Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 160505

Area Forecast Discussion
National Weather Service Marquette MI
1205 AM EST Mon Dec 16 2019

.SHORT TERM...(This evening through Monday)
Issued at 345 PM EST SUN DEC 15 2019

Shortwave that ushered in colder air that increased LES last night
is heading for New England. The LES in the wake of the wave late
yesterday aftn into this morning ended up being more substantial
than expected for some areas, largely due to higher than
anticipated snow-to-water ratios. Some locations had as much as 6
to 10 inches of fluffy snow. Of course, with the high SLRs, the
snow was less impactful. Winds have been backing today due to sfc
high pres moving e into WI, and as a result, lingering LES is
shifting to the n and ne, leaving behind mostly sunny skies.
However, clouds ahead of the next shortwave are already spreading
into far western Upper MI.

Low-level winds will continue to back to the wsw/sw tonight ahead of
the next shortwave currently over southern Manitoba. This will shift
the remaining LES offshore over the next few hrs. However, with
winds up toward 850mb remaining westerly, the reorienting sw-ne LES
will probably continue to brush the w side of the Keweenaw tonight.
Late tonight/Mon morning, sfc trof associated with the Manitoba
shortwave will swing across Lake Superior. As the trof moves out
across western Lake Superior, sharpening low-level convergence will
organize a heavier snow band along the trof. This heavier snow will
move across the Keweenaw roughly in the 12-15z time frame on Mon,
potentially producing a quick 1-2 inches of snow. With the sfc trof
then weakening as it continues eastward, convergence also weakens.
Thus, the band of shsn accompanying the trof will weaken with time
on Mon. Snow accumulations southward in Ontonagon County and later
in the day east of Grand Marais should be under an inch.

As for temps, challenging fcst tonight. The incoming clouds will
work to hold temps up, but based on satellite imagery and fcst
soundings, it appears there will be some breaks in the clouds,
especially late tonight. For now, took a conservative approach with
min temps generally in the single digits above zero for much of the
fcst area and as low as zero interior w. If clouds break for even a
short period, temps will easily fall thru the single digits blo
zero. High temps Mon will range from the mid teens to lower 20s in

.LONG TERM...(Monday night through Sunday)
Issued at 342 PM EST SUN DEC 15 2019

Models still show broad troughing across the CONUS that is progged
to erode and shift eastward through the early portions of the work
week. Global ensembles are in fairly decent agreement in terms of
500mb height anomalies through the next week or so as our broad
troughing transforms into broad ridging across the CONUS. On more of
the deterministic side, the general troughing across the CONUS will
continue into Monday as ridging builds across the West Coast Sunday
night into Monday. As this ridge builds and moves inland across the
West, steeper troughing will occur downstream and cause a period of
NW flow Tuesday into Wednesday as a shortwave crosses the area
bringing another quick shot of Arctic air. As the previously
mentioned ridge continues east across the CONUS, heights will begin
to rise Wednesday afternoon, gradually cutting off LES as winds back
more southerly Wednesday evening. Models are in better agreement
today than yesterday going into Thursday, as heights continue to
rise and 850 temps begin to warm. Models continue to suggest a very
subtle shortwave to pass over Lake Superior Thursday afternoon which
may bring a period of -SHSN across the NW LES belts and eastern UP.
On Friday going into the weekend, models begin to disagree with
some suggesting a low pressure wave to develop across the Plains and
move east across the CONUS, while others continue a dry trend.

Monday night through Wednesday, models suggest 850 mb temps to
plummet as a shortwave approaches the area. 850 temps at 00Z Tuesday
will range from -12C to -14C and will fall to -24C to -27C  by
Tuesday night. As the shortwave approaches, westerly winds will veer
more from the NW as the LES machine kicks up with winds maintain a
more consistent direction. As colder air continues to filter in,
saturation through the DGZ becomes limited to almost the sfc. Snow
accumulations will begin to suffer from this and transition to more
of a visibility-restricting snow rather than the usual fluffy LES.
For QPF, trended more towards WPC/SREF rather than any deterministic
model as they weren`t too keen on PoPs either. Overall for that 36-
hour period, may see 1 to 4 inches west, 3 to 5 inches across the
Keweenaw, and 3 to 6 inches across the east. Maybe an inch or so for
Marquette with a couple inches across the Michigamme Highlands.

Behind this shortwave, heights will begin to rise on Wednesday
afternoon as winds begin to back more from the SW. As these winds
shift, expect PoPs to decrease. As mentioned before, as the heights
begin to rise, they are accompanied by WAA and associated isentropic
lift Wednesday night into Thursday morning. As a weak embedded
shortwave moves across Lake Superior, chances for some -SHSN
increase again..mainly for the Keweenaw and eastern Upper Michigan.
As winds are more southerly during this time frame, lake-enhancement
chances are zero with any accumulations being more synoptically
driven...stay tuned.

As high pressure and a positive 500mb height anomaly remains to the
north of the Great Lakes Thursday night expect 850mb temps to remain
in the single digits blo zero. The GEM wants to bring another wave
across the Plains and is more north than it was yesterday. However,
the EC and GFS aren`t as keen on this idea. On Friday night into
Saturday the GFS and GEM bring light snow showers across the area,
while the EC remains dry. On Sunday, models show another quick wave
passes through the area. The EC brings this low to the north of Lake
Superior with the GFS and GEM bringing it a little closer. Will wait
until things get a little closer to go into too much detail, but the
NBM continues slight chance PoPs into the weekend.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1204 AM EST MON DEC 16 2019

Approaching sfc trof will bring a return to MVFR cigs at KIWD and
KSAW overnight tonight thru Mon morning. As winds veer again late
tonight/Mon morning, MVFR conditions/-shsn will return at KCMX,
though a period of IFR will likely occur around the time of the trof
passage Mon morning. As winds shift more westerly behind the trof
passage KSAW will see some improvement to VFR late Mon
morning/early afternoon.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 345 PM EST SUN DEC 15 2019

As the next sfc trof approaches, expect w to sw winds in the 20-30kt
range across Lake Superior tonight, strongest over the w half.
This trof will sweep across Lake Superior Mon with winds then
diminishing a little late Mon into Mon evening. An approaching
stronger arctic cold front Mon night will bring an increase in wsw
winds up to 30kt across western Lake Superior after midnight. This
cold front will sweep across Lake Superior on Tue. Behind it, expect
nw winds to 30kt, continuing into Tue night/early Wed morning.
Incoming pres rises combined with the increasingly colder air
flowing across the lake support a good potential of gales to around
35kt Tue aftn/night, at least over the e half of Lake Superior.
Gales could linger into Wed morning, but otherwise, winds will
quickly diminish from w to e on Wed as a sfc high pres ridge
arrives. Should see a period with winds under 15kt as the ridge
passes. After the ridge passes, expect an increase in winds heading
into Thu, possibly up to around 25kt.

There will be some freezing spray tonight thru Mon, but the more
significant freezing spray will arrive after the arctic cold front
passes on Tue. Heavy freezing spray will probably occur Tue night
into Wed morning.

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


SHORT TERM...Rolfson
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