Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 201816 AAC
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
116 PM CDT WED JUL 20 2016

.UPDATE...
Issued at 116 PM CDT Wed Jul 20 2016

Please see updated 18Z Aviation Discussion below.

UPDATE Issued at 1145 AM CDT Wed Jul 20 2016

Very subtle impulse evident in water vapor imagery and PV model
depictions across central MN late this morning, appears to be
responsible for supporting the TStorm activity along I-94 just to
the south of our area. In the immediate short term, it appears
that most or all of this activity will stay south of the WFO
Duluth Wisconsin counties. With that in mind, the surface warm
frontal boundary appears to be sharpening up roughly along the
familiar I-94 corridor late this morning, and a low level
warm/moist advective pattern is still in place across the entire
frontal zone. Thus, we simply cannot rule out chances for TStorms
just about anywhere, although the best chance tonight and Thursday
morning would seemingly consolidate farther north along the
International Border region as the wave comes out of the Dakotas
with a much better defined focus for low level jet inflow.

Stratus deck across much of our western CWA continues to hang
tough and resist mixing out late this morning, which is putting a
bit of complexity to the heat headlines. A fairly deep morning
inversion evident on the MPX 12z sounding and weak subsidence
behind the departing PV lobe appear to be enhancing stability and
limiting mixing. However, we still believe that this will
eventually mix out, and when it does, temps and dewpoints will
likely jump several to many degrees resulting in heat indices
around 100 by mid to late afternoon. No changes to the current
heat headlines are planned at the moment.

&&

.SHORT TERM...(Today through Thursday)
Issued at 500 AM CDT Wed Jul 20 2016

Dangerous heat and humidity today and tomorrow due to a very strong
ridge across the Great Plains. Mainly sunny today then thunderstorms
possible tonight into Thursday, which could impact just how warm
temperatures rise across some locations. A few strong storms are
possible, mainly late tonight across far north-central and northeast
Minnesota, but the threat for organized severe thunderstorms is low.

On the synoptic scale a nearly 600dm ridge centered across KS/OK has
allowed very warm and most air to be advected up across the northern
Plains with a warm front draped across the Missouri river basin.
This warm front will lift northeastward today bringing with it the
low to mid 70s dew points currently over eastern South Dakota. While
temps aloft are certainly very warm (850mb temps in the 23-27C range
at their highest across east-central MN), the oppressive humidity
from the dew points which will approach the upper 70s across
northwest Wisconsin on Thursday is going to be especially notable.
Highs today and tomorrow will be near-record, but at this point do
not anticipate smashing through records...this is dangerous heat
threat driven just as much by the heat as by the humidity.

Early this morning a few showers tried to form at the leading edge
of a 30-35 knot LLJ across central Minnesota, but as these have
struggled despite 2000 j/kg MUCAPE aloft, have greatly reduced the
POPs today. The widespread convection that some convection-allowing
models were producing has failed to materialize, and as the mid-
level ridge axis associated with the massive upper high across the
Plains crosses from west to east over the upper Midwest today
believe the chance for precipitation is very low. Southerly winds
will increase today with the surface high over the lower Great Lakes
and a weak low developing over the western Dakotas toady, but the
pressure gradient is not expected to be all that strong nor are
low/mid level winds, so despite some fairly deep mixing under mainly
sunny skies do not anticipate particularly windy conditions. A lake
breeze is anticipated due to the land/water temp differential, and
because these southerly winds are not expected to be very strong,
the lake breeze should be able to move well inland, resulting in
cooler temperatures by the lake. This was the main reasoning behind
not issuing a heat advisory for the South St Louis/Carlton county
zone which includes Duluth. Otherwise upgraded part of the excessive
heat watch to an excessive heat warning for Cass and Crow Wing where
the worst of the heat and humidity is expected today, with a heat
advisory to the north (Itasca and Koochiching) and east (Aitkin and
Pine).

Tonight...diurnal convection along and ahead of the warm front in the
central North Dakota and southern Manitoba is expected to continue
eastward into north-central MN and northwest Ontario. Weaker mid-
level winds may preclude a threat of severe weather, but with strong
upper level winds and plenty of elevated instability showers and
storms should be able to survive in some state overnight. Given the
2000-4000+ j/kg MUCAPE expected aloft a few strong storms are
absolutely possible, and an isolated severe threat cannot be ruled
out...but the coverage of storms is questionable at this point.
There is also the possibility for storms to be mainly confined north
of the international border given a better overall environment per
wind field and MCS Maintenance Probability. Otherwise fog is
expected to develop over Lake Superior, with some fog developing
inland given the high amount of low level moisture in place. Lows in
the low 70s, cooler in the upper 60s by the lake.

