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Area forecast discussion 
National Weather Service Marquette Michigan
146 PM EDT Thursday Apr 24 2014

Update...
issued at 1202 PM EDT Thursday Apr 24 2014

Low pressure trough is gaining strength over middle Continental U.S.. warm air
advection ahead of surface-850 mb trough and increasing moisture is
supporting swath of precipitation from Minnesota across Wisconsin.
Thus far appearance of radar echoes and surface observation pointing to mostly
snow on northern fringe of the precipitation over northern Wisconsin.
Upstream the heaviest precipitation is occurring over west-central Wisconsin
where couple observation showed 3hr precipitation amounts over 0.40 inches. With
the precipitation farther into eastern Wisconsin...3 hour amounts are more in
the 0.10-0.20 inch range. Seems that the heavier precipitation over west-central
Wisconsin lifts into northern WI and mainly western Upper Michigan
this afternoon. Amounts may be enhanced later today as moisture advection
at 850 mb combines with increasing larger scale lift from shortwave
trough/q-vector convergence at 850 mb-500 mb moving in from northern plains.
Also smallish but present h25 jet streak lifts south-southwest-north-northeast across that
area with increasing diffluence/divergence likely. Farther east into
central Upper Michigan and eventually eastern County Warning Area...precipitation is mostly
supported by moisture advection and isentropic ascent. Precipitation
amounts with this forcing will be more affected by very dry air seen
on 12z apx sounding feeding in from the east. Thus...expect amounts to
be held down compared to western County Warning Area.

Ptype is main issue and snow amounts. Top down look at soundings
show not much warm layer aloft...so snow will be falling into the
lower layers. Question then is how much warming occurs in the blyr.
Initally looked like based on ruc13/nam12 output...which initialized
surrounding soundings well...that the 950mb wet bulb temperatures would be
enough above zero to result in mostly rain. But...think the models
are underplaying the extent of dry air and ultimately the evaporative
cooling. This is showing up with more snow in northern WI and it is
lasting longer than 950mb wet bulb temperatures would suggest. Have worked
and reworked ptype grids for this afternoon and evening. For now...kept
higher probs for snow into the evening over the higher terrain of
west and north central...with better shot at only rain over lower
terrain elevations of west half of County Warning Area and across all eastern County Warning Area
since temperatures have warmed into the lower 40s there already this
morning. Road temperatures all over Upper Michigan are in the 40s...so do not
expect much snow accumulation on roads even if it does snow harder.
Most of the snow accumulations this afternoon...up to an inch...will be
on grassy surfaces. Snow accumulations this evening should increase
especially northwest County Warning Area. That still seems on track. Total snowfall
will be in the 3-6 inch range over the higher terrain of northwest
Upper Michigan...with amounts more in the 2-4 inch range from Iron
County into higher terrain of western Marquette County. Will be
keeping the advisory for the Keweenaw as that is where the highest
probability of seeing the most snow is still projected. Snow amounts
of 1 inch or less are expected over the eastern County Warning Area...mainly to the
east of Marquette and Iron Mountain.
&&

Short term...(today and tonight)
issued at 459 am EDT Thursday Apr 24 2014

Warmer and drier initially...with only 1 main band of relatively
light precipitation crossing Upper Michigan...stretching from The Arrowhead of Minnesota
through Gogebic Colorado and near mnm. There is a significant lack of
precipitation from there until S WI /farther away from the initial
shortwave/waa/...which GOES along with the relatively slow start of
significant precipitation across the County Warning Area. The 500mb ridge over the upper
Great Lakes will continue to shift NE of the area today as north and S
steam low near from the west /over north Minnesota and MO at 00z Friday/. The surface
reflections will not be far off...with the trough pushing across the
County Warning Area overnight as the north 500mb low pushes across the west half of the County Warning Area
by daybreak Friday.

Back to the near term...dew points in the low teens over NE WI and
central Upper Michigan has helped keep the early morning precipitation confined
mainly S of the County Warning Area. Evaporative cooling in the dry air has resulted
in a few pockets of snow S of the border. Will keep the mention of
mixed precipitation at the leading edge through 15z...until near surface temperatures
warm enough with the late April sun to result in mainly rain.
Guidance /and specifically the lav/ has imt surface temperatures hovering
between 40 and 44f from 13z- 23z...which will result in likely snow
with little chance of snow. Dry air will abound with dew points in
the middle 20s...which could still briefly result in quick bursts of
snow in stronger bands. However at this point any moderate to heavy
precipitation is confined to far West Lake Superior and S WI.

