Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200750
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
350 AM EDT Thu Apr 20 2017

.UPDATE...
Issued at 952 PM EDT WED APR 19 2017

No notable changes to the fcst have been made this evening. Water
vapor imagery and RAP analysis show a vigorous shortwave moving
across the Dakotas. Ahead of this feature, strong 850mb moisture
transport is currently aimed across IA into se MN/w central WI,
right where radar shows a solid area of pcpn. Northern extent, just
about to cross into western Upper MI, is shra with and some embedded
thunder farther s. Thunder is much more numerous from near Eau
Claire, WI ssw thru IA where mucape is 500+j/kg.

Latest RAP shows nose of strong moisture transport translating ene
across central WI to northern Lake MI thru Thu morning though there
is also a strengthening nw extension of this moisture transport with
time across Upper MI. This will support downstream spreading of the
solid shra area across Upper MI thru the night. The strengthening
northwestward extension of moisture transport will support more
persistent pcpn thru Thu as well, especially into nw Upper MI. Ptype
continues to be a huge challenge. With no cold/dry air initially in
place, ptype change will depend solely on whether height falls and
upward motion lead to sufficient column cooling for snow, a process
that is very difficult to assess. Fcst soundings from hourly runs of
the HRRR/RAP show variations in hourly ptypes from run-to-run, not
surprising given the temp profile hovering around critical threshold
for rain or snow across the w and n. At this point, given the lack
of antecedant cold/dry air, believe a change to all snow will be
difficult tonight. Fcst from the dayshift appears to adequately
handle this continued uncertainty given no strong model trends
toward a colder solution from the 18z runs or the avbl hourly model
runs since 18z. So, Keweenaw headline will remain intact, and there
will be no significant changes in fcst snow amounts where some snow
is included in fcst. It`s possible we could have a surprise with
several inches of hvy/wet snow over a wider area of the higher
terrain of the w and n central for the Thu morning commute, but that
appears to be a very, very low probability right now. This will be a
situation where obs/webcams will need to be watched closely, and if
obs suddenly show rain turning to snow late in the night, a major
fcst update will be required.

Given the strength of moisture transport with precipitable water
inflow approaching 250pct of normal, pcpn amounts were increased a
little for the overnight/Thu morning. Thunder mention was also
expanded slightly into s central Upper MI overnight. Continued
height falls and resulting cooling column on Thu as deepening
shortwave trof arrives will increase the potential of ptype to
become snow over the nw.
&&

.SHORT TERM...(This evening through Thursday)
Issued at 347 PM EDT WED APR 19 2017

The main forecast concern is the arrival of rain and snow later
tonight and on Thursday as an area of low pressure tracks just south
of Upper Michigan. There is still quite a bit of uncertainty in
overall precipitation amounts given the spread among the models.
However, the Keweenaw Peninsula and the higher terrain across the
north central and west looks to have the highest chance at seeing
accumulating wet, heavy snow. Along with snow, the system will bring
gusty east-northeast winds to the whole area.

The deterministic and ensembles are in fairly good agreement with
low pressure lifting northeast across southern and central
Wisconsin, and eventually across northern portions of Lake Michigan
tonight and through the day on Thursday. Precipitation wise, there
is still some discrepancies among the models with the NAM being the
most robust with the amount of QPF expected. Considering the
moisture transport is predominately anchored across south central
and up into eastern portions of the area later tonight, thinking
that is where the highest QPF amounts will come to fruition.
Precipitation still has to make it all the way across Wisconsin, so
do not expect precipitation to reach south and western portions of
the area until roughly after 8pm EDT. Across the south central and
east, as warm air advection increases, expect precipitation to
remain all liquid. Some locations may also hear a few rumbles of
thunder as MUCAPE values upwards of 200 J/Kg lift into the area
ahead of the surface low. Further to the north across north central
and the western portions of Upper Michigan, things get quite a bit
more complicated. At first, precipitation is expected to fall as
rain, but as lift increases across the area expect rain to begin to
mix with snow, and then eventually transition over to all snow by
the morning hours on Thursday. Thermal profiles do not look terribly
impressive as we never quite reach the dendritic growth zone and in
some locations teeter on the edge of rain versus snow. However,
given the ample lift, thinking that we will see a good chance at
seeing accumulating wet and heavy snow through Thursday across the
north central and west.

