Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191745

Area Forecast Discussion
National Weather Service Marquette MI
145 PM EDT Sat May 19 2018

.SHORT TERM...(Today and tonight)
Issued at 514 AM EDT SAT MAY 19 2018

A lot of moving parts to today`s forecast. Does appear that most
areas will see some showers due to two systems trying to converge
across the area. Could even see some bonus wetting rainfall in parts
of the east half of Upper Michigan, but given latest radar trends
not so sure on that. Given the dry stretch we have been in
essentially since the mid April storm over most of Upper Michigan,
fair to say that any rainfall will be welcome. Other impacts
today will be developing strong/gusty winds on Lk Superior and
eventually northern Lk Michigan

WV loop and mid-level heights show an overall west to east flow
pattern in place across the Conus. Flow is split though, with
southern stream shortwave H7-H5 trough over IL/IN while northern
branch shortwave axis is along Ontario/Manitoba border. Regional
radar shows no rain over Upper Michigan at present but that will
change shortly. Rain showers lifting across northern Lower MI and
northeast WI to the north of the southern stream shortwave are
pegged well by H7 moisture transport. This forcing is forecast to
steadily lift north into cntrl Upper Michigan so have widespread
light showers spreading into Menominee in the next hour or two, to
Escanaba and Manistique by 7 am and into the Marquette, Munising and
Newberry areas by 10 am. Based on radar trends, think the 0.5 inch
or more rainfall shown by RAP and HRRR in swath from Door Peninsula
to eastern Marquette county are likely way too aggressive, but some
light rain should occur. Otherwise, main issue here is how far west
will steady rain expand. Right now, looks like line will be vcnty of
Marquette to Hermansville in northern Menominee county. Expect this
initial batch of rain to exit eastern forecast area early aftn.
Could be some redevelopment of showers over north central late
morning into early aftn as northern branch shortwave trough catches
up with lingering deeper moisture from lead system. Main axis of
showers over northern MN with northern branch shortwave arrives over
Keweenaw by early aftn and then translates across rest of area into
early this evening while diminishing as stronger forcing aloft lifts
across northern Ontario.

Next issue is tied to affect of sfc cold front passage. Expect front
to move into far western Upper Michigan by mid morning and into
central Upper Michigan by mid aftn. Front will surge into scntrl and
eastern Upper Michigan by early evening. Northeast to north winds
will become gusty to 20-30 mph behind the front. Even stronger wind
gusts over 30 mph will be possible this aftn into this evening near
Lk Superior and also over central forecast area from Marquette and
Munising to Sawyer and Escanaba. Temps behind the front will quickly
fall into the 40s/50s. Temps ahead of the front were a real
challenge due to the initial system lifting in from the south.
Overall kept the idea that temps could reach low 70s inland west
(thanks a lot to a very warm start this morning as LNL is still 54F
as of 5 am) before the front comes through. Farther east though, did
lower temps significantly over much of the east half with the
expected clouds and rain this morning and then not much time to
recover before the front blasts through this aftn.

Weather will quiet down tonight with some clouds and gusty winds to
start the evening giving way to some clearing and diminishing winds
overnight as high pressure builds in from the west. Just a small
chance of showers early in the evening but otherwise should be dry
tonight. Lows will tumble into the 30s later tonight, coldest inland
west where temps may drop to freezing.

.LONG TERM...(Sunday through Friday)
Issued at 427 AM EDT SAT MAY 19 2018

Latest round of medium range ensemble guidance shows no changes to
the overall pattern from guidance viewed 24hrs ago. Over the next
7-10 days, pattern will feature mean ridging over western Canada
and mean troffing over eastern Canada. To the s, shortwaves will
occasionally progress across the CONUS in a weak southern stream.
Since the big late season snowstorm in mid Apr, it`s been dry for
the last 30 days, especially so over the w half of Upper MI. W of
a Grand Marais to Manistique line, pcpn over the last 30 days has
been less than 50pct of normal with the majority of that area now
less than 25 pct of normal. The upcoming pattern will favor
continuation of overall dry weather as the ridge/trof pattern over
Canada will work to force the more important pcpn producing
southern stream shortwaves mostly s of Upper MI while the more
dynamic northern stream shortwaves pass well to the ne. There will
be 2 opportunities for rainfall over the next week or so.
Fortunately, some areas will see rain today. However, after today,
the next chc of meaningful rainfall won`t arrive until the end of
the upcoming week. Temps over the next 7 days will fluctuate
around normal as shortwaves dropping into and reinforcing the mean
eastern Canada trof will send cold fronts occasionally s thru the
Upper Lakes, bringing periods of cooler weather, especially so
close to Lake Superior where cooling will be significantly
amplified by the chilly lake waters. Overall though, for most
locations, more days will be above normal than blo normal.