Another significant change was to confine event quantitative precipitation forecast over 0.8in to
the Keweenaw peninsula. Will continue to monitor the convection to
our S and what impact that has on this evolving system. The 06z NAM
has come in with less quantitative precipitation forecast...which was expected...but continues to
hit the central County Warning Area from Watersmeet to MQT and imt with over 0.5in
of liquid this afternoon /faster than the previous run/.
Overall...not too far off from current forecast...but expect some
adjustments as we move through the day. Also continued the idea of a
mainly dry airmass remaining over the east third of Upper Michigan...and with
good mixing dew points lingering in the 20s...with relative humidity bottoming out
near 30 percent...and even lower east of early.

Otherwise...still have 3-8in of snow forecast over the Keweenaw
peninsula from late today through Friday morning. Have transitioned
the Winter Storm Watch to a Winter Weather Advisory. Will not
continue the Special Weather Statement for other areas...although 12hr snow amounts across
grassy /and still snow covered/ surfaces may be able to pick up
2-4in. Most areas will experience a slushy could of inches.

May have a slower end of the higher probability of precipitation than currently have
indicated after 06z Friday...as models continue to come in a bit
drier on the back side of the surface-700mb low /which should be set up
across the west third of Lake Superior at 12z Friday/.

Long term...(friday through wednesday)
issued at 417 am EDT Thursday Apr 24 2014

Main forecast concerns in the long term are focused on probability of precipitation/ptype/
additional snow amounts on Friday/Friday night. Hudson Bay hi pressure should
bring a dry but cool period of weather this weekend into early next week.

Friday...warm conveyor belt ribbon of moisture with 700 mb specific humidity as
hi as 4g/kg and deep layer qvector cnvgc under diffluent upper flow
ahead of strong shortwave moving through Western Lake supply are forecast to still be
influencing the Keweenaw and much of the east half of the County Warning Area at
12z on Friday...with middle level dry slotting on the southern flank of the
shortwave impacting areas near the WI border. Exactly how far north or S
this shortwave tracks west-east through Upper Michigan will influence how long heavier
precipitation under the warm conveyor belt can linger at any given
point...with locations to the S of the 700 mb low track under more
aggressive middle level dry slotting seeing a quicker end to the heavier
precipitation. The 00z NAM/GFS/hier res Canadian model/local WRF arw/European model (ecmwf) have
all trended farther to the north with the shortwave/700 mb low track and show
aggressive middle level drying moving west-east through Upper Michigan and quickly
diminishing the precipitation by early afternoon except perhaps for some scattered rain/snow
showers over the north and especially the Keweenaw closer to the path of
these features. With more aggressive middle level drying and less
precipitation...bumped up forecast hi temperatures for all but the northern County Warning Area even though
lingering low level moisture will allow for a good deal of SC to linger under
strengthening middle level inversion. The warmest area will be over the
scentral...where downsloping west-northwest flow will allow for more breaks in
the clds/warming. Increased hi temperatures into the 50s in this area.

Friday night...steady height rises/dnva/deep layer qvector dvgc in the wake of
the departing shortwave to the east will be influencing Upper Michigan...but some
models including the 00z GFS show another shortwave sliding southeastward through
the upper lakes in the wake of the lead disturbance bringing more deeper
moisture/some heavier precipitation to the area. Given the strength of the lead
shortwave and fairly aggressive deep layer qvector dvgc in its wake...
prefer the 12z ecwmf/00z NAM that suppress this second disturbance
and maintain more middle level drying. However...lingering cyclonic low level NE
flow in the presence of lingering low level moisture may allow for some light
rain/snow showers to persist in the upslope areas near lake supply for a good
portion of the night.

Sat...surface hi pressure is forecast to build over Hudson Bay...with surface ridge
axis extending S into the upper lakes under steadily rising heights...in
line with going dry forecast. Although there may be some lingering low
clouds mainly near lake supply in low level north-northeast flow within shallow cool layer
under lowering/strengthening inversion...these clouds should burn off with
daytime heating. Despite the return of some afternoon sunshine...
locations near lake supply will be quite chilly with 850 mb temperatures rising no
higher than -3c and the low level north-northeast flow off the water still covered with
a good deal of ice. Held forecast hi temperatures in the well below normal
middle-upper 30s near lake supply.

