Area Forecast Discussion
Issued by NWS Marquette, MI

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592
FXUS63 KMQT 250715
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
315 AM EDT Tue Apr 25 2017

.SHORT TERM...(Today and tonight)
Issued at 314 AM EDT TUE APR 25 2017

Upper air pattern consists of a 500 mb trough over the Rockies and a
shortwave over the northern plains this morning. This shortwave
moves to the east into the upper Great Lakes this afternoon. The
trough over the Rockies moves into the northern plains late tonight.
Nam shows deeper moisture and 850-500 mb q-vector convergence
arriving this evening and remaining overnight. GFS and ECMWF show
this too. However, NAM looks to be too cold with sfc temperatures
tonight and did not use them for this forecast. Went with the warmer
temperatures of the GFS and ECMWF which keep the pcpn as all rain.
One other major change to the going forecast was to keep the dry air
in longer today and pushed the timing of pops back a bit with slight
chance only in the far west late today and then categorical pops
overspreading the area tonight. These were the only major changes
done to the going forecast.

.LONG TERM...(Tuesday night through Monday)
Issued at 337 PM EDT MON APR 24 2017

Still expecting an active weather week with multiple chances for
precipitation across the area.

As longwave troughing digs across the plains, numerous weak
shortwaves embedded within the southwest flow aloft will traverse the
area. This will also allow warm and moist air to stream northeast
ahead of the slow moving surface trough expected to extend northeast
into western portions of Upper Michigan by Tuesday night. The
combination of increasing upper-level support and warm air advection
should allow for fairly widespread rain showers to spread across the
much of Upper Michigan Tuesday night through the day on Wednesday.
With the first round of moisture transport lifting northeast across
the area, expect the focus for moderate to heavy rain to remain
across the west and central, where surface convergence will be
maximized. During the day on Wednesday, expect rain showers to
linger across the area as moisture transport continues to linger.
There are some differences among the model QPF, likely due to how
they each are handling the timing and strength of the mid-level
baroclinic zone. Therefore, there is some uncertainty as to what
locations will see the highest rainfall totals during the day on
Wednesday, but some locations may see over an 1 inch of rain.

Impact wise, Wednesday is a challenge. We could be looking at a day
where we have showers and thunderstorms across the central and east,
and wintry precipitation across the west. It will all be dependent
on how the surface trough traverses Upper Michigan, and on how much
unstable air can lift northward and how much shallow cold air can
undercut the warm, moist air ahead of and behind the surface trough,
respectively. Based on the current model guidance and trends, looks
like the potential for any freezing rain across the west will be
Wednesday night into Thursday morning. As colder air arrives into
Thursday morning, cloud ice will dissipate and leave behind freezing
drizzle before possibly transitioning over to snow in the west. Ice
accumulations from the forecast builder are showing upwards of a
quarter of an inch in some locations across the far west in the
higher terrain. Thinking this is overdone a bit considering the
increasing ground temperatures over the past few weeks. While ice
accumulations will be possible, elevated surfaces should have much
better chances at seeing any accumulations.

The big question on Thursday will be if any locations see any system
snow. There is still quite a bit of uncertainty in regards to the
track of low pressure with the Canadian now tracking the low north
across western and central Upper Michigan, leaving any chances for
system snow across the far southwest. The GFS is the most
progressive and lifts the low across eastern Upper Michigan and up
into Southern Ontario. Precipitation wise, the models remain
different, with the GFS being the less robust QPF wise as the system
is less wrapped up compared to the other deterministic models.
Therefore, confidence still does not remain high in regards to where
precipitation will track on Thursday. However, given the fact that
upper-level energy is progged to become negatively tilted, as a
stout shortwave lifts across the region, leaning towards the
ECMWF/Canadian solutions at this time. That being said, we`re still
looking at the potential for freezing rain to transition over to
snow across the far west and additional rainfall across the central
and east on Thursday.

Depending on when the system lifts out of the area, precipitation
will come to an end sometime Thursday night through early Friday
from south to north. We will see a break Friday and Saturday from
precipitation chances as high pressure clips the region. However,
towards the end of the weekend and into the beginning of next week
precipitation chances will return across Upper Michigan as yet
another system ejects out of the Plains and up across the Great
Lakes.
&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1248 AM EDT TUE APR 25 2017

Under considerable mid and high clouds, a dry low-level air mass
will dominate the area thru this aftn, allowing VFR conditions to
prevail at KIWD/KCMX/KSAW. LLWS will continue at all terminals
overnight. KMQT VAD wind profile has been showing 35-40kt at 500ft
AGL over the last several hrs. A sfc trof drifting se into Upper MI
late this aftn/evening will result in deteriorating conditions as
shallow cold air undercuts warmer air and -ra begins to develop.
Conditions will deteriorate the most at KIWD/KCMX as the trof will
pass both terminals. KIWD will probably drop to IFR this evening
with KCMX falling to low MVFR. Still ahead of the trof, KSAW may
fall to MVFR near the end of this fcst period.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 314 AM EDT TUE APR 25 2017

Northeast gales look to start up across west and central lake
Superior late today and continue through Wed evening. By late
Wednesday night into Thursday morning winds will begin to subside to
20 to 30 knots as winds become northerly. Late Thursday through
Friday, winds will further decrease to 10 to 20 knots as winds
become westerly. Winds of 10 to 20 knots are expected through the
weekend and into early next week.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Watch from Wednesday morning through Wednesday evening for
     LSZ243-244.

  Gale Watch from this evening through Wednesday evening for
     LSZ162-263.

  Gale Watch from this evening through late Wednesday night for
     LSZ264.

Lake Michigan...
None.
&&

$$

SHORT TERM...07
LONG TERM...Ritzman
AVIATION...Rolfson
MARINE...07



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