Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 181912
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
312 PM EDT Tue Apr 18 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 305 PM EDT TUE APR 18 2017

Low pressure continues to track towards western portions of the area
this afternoon as a robust shortwave, evident on the water vapor
imagery, continues to lift northeast. With warm, moist air advecting
in ahead of this system, fairly widespread rain developed across
Minnesota and Wisconsin and streamed northeast into western portions
of the area throughout the late morning and early afternoon hours.

Through the rest of the afternoon and into the overnight hours,
expect the ongoing rain to lift northeast across the west and
central portions of Upper Michigan as warm, moist accent continues
ahead of the upper level vort-max. Across the west, rain is expected
to remain light, but training precipitation will allow precipitation
amounts to possibly exceed a quarter of an inch through the rest of
the afternoon and overnight hours. Further east across central and
eastern portions of the area, rainfall amounts are expected to be
much lower as the main forcing lift northeast across central Lake
Superior. During the overnight hours, as the trailing cold front
pushes east across the area, expect the widespread rain to come to
an end from west to east. However, with increasing cold air
advection behind the system, forecast soundings are consistent with
stratus settling into the area. Therefore, we could see some spotty
drizzle develop and linger into early Wednesday morning across the
west and central, especially across the higher terrain.

On Wednesday things will dry out, but models are fairly persistent
in maintaining stratus through a good portion of the day. Could see
a few pockets of clearing, especially across the south where
downsloping winds will be persistent, but upper-level clouds will
begin to stream northward ahead of another approaching system.

.LONG TERM...(Wednesday through Monday)
Issued at 417 AM EDT TUE APR 18 2017

Focus is on a system that has potential to bring moderate to heavy
snow to portions of the area Wed night through Thu.

Current guidance shifted north substantially from 24 hours ago but
has been more steady for the last 2-3 runs. As it looks now, a
shortwave will drop into the area and deepen over the CWA, causing a
SFC low to move S of the CWA. This will lead to widespread precip,
with the greatest amounts falling as rain out ahead of the SFC low
and also in an area of deformation to the left of the SFC-850mb low
track (this precip is more likely to be snow, so that`s what was
looked at the closest). Strong dynamic cooling and wet-bulb cooling
will quickly turn precip to all snow over mainly the north-central
and west late Wed night into Thu. Upslope flow will add to forcing
and snowfall amounts over the north-central. Several inches of wet,
heavy snow is possible over the north-central since that`s where the
deformation zone is shown to set up and coincides with the upslope.
Impacts would be on the higher end since the wet, heavy snow would
fall moderately to heavily at times during the commute times
(possibly both morning and evening), so advisories and/or warnings
may be needed.

Some thoughts on confidence with the system: There a lot of
variables at play, especially since ptype is borderline between
rain and snow. The track of the system could change
- changing coverage and amounts of snow and even ptype, the strength
could change - leading to lower or higher amounts and differences in
ptype. Plenty of uncertainty still exists given the volatility of
the situation. Stay tuned.

Changes from the blended initialization for this system:

1. Decreased MaxT values using a GFS/NAM blend to lower values into
the mid 30s Thu.
2. Increased QPF some to show a little more upslope enhancement
north-central.
3. Snow ratios were way too low due to previous forecast and
incorrect zero values from the ECMWF and CMC. Increased those using
a NAM/GFS blend.
4. Increase ProbIcePresent using a GFS/NAM blend, only increasing
above SuperBlend. The values were too low due to previous forecast
inclusion (previous forecast was farther south with less ice
probability).
&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 149 PM EDT TUE APR 18 2017

Low pressure lifting northeast across western portions of Upper
Michigan this afternoon and evening will spread rain across all
terminals, with KIWD/KCMX being impacted already this afternoon and
KSAW later this afternoon and evening. The increasing pressure
gradient across the area will work in concert with falling
precipitation to mix down gusty winds through the rest of the
afternoon. Visibilities will also be impacted from the rain as they
may drop down into the MVFR category within the heavier pockets of
rain. The rain will come to an end at KIWD/KCMX later this evening,
and may linger into the overnight hours at KSAW. Behind this system,
expect low stratus to fill in with ceilings possibly dropping down
into the LIFR category at times. Depending on how deep the stratus
can grow, we could see some lingering drizzle in locations that see
remnant deeper moisture. As a 45 to 55 knot low-level jet tracks
northeast across central and eastern portions of the area tonight,
have included mentions of low-level wind shear at KSAW as the
surface winds are expected to relax a bit. With gusty northwest
winds expected to also filter southward across the area tonight into
Wednesday morning, the boundary layer looks like it will be a bit
too mixy for the development of any visbility restrictions at this
time.
&&

.MARINE..

Southeast gales to 35 knots over the e half of Lake Superior this
afternoon under the tight pres gradient ahead of a lo pres tracking
thru MN toward the Upper Lakes will diminish this evening following
the passage of the lo pres. In its wake, expect winds to shift to
the nnw up to 25-30 knots tonight before further diminishing and
veering to the ne on Wed as trailing high pres crosses Ontario/Lake
Superior. Depending on the track of another lo pres approaching the
Lower Great Lakes on Thu, ene winds up to 25-30 kts are likely then.
If the lo pres is deep enough, there could be some gales. As hi pres
builds back into the Upper Lakes late in the week following this lo
pres, winds will diminish under 25 kts on Fri and Sat. N winds could
increase up to 25 kts Sat night and Sun following a cold frontal
passage.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning until 11 PM EDT this evening for LSZ266-267.

  Gale Warning until 8 PM EDT this evening for LSZ244-245-264-265.

Lake Michigan...
None.
&&

$$

SHORT TERM...Ritzman
LONG TERM...Titus
AVIATION...Ritzman
MARINE...KC



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