Area Forecast Discussion
Issued by NWS Duluth, MN

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846
FXUS63 KDLH 250518
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1218 AM CDT Tue Jul 25 2017

.UPDATE...
Issued at 953 PM CDT Mon Jul 24 2017

Showers and a few thunderstorms continued to move through portions
of west central to central Minnesota and will brush our southern
MN zones through the late evening hours. Some of the guidance
suggests this activity will hold together as it crosses into
Wisconsin and we have leaned toward that as it has been
persistent. POPs were updated.

No significant changes were made to Tuesday`s forecast and the 00Z
NAM suggests precip coverage will not be very high during the day
Tuesday but increase in the evening, especially over the southern
two thirds of the Northland.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 359 PM CDT Mon Jul 24 2017

Big question mark of this forecast is the convective activity
tonight, and it`s resulting effect on tomorrow`s convective
potential. All day we have been watching a vort max and weak
cluster of showers and isolated thunderstorms roll from west to
east along the North Dakota/South Dakota border. Models, even the
mesoscale models, are not handling this feature very well.
Initially, it is not always placed correctly, with the most common
error having it too far to the southwest. Some are weakening it
over the next few hours, and bringing it across central MN
overnight and Tuesday, likely too slowly. Convection does not get
into the forecast area until during the day on Tuesday. Others
are using it to generate more convection this evening and move
across the southern half of the forecast area overnight. These
seem to make more sense, given the position of the low level jet
that is likely to develop this evening and then swing east. This
overnight convection is going to leave us cloudy with showers
Tuesday morning, with lows in the 50s most locations. The main
question then is how much clearing we will get, to then
destabilize tomorrow afternoon to set up for the convection
expected with the cold front tomorrow night. For now have gone
with a cloudier and more stable forecast, anticipating that the
best instability will be mainly south of the forecast area, with
the northern gradient of the CAPE in the vicinity of the southern
border of the forecast area. This could shift though, depending on
morning and early afternoon cloud cover. Have gone with a
relatively warm high temperature forecast based on what is going
on upstream, and that is likely to advect into the area tomorrow.

.LONG TERM...(Tuesday night through Monday)
Issued at 359 PM CDT Mon Jul 24 2017

A risk for strong to severe storms Tuesday night into early
Wednesday, then dry through the rest of the week. Seasonable
temperatures with highs in the mid 70s to low 80s through the long
term forecast period.

On the synoptic scale a mid-level closed low will be located over
central Manitoba Tuesday evening moving east into northwest Ontario
Tuesday night into Wednesday with an associated surface low moving
across southern Hudson Bay. From this low a cold front extends south
into the eastern Great Plains, with a warm sector ahead of the cold
front over the Upper Midwest late Tuesday. This cold front will
sweep east across the Upper Midwest Tuesday night into early
Wednesday and be the primary forcing mechanism for convection.
Within the warm sector late Tuesday elevated instability will be on
the order of 2000 to 3000 j/kg MUCAPE in central Minnesota, with
some guidance depicting 2000+ MUCAPE as far north as the Iron Range,
but at least from the Brainerd Lakes east to I-35 corridor. Surface-
based storms may be limited by warmer low/mid level temps during the
day, especially if Monday night convection in western MN results in
lingering clouds/showers across the Northland Tuesday morning
limiting surface heating. However, by the evening hours the front
coming across from west to east should provide enough forcing to
break through the cap and allow for scattered to numerous
thunderstorms to develop along the front, at least across central
and southern Minnesota. In northern Minnesota there remains some
level of uncertainty if/when storms will develop, as the front may
end up moving across much of northern Minnesota Tuesday evening
before storms finally get going. The best chance for storms will be
in east-central Minnesota across the I-35 corridor east into
northwest Wisconsin Tuesday evening into Wednesday morning. Storm
motion will be generally along-front which could result in flooding
concerns.

In summary, there is a risk for strong to severe storms Tuesday
night into Wednesday morning across the Northland. Storms may
develop as early as late Tuesday afternoon or as late as late
Tuesday night somewhere across central Minnesota - with storms
impacting parts of northern Minnesota and all of NW Wisconsin -
depending on the strength of the cap, frontal location, low level
jet ahead of the front, elevated instability, etc. There is a
conditional threat for flash flooding along the frontal zone,
probably somewhere across east-central Minnesota into much of
northwest Wisconsin. However, given the lower than usual confidence
in convective evolution and nearly every available convection-
allowing and parameterized model/ensemble producing solutions that
have the axis of heaviest rain south of the CWA. This matches up
well with WPC`s excessive rain outlook which depicts a marginal risk
for much of the Northland and a slight risk for much of central and
southern Minnesota.

Cold front exits the region late Wednesday leading to precipitation
ending. High pressure builds from west to east across the Upper
Midwest through the rest of the week leading to near seasonable
temperatures and sunny skies through Saturday. Saturday night into
Sunday a front moving from west to east will likely result in
scattered showers and thunderstorms. Some strong storms are possible
but at this point there is not a strong signal for severe weather.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1218 AM CDT Tue Jul 25 2017

A shortwave will continue to move across east central Minnesota into
Wisconsin tonight causing some showers near it. Other stronger
thunderstorms were occurring further west over northeast South
Dakota into west central Minnesota being at least partially driven
by an increasing low level jet. Showers and storms will spread north
and east later tonight as the low level jet veers and moves a bit
east. We expect some showers and storms to continue into Tuesday but
overall coverage should be low. Mainly VFR ceilings late this
evening will lower late tonight into Tuesday to MVFR over a good
portion of the Northland. Some fog will also occur tonight,
especially around Lake Superior. Fog was already observed at KASX.

A better chance for strong to severe thunderstorms will occur
Tuesday evening as a shortwave and frontal boundary move through the
area. The best chance for storms will be over the south half to two
thirds of the Northland.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  57  77  63  79 /  30  50  50  20
INL  60  78  58  77 /  10  30  20   0
BRD  63  83  65  80 /  50  50  50  20
HYR  56  80  65  79 /  40  40  70  60
ASX  54  81  65  80 /  10  40  70  40

&&

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

$$

UPDATE...Melde
SHORT TERM...LE
LONG TERM...JJM
AVIATION...Melde



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