Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 240830
Area Forecast Discussion
National Weather Service Marquette MI
430 AM EDT Fri Mar 24 2017
.SHORT TERM...(This evening through Friday)
Issued at 402 PM EDT THU MAR 23 2017
This afternoon temperatures have been slow to warm, especially
across the interior central portions of the U.P. given the ample
cloud cover, as mid and upper level clouds continued to stream
northeast ahead of a developing lee cyclone across the High Plains
this afternoon. Current radar imagery shows returns beginning to
show up across much of Minnesota; however, given how dry the air
mass currently is only a few select sites are reporting
precipitation this afternoon.
The main forecast concern tonight through Friday is the potential
for freezing rain, and possibly some sleet, across much of Upper
Michigan tonight into the morning hours on Friday. This will likely
result in a slick commute during the morning hours. Models are in
good agreement with a convective band, currently developing in
central Minnesota, lifting northeast across much of Upper Michigan
tonight as warm air advection/isentropic lift increase and work
strengthen a mid-level baroclinic zone. A few of the models are
suggesting upwards of around or even great than 0.50`` of QPF with
this heavier band. However, given how dry the low-levels are,
currently thinking the models are likely overdoing amounts.
Therefore, have opted to run with a lower QPF, but given the thermal
profiles and expected wet-bulbing tonight this still resulted in
around quarter of an inch of ice accumulations across the central
portions of Upper Michigan. The highest ice accumulations are
expected to occur across the interior and central portions of the
area, especially across the higher terrain. These locations will see
more cooling this evening and once precipitation starts to fall, the
wet-bulbing process will allow for freezing rain to develop as warm
air advection aloft continues to stream northward. One concern is
that there may be periods when rain mixes in with the freezing rain,
and/or begin to transition over to rain towards the morning hours.
Therefore, there uncertainty still exists in the overall ice
accumulations. Further to the west, ice accumulations are still
possible; however, the thermal profiles point more towards a mix of
rain and freezing rain so ice accumulations are expected to be a bit
less. Across eastern portions of the area, a mixture of sleet and
freezing rain are expected to begin late tonight. Closer to the
lake, ice accumulations are expected to remain a bit less,
especially across western Gogebic county and north of Lake Michigan
as southerly winds should keep temperatures just above freezing.
Late Friday morning through the rest of the afternoon, warm air
advection will weaken as a weak back door cold front pushes south
across the area. This will allow the focus for additional
precipitation to be across south central and eastern potions of
Upper Michigan. The freezing rain will begin to transition over to
rain, with a few locations possibly seeing some snow mixed in the
afternoon near Lake Superior. Elsewhere, skies will remain cloudy.
.LONG TERM...(Saturday through Thursday)
Issued at 428 AM EDT FRI MAR 24 2017
Split flow will dominate the CONUS/southern Canada thru the upcoming
week with pcpn largely tied to southern stream energy that drops
into the sw CONUS and then tracks ene across the CONUS. One system
emerging over the western Plains today will weaken as it is kicked
ne to the Great Lakes early next week by the next shortwave trof
reaching the western CONUS. This will lead to rain and some fzra at
times Sat night thru Mon as the lead and trailing shortwave trof
affect the area. After a drier period midweek, a pair of southern
stream shortwaves may bring more pcpn late next week/weekend.
Overall, it appears pcpn amounts will generally be on the lighter
side. As for temps, split flow across N America will keep arctic air
bottled up way to the n, resulting in overall above normal temps
across the Upper Lakes for the next 1-2 weeks.
Beginning Sat, strong sfc high pres building across northern Ontario
today/tonight will become centered near James Bay by Sat evening.
Dry air emanating from this high will suppress pcpn associated with
warm front extending into the Lower Lakes from southern stream mid-
level low that will reach MO. However, there is a push of moisture
and weak isentropic ascent from the s during the aftn which may aid
a northward advancement of -ra into southern Upper MI during the
aftn. Prior to that, despite the strong sfc high pres passing by to
the n, which would normally suggest significant low-level drying,
fcst soundings show considerable low-level moisture blo about 4kft,
especially over roughly the w half of Upper MI, farther from the
departing sfc high. Not out of the question that there could be some
-dz/-fzdz during the morning where low-level easterly flow upslopes.
Sat ngt thru Mon ngt, mid-level low over MO Sat evening is fcst to
open up/weaken as it lifts across Lower MI to southern Ontario and
the Lower Lakes. This occurs in response to upstream shortwave trof
moving across the Plains Sun and reaching the Mississippi Valley
late Mon. As a result, deep moisture will expand across the area
with all model guidance indicating periodic pcpn. The main fcst
challenge is that the low-level flow will remain easterly thru Sun
before backing northerly into Mon. This will act to maintain some
colder near sfc air blo an elevated warm layer with h85 temps above
0C, allowing the potential of more -fzra, mainly at night.
Fortunately, forcing is weak, so pcpn amounts should be light
overall, and there should not be any significant icing.
With shortwave trof over the Mississippi Valley late Mon shifting e
of the area by Tue morning, expect dry weather to return for Tue/Wed
as Hudson Bay sfc high pres builds into the Upper Great Lakes.
Wed night/Thu, there is uncertainty on the the strength/track of a
northern stream shortwave running roughly along the U.S./Canadian
border. 00Z ECMWF has significantly backed off on the strength of
this wave, and now does not generate any pcpn. 00Z CMC still
maintains a stronger wave with pcpn while the 00Z GFS is similar to
the ECMWF. With some weighting from previous model runs, fcst will
reflect a chc of pcpn Wed night into Thu.
Late week, at least one batch of southern stream energy may make a
run toward the Great Lakes, but there is little model agreement or
consistency at this point.
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 102 AM EDT FRI MAR 24 2017
Expect conditions to deteriorate overnight as periods of rain at IWD
and freezing rain (SAW) or sleet/snow (CMX) results in low level
moistening and lower cigs. Expect mainly MVFR cigs should drop to
IFR and LIFR cigs by late tonight. Slight warming into Friday
morning should bring a transition to mainly rain at SAW/CMX. Drier
air moving in with nrly winds Friday will lift to cigs MVFR at
CMX/IWD by afternoon while upslope flow into SAW maintains IFR cigs.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 327 PM EDT THU MAR 23 2017
The strongest southerly winds will be confined to the eastern half
of the lake with speeds of 20 to 30 knots. These winds will diminish
to around 5 to 10 knots and veer to the west overnight into Friday
morning. West winds will veer north-northeasterly and increase to 20
to 25 knots through the afternoon hours on Friday. Then expect ne
veering e winds to increase up to 25 to perhaps 30 kts on Fri night
into Sun under the tightening pres gradient between hi pres passing
from Ontario into Quebec and lo pres in the lower Great Lakes. The
strongest winds are most likely over western Lake Superior, where
the lake topography will enhance the ene flow. As these features
weaken and exit to the e, winds will diminish on Sun and Mon. Winds
on Tue should remain relatively light as hi pres builds into Ontario.
Winter Weather Advisory until 11 AM EDT /10 AM CDT/ this morning