Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 271958

Area Forecast Discussion
National Weather Service Marquette MI
358 PM EDT Thu Apr 27 2017

.SHORT TERM...(This evening through Friday)
Issued at 357 PM EDT THU APR 27 2017

12Z raobs/latest wv imagery and RAP analysis show closed lo centered
over nw MN, with shrtwv embedded in sly flow alf to the e of this
feature moving n into scentral Upr MI. The steadiest pcpn has fallen
over the w half of the cwa on the cyc side of the shrtwv passage.
Since the dynamic cooling associated with the enhanced uvv under the
sharper dpva on this side of the shrtwv track has eroded the
elevated warm lyr, the pcpn has changed to mainly just sn over the w
half, with just some sct rain showers over the warmer e half under
dry slotting within the jet surge region.

Late Today/Tngt...Arrival of dnva/deep lyr qvector dvgc/subsidence
in the wake of shrtwv passing to the n of Upr MI by 00Z Fri wl
result in diminishing pcpn s-n late this aftn/evng. Although quite a
bit of mid lvl dry air is progged to surge into the area thru the
ngt, lingering cyc wly flow and h85 temps falling as lo as -10C over
the w, cold enuf for les, wl maintain hier likely pops over the nw
cwa. As for going headlines, wl maintain the headline thru 00Z for
the Keweenaw Counties as well as Baraga and Iron Counties, 21Z for
Gogebic/Ontonagon, but canx the headline for Marquette County.

Fri...Although Upr MI wl remain under a cyc flow alf on the sw flank
of exiting shrtwv/sfc lo pres toward James Bay, dry air in the mid
lvls and a tendency for the near sfc flow to become more acyc as a
weak rdg of hi pres builds into the area during the aftn as well as
some llvl drying/daytime heating and mixing wl grdly end pcpn chcs.
But a good deal of clds wl linger, especially over the hier terrain
of the nw half. The day wl be a cool one over the nw cwa with max
temps having a hard time rising much above 40. With downsloping flow
into the scentral, expect warmer temps into the 50s.

.LONG TERM...(Friday night through Thursday)
Issued at 357 PM EDT THU APR 27 2017

Main weather concern in the extended will be below normal
temperatures along with a stronger system possible with a wintry mix
Sunday through Tuesday.

Friday night through Saturday: A surface ridge and drier air is
expected to build into the area during this time period allowing
skies to become partly cloudy with only minor chances for rain and
snow showers, again, the main focus would be early in the day Friday
over the Keweenaw Peninsula. Temperatures are expected to be
slightly below normal through this time period.

Saturday night through Tuesday: Low pressure is expected to develop
over the Southern Plains late Saturday night and slide through the
Upper Great Lakes Sunday through Tuesday. Models are coming into
better agreement on the details of the system as it slides through
the area; however, some timing and placement differences continue
with the solutions. The GFS/Canadian have similar tracks and timing;
however, the GFS is deeper with the surface low and upper level low.
Each of the models each have the low moving out of the area Tuesday
afternoon. The latest run of the EC is keeping the surface low and
850mb low farther west, taking the low over the western U.P. If the
GFS/Canadian are correct there could be substantial accumulating
snowfall across portions of the west half of the U.P.; however, if
the EC solution is correct, then most areas may end up seeing mainly
rain with maybe even some dry slotting expected over the east half.
850mb temperatures are progged to be as high as 8 to 9C with the EC,
while the GFS/Canadian have 850mb tempeatures over the west half as
low as -4 to -5C. Until better sampling occurs with this system it
is likely that there will continue to be variances in the models,
with improvement expected by Friday as the wave of energy is better
sampled. Consensus is still the way to go at this point in the
extended due to the reduced confidence in the system track. This
will give a continued mix of rain and snow central, rain changing to
snow west and mainly rain east.

Tuesday night through the extended: High pressure and drier air will
slide into the area Tuesday night through Wednesday, which will
allow skies to become clear to partly cloudy and temperatures to
slowly moderate to near or slightly above normal. A weak system may
slide through the area Thursday; however, moisture looks to be
fairly limited only bringing isolated rain showers to the area.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 156 PM EDT THU APR 27 2017

Surface low pressure that has brought the wintry weather to the
Upper Peninsula has slowly lifted north across the area and is
starting to move north towards Lake Superior. The pressure gradient
should weaken marginally as the low lifts overhead, causing variable
wind direction and speeds before increasing and becoming westerly to
slightly southwesterly around 00z. Prior to this time IFR conds will
likely persist with CIGs hovering around 800-1000ft agl. It is
possible that CIGs could briefly dip to around 500ft agl at KCMX and
KIWD; however, this should only be briefly between 18-21z. Snow
coverage has been mainly focused at KCMX and KIWD where VSBYs
continue to range from 1/4sm to 3/4sm. Based on radar returns and
satellite trends expect VSBYs to slowly improve with the axis of
heavier/steady snow shifting northwest of the TAF sites. Forecast
guidance does indicate that later this evening the moisture axis
will pivot southeast/east across the TAF sites and bring another
round of light snow to the TAF sites. Expect the bulk of this to be
northwest of KSAW, so have held onto a dry TAF there. CIGs will
begin to slowly approach MVFR conds around 2-4z, but could see a
brief lull in improvement at KCMX where steadier snow could linger
longer. Otherwise snow/precip should end after midnight for KCMX and
eventually see dry air starting to filter in by midday/early
afternoon Fri.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 357 PM EDT THU APR 27 2017

Expect nw winds slowly backing to the wsw to run as hi as 30 kts
into Fri under the tight pres gradient on the southern flank of deep
lo pres moving from northern Lake Superior toward James Bay. The
strongest winds later tonight thru Fri will persist in the area
between Isle Royale and the Keweenaw, where the land topography
enhances the wsw flow. Winds will then diminish to 25 kts or less
Saturday into Sunday as high pressure slides across Lake Superior. A
fairly strong low pressure system will slide from the Central Plains
into the Upper Great Lakes region from Sunday night through Tuesday
morning allowing northeast winds of 30 kts to gust as high as 40
knot gales over mainly the western half of Lake Superior. High
pressure will build in once again for Wednesday into Thursday
allowing winds decrease to less than 25 knots.

Upper Michigan...
  Winter Weather Advisory until 8 PM EDT /7 PM CDT/ this evening
     for MIZ001-003-004-010-084.

  Winter Weather Advisory until 5 PM EDT /4 PM CDT/ this afternoon
     for MIZ002-009.

Lake Superior...
Lake Michigan...


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