Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 150335
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1035 PM CDT Thu Sep 14 2017

.UPDATE...
Issued at 1027 PM CDT Thu Sep 14 2017

A dangerous flooding threat is developing across portions of the
Northland this evening as thunderstorms continue to develop and
track across the area. The strongest storms producing the most
significant rainfall extended from western Cass County east
northeast through the Iron Range and toward Lutsen. Radar and
observations show 2 to 5 inches of rainfall in the Zim, Makinen,
Skibo, and Whyte areas. More rain is on the way and another 1 to
3 inches could occur through 1 am. Significant flooding will be
possible in those areas.

We shifted higher chances for showers/storms further south as the
line of storms has been sagging south with time along with the low
level boundary. Strong FGEN forcing is forecast through much of
the night and there is a pool of unstable air over much of the
region. A strong low level jet is also in place but it will shift
east with time tonight. A shortwave was moving through as well
and there could be a diminishing trend late tonight as the jet
diminishes and weak subsidence behind the shortwave occur.

UPDATE Issued at 633 PM CDT Thu Sep 14 2017

Strong to severe thunderstorms continued across portions of
northeast Minnesota with additional showers and storms continuing
to form west to the North Dakota border. Strong low level FGEN is
present and will be through much of tonight and a low level jet
will be strengthening this evening but should then shift east more
into northern Wisconsin later tonight. We think showers and
storms will continue through much of tonight, especially over
northern Minnesota. There will be a threat for very heavy rain. A
report just west of Crane Lake was around 2.5 inches of rain as of
530 pm. We will be issuing a Flash Flood Watch for much of far
north to northeast Minnesota through 11Z to account for the
possible heavy rainfall.

&&

.SHORT TERM...(This evening through Friday)
Issued at 311 PM CDT Thu Sep 14 2017

Increasing chances of showers and thunderstorms will occur this
evening as a more active weather pattern sets up across the region.
A mid-level shortwave trough, along with enhanced 850-700 mb layer
frontogenetical forcing, will act as the mechanism for these showers
and storms. The environment should be capped in some locations,
given values of MLCIN in the 50 to 150 J/kg range. However,
there`s plenty of elevated instability, with MUCAPE values from
the 14.12z GFS/CMC/NAM models between 1000 to 2000 J/kg, so if
storms can break through the capping inversion, there is plenty of
instability for them to tap into. The HRRR model is indicating
some stronger convective cells out ahead of the leading wave, so
that will need to be watched from 23z this afternoon onward. So
far this afternoon, we`ve issued a few SPSs due to a single strong
thunderstorm that developed over northwest Minnesota and
translated east-northeastward over Koochiching county. However, it
appears to be struggling to sustain its updraft despite the
amount of instability in the region. Heavy rainfall is possible
with some of these storms, given Pwat values between 1.3 and 1.6"
tonight.

Along with the chances of showers and storms tonight, areas of fog
is expected to develop due to on-shore flow tonight, along with
low condensation pressure deficits and light winds. Fog is
expected to begin along Lake Superior, and build further inland as
the night goes on. Most of the heavy rainfall is expected over the
Iron Range eastward into the Minnesota Arrowhead regions. Chances
of thunderstorms should decrease after midnight due to the loss
of favorable instability. The respite from storms will be short-
lived as another round of showers and storms are expected again
Friday as another shortwave trough moves into the region. The
convective-allowing models are struggling to resolve the activity
for Friday, as the NAMNest model is more active than the WRF
NMM/ARW models, which are going drier. While uncertainty does
exist, the synoptic models are showing decent agreement on
precipitation chances around the forecast area. Chances of
thunderstorms will increase Friday afternoon as better
destabilization builds. A strong baroclinic zone will remain over
the region given more southerly winds over northwest Wisconsin and
more northerly winds along the International Border. High
temperatures Friday will range from the upper 50s and lower 60s
north to the middle to upper 70s south, with some lower 80s also
possible.

.LONG TERM...(Friday night through Thursday)
Issued at 254 PM CDT Thu Sep 14 2017

The Northland will begin the period with cool, easterly low level
flow, and warm and humid southwest flow aloft. An area of low
pressure will be in the Central Plains Friday evening. Much cooler
wrap around air will be in western North Dakota and in Canada,
waiting to swing into the Northland once the Central Plains low
moves through the region. Passing shortwaves and the strong nocturnal
low-level jet could trigger showers and thunderstorms across the
Northland Friday night, while the Central Plains low lifts to
northern MN.

The low will continue to move through northern MN Saturday, lifting
into Ontario Saturday night. It`s cold front will slowly work its
way eastward across northern MN Saturday, then rapidly swing through
the Northland Saturday night when a deep upper-level low lifts into
the Northern Plains and south-central Canada. The Northland could
get showers and thunderstorms Saturday and Saturday night. A few
storms could be strong, capable of small hail and heavy rain.

People across the Northland may wake up to what feels like fall on
Sunday. Much cooler air will move into the region amid the westerly
flow in the wake of the cold front. Expect a cool and breezy day.
Concerned models may be too warm, but stuck with model consensus for
now. We might cool the forecast with time. Cloud cover will play a
part. Most models think it will be mostly sunny, but the residual
moisture from the previous day, combined with the very cold air,
might trigger broken cumulus in the afternoon, which would limit
heating. The forecast for now is for highs in the upper 50s to lower
60s.

Southerly flow will redevelop Monday and bring back warmer air into
the region into the middle of the week. The moisture return will
also increase the chances of showers and storms. The GFS has much
more robust precipitation than the European. The best chances will
likely be when the cold front swings through during the middle of
the week, but the GFS has this occurring significantly sooner than
the European and Canadian.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 633 PM CDT Thu Sep 14 2017

A stalled frontal boundary and low level FGEN has led to showers
and strong to severe thunderstorms over northern Minnesota this
afternoon and early evening. The showers/storms will continue
overnight as the strong FGEN forcing is forecast through the
night. Ceilings will lower for most areas overnight along with fog
developing. IFR/MVFR conditions will expand, especially over
northern Minnesota and they will continue into Friday. An area of
low pressure will then move toward the region on Friday producing
more showers/storms and IFR/MVFR conditions.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  59  67  57  72 /  70  50  60  40
INL  53  59  53  63 /  60  80  80  50
BRD  61  75  62  69 /  30  60  60  50
HYR  63  80  63  79 /  20  30  40  30
ASX  59  74  60  78 /  40  30  40  40

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Flash Flood Watch until 6 AM CDT Friday for MNZ010>012-018>021-
     025-026.

LS...Small Craft Advisory until 10 PM CDT Friday for LSZ144-145.

&&

$$

UPDATE...Melde
SHORT TERM...JTS
LONG TERM...Grochocinski
AVIATION...Melde



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