Across the north central portions of the area, the highest snowfall
accumulations are expected to remain across the high terrain, where
2-4 inches looks possible. However, do expect the snow to transition
back over to rain briefly during the mid/late morning hours. Models
are fairly consistent with a dry slot moving up and across the area,
so would not be surprised if we see a break in precipitation during
the afternoon, before wrap around precipitation moves back in from
the north. As this wrap around precipitation comes back in, expect
it to mostly be snow across the central portions of the area as
colder air begins to advection further south behind the system.
Further west expect precipitation to remain mostly snow with 1-5
inches of snow possible. The higher amounts are expected to occur
across the Keweenaw where upslope flow will augment lift and overall
snowfall amounts.

.LONG TERM...(Friday through Wednesday)
Issued at 350 AM EDT THU APR 20 2017

Models suggest that a progressive split flow pattern will prevail
into the middle of next week with temperatures generally remaining
below average.

Friday through Saturday, High pressure building into the northern
Great Lakes in the wake of Thu`s departing low will bring a drying
trend to the cwa Fri, with gradual clearing as the low level flow
becomes more anticyclonic. Expect some lingering -shsn/shra and
fzdz/dz from Marquette eastward in the morning where cyclonic nnw
flow will persist a bit longer. Lingering clouds and northerly winds
off of Lake Superior will limit max temps to the lower to mid 40s
near the lake and upper 40s to lower 50s well inland. The
combination of light winds and clearing with PWAT values falling
under 0.25 inch will allow temps to fall into low to mid 20s inland
west near the lower end of guidance. A good deal of sunshine and 850
mb temps rebounding to around 4C on Saturday will allow max temps to
rebound as high as the low 60s over the western interior.

Sunday, A nrn stream shortwave trough is expected to move through nw
Ontario and drag a cold front across the nrn Great Lakes from
Saturday night into Sun morning. With only moderate fgen forcing and
limited available moisture, only chance pops for rain showers mixed
with snow were mentioned for mainly the north before the dynamics
weaken. Even if there is a return of at least some sunshine with
trailing high pres on Sun, a north wind off Lk Superior and h85
temps falling as low as -5 to -6C will result in below average temps
ranging from the upper 30s/low 40s north to upper 40s to near 50f
south central.

Mon-Wed, a developing WAA pattern ahead of the next significant
shortwave moving out of the Central Plains may bring some light rain
to the west as early as Sun night. However, the models were in
reasonable agreement with the timing of higher pcpn chances from
Monday night into early Tuesday as the shortwave and associated sfc
low move through the region.  Although there is still some
uncertaintly with the track, a northerly trend with the path of the
system will favor mainly rain.  Cold advection in the wake of the
system will lead to diminishing pcpn changing over to a mix of snow
and rain for Tue night into Wed.
&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 127 AM EDT THU APR 20 2017

Approaching disturbance will spread pcpn and deteriorating
conditions into Upper MI overnight. Expect conditions at
KIWD/KCMX/KSAW to fall to IFR overnight and then to LIFR this
morning. The rain may mix with or change to snow at times with snow
probably more likely to become the predominant ptype at KCMX. May
not be until this evening that pcpn becomes all snow at KIWD/KSAW.
LLWS is possible at KIWD overnight. Meanwhile, easterly winds should
become gusty to 25-30kt at KCMX late overnight thru at least mid
aftn.
&&

.MARINE..

East-northeast gales of 35 to 40 knots are expected late tonight
through the day on Thursday. Winds will decrease to around 20 to 30
knots as they back to the north Thursday night through Friday. Friday
into Saturday, winds will further decrease to around 10 to 20 knots
and back to the southwest. Sunday through Monday, winds will be
generally 15 to 25 mph with varying directions as high pressure
exits the region and a cold front pushes south across the area.
Tuesday winds will increase to 25 to 30 knots as another system
lifts out of the Plains and up across the northern Great Lakes.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 11 PM EDT this evening for MIZ001-
     003.

Lake Superior...
  Gale Warning from 8 AM this morning to 6 PM EDT this evening for
     LSZ249>251-266-267.

  Gale Warning until 5 PM EDT /4 PM CDT/ this afternoon for LSZ162-
     263.

  Gale Warning from 8 AM this morning to 5 PM EDT this afternoon
     for LSZ244>248-264-265.

Lake Michigan...
  Gale Warning until 2 PM EDT this afternoon for LMZ248-250.

  Gale Warning until 1 PM EDT this afternoon for LMZ221.

&&

$$

UPDATE...Rolfson
SHORT TERM...Ritzman
LONG TERM...Voss
AVIATION...Rolfson
MARINE...Ritzman


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