Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Marquette Michigan
741 am EDT Sat Apr 19 2014

Short term...(today and tonight)
issued at 509 am EDT Sat Apr 19 2014

WV loop shows a vigorous shortwave crossing southern Saskatchewan
this morning. Surface low is tied to the wave in similar location with
trough extending into the Dakotas. Meanwhile...confluent flow aloft
is sustaining large high pressure ridge from James Bay across the
upper Great Lakes. Gradient of moisture is evident with 00z radiosonde observations
showing precipitable waters varying from around 0.20 inches at kinl to near 0.70
inches at kbis. Warm air advection noticable with +10c 850 mb temperature at
kbis and -4c at kinl and kgrb. Already seeing cluster of showers
developing in this warm air advection regime within last few hours
over mainly northern half of Minnesota. Some lighter radar echoes are
pushing across western Upper Michigan...but due to the dry air below 800 mb
in vicinity of surface is not likely reaching the ground as any
precipitation. Precipitation over Minnesota is mainly along and ahead of best 700 mb moisture
transport and within swath of h925-700 mb warm air advection. Expect
precipitation to eventually work its way to surface over western Upper Michigan
this morning given strength of the middle level moisture/temperature

As it has looked for a while...ptype could be brief issue as the
precipitation first begins. Soundings indicate snow and freezing rain could
both be possible mainly over Keweenaw this morning. Snow amounts
will be minimal and any ice amounts should be less than 0.05 inch.
By late morning...low-level surface warm air advection will allow
precipitation to take form of rain. Quandary for today is just how much
precipitation will occur over northwest County Warning Area. No doubt the temperature advection is
strong and isentropic ascent is focused...but prefer to lean away from
the rather wet GFS output...tracking a bullseye of well over 0.5
inch of quantitative precipitation forecast from Western Lake Superior to the keweeanw peninsula. Sref
probs over northwest County Warning Area show less than 10 percent probability of seeing
such amounts. Given the dry low-levels which are not completely
eroded...prefer the drier look of the NAM/regional Gem and European model (ecmwf).
Batch of showers will gradually sink east-southeast into central County Warning Area by late this
afternoon. Despite the clouds/rain in some areas...mixing to 925-900mb
still indicates temperatures later today could reach upper 40s or even lower
50s. Coolest temperatures where southeast low-level winds ahead of the low remain generally Keweenaw and near the Lake Michigan shore.

Expect rain to become quite widespread tonight over especially the
central and east County Warning Area. Primary shortwave as impressive as it looks
now...deflects more north across Manitoba and northern Ontario
instead of tracking east across upper Great Lakes. Surface low will follow
suit...leaving weakening surface trough to push over the upper Great
Lakes tonight...slowing down as it does so since upper flow becomes
parallel to the surface front. Appears warm and moist advection along
with divergence aloft of increasing jet streak across Lake Superior
and northern Ontario will be primary driving forces behind precipitation
chances through late tonight. 850 mb trough is forecast to shift west
to east across Upper Michigan tonight outpacing the surface front...and
this along with increasing 850 mb-700 mb moisture transport into the
trough with precipitable waters surging up near 200 percent of normal will focus
widespread rain across much of the County Warning Area. NAM/Gem-regional
and European model (ecmwf) which were preferred during the daytime today...appear too
light with quantitative precipitation forecast. On flip side...00z GFS still appears too wet showing
6 hour quantitative precipitation forecast amounts over 0.90 inches...but think an area of rain with
amounts 0.25-0.50 inch in 6 hours is likely given the extent of moisture
aimed right into central Upper Michigan on nose of 45-50 knots SW 850 mb jet.
Ramped up probability of precipitation to categorical later this evening through the
overnight hours. By late tonight...after 06z central and 09z east...850 mb
trough slides mainly to the south and east of County Warning Area...ending potential
for higher probability of precipitation.

Once the rain diminishes over the west tonight...expect surface dewpoints
to push up around 40 degrees which flowing over a wet and melting
snowpack should result in good deal of fog especially as soundings
show middle-level drying occurring atop saturated sub 850 mb layer. Fog
could form later in the east as well as the rain ends...but for now
just kept it in for areas where dewpoints get at least into the middle 30s
and the larger scale setup is favorable for fog. A mild night with
the higher dewpoints as most areas stay in the upper 30s or lower 40s.
Interior West County warning area may see temperatures as low as middle 30s which would
probably result in dense fog.

Last but certainly not least...given the warmer temperatures...rain...and
melting snow...expect river levels to begin rising tonight and we
could begin to see ice jam issues develop again. More details on
this are in the hydrology section below.

Long term...(sunday through friday)
issued at 428 am EDT Sat Apr 19 2014

Main forecast concern in the longer term is focused on the potential
interaction between a stalled fnt/ribbon of higher moisture just S of Upper Michigan
and a shortwave that is forecast to move east across southern Canada on Monday and if/
how much rain will fall over Upper Michigan and impact area streams/Hydro.
Confidence in this forecast is lowered by poor model agreement on the
interaction between these features. shortwave/surface low over northwest Ontario on Sun morning move east closer to
James Bay by late in the day...a shortwave ridge and middle level drying are
forecast to advance into the upper lakes behind departing/weakening
attendant cool fnt and warm conveyor belt moisture ribbon. Although some
model differences remain on how aggressive this middle level drying will
be...the previously slower Canadian model shows enough drying to end the
precipitation over all but the far southeast County Warning Area by 00z. Opted to retain flavor of
going forecast that shows lingering probability of precipitation over the southeast half diminishing
through the day...and ending over all but the far southeast by 00z Monday.
Otherwise...with diurnal heating...expect low clouds/fog over the melting snow
pack to dspt by the afternoon. 850 mb temperatures in the 6-8c range will support above
normal temperatures...but light winds associated with weak hi pressure under the
shortwave rdging should allow for lake breezes that will bring local
cooling near the shores.

