Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Marquette Michigan
308 PM EST Wednesday Mar 4 2015
Short term...(this evening through thursday)
issued at 307 PM EST Wednesday Mar 4 2015
WV imagery shows a shortwave moving east across Upper Michigan on
the east side of the trough axis stretching from James Bay to the
eastern Dakotas. Beneath this shortwave...rap analyzed 850mb temperatures
are in the -23 to -26c range over the County Warning Area and has led to lake effect
snow in the areas down winds of the gaps in or slushy areas of ice.
Based off today/S visible and modis satellite imagery...those areas
are over much of lsz162 and then area northeast of Isle Royale and
to the southeast of the Keweenaw peninsula. Areas with enough fetch
over those partially open areas have been producing lake effect
snow...mainly in the west-northwest wind snow belts. Elsewhere...the
influence of diurnal heating and the shortwave has led to partly to
mostly cloudy skies across much of the rest of the region. This
diurnal heating has helped maintain some of the lake effect snow
showers into the north central County Warning Area. In addition to the snow...have
seen gusty west-northwest winds...especially over the exposed
locations of the Keweenaw peninsula. The highest gust reported thus
far at kcmx has been 41mph and when the snow has moved through it
has dropped visibilities to 1/4 mile. But looking at webcams across
the rest of the Keweenaw peninsula...those poor conditions appear to
be very localized right within the stronger bands seen sliding north
on visible satellite. North of that area over Keweenaw
County...webcams have been showing mainly partly cloudy skies and an
occasional snow shower. As for temperatures...a very cold afternoon
is in place over the western County Warning Area...with 2pm temperatures around
between 2 and 5 degrees. Temperatures gradually trend warmer heading
to the southeast...with the warmest temperatures around 15 degrees
along the Lake Michigan shoreline.
The focus on the forecast will be the gradually diminishing lake
effect and cold lows tonight. First for the lake effect...with the
shortwave shifting east of the area this evening...expect the larger
scale support to diminish this evening. Then with the surface ridge
moving east into the area overnight tonight and through
tthursdaymorning (increasing subsidence and lowering inversion
heights)...expect the conditions to become less favorable for lake
effect through the night. Models have started to get a better ice
analysis and that has finally led to them starting to show some lake
effect for areas down wind of the open areas. While that is some
help...opted to focus ice observations on satellite and then follow
the mean 925-850mb flow from the models to come up with the lake
effect probability of precipitation and snowfall amounts for tonight. Will have the highest
probability of precipitation (likelies) around the Ontonagon/Alger County areas this evening
with the west-northwest winds still in place. But there are hints of
winds backing towards a northwest wind direction late this evening
and early during the overnight hours just ahead of the surface
ridge. This would shift the bands into those more northwest wind favored
areas for a brief time before backing through the rest of the night
and into tthursdaymorning. As the winds back...inversion heights
fall below 5kft and with some moderation of the temperatures aloft and
drier air will diminish the lake effect through the night and into
tthursdaymorning. Expect the lake effect to mainly affect the
northern portions of the Keweenaw peninsula heading into
tthursdayafternoon. But think the dry air from the high will likely
limit much the potential for lake effect and only mention slight
chance probability of precipitation downwind of the open areas in lsz162. Did have some
concerns on the reduced visibilties at kcmx this afternoon with the
gusty winds...but looking at webcams across the rest of the Keweenaw
peninsula...it looks like the worst conditions of 1/4-1/2mi are
confined mainly to the open areas around the Airport.
Otherwise...with the winds dying down this evening and the small
snowflakes limiting accumulations...shouldn/T see much impact with
the lake effect.
Should see a cold night across the area tonight...as the high
pressure ridge slides across the area. With winds lightening up
after sunset and clear skies away from the lake effect
areas...should see lows falling into the teens below and even 20s
below zero at the traditional cold spots. With the decoupling
ooccurringduring the evening and limited pressure gradient...expect
winds to fall to 5mph or less for most locations. Even with the
light winds...wind chills will probably near Wind Chill Advisory
criteria over some of the inland areas. But with both winds and wind
chill values looking to be very marginal...will not issue a Wind
Chill Advisory. Debated an Special Weather Statement...but not sure if the winds would
even warrant it and opted to stick with the mention in the severe weather potential statement.
