Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 181729
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1229 PM CDT Mon Sep 18 2017

.UPDATE...
Issued at 1221 PM CDT Mon Sep 18 2017

Updated for the 18z Aviation Discussion below.

UPDATE Issued at 730 AM CDT Mon Sep 18 2017

Several runs of the HRRR and other short term models are pointing
to a better opportunity for some showers, especially this
afternoon, from the Twin Ports east through northwest Wisconsin.
Increased pops to account for this trend, as well as the
possibility of showers elsewhere this afternoon.

UPDATE Issued at 712 AM CDT Mon Sep 18 2017

Update for new 12Z Aviation Discussion below.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 350 AM CDT Mon Sep 18 2017

High pressure covered the forecast area at 08Z. Meanwhile, a
southwest flow aloft was working to bring the occasional embedded
upper level impulse across the area. Warm air advection was
beginning to affect the region with clouds on the increase. The
early morning fog is diminishing with the arrival of the cloud
cover. A batch of showers/sprinkles was just arriving over the
southern edge of the forecast area on the leading edge of the WAA
with an assist from some 700mb FGEN. Most of the short term hires
models point to this activity diminishing by 12Z and have
followed. The next batch of showers appears to be ready to
develop/spread into the southern edge of the region by mid
morning. This is in response to one of the aforementioned
impulses. Another impulse will clip Koochiching county as well and
have introduced some pops. The northern impulse quickly departs
by early afternoon ending the rain chance. A stronger vorticity
maxima is progged to move over northwest Wisconsin this afternoon.
This is well advertised by the hires as well as the deterministic
models and have pops aligned accordingly. Instability is limited
and have no thunder mentioned as seen in most models. With he
cloud cover, expect max temps in the 60s.

Differences amongst the models in the handling of another impulse
moving through Wisconsin this evening. The ECMWF/NAM and GEM have
QPF over the far southeast portion of the region in the evening,
while the GFS is dry. The ARW/NMM also hint at some QPF in the
early evening. Maintained the previous forecast of pops initially,
then trended downward after 03Z, ending after 06Z. Some weak
upper level and surface ridging cover the area overnight.

This ridging persists to some extent on Tuesday. However, strong
WAA is underway by the afternoon with a 45 to 50 knot low level
jet racing into the region. Clouds will be on the increase, but no
rain is expected as the moisture is above 5K feet and mean RH is
50 percent or less on the majority of the models. Max temps a bit
warmer with 60s along the North Shore due to an onshore flow, with
70s elsewhere.

.LONG TERM...(Tuesday night through Sunday)
Issued at 350 AM CDT Mon Sep 18 2017

A fairly active period lies ahead during the long term. A
persistent upper-level trough will take up residence over the
western half of the continent and several shortwave troughs will
kick eastward into the Northern Plains and Upper Midwest from
Tuesday night through the weekend. Southerly winds near the
surface and aloft will result in warm air and moisture advection
into the region. Temperatures will generally trend above to much
above normal for late September. The first shortwave trough
arrives Tuesday night as a cool front advances eastward from the
Dakotas. Convergence along the front will encounter a modestly
unstable airmass which will support a chance of thunderstorms. The
storms will likely develop to the west and lift north- northeast,
moving into north-central Minnesota after 06Z. Shear and
instability profiles point to a threat of strong to severe
thunderstorms and the SPC has included much of the CWA within the
Marginal Risk area. Large hail and damaging wind gusts appear to
be the greatest threats.

The cool front is forecast to move out of the area on Wednesday.
Southerly flow ahead of the boundary will recharge the airmass
over northwest Wisconsin. Another round of thunderstorms is
possible Wednesday afternoon before the front exits the Northland.
Some of those storms may be strong, as well thanks to the
combination of moderate instability and deep layer shear of 30 to
40 knots.

High pressure will move across the area Wednesday night and
Thursday. A warm front is expected to lift northward across the
area Thursday afternoon with warm southerly breezes returning.
Thunderstorms are a possibility once again Thursday night thanks
to convergence and forcing for ascent over the warm frontal
surface, combined with an approaching shortwave from the
southwest. The front is forecast to loiter over the Upper Midwest
Friday through Saturday night with several rounds of showers and
thunderstorms forecast. This pattern will be similar to the one we
experienced late last week into Saturday. The potential for heavy
rainfall exists with robust moisture transport into the frontal
zone. Cloud cover and widespread rainfall is expected for Sunday,
which will keep temperatures cooler. By Sunday night the front is
forecast to move eastward, exiting the area on Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1230 PM CDT Mon Sep 18 2017

VFR conditions early this afternoon will eventually transition to
MVFR/IFR cigs/vsbys from southwest to northeast this afternoon and
evening. Some TAF sites could be a bit breezy this afternoon as
the boundary layer mixes, transporting stronger winds aloft to the
surface. Chances of rain showers are expected to ramp up this
afternoon as well, with the best chances over KHYR. Low-level
moisture advection will lead to decreasing ceilings, down to MVFR
/high-end IFR categories overnight. Moreover, on-shore flow and
light winds over the TAF sites will lead to MVFR vsby reductions
over KDLH, KHIB, and KBRD.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  60  51  67  58 /  30  20   0  60
INL  64  48  70  56 /  20  10  10  70
BRD  62  51  72  59 /  10  10  10  70
HYR  62  52  72  60 /  70  30   0  50
ASX  64  50  72  58 /  60  30   0  50

&&

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

$$

UPDATE...JTS
SHORT TERM...GSF
LONG TERM...Huyck
AVIATION...JTS


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