Beginning Sun...In the wake of the cold front passing today, another
very dry air mass will settle over the area for Sun. Based on mixing
heights and dry air aloft that can be mixed down, favored the low
side of bias corrected guidance for dwpts. Under abundant sunshine,
expect highs in the interior up around 70F with RH falling to 15-
20pct. Fortunately, winds will be on the lighter side on Sun to
prevent enhancement of fire wx concerns. Will be cooler along the
Great Lakes, especially Lake Superior. With sfc high pres over the
area Sun night, winds will fall off to calm for much of the area,
leading to a good radiational cooling night with only some high
clouds passing at times. Precipitable water increases from during
the day Sun, so it won`t be a perfect setup for unusually cold
conditions. Favored the low side of guidance, led by the global CMC
bias corrected which is normally a superior performer on radiational
cooling nights. Traditional interior cold spots should fall into the
upper 20s/around 30F.

Mon into Tue...Medium range guidance has moved into much better
agreement for this time period. In recent days, most of the guidance
with each run was suggesting a shortwave over the Plains would
either be strong enough or track far enough n to bring pcpn into the
fcst area at some point Mon into Tue. With the 00z guidance today,
models have moved toward better agreement on dry weather prevailing,
which had been viewed as the more likely scenario over the last
couple of days. Daytime RH should mostly fall into the 20-30pct
range Mon and Tue with Mon the drier day of the two. Fortunately for
fire wx concerns, winds will be on the lighter side both days.

As was the case 24hrs ago, models continue to show a northern stream
shortwave dropping into/reinforcing eastern Canada trof midweek.
Cold front associated with wave will pass across the fcst area Tue
night or Wed morning. Other than a wind shift, front will pass
uneventfully given lack of moisture and forcing. With sfc high pres
building across northern Ontario, Wed will be cooler near Lake
Superior under gradient n to ne wind enhanced by lake breeze
component. Depending how aggressively the high builds southward,
high temps Wed could be only in the 40s lakeside while in the
interior toward the MI/WI state line temps rise well into the 70s.
High pres will linger into Thu, providing continued dry weather.
Daytime minimum RH will still be low Wed/Thu, mostly 25-35pct.

Fri into the Memorial Day Holiday weekend...Despite being so far out
in the model runs, there has been a fairly consistent signal in
recent days for a potentially wet period late in the upcoming week.
The pcpn would be the result of the remnants of an early week closed
mid-level low over the sw states. This energy is fcst to lift ne
into the northern Rockies, then progress ese ahead of the next
northern stream shortwave dropping se and reinforcing the eastern
Canada trof. So, at the moment, while it would be unfortunate for
outdoor activities during the early part of the holiday weekend,
there appears to be a fairly decent potential of much needed
rainfall in the Fri/Sat time period.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 130 PM EDT SAT MAY 19 2018

A sharp cold front moving through Upper Mi today will bring a
period of MVFR conditions to the TAF sites today. Expect isolated
to scattered rain showers along and behind the front. Greatest
chance for rain this afternoon will be at CMX as the front crosses
the area. North winds will also gust up to 20-25 kts behind the
front this aftn. Conditions should improve to VFR and winds should
begin to die down over the western TAF sites by early evening as
high pressure and drier air pushes in from the west. MVFR
conditions will continue into early evening at KSAW as will the
gusty north winds. By late tonight, expect decreasing clouds and
diminishing winds at KSAW. VFR conditions with lighter winds are
expected on Sun. &&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 514 AM EDT SAT MAY 19 2018

Southeast winds to 25 knots over mainly east Lk Superior will give
way to strong northeast to north winds through the aftn as strong
cold front crosses Lk Superior west to east. Could see gale gusts
over north central sections late morning into the aftn. As high
pressure quickly builds in late tonight expect winds to diminish blo
20 kts across all of Lk Superior by daybreak Sun. These light winds
of mostly 15 kts or less will continue through much of next week as
high pressure parks itself over the Upper Great Lakes.

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


LONG TERM...Rolfson
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