Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 211959

Area Forecast Discussion
National Weather Service Marquette MI
359 PM EDT WED SEP 21 2016

.SHORT TERM...(This evening through Thursday)
Issued at 358 PM EDT WED SEP 21 2016

Dry air exists over the northern CWA where a SFC ridge extends. A
SFC low over the central plains has an inverted trough extending NE
across WI and lower MI, with an area of convection along the
elevated portion of the warm front over a good portion of WI. Most
do not initialize well with the current convection, and those poorly
initializing models blow convection up across the SW CWA this
evening as the warm front moves north and LLJ ramps up. If the front
can move into the area with the LLJ, heavy rainfall would be a
significant issue this evening and tonight as warm cloud depths
would be over 11kft, PWATs near 1.75" and storm motion slow and
nearly parallel to the front. Several inches of rain would be
possible especially along the WI border. However, models that do
initialize well (or at least better) with the WI convection (HRRR,
HRRR-EXP, Canadian-Regional) keep heaviest precip will south of the
area as the LLJ will be hindered north of that convection and the
front may not even make it into the area. These models do bring
precip into the area, just not the heaviest. Could still see 0.50-
1.00 inches right along the WI border. Thu should see overall
diminishing precip chances, but isolate to scattered showers will
continue to be possible through the day, especially over the south.
The Keweenaw will see the lowest precip chances through tomorrow,
possibly being dry much of the time.

.LONG TERM...(Thursday through Tuesday)
Issued at 432 AM EDT WED SEP 21 2016

An increasingly amplified pattern is still on track to develop
across N America for the remainder of this week into the weekend.
Ridge/positive height anomaly currently moving into nw Canada will
strengthen as it shifts across the Northwest Territories to Nunavut
by the end of the week. The magnitude of the positive height anomaly
at 500mb will reach 3 standard deviations above the long term late
Sept avg. To the s of this anomaly, a trof will amplify over the
western CONUS over the next few days, and the building downstream
ridge over the central CONUS will then link up with the n central
Canada positive height anomaly, leading to a sharp mid continent
ridge for a brief time. In response, trof over se Canada will deepen
and expand into the ne CONUS this weekend. This suggests that after
wet weather into Thu, a drier period should mostly dominate Fri/Sat
and potentially thru Sun as sfc high pres associated with the sharp
upstream ridge builds se into northern Ontario and the Upper Great
Lakes. Early next week, a more progressive flow regime should begin
to take shape again. Initially, building of a ridge into western N
America will send a shortwave se into the Upper Lakes later Mon/Tue.
This wave will incorporate at least some of the energy in the
western CONUS trof with the remainder dropping s. A period of shra
will accompany this shortwave across the area at some point Sun/Mon
with drying following for Tue. As for temps, readings will probably
not stray far from late Sept normals during this period.

Beginning Thu, last in a string of weak shortwave energy lifting ne
thru the western Great Lakes will move e of the area by late aftn.
Meanwhile, downstream of the western Canada ridge, a stronger
shortwave will drop into northern Ontario during the day and then
into Quebec Thu night. Following this wave, sfc high pres associated
with the sharpening mid/upper ridge in central Canada will build se
into northern Ontario Thu night, pushing frontal boundary extending
from the Plains to the Great Lakes southward. As a result, expect a
trend for shra Thu morning to diminish and/or end from nw to se
during the aftn thru Thu night.

With sfc high pres dominating northern Ontario on Fri and frontal
boundary/baroclinic zone shifted farther s and sw, expect a dry day.
Will need to watch development of pcpn into the northern plains
where strengthening southerly flow/isentropic ascent ahead of
western CONUS trof leads to an expanding pcpn area. Right entrance
upper divergence with a reoriented upper jet in a nw-se direction
across northern Ontario to New England could aid the expansion of
pcpn toward Upper MI late Fri or Fri night.

ECMWF has been most insistent on pcpn briefly streaking se into at
least western Upper MI Fri night into Sat underneath right entrance
of upper jet and within an eastward extension of isentropic ascent
from the northern Plains. GFS/CMC have been more varied on whether
or not the pcpn will reach the area, but since majority of GFS/CMC
ensembles support the streak of pcpn, fcst will reflect chc pops
spreading into the far w Fri night and expanding e into central
Upper MI Sat morning before pcpn area dissipates.

Fcst for Sun thru Tue is highly uncertain, much more than is
typically the case at this time range and no different from the last
few days. Over the last 4 days, medium range guidance has shown
considerable spread in what happens with the western CONUS trof and
how the flow evolves across southern Canada this weekend thru early
next week. The 00z GFS is back to showing a mid level low closing
off over the Upper Mississippi Valley/western Great Lakes early next
week, a solution that appeared once days ago though it got to that
solution in a different manner. At this point, consensus of recent
days guidance is for a shortwave which incorporates at least some of
the energy in the western CONUS trof to reach the area early next
week, but wouldn`t be surprised at all if something completely
different occurs. Maintaining some continuity with previous fcst,
will show chc pops spreading slowly e across the area Sun/Sun night,
lingering Mon then trending dry on Tue.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 228 PM EDT WED SEP 21 2016

Deep moisture and widespread convection impact most KIWD and KSAW
this evening into Thu morning. KCMX will be on the NW edge of
precipitation and may, therefor, end up with better or worse
conditions. Above average confidence in the overall forecast for
KIWD and KSAW as models are in good agreement. However, will likely
need to add thunder into TAFs as that threat timing can be better
established. Also, VIS may end up being lower during heavier
convection, with models showing some areas of very heavy rainfall
possible, especially toward KIWD.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 358 PM EDT WED SEP 21 2016

NE flow over Lake Superior with SFC trough moving into Upper MI and
SFC ridge over Ontario could support some higher wind gusts to 25
knots over the western half of the lake into Thu and across the
entire lake Thu night into Fri. As the Canadian high builds more
over the Upper Lakes, winds will dip below 20 kts Friday night into
Saturday night. Southerly winds will increase late Sunday into Mon
to 25 to 30 knots over mainly the north central and eastern part of
the lake as a low pressure trough approaches from the west.

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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