Thursday...Warm front advances eastward with scattered morning
convection expected. Coverage of convection will depend on overnight
convection...and any morning storms could leave cloud cover which
results in less diurnal heating and thus not as warm as anticipated
temperatures. Still, Thursday is looking like the warmest day across
east-central Minnesota and northwest Wisconsin, with winds shifting
southwest to west and lack of a lake breeze resulting in the heat
and humidity making it all the way to the Lake Superior shoreline.
Highs in the upper 80s to low 90s with dew points in the mid to
upper 70s across northwest Wisconsin. Heat index values will exceed
100 in many locations across east-central MN and northwest
Wisconsin. Continued with an excessive heat watch for all of
northwest Wisconsin due to slightly lower confidence in the
overnight storms...but anticipate but much of this area will need to
be upgraded to an excessive heat warning if convection evolves as
currently expected.

.LONG TERM...(Thursday night through Tuesday)
Issued at 500 AM CDT Wed Jul 20 2016

The heat lets up for the long term...though we remain in a pattern
of heat and humidity with periodic chances for showers and
thunderstorms.   Thursday evening the cold front that will have been
slowly sagging south through the area late tonight and Thursday
finally gets far enough south of the forecast area for precipitation
chances to come to an end, which continues on Friday. Friday will be
cooler with the front south of the area, but it will still be warm
and muggy with highs in the 80s nearly everywhere.  The weak ridge
of high pressure that keeps our weather quiet for Friday shifts east
on Friday night.  Models have been in fairly good synoptic scale
agreement through Friday night, with convection the main question
mark through the period.  As we move into the weekend some
uncertainty begins as an upper level shortwave moves along the
US/Canadian border, which should shove a round or two of showers and
thunderstorms across the Northland, along with more heat and
humidity.  The main differences are in the timing and magnitude of
these features, also affecting the convection during this period.
For now, it appears that the greatest chance for showers and
thunderstorms is on Saturday and Saturday night as the main trough
axis moves across.  The extra cloud cover should keep the heat from
getting to dangerous levels, but the humidity will still keep things
uncomfortable.  Precipitation chances should come to an end on
Sunday with drier conditions expected into early next week as weak
ridging builds aloft with surface ridging as well.  Cooler
temperatures are expected as well, with highs only in the 70s and
low 80s both Sunday and Monday.  Precipitation chances return for
Tuesday and Wednesday, but model differences are such that
confidence is not very high.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 0116 PM CDT Wed Jul 20 2016

Low stratus deck over north-central Minnesota early this afternoon
will continue advancing northward through early evening. Still
think clouds will mix out and dissipate by late afternoon. Added a
TEMPO group at INL with MVFR CIGS in case clouds do not erode
before arriving. Attention then shifts to precip/thunder chances
overnight and associated lower ceilings and visibilities. Think
previous forecast had the right trend introducing VCTS with a
period of MVFR visibilities and -SHRA. Added some lower visibility
immediately following the most likely time for precip at INL and
HIB. Think conditions will improve once again Thursday morning
after showers/storms move out.

&&

.CLIMATE...
Issued at 500 AM CDT Wed Jul 20 2016

Near-record high temperatures are expected today and tomorrow.
Provided below are the records for various locations across
northeast Minnesota and northwest Wisconsin. Please note that
other than our two official climate sites (Duluth and
International Falls) the records are considered "unofficial."

Record Highs for Wednesday July 20...

Duluth................98 in 1901
International Falls...97 in 1923
=>Please note stations below are not official climate sites
Brainerd..............97 in 1977
Hibbing...............91 in 2011
Grand Portage.........90 in 1977
Superior..............94 in 2011
Hayward...............102 in 1901
Spooner...............95 in 1940
Hurley................88 in 2011
Grantsburg............94 in 1977
Madeline Island.......88 in 2004

Record Highs for Thursday July 21...

Duluth................93 in 1960
International Falls...96 in 1923
=>Please note stations below are not official climate sites
Brainerd..............99 in 1901
Hibbing...............90 in 2014
Grand Portage.........83 in 1977
Superior..............95 in 1963
Hayward...............95 in 1901
Spooner...............96 in 1934
Hurley................95 in 2011
Grantsburg............96 in 2011
Madeline Island.......92 in 2011

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  84  69  90  64 /  10  40  40  10
INL  89  71  87  63 /  10  60  30   0
BRD  90  74  92  65 /  10  20  20  10
HYR  88  73  92  64 /  20  30  40  10
ASX  88  72  91  65 /  10  40  40  10

&&

.DLH Watches/Warnings/Advisories...
WI...Excessive Heat Watch from Thursday morning through Thursday
     evening for WIZ001>004-006>009.

MN...Heat Advisory until 9 PM CDT Thursday for MNZ035-036-038.

     Heat Advisory until 9 PM CDT this evening for MNZ010-018-026.

     Excessive Heat Warning until 9 PM CDT this evening for MNZ025-
     033-034.

     Heat Advisory from 7 AM to 9 PM CDT Thursday for MNZ037.

LS...None.
&&

$$

UPDATE...Huyck
AVIATION...Huyck


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