Sat ngt/sun...longer range models are very consistent showing upper
ridge building over scentral Canada into the Great Lakes to the NE of potent
shortwave emerging out of the desert SW into the Central Plains. But a
good number of the extended models show deeper moisture returning to the
upper Great Lakes well to the NE of the closed low. Given the trend toward
building ridge and presence of Hudson Bay hi pressure with dry east-northeast low level flow/
Spring climatology for Hudson Bay hi pressure...suspect the 00z ecwmf is
on the right track with a dry forecast for Upper Michigan. Since other models
are more aggressive with returning moisture...tended toward the low end
of guidance/European model (ecmwf) forecast temperatures for Sat night...which could be quite
chilly with min temperatures falling toward the low 20s.

Extended...as the closed low/accompanying surface low/larger scale cyclonic
flow to the SW slowly move northeastward...maintained gradual increases in probability of precipitation
shown by model consensus in the Monday through Wednesday time. Tightening pressure
gradient between the slowly retreating Hudson Bay hi pressure and aprchg
deep low pressure will result in steady/gusty east winds. Forecast thermal fields
that support well below normal temperatures also indicate some of the precipitation
may be at least mixed with snow at times.
&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 144 PM EDT Thursday Apr 24 2014

Light rain and snow gradually spreads across the terminals this
afternoon. Precipitation will change to mainly snow by late today at
cmx...but could stay a mix of rain and snow much of the night at iwd
and saw. Expect IFR to MVFR conditions...first coming from the visibility
and eventually due to lowering ceilings. The most persistent lower
conditions are expected at cmx tonight with upsloping easterly
winds. Late tonight into Friday morning...the precipitation...mainly
in the form of snow...diminishes at the taf sites...but lower IFR
ceilings will remain. Expect slow improvement to MVFR conditions by
Friday afternoon.
&&

Marine...(for the 4 am Lake Superior forecast issuance)
issued at 350 am EDT Thursday Apr 24 2014

As the high pressure ridge over Lake Huron early this morning drifts
off the East Coast Friday morning...a low over the Central Plains
will shift to the lower Great Lakes. Southeast gusts will near 30-35kts
late this evening over mainly Central Lake Superior. The low will
continue NE into New England on Saturday. A large Canadian high
pressure ridge will then build across the upper Great Lakes Saturday
into Monday. Another round of stronger east winds nearing 25-30kts will
be possible Monday...in between the exiting ridge of high pressure
and nearing low pressure from the plains states.
&&

Hydrology...
issued at 417 am EDT Thursday Apr 24 2014

Runoff from recent above normal temperatures and snowmelt continues to flow
through the ground...so some area streams and rivers are still running
high and even rising slowly...despite the cooler temperatures that
were seen recently. Locations that still are still near or above
bankfull at this time include the Sturgeon river near Chassell and
the paint river near Crystal Falls. While the paint river near
Crystal Falls is not expected to reach flood stage in the short
term...the Sturgeon river near Chassell will be close and will
continue to be monitored.

Reports indicate little ice remains on area rivers...so the ice jam
flooding threat has greatly diminished. The only exception might be
at the mouths of rivers that flow into the Great Lakes where
significant ice remains at the shore or just offshore.

More precipitation will return today into Friday as another low
pressure system moves from the plains toward the Great Lakes...
potentially adding to runoff. At this point the best chance of
significant precipitation looks to be over the west half of Upper
Michigan...and specifically the Keweenaw peninsula...where 0.50-1.25 inch
of liquid will be possible by Friday afternoon. There is some
uncertainty on how much will fall as rain and how much will fall as
snow...but the best chance of snow will be over the Keweenaw
peninsula. If more of the precipitation falls as snow...runoff will
be delayed until warmer weather returns next week.

Overall...widespread flooding is not foreseen at this time. Those
living around rivers...creeks...and streams should monitor river
levels over the next week.
&&

MQT watches/warnings/advisories...
Upper Michigan...
Winter Weather Advisory from 6 PM this evening to 11 am EDT
Friday for miz001-003.

Lake Superior...
none.
Lake Michigan...
none.
&&

$$

Update...jla
short term...kf
long term...kc
aviation...jla
marine...kf
hydrology...kc/kf