Highs should start to trend warmer tomorrow under increasing
southwesterly winds...but still remain well below normal for this
time of year.
Long term...(thursday night through wednesday)
issued at 254 PM EST Wednesday Mar 4 2015
NAM shows a 500 mb ridge on the West Coast with a trough over the
desert SW and a broad trough over the east half of the U.S. 00z Friday.
There is also a shortwave over the northern and Central Plains 00z
Friday. This shortwave heads east Thursday night into the upper Great Lakes.
Will go dry for Thursday night and then have flurries for Friday for the County Warning Area
with the next shortwave having limited moisture for Friday. Will go
with a chance for snow for late Friday night into Sat morning with
another front passing across the area. Did not make too many changes
to the going forecast for temperatures or weather. Have temperatures
rising on Thursday night with a non diurnal curve with southwest winds.
In the extended...GFS and European model (ecmwf) show a 500 mb ridge on the West
Coast 12z sun with a deep and broad trough across the rest of the
U.S. With the core of the cold air to the north of the upper Great
Lakes. An Alberta clipper is poised to move through on Sunday. This
clipper is to the east of the area 12z Monday on the manual forecasts with
the upper flow becoming more zonal. Another Alberta clipper system
moves through on Tuesday with the upper flow becoming zonal again for
Wednesday. With more zonal upper flow...temperatures will start warming up
with temperatures going above normal this forecast period. The
clipper systems have limited moisture and very little cold air to
work with and temperatures are warm enough for a rain/snow mix with
the best chances for seeing any precipitation across the northern County Warning Area. Will
have low chance to slight chance probability of precipitation across the north.
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1247 PM EST Wednesday Mar 4 2015
An upper level disturbance combining with cold temperatures aloft
has led to lake effect snow off the limited gaps in the ice over
western and Central Lake Superior. With the cold air expected to
remain through through tonight...the lake effect potential will
continue for those locations favored by west-northwest winds.
At the present time...the heaviest bands are to the north of
kiwd...but expect the diurnal/shortwave driven clouds to produce
MVFR ceilings at kiwd around taf time. Then as winds shift to a
more favorable direction later this afternoon and evening...have
brought visibilities down. With the small snowflakes...there is the
potential for IFR visibilities...but confidence in the strongest
bands sinking far enough southwest into kiwd was low and left
ceilings at MVFR for now.
The strong winds and blowing snow at kcmx will combine with the
occasional snow showers to produce IFR visibilities for a good
portion of the afternoon. With winds shifting more to the northwest
this evening...the fetch off the open water will be limited and
have brought up visibilities with the weakening winds. The lake
effect potential will linger through the night but should diminish
Finally at ksaw...the combined diurnal and lake effect clouds and
snow showers will continue this afternoon and then have conditions
improving as the snow GOES down. Could see a brief period late this
evening and during the early overnight hours where a snow shower
sneaks into the site (as winds turn more northwesterly)...but opted
to keep conditions VFR.
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 307 PM EST Wednesday Mar 4 2015
The west-northwest gales to 35kts continue over portions of
Eastern Lake Superior this afternoon and expect them to diminish
below gales late this afternoon or early this evening as a high
pressure ridge starts to move into the area. Feel the going ending
times for the Gale Warning are in good shape and will let them
expire as expected. Winds will back to the southwest and increase on
Thursday and Thursday night ahead of a trough that will move through
the upper Great Lakes region on Friday afternoon (winds are
expected to stay below 30kts). Friday night through the
weekend...the upper Great Lakes region will see a series of quick
moving troughs/ridges...that will shift the winds around frequently.
Overall...it appears winds will stay below 30kts behind the troughs.
With the increase in winds over the last day...the ice over Lake
Superior has been shifting around and become broken up over lsz162.
While the cold temperatures has led to some growth today...expect
the quickly shifting winds and warming temperatures through the
weekend to lead to that zone to be more water than ice and opted to
start adding waves back in for that zone.
Gale Warning until 7 PM EST this evening for lsz266-267.
Gale Warning until 4 PM EST this afternoon for lsz265.