Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200541

Area Forecast Discussion
National Weather Service Marquette MI
141 AM EDT Thu Oct 20 2016

.SHORT TERM...(This evening through Thursday)
Issued at 409 PM EDT WED OCT 19 2016

Pattern Synopsis/Forecast: Low amplitude pattern in place across
North America this afternoon.  Broad short wave troughing over the
central plains with flat ridging over the southeastern states/mid
Atlantic region...and another short wave ridge along the west coast
downstream of a rather substantial cyclone centered over the Gulf of
Alaska.  Surface analysis shows a cold front cutting across central
Upper Michigan and stretching back to the west into southern
Minnesota and South Dakota.

Pattern becomes more amplified over the next 24 hours as upstream
short wave ridge builds eastward...and a sharper short wave trough
advances into the Midwest/upper Great Lakes.  This will induced a
frontal wave along a cold front that currently lies along the Ohio
River...this cyclogenesis acting in concert with high pressure
building east into the Midwest downstream of the upper ridge axis
will continue to funnel northerly winds and colder air into the
upper Great Lakes through Thursday.

Primary Forecast Concerns:  The arrival of sub-zero temperatures at
850mb certainly brings the potential for lake convection into play
(with mean Lake Superior water temperature around 12C).  Narrow
surface ridge builds across the U.P. tonight...likely a consequence
of the land-lake temperature differential.  Current satellite trends
shows low clouds spilling out of Minnesota and across western Lake
Superior and northwest Upper Michigan...south edge of cloud deck has
mixed out allowing for more sun across southwest/south central
Upper.  Expect clouds to continue to spread east during the late
afternoon/evening along at least the Lake Superior shoreline
counties...then as winds veer more toward a more northerly component
tonight expect clouds to get pushed back farther inland.  Expect
cloud cover to be fairly prevalent through the day Thursday.

As for precipitation chances...given the arrival of cold air and
veering flow allowing for a longer northwesterly fetch over the
lake...can envision some shallow bands of showers developing later
tonight and especially Thursday with a bit of a diurnal component
and inversion heights getting pulled up a bit with more cyclonic
curvature aloft and a dynamic PV anomaly swinging into the upper
Lakes.  So will bump PoPs from the consensus forecast which looked a
bit dry (and increased temporal resolution to six hours during the
day Thursday so as not to get too cute).

.LONG TERM...(Thursday night through Wednesday)
Issued at 409 PM EDT WED OCT 19 2016

Pattern Forecast: Short wave trough axis will lie across the Great
Lakes/Ohio Valley Friday...with broad upper ridging across the
western half of the U.S.  Surface high pressure downstream of this
upper ridge will build slowly east toward the region for the end of
the secondary cyclogenesis off the east coast slows the
pattern down for the weekend.  This keeps thermal troughing hanging
across Michigan into Saturday before rising heights/warm advection
nudge into the state to end the weekend. Pattern evolution into
early next week will depend on effects of east coast/Atlantic
Canada cyclone and how effectively it can slow things up.

Primary Forecast Concerns: Lake induced precipitation probably still
an issue Thursday night into Friday as low level temperatures
continue to cool.  Lighter wind fields also suggest some thermally
induced troughing that may focus convergence into central Upper
(though a bit early to pin down such mesoscale details).  Again have
blended in some of the SREF PoPs into the consensus forecast to get
this idea into the forecast (though PoPs admittedly could be
higher).  Another possibility is potential for snowflakes overnight
Thursday into Friday morning across the higher interior terrain
where temperatures likely to drop near freezing and shrink the
surface based warm layer.

Rising heights/high pressure builds in for the start of the
weekend...and thus synoptically at least things should dry out.
Beyond that don`t see anything that high impact heading into next
week...evolution of downstream cyclone over Atlantic Canada will
bottle things up a bit.  Maybe a passing disturbance in the Monday
time frame but that again depends on whether the downstream system
throws some cyclonic flow back in our direction.  Next significant
precip threat may arrive by the middle of next week.  No big
extremes in temperatures expected into early next week.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 139 AM EDT THU OCT 20 2016

Anticipate mainly MVFR ceilings to persist through the forecast
period at IWD/CMX with VFR cigs at SAW tonight before veering low
level winds more to the northwest that should bring MVFR ceilings in
toward Thursday morning. Included a TEMPO group for lake effect showers
overnight at KCMX. &&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 409 PM EDT WED OCT 19 2016

Rising surface pressures and an associated weakening gradient
expected to keep marine concerns to a minimum beyond this
evening...where some gustiness will persist in a low level cold
advection pattern behind a departing cold front.  Some marginal
small craft conditions east of MQT this evening along the south
shore of Lake Superior.  Winds mostly below 20 knots expected by
Thursday...and 15 knots or less by Friday.  Surface ridging will
dominate this weekend...with relatively light winds expected
especially by October standards.  Depending on how pattern
evolves...will likely see an increase in winds in the Monday time

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


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