Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 160601
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
101 AM CDT Wed Aug 16 2017

.UPDATE...
Issued at 100 AM CDT Wed Aug 16 2017

Updated aviation section below for 06Z TAF issuance.

UPDATE Issued at 1008 PM CDT Tue Aug 15 2017

Latest short term hires models continue to slow down the onset of
precipitation over the forecast area. This includes the HRRR and
RAP. 00Z NAM12 has arrived and is on board with the slower onset.
Have adjusted pops/weather for the rest of tonight as well as
tomorrow morning to reflect this approach.

UPDATE Issued at 651 PM CDT Tue Aug 15 2017

Some very light rain showers have moved into Cass county.
Meanwhile, some showers have developed from near Cook to northwest
of Ely. Have updated pops/weather to account for this activity.
Rest of the forecast on track.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 314 PM CDT Tue Aug 15 2017

High pressure over the western Great Lakes region will shift to the
eastern Great Lakes into the northeastern United States and eastern
Ontario by Wednesday afternoon. Meanwhile, low pressure over the
Central and Northern High Plains will shift east into western
Minnesota Wednesday afternoon. This area of low pressure will bring
an influx of deep moisture in from the west, with precipitable water
values increasing to 1.5 to 1.75" by Wednesday afternoon. An
approaching upper-level trough from the west, as well as multiple
shortwaves embedded in the southwest flow aloft, will bring
moderate large-scale forcing for ascent across the Northern Plains
into the western Great Lakes. This forcing will develop showers and
thunderstorms and moderate, to at times heavy, rain across the
Northland. The showers and storms will spread in from the west late
tonight and Wednesday. It should take some time to saturate the
drier low levels, because of the easterly flow, so prefer model
solutions slower to bringing in the rain into the Northland, such as
the GFS and NAM. There is also considerable model disagreement on
the track and timing of the heaviest areas of rain. Think this is
because there may be too many shortwaves, and not a dominate one, so
the models have significant differences in the track of the main
surface low. Any thunderstorms should be relatively weak because of
a lack of CAPE. The thunderstorms should just produce heavier rates
of rain and some thunder.

There will be somewhat light winds and high low-level saturation
late tonight, as well as increasing mid/upper-level cloud cover from
the approaching low pressure from the west. Think the overall
potential for fog is fairly low, especially because of the cloud
cover, which will weaken radiational cooling processes. However, 5
to 10 mph easterly and very humid flow from Lake Superior could help
produce fog along the higher terrain of the Twin Ports area. The
expected increasing cloud cover aloft, though, is leading to me
believe this will more likely just be low-level stratus rather than
fog, because of the weaker radiational cooling to help lower that
stratus to the ground-level. Meaning, I kept fog out of the Twin
Ports area, but the evening shift can reevaluate. Lows should range
from the lower 50s in the Arrowhead to the middle and upper 50s
across much of the rest of the forecast area. The cloud cover and
rain will limit heating Wednesday. Highs should only be in the lower
60s across northern Minnesota, to the upper 60s to around 70 degrees
from central Minnesota into northwest Wisconsin.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 314 PM CDT Tue Aug 15 2017

The low pressure system is forecast to deepen Wednesday night as
it lifts northeast. Model consensus is for the low center to
track through southeast Minnesota into western Wisconsin by 12Z
Thursday, continuing northeast during the day and exiting Thursday
night. Plenty of moisture will be present with this system with
PWAT values from 1.5 to around 1.7 inches, well above normal for
this time of year. There remains differences in the track of the
low but despite those differences confidence remains high that
much of the Northland will receive significant rainfall from this
system. Amounts across far eastern Minnesota into northwest
Wisconsin will be from 1 to 2.5 inches with some higher amounts
likely. Several of the models show smaller areas with amounts of 3
to 4 inches but picking that area out at this time is still too
difficult. Although flash flood guidance is still fairly high over
much of the Northland, flooding will be a concern especially if
those higher rainfall amounts occur along the North Shore and
northwest Wisconsin.

The rain will end Thursday night but any drying will be short
lived as a shortwave moves through the area causing a chance for
showers and a few thunderstorms Friday into Friday night. We have
a dry forecast Saturday then have chances for more showers/storms
Sunday afternoon into early next week over parts of the
Northland.

Highs will be below normal Thursday but moderate to and then above
normal Friday into Sunday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 100 AM CDT Wed Aug 16 2017

VFR through the first half of the forecast as high pressure remains
nearby. By late morning, light rain will approach the BRD and INL
terminals as low pressure moves into western Minnesota. As the rain
slowly spreads east, ceilings and vsbys will lower into the MVFR
range. The exception will be HYR which will remain VFR through the
forecast. The best opportunity for thunder will be at BRD in the
later afternoon. Timing is difficult and have a VCTS mention along
with IFR ceilings. Will see IFR ceilings at HIB/INL toward the end
of the forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  56  65  58  67 /  10  80  90  70
INL  58  63  56  73 /  10  90  60  30
BRD  61  70  60  74 /  30  80  70  20
HYR  58  72  62  67 /  10  50  90  70
ASX  55  71  61  66 /   0  40  90  70

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

UPDATE...LE
SHORT TERM...Melde/Grochocinski
LONG TERM...Melde
AVIATION...GSF/LE


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