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Area forecast discussion
National Weather Service Marquette Michigan
742 PM EDT Wed Sep 18 2019

Short term...(this evening through thursday)
issued at 415 PM EDT Wednesday Sep 18 2019

WV imagery and rap analysis indicated a mid/upper level trough
through the Pacific northwest and a ridge from the lower mississipi
valley into the central Great Lakes resulting in SW flow toward
Upper Michigan. A vigorous shortwave trough over southeast Manitoba
was lifting to the northeast dragging a cold front into northwest
Minnesota. The band of shra/tsra from earlier today had dissipated leaving
a band of mid/high clouds over western Upper Michigan. Additional
light showers were developing over northeast Minnesota in an area of
moderate 700-500 qvector conv and 850-700 fgen. Otherwise, breezy
southerly winds have pushed temps again to around 80 with dewpoints
into the lower 60s.

Tonight, although the strongest forcing with the shrtwv will remain
to the north strong 925-850 mb moisture transport/conv associated
with the strengthening 40-50 knot low level jet will support sct
shra/tsra development into Upper Michigan late this evening and
overnight. MUCAPE values to 1k j/kg will support at least isold ts
but with effective shear of 20-30 knots potential for any stronger
storms is limited with the higher potential to the south where
instability is higher. South winds will again be gusty, especially
over the north where gusts in the 20-30 mph are expected.

Thursday, expect the front to weak over Upper Michigan leaving the
potential for additional shra/tsra development. Expect the best pcpn
chances over the southeast half especially in the afternoon when
MLCAPE values climb into the 500-1000 j/kg range. Temps should
again climb into the mid to upper 70s. Southwest winds will again be
strong enough across Lake Michigan for a moderate to high swim risk
for the beaches in Schoolcraft County.

Long term...(thursday night through wednesday)
issued at 341 PM EDT Wednesday Sep 18 2019

For the remainder of this week, the warm pattern (above to much
above normal temps) and humid conditions for mid sept will continue
due to western North America mid-upper level trough and eastern North
America ridging. Late this week, the western trough will shift E and
NE, crossing the western Great Lakes sun. This will result in
cooling early next week, bringing temps back down to around normal.
As for pcpn, vigorous shortwave currently moving across the western
Dakotas will move across northern Ontario Thu. Associated cold front
will weaken/stall/dissipate as it moves over the area as amplifying
western trough works to maintain/strengthen ridging over the western
Great Lakes. Decaying front could perhaps support some shra/tsra
across the fcst area Thu night into Fri morning as models indicate a
weak shortwave moving across the area. Mid-level trough arriving sun
will likely provide a better potential of shra/tsra late Sat/Sat
night as the associated cold front moves across the area. Dry
weather should then prevail until the midweek period.

Beginning Thu night, weak shortwave moving across the area may
support some shra/tsra development Thu night. However, coverage
should be limited if development occurs. Will likely see another
round of low clouds/fog take over under remnant frontal
boundary/light convergent wind field that includes weak onshore flow
off the Great Lakes for portions of the fcst area. Also any added
moisture/rain from shra/tsra that may develop would enhance
potential for areas of dense fog.

Can't totally rule out isold convection on Fri, but with weak
shortwave exiting and 500mb heights rising a bit, pcpn chances
appear very limited. If low clouds/fog expand as expected Thu night,
light southeasterly low-level winds on Fri will help the low
clouds/fog potentially to persist into part of the afternoon,
especially closer to Lake Michigan. Will be another warm/humid day with
high temps in the 70s and dwpts mostly 60-65f. Fog/stratus may
expand again Fri night, especially east half under southerly upslope
winds off Lake Michigan.

Mid-level trough moving out across the plains on Sat with associated
cold front approaching the upper Mississippi Valley will result in
increasing southerly winds. With mixed layer winds to around 25kt,
should become a breezy day with winds gusting to 20-30mph, highest
west. Showers/T-storms should move into the W half of the fcst area
during Sat afternoon and then progress eastward during the evening.
With the cold front and moisture outrunning the better shortwave
dynamics, models not as bullish with qpf amounts. However, with
precipitable waters still running around 1.5 inches, there is a potential for
brief heavy rain with the T-storms.

With the cold front likely clearing the area Sun morning, mostly dry
weather will return sun, and conditions will become less humid under
breezy westerly winds. Under a favorable westerly wind direction,
fairly tight pres gradient and at least weak caa, winds could gust
35-40mph on the Keweenaw sun. A secondary shortwave will be dropping
thru the passing trough, but given limited instability, not much
more than sprinkles expected Sun afternoon into Sun night.

Dry weather will continue Mon and probably Tue under building high
pressure. Next shortwave arriving Wed and warm air advection/isentropic lift ahead
of it will bring the next chance of showers at some point Tue

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 733 PM EDT Wednesday Sep 18 2019

Southerly winds will remain gusty this afternoon into this evening
at all terminals. Showers and a few thunderstorms are possible
across all terminals tonight. However, confidence in timing and
coverage remains low so only have vcsh mentions for now to highlight
a general trend in timing. Although a low level jet will also be
develop that could support some llws, mixing should remain high
enough so that gusty winds will remain at the surface. Low level
moisture with lingering SW flow Thursday morning should support MVFR
cigs at ksaw.

Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 415 PM EDT Wednesday Sep 18 2019

Stability may remain high enough as the low level jet strengthens
tonight so that gusts remain below gales. However, there may be
brief periods of a few gale force gusts over the east half.
By Thursday, a weakening front sags south of the lake, and winds
diminish below 20 knots. This front remains fairly washed out and
high pressure generally takes hold through Friday night, keeping
winds below 20 knots. Saturday through Sunday, winds southerly winds
will veers westerly throughout the weekend as a cold front pushes
eastward. Ahead of and behind the front, winds of 20-30 knots are
expected. It is possible there could be a window of gales in there
as well.

Occasional fog will remain possible through the end of the week,
likely until we can get drier air to move in with a stronger cold
front arriving over the weekend. The most likely locations for fog
occurrence will be over the west half today, as well as locations
near the Minnesota arrowhead.

MQT watches/warnings/advisories...
Upper Michigan...
Lake Superior...
Lake Michigan...


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