Sun ngt/Mon...Sun night will start dry except perhaps over the far
scentral closer to lingering stationary fnt/moisture axis. But as next shortwave
moving east-southeastward across scentral can in the northwest flow east of building ridge over western
Canada aprchs and generates some height falls over the upper lakes...some
of the models...especially the 00z ecwmf/ deep moisture to
the S expanding back to the north late Sun night and impacting mainly the
scentral and east. The NCEP models are much drier and indicate mainly
scattered rain showers associated with the passage of the incoming shortwave.
The 00z Canadian model shows the precipitation expanding back farther to the north
but not until Monday. While the building ridge over the southeast Continental U.S. Supports the
farther north scenario favored by the non NCEP models...the rather large
separation between the disturbances in question and absence of a sgnft
backing of the upper level winds to a more SW direction indicate the
drier NCEP guidance is on the right track. The models typically have
a difficult time handling interaction/phasing between disparate confidence is low in this portion of the forecast.
Fortunately...even the wetter scenario favored by the non NCEP
models points to heavier rain over the scentral and eastern County Warning Area...where
less snow remains. Otherwise...maintained mention of patchy fog late Sun
night into Monday morning with light winds/potential for drier middle levels over
melting snow.

Monday night...incrsg north-northwest flow with h925 winds incrsg up to 25-30 kts
associated with digging shortwave through the Great Lakes is forecast to drop
850 mb temperatures as low as -6 to -7c by 12z Tuesday. While the incoming airmass
is not cold enough for lake effect snow...some of the models show enough
low level moisture to justify chance probability of precipitation. With the arrival of the colder air...
expect the rain showers to mix with or change to snow...especially over the
higher terrain of the west.

Tuesday into Wednesday...Canadian surface hi pressure ridge under upper ridge trailing departing
shortwave will bring a period of cooler and drier weather to the County Warning Area.

Extended...not surprisingly...there remains sgnft disagreement among
the longer range models on the handling of next low pressure that is
likely to impact the upper lakes later on Wednesday into Friday. The 00z European model (ecmwf)
indicates a colder scenario with the surface low pressure tracking to the S
of Upper Michigan and building hi pressure just north of Lake Winnipeg. This forecast would
result in some mixed precipitation at the onset and later in the week. The
00z GFS and Canadian models on the other hand show a deeper low farther
to the north along with a stronger southerly flow of warmer air. Will rely on
model consensus for now.

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 741 am EDT Sat Apr 19 2014

Although moisture aloft continues to increase today...lingering dry
low-levels should allow conditions to remain VFR even if some rain
occurs. Best chance of more steadier showers is this afternoon at kcmx so
have went with an MVFR visibility. Sprinkles may affect kiwd mainly in
the morning. Ksaw should stay dry today. Better chance of rain showers will
occur late afternoon into the early evening at kiwd/kcmx and later in
the evening through the early overnight hours at ksaw. Depending
on how much rain occurs today and how quickly middle-level moisture can
depart later tonight...some fog is possible late tonight at all the
terminals. With uncertainty...did not include anything lower than
MVFR visibility at this time.

Marine...(for the 4 am Lake Superior forecast issuance)
issued at 509 am EDT Sat Apr 19 2014

East to southeast winds likely 25-30 kts today into tonight as low
pressure lifts from Manitoba across northern Ontario. Expect winds
to stay below 25 kts through the rest of the forecast period.

issued at 507 am EDT Sat Apr 19 2014

As mentioned in previous forecast discussions...the recent heavy
snowfall across western Upper Michigan has replenished some of the water
content that was lost during the warmer conditions over the past two
weeks. The western high terrain now has 6 to 8 inches of water
equivalent...with localized 10 inch amounts. Since temperatures are
expected to be at or slightly above average across Upper Michigan this
weekend into Monday /the upper 50s and low 60s away from local lake
cooling on sun and Monday/ with dewpoints rising as hi as the low 40s...a
good deal of melting should occur. Except for tonight...low temperatures will
fall to at least near freezing...limiting concerns of rapid melting.
Cooler air will return Monday night into Thursday...somewhat moderating the
melt down. Highs are still expected to range from the 40s to the low

As for additional 0.25 to 0.75 inch of liquid in
the form of mostly rain is expected this afternoon into early Sun
afternoon. Fortunately...the heavier rain is forecast over the east
where there is generally less snow on the ground. But with the
additional liquid added to the snowpack from the recent snow
storm...warm temperatures/greater snow melt...and light to moderate
rainfall...a prolonged period of higher river flows are expected.

Though widespread flooding is not a concern at this time...remaining
ice on the rivers could lead to potential ice jams once the warmer
air arrives through Monday. Those living around rivers...creeks...and
streams should monitor both river levels and ice conditions. Ice
jams can form and break quickly...resulting in rapidly fluctuating
river levels.

MQT watches/warnings/advisories...
Upper Michigan...
Lake Superior...
Lake Michigan...


Short term...jla
long term...kc