Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 122227

Area Forecast Discussion
National Weather Service Marquette MI
527 PM EST Sun Nov 12 2017

.SHORT TERM...(This evening through Monday)
Issued at 329 PM EST SUN NOV 12 2017

With a lingering SFC trough over Lake Superior, W-NW flow favored
upslope area may see some very light snow/drizzle/freezing drizzle
through tonight, then tapering off from W to E on Mon. Uncertainty
with ptype exists due to borderline moisture profiles for dendritic
growth. Regardless, no significant impacts are expected given very
light nature of any precip.

Lows tonight will be in the 20s and highs Mon in the 30s.

.LONG TERM...(Monday night through Sunday)
Issued at 335 PM EST SUN NOV 12 2017

Over the last several days, medium range models have not waivered in
showing a persistent strong ridge over the N Pacific thru this week.
Daily 500mb height anomalies centered over the Aleutians/Bering Sea
will be a very impressive 400+m. Longer range guidance suggests this
feature will persist for at least the next 10 days and perhaps the
next 2-3 weeks. This positive height anomaly will force persistent
troffing downstream over the ne Pacific. Shortwaves ejecting from
this ne Pacific trof will progress downstream across the northern
CONUS in lower amplitude/more progressive flow. With lower
amplitude/progressive flow the rule, temps across Upper MI should
fluctuate within a few degrees of mid Nov normals on most days this
week (normal high temps are generally in the upper 30s to lwr 40s).
As for pcpn, the next round of widespread pcpn will arrive Tue night
when a shortwave and associated cold front arrive. Conditions will
be warm enough so that this round of pcpn Tue night/Wed morning will
be all rain. Some LES will follow in caa regime later Wed into early
Thu. A stronger shortwave and low pres system are still on track to
affect Upper MI late in the week, and it could be a significant
system with regard to pcpn and wind. Ptype will probably be rain
and/or snow initially before becoming all snow.

Beginning Mon night, return southerly flow will develop btwn exiting
high pres ridge and a low pres trof emerging over the western
Plains. Dry weather will prevail.

Shortwave moving out across the Northern Plains Tue aftn/evening
will reach the western Great Lakes Wed morning. Ahead of this wave,
persistent waa/isentropic ascent during Tue could yield some
-ra, but mid-levels remain rather dry, suggesting minimal chc of
measurable pcpn. May end up being -dz if pcpn does occur. Rain will
then move across the area Tue night into Wed morning when deep layer
forcing and cold front associated with shortwave arrive. Models
continue to be in good agreement on timing this feature. Main area
of rain will exit the western fcst area Wed morning and the e in the
early aftn. Will be blustery behind the front on Wed, especially
over the Keweenaw and along Lake Superior where w to nw winds will
probably gust upwards of 40mph given up to 35kt winds in the mixed
layer. Over the last 3 days, models have trended toward more
supportive conditions for LES to develop in the caa regime later Wed
into Thu morning due to trailing shortwave, more sharply cyclonic nw
flow and 850mb temps falling to around -10C. Expect some minor snow
accumulations...nothing to warrant a headline. With high pres
building over the Upper Lakes during Thu, LES will end.

A stronger shortwave ejecting from the ne Pacific trof will reach
the Upper Great Lakes late week. Over the last several days, medium
range models, ECMWF and GFS in particular, have indicated the
potential for this shortwave to spin up a strong sfc low over the
Great Lakes. Overall, given 12z guidance and recent days medium
range model runs, there is increasing confidence for a strong storm
system to impact the Upper Great Lakes Fri/Sat. Support from GFS/CMC
ensembles is improving as well, and there has been some increase in
the number of sub 980mb lows showing up in the CMC ensembles. Track
of the main sfc low, critical for impacts in Upper MI with regard to
ptype, potential hvy snow, strong winds, will be a point of
contention until we move much closer to the event as ensembles have
a large spread in location of the main sfc low...not a surprise
given the time range. However, similar to yesterday, it still
appears that 2 unorganized sfc lows will track eastward Thu night,
one moving across s central Canada and the other moving across the
Central Plains. The latter low will become the main low as it winds
up heading thru Lower MI Fri night and into sw Quebec late Sat. This
should result in rain and/or snow developing across the area late
Thu night/Fri, then becoming all snow before transitioning to
blustery nw flow LES for Sat. For what it`s worth, 12z CMC/ECMWF
suggest much of the heavier pcpn will fall as rain. If pcpn falls
only as snow, period of strong forcing will provide potential of
significant snow accumulations with lake enhancement further
boosting snow totals near Lake Superior. Strong nw winds developing
as the system departs will create blsn. On Lake Superior,
development of large waves combined with above avg water levels for
this time of year could lead to significant beach erosion/flooding
for nw facing beaches, especially east of Marquette. Of course, this
will depend on how strong the storm system and winds are. Will
certainly be a system to monitor as the week progresses.

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 526 PM EST SUN NOV 12 2017

Not a lot of change expected in the forecast period. Greatest
uncertainty is with DZ/FZDZ in the forecast at KCMX; mainly with
coverage and intensity. Don`t think there will be significant
amounts of FZDZ, though. Conditions will also stay mostly MVFR.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 329 PM EST SUN NOV 12 2017

Lighter winds under a weak pressure gradient will persist into
Monday. Tuesday, southerly winds will increase to 20 to 30 knots as
the pressure gradient strengthens ahead of an approaching cold
front. This front is expected to track across Lake Superior on
Wednesday, with W-NW gales 35-40 knots still looking possible
Wednesday afternoon into Wednesday night.

Southerly gales of 35-40 knots will be possible Friday ahead of
stronger storm system developing over the Great Lakes. Higher end NW
gales or even storms seem like a good bet behind the storm system
late Fri night through Sun, although the strongest winds would be
Sat into Sat night.

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


LONG TERM...Rolfson
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