Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 240542 AAC
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
1142 PM CST Thu Nov 23 2017

.UPDATE...
Issued at 1141 PM CST Thu Nov 23 2017

An updated aviation discussion is below for the 06z TAF issuance.

UPDATE Issued at 835 PM CST Thu Nov 23 2017

Surface low over the Canadian Prairie provinces continues to
deepen this evening ahead of a rapidly moving disturbance over the
Pacific NW that will move eastward along the northern tier of
states for the next 24 hours. Strong pressure falls and and
increasingly strong southerly gradient should act to keep winds up
more than is typical for the overnight hours tonight, and this
combined with rather widespread cloud cover and a continued slow
northeastward movement of the surface warm front should lead to
steady or slowly rising temps during most of the overnight hours
in most areas.

A localized area of enhanced lift attributed to mid level
frontogenesis over western Lake Superior and northern Wisconsin
has led to the development of a rather persistent area of light
showers. Spotter reports indicate that this seems to be reaching
the ground mainly in the form of rain. However, there continue to
be a few transient radar echoes between 35-40 dbz, and underneath
those heavier cores, some mixed precip/snow/graupel is possible
for the next few hours - but should not amount to much nor affect
road conditions in a negative manner with temps above freezing.

The two main adjustments to the forecast earlier this evening were
to increase PoPs to account for the showers to the east of Duluth,
and to raise temps overnight, especially over northwest Wisconsin,
where temps will likely be steady or rise a few degrees into the
mid-upper 30s now that the surface warm front has passed, despite
the snow cover.

&&

.SHORT TERM...(This evening through Friday)
Issued at 316 PM CST Thu Nov 23 2017

Main concerns for the short term are the slight chance of drizzle
or freezing drizzle in far northeast Minnesota tonight and warm
temperatures with rain chances on Friday.

Mainly clear skies were found across most of the Northland this
afternoon. Warm air advection aloft will continue tonight with 850
mb temperatures already well above freezing for much of the
Northland and a thermal ridge farther west over the western
Dakotas. Isentropic ascent has produced a narrow arc of clouds
from Aitkin County northwest into northwestern Minnesota. Look for
that arc of clouds to expand southeastward as the forcing lifts
northeast. Considerable dry air below the cloud layer was found
across the region with ceilings in the 7 kft range. BUFKIT
soundings from the NAM and RAP over northeast Minnesota keep a
substantial dry layer in place below the cloud deck, which will
limit drizzle/freezing drizzle potential tonight. Have moved the
precip mentions farther north with this forecast and raised
overnight low temperatures above the consensus blend.

A shortwave trough indicated in the RAP analysis and GOES-16
water vapor imagery over Alberta and southern British Columbia
will quickly advance across the Canadian Prairies tonight and into
Minnesota on Friday. Surface low pressure will scoot eastward
across northern Ontario with a cool front sliding through the
Northland. Light rain is forecast to develop along and ahead of
the front and move through the region. Temperatures aloft will
cool behind the front, but a potential for mixed precipitation
will hold off until late afternoon or evening. Very mild
temperatures are expected with lows tonight from the middle 20s
to the middle 30s, 10 to 20 degrees above normal. Continued mild
for Friday with highs near 40 north and the upper 40s southwest,
10 to 18 degrees above normal.

.LONG TERM...(Friday night through Thursday)
Issued at 316 PM CST Thu Nov 23 2017

The Friday system exits the system fairly quickly Friday night,
leaving some drizzle/freezing drizzle/snow chances for mainly the
Arrowhead and parts of northwest Wisconsin Friday night. This
should not have much of an impact as even if we do get these
weather types, we may only get some patchy ice accumulations. A
weak ridge axis moves across the area on Saturday and Saturday
night, with temperatures on the chilly side. Another shortwave
will move across Manitoba and Ontario late Saturday night and
Sunday, once again bringing a weak trough axis across the area. A
few models are producing precipitation, but most of them are drier
and have little if any precipitation and have left pops out of
the forecast with just an increase in cloud cover. Another ridge
slides through the area Sunday night.

We are finally beginning to get some consistency early next week,
with a longwave trough that swings across the CONUS. The GFS is
still more phased than the ECMWF, but much better than model runs
in the last few days. This should bring some warm temperatures
into the area, with highs rising several degrees above normals.
Late Monday and Monday night into early Tuesday some precipitation
chances will move through the area behind the surface boundary,
so INITIALLY we have rain which then becomes mixed with and
becomes all snow. We may see POPs increase in the next few runs as
long as the consistence continues to increase.

Later in the week confidence remains low, as model differences
become more significant. For now we have some chances for snow in
the Wednesday night/Thursday time range, with near normal
temperatures.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1141 PM CST Thu Nov 23 2017

There is very little change in the general aviation forecast or
confidence for the 06z issuance. A disturbance currently over
Alberta will move rapidly eastward along the northern tier of
states over the next 24 hours. Strong southerly flow and warm
advection is in place, and will persist overnight and Friday
morning. There is expected to be a 3 to 5 hour window of rain
showers at most terminals during Friday morning and into the
midday hours, followed by the passage of a rather strong cold
front. The front will bring a shift to gusty northwest winds by
the end of the period. Low level wind shear is also expected at
all terminals through Friday morning, with southwest to west flow
between 35-45 knots within a couple thousand feet of the surface.
Overall, we have trended ceilings and visibilities upward a bit
with this issuance, and also tried to reflect slightly higher
confidence in exact timing of rain showers.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  33  44  23  29 /  20  50  10   0
INL  30  42  16  25 /  30  60  20   0
BRD  35  46  27  34 /  20  40   0   0
HYR  33  44  27  32 /   0  50   0   0
ASX  33  46  28  32 /  30  40  10  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 6 AM CST Saturday for LSZ121-140>143-
     146>148.

     Small Craft Advisory from 4 AM Friday to 6 AM CST Saturday for
     LSZ144-145.

&&

$$



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