Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 131845 AAD
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
145 PM CDT Sun Aug 13 2017

.UPDATE...
Issued at 144 PM CDT Sun Aug 13 2017

Update for new 18Z Aviation Discussion below.

UPDATE Issued at 1137 AM CDT Sun Aug 13 2017

updated to move likely pops to the twin ports by early afternoon.
The atmosphere has moistened up to allow the precip to reach the
ground. The rain should continue off and on this afternoon. rest
of fcst unchanged.

UPDATE Issued at 857 AM CDT Sun Aug 13 2017

Adjusted pops based on current obs and trends. Meso models
indicate the forward edge of the precip will slowly work its way
east late this morning. There is dry air it still has to moisten
up before reaching the carlton county/twin ports region. If that
occurs, it won`t ne until the afternoon. Rest of fcst unchanged.

&&

.SHORT TERM...(Today through Monday)
Issued at 352 AM CDT Sun Aug 13 2017

As advertised, the upper level closed low has been making headway
into western Minnesota overnight. Early this morning the low
aloft was centered over North Dakota while at the surface the low
was form over the the lee of the Colorado Rockies with a trough
extending across south dakota into west central MN. Showers and
storms were occurring ahead of the forming low in the strong warm
air advection from north dakota, western MN, into Nebraska. With
the evolving surface pattern, in conjunction with the upper
support, expect the rain area to progress east into the DLH
forecast area, first in the southwest this morning, then spreading
east and northeast into the afternoon. The upper wave will be
over MN tonight, then traverse over Wisconsin on Monday, while the
surface low cross across southern MN and central WI. With this
situation expect plenty of moisture being advected into the region
on 25 to 30 knot low level jet. A strong baroclinic zone develops
overnight across the northland just south of the twin ports, so
we will see a prolonged period of rain across the southern
forecast area, mainly south of U. S. Highway 2 in MN and much of
the northwest corner of WI. Have not added chances of rain in far
northern MN, around the International Falls area as of now looks
like the rain will remain south of that area as models are keeping
that area under high pressure, but confidence is rather low and
may need to add some rain chances farther north.

.LONG TERM...(Monday night through Saturday)
Issued at 352 AM CDT Sun Aug 13 2017

A fairly active extended period with several periods where there
are chances of showers and thunderstorms. Temperatures will remain
near normal with highs in the 70s across the Northland. Low
temperatures will range from the upper 40s to low 60s.

Monday evening into Tuesday will be a transition period as a
trough digs from the western Great Lakes into the central Great
Lakes. Behind the trough, high pressure will build in. This will
transition cyclonic northwesterly flow, to westerly/southwesterly
flow on the western side of the ridge axis. In addition, low level
flow will become more southerly, which will advect warm, moist
air into the Northland. Will remain dry initially late Monday
night into early Tuesday as high pressure slides through.
Precipitation chances will increase from southwest to northeast
Tuesday afternoon and evening as a shortwave lifts across the
northern Plains. At the surface a broad area of low pressure will
develop across the Dakotas. This system will continue moving
northeastward on Wednesday. Thunderstorms still cannot be ruled
out as there will be a few hundred J/kg of MUCAPE to work with.
PWAT values will range anywhere from 1.5 to 2.0 inches on Tuesday
and Wednesday, which is greater than the 90th percentile based on
SPC Sounding Climatology information at INL and MPX for this time
of year. GEFS current and previous ensemble guidance show low
probabilities of 1 inch of precipitation in a 6 hour period on
Tuesday and Wednesday. So, there is potential for localized
flooding due to heavy rainfall.

Current deterministic forecast guidance is in disagreement on how
quickly this system exits the region. The GFS is currently the
slowest piece of guidance, which lingers precipitation chances
across eastern Minnesota and northwest Wisconsin on Thursday. This
is due to the shortwave absorbing into a cutoff low located in
central Canada. The ECWMF/CMC are more progressive with the
system, lifting the shortwave into the central Great Lakes. Both
the ECWMF and CMC have the cutoff located across central Canada,
but do not have the shortwave being absorbed into the cutoff. Due
to these differences have low confidence in precipitation chances
on Thursday. The cutoff feature will be the main area of focus
late in the week and heading into the weekend. The ECMWF/GFS
currently depict a similar scenario where the cutoff rotates
southeastward from central Canada into western Ontario on
Saturday. The CMC is a bit faster, moving the cutoff into eastern
Ontario, and western Quebec. Behind the cutoff, a ridge will slide
into the region from the west on Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 144 PM CDT Sun Aug 13 2017

Low pressure at the surface and aloft over western Minnesota and
the eastern Dakotas this afternoon, with high pressure over the
Duluth area. The surface ridge will push northeastward over Lake
Superior and the Minnesota Arrowhead this afternoon and evening.
Meanwhile the low pressure will slowly meander southeastward into
southern Minnesota. Rain showers and isolated thunderstorms are
expected over most of the forecast area. The best chance of storms
will be near BRD. Visibility may dip to MVFR as heavier showers
move through the terminals. Rain coverage is forecast to increase
through this evening and then taper off Monday morning. With the
rain and overcast skies, think we`ll have some difficulty
generating fog. Visibility may dip to less than 3SM for a time
overnight at DLH and BRD, but think ceilings will remain in MVFR
range overnight. If clouds clear out of INL late tonight,
radiational cooling would be sufficient for fog development.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  74  54  70  54 /  60  60  30  10
INL  77  51  77  52 /  40  30  10   0
BRD  66  55  72  56 /  70  60  20  10
HYR  75  55  70  53 /  30  60  60  10
ASX  79  56  72  53 /  20  50  50  10

&&

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

$$

UPDATE...Stewart
SHORT TERM...CLC
LONG TERM...WL
AVIATION...Huyck



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