Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Marquette Michigan
745 am EDT Thursday Oct 2 2014
Short term...(today and tonight)
issued at 444 am EDT Thursday Oct 2 2014
Despite the southerly flow in low-levels...main warm front is well
to south over central Mississippi River valley. Front essentially is
just to south of where multiple clusters of thunderstorms and rain are currently
occurring. Strong low pressure over northern Manitoba moving toward
Hudson Bay and a north-south oriented front from the low toward the
upper Mississippi River valley is reason for the south winds over upper
Showers have developed over southern and eastern County Warning Area this morning
out ahead of shortwave and on nose of jet streak over Wisconsin and
within area of greater moisture advection. There is also a touch of
middle-level instability but no thunderstorms and rain have been observed thus far.
Expect rain showers over mainly eastern County Warning Area into at least early afternoon while
rest of County Warning Area should be within a lull as much stronger system in form
of two main shortwaves...one over Four Corners and the other stronger
one over western Canada diving southeast over southern British
Columbia and Alberta...does not begin to affect upper Great Lakes
until later this afternoon and more emphatically into tonight. Back to
today...expect temperatures to end up a bit above normal /normal highs upper
50s to low 60s/ as 950-900mb temperatures continue to warm ahead of larger
scale upper trough over western Canada and rockies and cloud cover by
afternoon should thin out some. Expect maximum temperatures into the 60s...with shot
at even some upper 60s for some locations over west half of County Warning Area.
Into this evening the western Canada shortwave dives across northern
plains while The Four Corners wave heads across Kansas into western
MO. Overnight the northern plains shortwave will become the main
shortwave as it phases with the Southern Plains wave. Lift will
increase due to deepening of larger scale trough from scntrl Canada
to Southern Plains/12 hour height falls up to 150dam spreading toward
upper Great Lakes and broad moderate/strong 700 mb-500 mb q-vector
convergence over upper Great Lakes. Enhancement to lift as 300 mb jet
streak amplifies from upper Great Lakes to northern Ontario/Hudson
Bay...placing much of Upper Michigan within right entrance region.
With the background of this larger scale support...strong south-southwest-north-northeast
moisture advection ramps up ahead of the initial north-south
oriented surface trough and as wave of surface low pressure that is forming
over Southern Plains this morning steadily deepens as it lifts along
trough to a position somewhere vicinity of Eastern Lake Superior by
daybreak Friday. Overall...consensus of model guidance and expected
forcing and moisture advection supports large shield of moderate
rain lifting across Upper Michigan this evening and continuing though
most of the night. Quantitative precipitation forecast amounts seem likely to reach 0.75 inches over
east County Warning Area...while amounts should stay below 0.50 inch over West County warning area as
that area is farther removed from advection of moisture with precipitable waters
over 200 percent of normal. Strength of dynamics suggests some embedded
thunderstorms and rain may occur...though best chance will be over east half of County Warning Area
later this evening and overnight closer to stronger 850 mb-700 mb moisture
transport and track of deepening surface low.
Even with the deepening low moving across tonight...appears stronger
winds will not materialize until more so on Friday. Mins tonight
will be on the mild side for early October...with near 50 degree
readings west to middle-upper 50s for the east.
Long term...(friday through wednesday)
issued at 523 am EDT Thursday Oct 2 2014
The first half of the long term will be dominated by a deep trough
that will be developing over the eastern Continental U.S. Over the next few days.
Impressive height anomalies maximum out over the lower Ohio Valley early
on Sat where 500mb heights will be 3.5 Standard deviations below the
long term early Oct average. Trough will evolve into a large middle-level low
centered over northern Ontario from late Sat through the early part of next
week. This pattern will bring a below normal temperature regime. Daily maximum
temperatures will be the most anomalous with many days having highs well
below normal. As would be expected...the weather will be unsettled
with lake effect/lake enhanced precipitation under cold deep cyclonic flow.
