Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 230928

Area Forecast Discussion
National Weather Service Marquette MI
528 AM EDT Sun Oct 23 2016

.SHORT TERM...(Today and tonight)
Issued at 527 AM EDT SUN OCT 23 2016

Today: A shortwave now moving into northern Mn will slide across the
Upper Great Lakes today. Deepening moisture and deep layer q-vector
convergence associated with this feature and its associated sfc low
moving just south through northern Wi will spread rain showers into
western Upper Mi early this morning and into central and eastern
Upper Mi later this morning into the afternoon. Since this will be a
relatively fast-moving system with limited moisture, expect pcpn to
be fairly light. Temperatures will be a bit cooler than yesterday
with highs topping out in the upper 40s to lower 50s...coolest
northwest half.

Tonight: Increasing cold advection in a north-northwest flow will
lower h85 temps around -5C across eastern Lake Superior resulting in
a lake sfc-h85 delta-t of 17-18c. NAM and RAP Model forecast
soundings show inversion heights around 800 mb or above 5 kft with
lake induced CAPEs at or above 300 j/kg. This instability will be
enough to support scattered lake effect rain showers downwind of
Lake Superior so will maintain high chance pops into Alger-Luce and
northern Schoolcraft counties. Some lake effect showers will also
reach into the eastern portion of Marquette County in the evening
before shifting east overnight as winds back from a 340 (north-
northwest direction) to 320 or due northwest direction. The rest of
the CWA should be dry tonight. Min temps will range from the lower
30s over the interior west to the upper 30s/lower 40s east and along
the Great Lakes shores. Will likely be a bit breezy especially along
the Lake Superior shore from Marquette east to Whitefish Point as
northwest wind gusts may approach 30 mph at times.

.LONG TERM...(Monday through Saturday)
Issued at 344 AM EDT SUN OCT 23 2016

Highly amplified pattern aloft to start the week with deep trough
over Quebec and New England while sharp ridge builds over most of
west half of the Conus. NW flow across Lk Superior Mon-Mon night
will be seasonably chilly with h85 temps around -6c. These temps
along with Lk Superior water temps 10-13c will lead to sufficient
over-water instability for lake effect showers /rain as ptype per
wbzero heights over 1000ft agl/ with delta t/s 16-19c. Soundings
show unfavorable setup for lake effect over western Lk
Superior/western cwa with inversions less than 2kft while longer
over water fetch and cooler air aloft with inversions up to 6kft
over eastern Lk Superior/eastern cwa results in better chance of
at least scattered lake effect showers.

Could see isolated lake effect showers trying to move into the
ncntrl late Mon night into Tue morning as high pressure builds
across northern Ontario and ridge slides over western cwa. Ptype a
bit more tricky than in the east as wbzero lowering to 500-1000 agl
and onshore/upslope northeast winds could result in some snow mixing
in with the rain. Dry air blo inversion should limit coverage of
lake effect into Tue morning.

Attn late Tue night into Wed will be on shortwave crossing the
central plains that undercuts the ridge in place and an associated
sfc low pressure and warm front. Sfc-h85 lows remain south of Upper
Michigan so that likely will limit widespread precip with this lead
shortwave/sfc low. NAM is strongest with the sfc low/dry air holding
the initial surge of precip well to the south over southern WI
through 12z Wed. Even if precip begins to affect cwa later on Wed, as
the previous shift alluded to the main period of concern is Wed night
into Thu as this initial system may merge with another system
approaching in nw flow aloft. Depending how quickly this phasing
occurs, sfc low may track farther north across Lk Michigan and
northern lower MI and there would be enough precip and cold air
around to result in a mix of rain/snow mainly over west and ncntrl
cwa on Wed Night and possibly over parts of the east cwa later Thu.
Only a few model runs from the GFS/ECMWF/GEM have been completely
phased aloft/far enough north with sfc low/cold enough in terms of
h85 temps and low enough in terms of 1000-850mb thickness to support
accumulating snow Wed Night into Thu. Forecast sfc temps in the mid
30s Wed night into Thu morning also suggest minimal snow accumulation
as long as the more intense forecasts with regard to stronger low-mid
level forcing do not materialize. Degree of phasing aloft with this
system will be bigger thing to watch in the coming days as that will
affect how far north the sfc low tracks and how much cold air can
occur with a deepening system. Will keep with mix of rain and snow,
similar to previous forecast.

After the initial shortwave/sfc low tracks east of the Upper Great
Lakes Thu night into Fri, will still have scattered lake effect
showers continuing. Decent agreement that h85 temps will be down to
at least -6c across Lk Superior which with sufficient h85 moisture
and indication of stronger low-level convergence with lake induced
troughing should be enough to support the scattered lake effect
rain/snow showers. If stronger shortwave drops through in this flow
pattern with this already favorable low-level environment, then
coverage and intensity of the lake effect would increase late Thu
night into Fri.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 140 AM EDT SUN OCT 23 2016

VFR conditions will prevail at all TAF sites overnight. Low pressure
will approach the area Sunday morning bringing the possibility of
rain showers at each of the TAF sites along with MVFR ceilings.
Conditions will improve to VFR by Sun evening at IWD as drier air
moves back in behind the low.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 527 AM EDT SUN OCT 23 2016

Winds will remain below gales through the period. A tightening
gradient between a deep low pressure system moving through Quebec
and a high pressure ridge building into the Plains could lead to a
period of NW winds gusting to 30 knots over eastern Lake Superior
tonight into Monday. High pressure will build across the area Monday
afternoon through Wednesday, keeping winds generally light across
Lake Superior. There will be a trough passage on Thu but winds
will remain fairly light.

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


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