Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 300820
Area Forecast Discussion
National Weather Service Marquette MI
320 AM EST Wed Nov 30 2016
Issued at 956 PM EST TUE NOV 29 2016
Forecast for rest of tonight and again later Wed aftn into Wed
evening still on track. Did make a few changes to Wed morning
forecast across central Upper Michigan. Any light rain/snow this
evening should continue to fade away/end as weak shortwave lifts to
north of Lk Superior. Attn for Wed morning is on shortwave currently
producing light rain over southern MN. One of many shortwaves
wrapping around large trough aloft centered over MN.
As that southern MN wave lifts to the northeast late tonight,
associated sfc trough heads across WI and becomes more closed off as
a sfc low while lifting northward across Lk Michigan on Wed morning.
Forcing features both aloft and at the sfc and perhaps also on
western fringe of forcing that is producing the light rain showers
lifting across lower MI this evening should all combine to generate
batch of light rain showers developing over central cwa on Wed
morning, possibly mixed with snow over higher terrain of west and
north central cwa based on wetbulb zero heights 500-1000 ft agl. 18z
NAM first showed this idea and was joined recently by the HRRR and
RAP and now the 00z NAM. Any snow should be minimal with warm ground
temps and light precip intensity. Since interior east will have shot
at getting cold tonight with no clouds overhead attm, if the precip
that moves in toward 12z/7 am ET starts out as rain, it is feasible
that there could be a non-zero risk of light icing first couple
hours. Current road temps there per MDOT are in the lower 30s. This
would be the one area that the light precip coming in around daybreak
could have an impact. Will pass this concern along to mid shift.
As Wed wears on, best chances of rain/snow should set up over
western cwa with cold air advection occurring on the west side of
sfc low that will be lifting to somewhere vcnty of Munising by early
Wed aftn. Blended the changes made for the morning into the forecast
for the aftn which still looked fine attm.
.SHORT TERM...(This evening through Wednesday)
Issued at 404 PM EST TUE NOV 29 2016
WV imagery and RAP analysis indicated a closed mid/upper level low
over cntrl MN. At the surface, an elongated trough or occluded front
extended from cntrl MN through nrn Lake Superior. An area of mixed
rain and snow over cntrl Upper Michigan supported by 850-700mb fgen
was gradually diminishing as the stronger forcing lifts to the
Tonight, Models suggest that 850-500 drying will spread across the
area. With levels also drying out, expect the remaining light pcpn
to end early this evening leaving mostly cloudy skies. continued
weak CAA will drop min readings into the upper 20s inland west to
the mid and upper 30s east.
Wednesday, As the mid level low wobbles into WI the low level trough
is expected to develop over srn or southeastern Lake Superior. 850
mb temps around -2C will provide enough instability (lake temps
around 7C) with the deeper moisture and 700 mb temps to around -11c
for an increase in lake enhanced pcpn into the west half during the
afternoon as winds become nrly. However, there is uncertainty with
how the mesoscale features will evolve and affect pcpn intensity.
Wet-bulb zero heights support mainly snow over the inland west but
a mix of rain and snow closer to the lakes.
.LONG TERM...(Thursday through Tuesday)
Issued at 320 AM EST WED NOV 30 2016
Thursday and Friday: Models indicate the closed low will linger
northeast of the Upper Great Lakes Thu into Thu night over Ontario
and Quebec before weakening and opening up as shortwave trough which
lifts east through Friday toward New England. Behind the closed
low/trough colder air will filter into the region, at the surface
and aloft, allowing the rain to transition to snow through the
period. Currently it looks like the north to northwest wind favored
snowbelts would be most likely to see the best chances for
precipitation. It does look like temperatures overall will trend
colder but not dramatically so for lake effect as 850 mb
temperatures are progged to cool only to the -5C to -8C range for
Thursday into Friday. Snow will be the primary precip type through
this time period during the overnight hours, but a mix of rain is
possible along the shoreline and east during the daytime hours.
Saturday: Light lake effect precipitation should be dwindling or
ending over the east half by early afternoon as the high pressure
ridge axis moves across Upper Michigan and winds back more west to
southwest. Models suggest a weak shortwave moving across the area
which along with diurnal instability could produce some isold -shsn
in the afternoon.
Sunday: Models have backed off from developing strong system over
Lower Mi. They now advertise that the next shortwave trough from the
Northern Plains will move into the area late Sun into Sun night
bringing the next chance of snow. Given limited moisture with this
system expect snow amounts generally less than an inch.
Monday into Tuesday: Models trending toward more amplified pattern
for next week as a 120+ kt 300-250 mb jet max and assoc shortwave
energy digging in from the eastern Pacific will carve out a broad
mid-upper level trough over the Western CONUS by early next week.
Downstream ridging into the Great Lakes region in response to the
developing western CONUS trough will keep Upper Mi mostly dry Mon
into Mon night with a slight warming trend. A few of the models
indicate shortwave energy lifting out the base of the western CONUS
trough and propelling a sfc trough toward the area which could
result in some pcpn moving back into the area by late Tue.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1158 PM EST TUE NOV 29 2016
Low level moisture wrapping into Upper Michigan from the sw ahead of
low pressure over MN will maintain mainly MVFR cigs through the
overnight hours at IWD and CMX. At SAW expect marginal MVFR cigs to
possibly scatter out late tonight leading to possible light fog
development toward sunrise on Wed. On Wed, conditions will begin
deteriorate at IWD and CMX as rain and snow increases in the aftn
and evening as the low crosses Upper Michigan and drags a sfc trough
over Lk Superior and northern Upper Michigan. Could see vsby down to
IFR at times, especially on Wed evening as ptype becomes mainly snow
and coverage and intensity ramps up. At SAW on Wed, scattered
showers are expected much of the day and into Wed evening. Vsby
should be mainly MVFR. The prevailing MVFR cigs could dip to IFR at
times in the aftn as winds begin to turn off Lk Superior.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 404 PM EST TUE NOV 29 2016
The low pressure system will linger over the western Great Lakes
into Wednesday. However the pressure gradient is not expected to be
as tight and should allow winds to diminish below 25kt by tonight.
Northerly winds to near 30 knots may develop Thursday as the slow
moving trough moves to the east of Lake Superior into Quebec. High
pressure will then build into the area into Saturday with winds
below 20 knots.