Air mass will be cold enough to support snow at times over the
higher terrain with some light accumulations certainly
possible...not that unusual for early Oct. Farther out...medium
range guidance has come into better agreement on timing the
transition to a more progressive/less amplified flow during the
middle and end of next week. This will lead to moderation of temperatures
back closer to normal after a cold early part of the week.
Beginning Friday...surface low will be lifting north through Eastern Lake Superior
during the morning. MDT to possibly heavy rainfall that overspreads
the area tonight will linger over the east through at least the morning
hours as a result of another shortwave lifting north through lower Michigan. European model (ecmwf)
remains slower than other models shifting this rain out of the eastern
forecast area Friday. In the wake of the main precipitation area...a more showery
precipitation regime will take over...but with middle level drying noted...a
good part of the day may actually end up dry over portions of the west
and central. Winds will increase and turn gusty...especially across
Lake Superior and the Keweenaw under a favorable wrly wind flow.
Friday night...models are in pretty good agreement that a reinforcing
second cold front will drop through the area bringing colder air more
firmly into the upper lakes...with 850mb temperatures dropping to -2 to -4c
by 12z Sat. In concert with fairly strong deep layer qvector
convergence that is prognosticated to shift across the area...lake enhanced
showers will increase. Wetbulb zero heights support the potential
for precipitation to mix with or even change to snow over the high terrain of
far west the near the WI border.
Over the weekend...deep...chilly and moist cyclonic flow will
dominate as middle/upper level low spins over northern Ontario. With
850mb temperatures in the -3 to -6c range...expect plenty of clouds and
lake effect precipitation. Shortwaves rotating around the low will bring
periods of heavier/more widespread lake enhanced precipitation. Precipitation on Sat
will be most favored in areas affected by northwest flow lake effect.
Backing winds on sun will shift precipitation to areas that are most affected
by westerly flow lake effect. Rain will mix with or change to snow
at times over the higher terrain...especially during the night and
With a lengthy period of strong northwest to west winds on Lake Superior...
including gales for a time...and High Lake levels (lake Superior
is currently about 6 inches below the record high for this time of
year)...beach erosion/flooding may become a problem for areas that
are exposed to waves generated by west to northwest winds.
As mentioned at the beginning of this discussion there is much
better agreement on transitioning flow during the middle and end of
next week. Agreement is good that the middle level low will linger over
northern Ontario through at least Monday...which will keep the upper lakes
under its unsettled influence. Low will begin to lift out Tuesday...
leading to a transition to dry weather and some temperature moderation.
Moderation/dry weather will continue Wednesday with a more zonally
oriented flow taking shape across the northern Continental U.S..
Aviation...(for the 12z tafs through 12z Friday morning)
issued at 743 am EDT Thursday Oct 2 2014
MVFR ceilings will continue through this afternoon at kcmx and kiwd. As
next system approaches this evening...conditions will rapidly
deteriorate to IFR/LIFR with upslope rain and fog. LIFR conditions
in fog at ksaw this morning will slowly improve to MVFR this
afternoon with some drying and limited daytime mixing. Conditions
will drop again to LIFR this evening as rain moves back into the
Marine...(for the 4 am Lake Superior forecast issuance)
issued at 444 am EDT Thursday Oct 2 2014
Expect diminishing S winds this morning over the east. Winds will
remain light through most of tonight as surface low to the north across
Lake Superior. Once the low lifts to the north of Lake Superior on
Friday...strong west winds will spread across Lake Superior due to
tight pressure gradient and the arrival of colder air. Gale force
winds expected later Friday afternoon...and these will increase to 35-40
kts Friday night into Saturday as winds shift to the northwest as
colder air moves across Lake Superior. Gale watch in effect for all
but far Western Lake Superior Friday afternoon through early Saturday
afternoon. As it stands now...gale warnings will eventually be
issued either later today or tonight.
Though gales should diminish on Saturday afternoon...west winds
20-30 kts will persist into Sunday and Sunday night with gusty
southwest winds expected Monday into Tuesday out ahead of another
low pressure system dropping in from scntrl Canada.
gale watch from Friday afternoon through Saturday afternoon for