Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 091944
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
244 PM CDT Wed Aug 9 2017

.SHORT TERM...(This evening through Thursday)
Issued at 244 PM CDT Wed Aug 9 2017

Showers and some isolated/scattered thunderstorms will continue
over portions of the Northland. A mid-level shortwave trough
located over North Dakota, along with difluent flow aloft and a
west-to-east sfc boundary, will focus this convective activity
later this afternoon and evening. The main concern will be a
strengthening low-level jet (LLJ) that is expected to develop over
northwest Wisconsin and adjacent areas of northeast Minnesota,
which will focus low-level convergence and enhance moisture
transport into these areas. Given Pwat values progged to be
between 1 to 1.5", there is a concern for localized flash flooding
over areas adjacent to Lake Superior, where the LLJ will be
focused. This area also has sharper changes in elevation, which
would exacerbate flash flood potential. Storm total QPF amounts
for this evening through the day Thursday could range between
0.50 to 1.50", with the bulk of it expected to fall this evening
and overnight. There is a much lower concern for severe weather,
given low values of MLCAPE generally up to 1000 J/kg and 0-6 km
deep layer shear of 20 to 25 kts, both per the 09.12z
GFS/NAM/ECMWF/CMC guidance. We remain in the mention of General
Thunder from the Storm Prediction Center Day 1 convective outlook,
which seems reasonable given the low values of instability and
shear.

Tonight, the mid-level shortwave trough will dive to the southeast,
darting across our southwestern counties. The strongest overall
forcing will be located over northwest Wisconsin as the LLJ moves
eastward ahead of the mid-level trough. There is also an increased
potential for fog to develop in many locations over the Northland
this evening and through the early morning hours Thursday as winds
become light, and boundary layer moisture increases due to the
rainfall, and dew point depressions drop to one degree or less.

We remain under this trough as it slowly moves eastward during
the day Thursday. A lobe of positive vorticity advection will
bring persistent forcing over the Northland, so continued chances
of precipitation into Thursday, albeit slightly smaller chances,
with the best chances remaining over adjacent areas of Lake
Superior and points southeast into northwest Wisconsin. Once
again, only a General Thunder mention over the Northland from the
Storm Prediction Center. Isolated thunderstorms will again be
possible Thursday. Due to the sfc low pressure center expected to
be located just to our south, northeasterly flow will help bring
cooler temperatures to the Twin Ports, and points along Lake
Superior. I slightly decreased Thursday`s highs to account for
this on-shore flow. Chances of showers and storms will diminish
Thursday evening and overnight into Friday morning.

.LONG TERM...(Thursday night through Wednesday)
Issued at 228 PM CDT Wed Aug 9 2017

An omega block pattern sets up across North America at mid/upper
levels this weekend into next week with a broad area of high
pressure across the Upper Midwest. A few low chances for
precipitation over the weekend into early next week associated with
a number of weak mid-level disturbances in the north/northwest flow,
but overall rainfall amounts would be on the light side. There will
likely be cumulus clouds each day given seasonably cooler
temperatures aloft and a steady supply of low/mid level moisture
most days. Temperatures near normal with highs in the 70s and lows
ranging from the upper 40s to mid 50s. A few thunderstorms are
possible Sunday and Monday afternoon, but severe storms are not
expected given limited instability and a weak wind field aloft.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1233 PM CDT Wed Aug 9 2017

VFR conditions will quickly turn to MVFR/IFR ceilings this evening
as a low pressure system approaches the region. A few storms are
possible this afternoon at some sites, with a steady rain expected
this evening. Ceilings will fall to MVFR/IFR conditions tonight,
with visibility falling to MVFR levels at times, especially at DLH
where fog/drizzle is expected to persist from late tonight through
Thursday morning. Some clearing from west to east mid to late
morning Thursday. Variable wind directions as the low moves across
the region, out of the south this afternoon, changing to more east
to northeasterly overnight at Minnesota sites but remaining with a
south to southeast direction at HYR in northwest Wisconsin.
Becoming north to northwesterly towards early Thursday afternoon.
Wind speeds generally less than 10 knots, except for some gusts to
around 15 knots this afternoon at DLH.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  56  64  54  72 /  80  60  20  10
INL  54  70  49  76 /  70  30  10   0
BRD  57  69  54  74 /  40  40  20  10
HYR  57  67  55  72 /  80  50  30  10
ASX  58  64  55  71 /  90  60  30  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory from 4 AM to 10 AM CDT Thursday for
     LSZ141>143.

&&

$$

SHORT TERM...JTS
LONG TERM...JJM
AVIATION...JJM



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