Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Marquette Michigan
1258 am EST Monday Nov 30 2015
Short term...(this evening through monday)
issued at 114 PM EST sun Nov 29 2015
High pressure centered near James Bay is stretching a ridge
southwest through the upper Great Lakes region and leading to light
winds across the area. That usually makes for a nice late fall day
across the area...but a pocket of moisture and cold air trapped
below the subsidence inversion around 875mb has led to an area of
clouds that were originally focused over Eastern Lake Superior
around midnight that have drifted south-southwest across the
Keweenaw and the rest of the eastern two thirds of Upper Michigan
under the light northerly flow this morning. With the cloud layer
flow weakening and turning southeast through the afternoon...would
expect the south-southwest advance to slow and then push back to the
north as the winds turn southerly through the evening (ahead of a
weak trough moving east just north of Lake Superior tonight).
Thus...expect the western half of the County Warning Area to clear out through the
night...while the eastern half to third sees the clouds remain as
the southerly flow aids lake enhanced clouds off Lake Michigan.
There does look to be a favorable but short period of southeasterly
flow off Lake Michigan to support clouds lingering in the central
before the flow shifts southwesterly through the night and should
advect the clouds out of that area. Where skies remain clear or
clear out...should see lows falling into the teens...while the
clouds will keep temperatures in the 20s over the eastern third.
Monday/S forecast for the east depends on the advection of the low
clouds...while the west will see a sunny start before high-middle
clouds increase through the day ahead the approaching system for
Monday night into Wednesday morning. Will have slight chance probability of precipitation
nearing the Wisconsin border towards evening ahead of the
strengthening low in Iowa at that time. As for the clouds over the
east...with the flow off Lake Michigan continuing but the
temperatures moderating...would expect at least scattered low clouds
to continue through much of the day...mainly for areas east of Big
Bay Delaware noc before the high-middle clouds move in towards the afternoon.
Highs tomorrow will be above normal and in the middle to upper 30s.
Long term...(monday night through sunday)
issued at 317 PM EST sun Nov 29 2015
No major changes planned to the forecast for much of the long term
period. The deterministic models as well as the sref and gefs
ensemble membership show remarkably low spread with the low track
for Monday night into Tuesday across the upper Great Lakes. The
majority of the members suggest a low track over the western u.P. Or
Western Lake Superior Tuesday. With the system being cut off from
the mean flow...the model evolution of slower movement seems
reasonable. As such...am not expecting the best isentropic lift and
associated precipitation to move into the Upper Peninsula until
around 12z across the south and in the morning hours across the
remainder of the u.P.
With the system going west...expect the main area of precipitaiton
to be fairly short lived...at least across the eastern half of the
forecast area where the dry slot will rapidly move into the forecast
area in the afternoon. This dry slot will likely cut off
precipitaiton to light drizzle during the afternoon.
The main problem with this system will be the precipitation type.
Not a great deal of cold air with the system in the first
place...and there will be little or no cold advection into the
system. As such...will have to rely on the cold air Reservoir
already with the system. With the track further west...expect the
snow to be mainly confined to the far western u... precipitation
type across the central u.P. More diurnally dependent. The eastern
half of the u.P. Will see mainly rain with maximum temperatures aloft
well above 0c. As for snow accumulations...expect storm total quantitative precipitation forecast to
be 0.20 to 0.5 inch...mainly late Monday night into Tuesday. As
such...areas that stay mainly snow throughout the event across the
interior west half...could see 2 to 5 inches of snow centering on
the morning commute times on Tuesday. Certainly could see some
slippery travel due to the wet/heavy snow Tuesday morning. Across the
east...little if any snow will fall until perhaps Tuesday night when the
low levels become cold enough for all snow.
As the surface low departs Tuesday night...the upper low will remain over
the western Great Lakes with plenty of moisture throughout the
region. Probably not cold enough for lake effect snow with 850mb
temperatures only around -6c...but there will likely be some scattered snow
showers across the area through Wednesday morning before height
start to rise by Wednesday evening.
The remainder of the week through Saturday looks fairly quiet and
mild as upper heights remain well above normal for this time of
year. Ridging centered over the Great Lakes for Saturday should
allow temperatures to rise into the 40s. If the warm European model (ecmwf) verifies...temperatures
in the upper 40s could not be ruled out as 850mb temperatures rise to +6c
in SW flow. Slightly cooler on Sunday with a weak cold frontal
passage...but still above normal for this time of year. Other than
perhaps a rain or snow showers Thursday night into Friday morning with a
weak disturbance moving north of the area...no significant precipitation is
expected after Wednesday.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1258 am EST Monday Nov 30 2015
Although low clouds have cleared at saw...not out of the question more
of these clouds still over scentral Upper Michigan could impact that site
early this morning. But downslope SW flow suggests these clouds should
not move over saw...so went with VFR forecast. Although some middle clouds will
oversrpead iwd early this morning...expect VFR weather to linger there and
at cmx as well. The middle clouds will overspread the entire u.P. On Monday.
As a low pressure moves closer on Monday evening...lowering clouds into the MVFR
range will impact iwd and saw but not cmx until after 01/06z. Some -sn
will arrive at iwd in the evening but likely not sgnftly reduce visibility
until after 06z with a downslope wind component.
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 114 PM EST sun Nov 29 2015
High pressure over Lake Superior will lead to winds below 20kts
through Monday evening. East-southeasterly winds will increase
Monday night into Tuesday as a low moves into southern Minnesota.
At this time...expect winds to top out around 30kts. The low will
lift northeast across the lake on Tuesday evening...with winds
turning to the north-northwest behind the low for Wednesday
(20-30kts). For the rest of the week...expect quick
arriving/departing ridges and troughs...with a brief period of
winds up to 30kts on Thursday ahead of the trough.