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Area Forecast Discussion (AFD)

Issued by Duluth, MN (DLH)

                            
000
FXUS63 KDLH 261128 AAA
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
628 AM CDT Fri Apr 26 2019

.UPDATE...
Issued at 619 AM CDT Fri Apr 26 2019

Updated for the 12z Aviation Discussion below.

&&

.SHORT TERM...(Today through Saturday)
Issued at 319 AM CDT Fri Apr 26 2019

Low pressure was located over north central Lake Superior at 
07Z/2am, with a cold front extending west southwest through the 
forecast area. A tight pressure gradient was combing with good cold 
air advection to produce some gusty winds. Some low clouds were 
spreading across northeast Minnesota behind the front, and will 
continue to spread over into northwest Wisconsin early this morning. 
The pressure gradient relaxes by this afternoon as high pressure 
arrives, but there should still be some good mixing to keep gusts 
going through the afternoon. The clouds should dissipate by late 
morning. This combination of gusty winds and minimum humidities in 
the 20 to 30 percent range will lead to near critical fire weather 
conditions in northeast Minnesota. Will use a special weather 
statement to highlight these conditions. Weak warm air advection in 
the afternoon will result in a variety of max temps today, but 
largely in the middle 40s to the middle 50s.

The region is under the influence of mid level and surface ridging 
for most of tonight. Late tonight, an approaching upper level trof 
will help in increasing the cloud cover. Neutral to weak cold air 
advection occurs tonight and will combine with the clouds to have 
min temps in the 20s over the Arrowhead and far eastern Wisconsin 
zones, where clouds will arrive late, to the low to middle 30s where 
the clouds come in sooner.

On Saturday, the upper trof moves past the forecast area, while high 
pressure remains in charge at the surface. There are minor model 
differences over the southern edge of the region with the 
strong/compact area of low pressure moving through Iowa, and its 
affect on the region. The NAM keeps the area dry, the ECMWF/GFS 
paint a ribbon of QPF, while the GEM is between these solutions and 
just touches the area. The trend with this system over the last 48 
hours has been farther south with the track of the surface low, and 
will follow that direction and favor the GEM with some morning 
precipitation over the far southern edge, dry in the afternoon as 
the system slides south. No accumulation is expected. Still cool 
with max temps from the lower 40s to lowers 50s, cooler near Lake 
Superior with an easterly flow.

.LONG TERM...(Saturday night through Thursday)
Issued at 319 AM CDT Fri Apr 26 2019

The extended forecast period shows a couple rounds of precipitation 
moving through the Northland, particularly late Sunday through the 
day Monday. Temperatures will generally remain below average through 
next week, especially along Lake Superior where easterly winds will 
lead to cooler on-shore flow.

Saturday night through much of the day Sunday looks to be dry, 
thanks to a surface high pressure ridge axis that will translate 
through the region. Skies should be mostly clear overnight, leading 
to overnight temperatures in the middle to upper 20s. Attention then 
turns to increasing cloud cover and chances of precipitation, 
especially Sunday evening into Monday morning, persisting through 
Monday afternoon. A mid-level impulse will eject out of a low-
amplitude upper-level trough and across the Northland. An elevated 
warm frontal zone will build into the region, along with broad mid-
level isentropic ascent. There will be plenty of large-scale forcing 
associated with this system, per the Thaler QG omega progs. Both the 
NAM and GFS soundings suggest the precipitation types will generally 
be a rain/snow mix, and will be diurnally driven, with more snow 
early Monday morning, and rain during the daylight hours Monday. One 
complicating factor with the snow scenario is will the strong lift 
associated with this system generate snow rates that will overcome 
the rate of melting since surface temperatures are well above 
freezing - between 40 to 50 degrees F. I'm thinking that it will be 
tough for any snow accumulation to occur, at least at first. I have 
made some adjustments to tamp down the snow amounts, but didn't 
eliminate them entirely. In general, snow amounts should remain 
light, with most locations seeing up to two inches. Snow amounts 
could be heavier along the North Shore, thanks to enhanced 
orographic lift. Some lighter precipitation will linger into Monday 
afternoon and evening, but will end from west to east Monday 
evening. Highs Monday will range from near 40 over the Minnesota 
Arrowhead to the middle 40s elsewhere.

Drier air will filter into the region Tuesday into Wednesday, along 
with high pressure building from the James Bay region. Easterly flow 
will persist Tuesday and Wednesday, which will keep it cooler by 
Lake Superior. Highs will generally be in the upper 40s to lower 
50s. Another round of precipitation, mainly in the form of rain, 
could build into the region Wednesday afternoon or evening, and 
continue through Thursday, but there is some uncertainty with this 
particular scenario due to differences among the model guidance.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 628 AM CDT Fri Apr 26 2019

Some MVFR ceilings have developed over a good portion of the
region behind a cold front that passed through earlier this
morning. However, this cloud deck should scatter out within the 
next hour or two. The main aviation concern for today will be 
breezy northwest winds, with gusts between 15 to 25 knots possible
as the boundary layer looks to mix pretty deep today per the 
latest model soundings. These winds should diminish later this 
afternoon and evening as we lose the boundary layer mixing. A mid-
level cloud deck will then build into the region overnight, which 
is associated with a potent system that should remain to the south
of the region.

&&

.MARINE...
Issued at 319 AM CDT Fri Apr 26 2019

Winds will remain elevated through the morning hours today, thanks 
to a tight surface pressure gradient persisting over the region. 
Also, as temperatures cool this morning, some stronger wind gusts 
should be able to mix down to the water surface. The latest models 
show that some gusts could reach criteria hazardous to smaller 
vessels early this morning, so have issued a Small Craft Advisory 
along the North Shore through 10 AM this morning. Gusts could reach 
up to 25 knots, especially near Silver Bay and Taconite Harbor. 
Conditions will improve this afternoon as the surface pressure 
gradient weakens. Lighter winds are expected through the upcoming 
weekend, thanks to high pressure remaining in control. Some stronger 
winds could return early next week over western Lake Superior.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  52  31  45  27 /   0   0   0   0 
INL  50  28  51  27 /   0   0   0   0 
BRD  55  36  51  28 /   0  10   0   0 
HYR  52  30  44  24 /   0   0  10   0 
ASX  51  30  42  25 /   0   0   0   0 

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 10 AM CDT this morning for LSZ140>145.

&&

$$

UPDATE...JTS
SHORT TERM...GSF
LONG TERM...JTS
AVIATION...JTS
MARINE...JTS