the I35 corridor. Latest satellite imagery does show
some erosion to the cloud cover along the north shore from Silver
Bay to Two Harbors. Cirrus on the increase as well from the
southwest. Delayed the start time of the rain this afternoon as
seen in the latest short term hires models and area radars. Made
other minor modifications.
.SHORT TERM...(Today through Thursday)
Issued at 402 AM CDT Wed Apr 19 2017
A challenging forecast tonight into Thursday with a potential for
accumulating snowfall across portions of the Northland. Surface
temperatures will generally drive whether or not precipitation
changes over to snow, with higher elevations such as along the north
shore having a greater probability of changing over to snow. The
south shore is where uncertainty is greatest as strong northeast to
north winds will advect the relatively warmer lake air over land,
which could result in temperatures remaining just warm enough to
produce mainly rain. As we approach 14 hours of daylight and a max
solar elevation of near 55 degrees (compared to ~20 degrees at
minimum in the winter and ~66 degrees at max), a more-rain-than-snow
scenario appears more likely on a climotological basis.
On the synoptic scale the active weather pattern continues as the
west-southwest flow aloft gives way to another shortwave trough over
the central and northern Plains today, deepening as it approaches
the upper midwest due to a strengthening upper level jet over the
desert southwest ejecting into the central Plains and mid-
Mississippi River Valley towards Wednesday night. A resulting
surface low deepens tonight over the Mid-Mississippi River Valley,
tracking east towards lower Lake Michigan by Thursday morning.
Today skies will briefly clear out as drier air builds in from the
north, but winds quickly turn easterly as the low begins early
development over the central Plains and a building high pressure
drifts east across the far northern reaches of Ontario. Mostly sunny
skies to kick off the day, then increasing clouds from south to
north. A rain shield will approach from the south this afternoon
into the evening, with a thunderstorm possible south of a line from
Spooner to Hayward to Watersmeet. Otherwise a light to moderate rain
expected towards late-day, with areas north of Highway 2 likely
remaining dry through the afternoon. Highs in the mid 40s to mid
50s, warmest towards the borderland where sunshine should prevail
for much of the day.
Tonight rain spreads across much of the region, especially along and
east of I-35, up the north shore, and across all of northwest
Wisconsin. Temperatures will fall to the 30s, with east-northeast
winds ramping up, especially along the lake shore. Considerable
uncertainty remains with regards to precipitation type, with surface
temperatures likely to drive if/when a changeover to snowfall
occurs. At this point, the model consensus is leaning slightly
cooler than previous runs, continuing a trend from the day shift.
The current forecast reflects a something closer to a "worst case"
scenario with regards to snowfall amounts, but if the trend
continues snowfall could be even more widespread in coverage than
currently forecast - especially if the unusually aggressive SREF
guidance is right. Overnight precipitation types will likely go back
and forth between rain and snow across much of the Northland, with a
more steady trend to snow towards Thursday morning. There is some
concern about loss of ice aloft as the low exits and drier upper
level air advects in from the north, but in general accumulating
snowfall would occur late Wednesday night in Thursday morning.
Expect a total of 2 to 4 inches of snowfall along the north shore
and areas inland, including the higher terrain of the Twin Ports.
Strong east winds gusting to around 30 mph in the morning will
result in little snow right along the lakeshore given the relatively
warmer lake temperatures. Along the south shore up to an inch or so
is possible, especially Thursday afternoon as winds turn more
northerly and temperatures remain steady or decrease.
A tough decision regarding whether and where to issue a winter
weather advisory for the snowfall potential. Current snowfall
forecast is just scratching the low end of our advisory criteria (3-
5"), but given the uncertainty and the fact that this snowfall
forecast is quite a bit higher than the previous forecast, have
decided to hold off issuing anything just yet.
.LONG TERM...(Thursday night through Tuesday)
Issued at 402 AM CDT Wed Apr 19 2017
The low pressure system will continue to pull away from the region
Thursday night bringing an end to the precipitation for most of the
Northland overnight. Light rain or snow will linger into the evening
over far eastern Minnesota into northern Wisconsin with a light mix
continuing overnight across portions of Ashland and Iron Counties.
High pressure will then build over Minnesota and Wisconsin on Friday
leading to a dry day with highs in the fifties for most areas. An
off lake wind will keep lakeside areas cooler. The high will move
south on Saturday and a cold front will drop out of Canada into
northern Minnesota Saturday afternoon. There may be some light rain
that occurs along portions of the International Border. The ECMWF
remains faster pushing the front through with the GFS/Canadian
slower and in decent agreement. We spread chances for light rain or
snow south with the front Saturday night across much of the
Northland and expect mainly light snow accumulation. The front will
continue south and weaken on Sunday and we went with a dry forecast
for now. Highs Sunday will range from the lower to middle forties
from the Arrowhead and around Lake Superior to the lower to middle
fifties from the Brainerd Lakes region through Siren to Park Falls.
A stronger shortwave and area of low pressure will affect the
Northland as early as Sunday night with a warm front returning
north, but more so Monday into Tuesday. There remains timing
differences between the models in how fast and what track the low
will take but the result is similar in that there will be chances
for rain or snow across most of the Northland.
.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 102 PM CDT Wed Apr 19 2017
Stratus is expected to linger over northwest Wisconsin this
afternoon thanks to moist northeasterly winds off Lake Superior.
At other sites, high cirrus will continue into this evening.
Approaching low pressure will reduce ceilings this evening and
bring a chance of light rain, mixing with or changing to snow, to
the terminals overnight. DLH and smaller airports along the North
Shore will likely see a period of all snow, with visibility less
than one mile at times. Maintained visibility trend at DLH at 2SM
with this update due to uncertainty in timing the worst
conditions. Winds are expected to remain gusty overnight, but
should the near-surface layer decouple, low-level wind shear is
likely. The greatest potential for LLWS will be at DLH and HYR.
As the area of low pressure lifts northeastward Thursday morning,
wind gusts and speeds are expected to diminish and back slightly
more northerly. Overall confidence in this forecast is average.
.PRELIMINARY POINT TEMPS/POPS...
DLH 44 33 41 31 / 20 100 90 20
INL 53 35 49 31 / 0 30 40 10
BRD 53 35 48 34 / 50 90 70 10
HYR 51 36 41 31 / 50 100 90 20
ASX 45 35 40 31 / 30 100 100 40
LS...Gale Watch from late tonight through Thursday afternoon for
Small Craft Advisory until 4 AM CDT Thursday for LSZ144>147.
Small Craft Advisory from 4 PM this afternoon to 4 AM CDT
Thursday for LSZ140>143.
Small Craft Advisory from 4 PM this afternoon to 10 PM CDT
Thursday for LSZ121-148.